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A History of Science,Volume II,

The Beginnings of Modern Science

Henry Smith Williams, M.D., LL.D.,assisted by Edward H. Williams, M.D.

This public-domain (U.S.) text was scannedby Charles Keller with OmniPage Profes-sional OCR software. The Project Guten-berg edition (“2hsci10”) was subsequently con-verted to LATEX by means of GutenMark soft-ware (version Jan 5 2003), and modified byRon Burkey to clean up formatting problems.Numbered endnotes have been converted tofootnotes for stylistic consistency with othertexts presented at sandroid.org. Illustra-tions missing from the Project Gutenberg edi-tion were scanned by S. A. Cohen; one fig-ure has been redrawn. Report problems [email protected].

Revision: ADate: 02/22/03

Contents

FOREWORD 1

I. SCIENCE IN THE DARK AGE 5

II. MEDIÆVAL SCIENCE AMONG THEARABIANS 17ARABIAN MEDICINE . . . . . . . . . . . 28ARABIAN HOSPITALS . . . . . . . . . . 35

III. MEDIÆVAL SCIENCE IN THE WEST 41THIRTEENTH-CENTURY MEDICINE . 43FIFTEENTH-CENTURY MEDICINE . . 52NEW BEGINNINGS IN GENERAL

SCIENCE . . . . . . . . . . . . . . . . 55ROGER BACON . . . . . . . . . . . . . . . 57LEONARDO DA VINCI . . . . . . . . . . 61

IV. THE NEW COSMOLOGY—COPERNICUS TO KEPLER ANDGALILEO 69JOHANN KEPLER AND THE LAWS OF

PLANETARY MOTION . . . . . . . 96

i

ii

GALILEO GALILEI . . . . . . . . . . . . . 106

V. GALILEO AND THE NEW PHYSICS 133STEVINUS AND THE LAW OF

EQUILIBRIUM . . . . . . . . . . . . 145GALILEO AND THE EQUILIBRIUM OF

FLUIDS . . . . . . . . . . . . . . . . . 148WILLIAM GILBERT AND THE STUDY

OF MAGNETISM . . . . . . . . . . . 159STUDIES OF LIGHT, HEAT, AND

ATMOSPHERIC PRESSURE . . . . 166TORRICELLI . . . . . . . . . . . . . . . . 170

VI. TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY 177ASTROLOGY . . . . . . . . . . . . . . . . 198

VII. FROM PARACELSUS TO HARVEY 219THE GREAT ANATOMISTS . . . . . . . 228THE COMING OF HARVEY . . . . . . . 235LEEUWENHOEK DISCOVERS

BACTERIA . . . . . . . . . . . . . . . 251

VIII. MEDICINE IN THE SIXTEENTHAND SEVENTEENTH CENTURIES 253THOMAS SYDENHAM . . . . . . . . . . 263

IX. PHILOSOPHER-SCIENTISTS ANDNEW INSTITUTIONS OF LEARNING 265SCIENTIFIC SOCIETIES . . . . . . . . . 278

X. THE SUCCESSORS OF GALILEO INPHYSICAL SCIENCE 285

iii

ROBERT BOYLE (1627-1691) . . . . . . . 286MARIOTTE AND VON GUERICKE . . . 294ROBERT HOOKE . . . . . . . . . . . . . . 301CHRISTIAN HUYGENS . . . . . . . . . . 306

XI. NEWTON AND THE COMPOSITIONOF LIGHT 317THE COMPOSITION OF WHITE LIGHT 320THE NATURE OF COLOR . . . . . . . . 329

XII. NEWTON AND THE LAW OFGRAVITATION 333

XIII. INSTRUMENTS OF PRECISION INTHE AGE OF NEWTON 357

XIV. PROGRESS IN ELECTRICITY FROMGILBERT AND VON GUERICKE TOFRANKLIN 367THE EXPERIMENTS OF STEPHEN

GRAY . . . . . . . . . . . . . . . . . . 371EXPERIMENTS OF CISTERNAY DUFAY 379DUFAY DISCOVERS VITREOUS AND

RESINOUS ELECTRICITY . . . . . 384LUDOLFF’S EXPERIMENT WITH THE

ELECTRIC SPARK . . . . . . . . . . 392THE LEYDEN JAR DISCOVERED . . . 398WILLIAM WATSON . . . . . . . . . . . . 404BENJAMIN FRANKLIN . . . . . . . . . . 406FRANKLIN’S THEORY OF

ELECTRICITY . . . . . . . . . . . . 411FRANKLIN INVENTS THE

LIGHTNING-ROD . . . . . . . . . . 413

iv

FRANKLIN PROVES THATLIGHTNING IS ELECTRICITY . . 417

XV. NATURAL HISTORY TO THE TIMEOF LINNÆUS 423

vi

SIR ISAAC NEWTON

FOREWORD

The studies of the present book cover theprogress of science from the close of the Ro-man period in the fifth century A.D. to aboutthe middle of the eighteenth century. In trac-ing the course of events through so long a pe-riod, a difficulty becomes prominent which ev-erywhere besets the historian in less degree—a difficulty due to the conflict between thestrictly chronological and the topical methodof treatment. We must hold as closely as pos-sible to the actual sequence of events, since,as already pointed out, one discovery leads onto another. But, on the other hand, progres-sive steps are taken contemporaneously in thevarious fields of science, and if we were to at-tempt to introduce these in strict chronolog-ical order we should lose all sense of topicalcontinuity.

Our method has been to adopt a compro-mise, following the course of a single sciencein each great epoch to a convenient stopping-

1

2 A HISTORY OF SCIENCE, VOLUME II

point, and then turning back to bring forwardthe story of another science. Thus, for ex-ample, we tell the story of Copernicus andGalileo, bringing the record of cosmical andmechanical progress down to about the mid-dle of the seventeenth century, before turningback to take up the physiological progress ofthe fifteenth and sixteenth centuries. Oncethe latter stream is entered, however, we fol-low it without interruption to the time of Har-vey and his contemporaries in the middle ofthe seventeenth century, where we leave it toreturn to the field of mechanics as exploitedby the successors of Galileo, who were also thepredecessors and contemporaries of Newton.

In general, it will aid the reader to recallthat, so far as possible, we hold always to thesame sequences of topical treatment of con-temporary events; as a rule we treat first thecosmical, then the physical, then the biologi-cal sciences. The same order of treatment willbe held to in succeeding volumes.

Several of the very greatest of scientificgeneralizations are developed in the periodcovered by the present book: for example, theCopernican theory of the solar system, thetrue doctrine of planetary motions, the lawsof motion, the theory of the circulation of theblood, and the Newtonian theory of gravita-tion. The labors of the investigators of the

FOREWORD 3

early decades of the eighteenth century, ter-minating with Franklin’s discovery of the na-ture of lightning and with the Linnæan clas-sification of plants and animals, bring us tothe close of our second great epoch; or, to putit otherwise, to the threshold of the modernperiod.

I. SCIENCE INTHE DARK AGE

An obvious distinction between the classicaland mediæval epochs may be found in the factthat the former produced, whereas the latterfailed to produce, a few great thinkers in eachgeneration who were imbued with that scep-ticism which is the foundation of the investi-gating spirit; who thought for themselves andsupplied more or less rational explanations ofobserved phenomena. Could we eliminate thework of some score or so of classical observersand thinkers, the classical epoch would seemas much a dark age as does the epoch that suc-ceeded it.

But immediately we are met with the ques-tion: Why do no great original investigatorsappear during all these later centuries? Wehave already offered a part explanation inthe fact that the borders of civilization, whereracial mingling naturally took place, were

5


peopled with semi-barbarians. But we mustnot forget that in the centres of civilizationall along there were many men of powerfulintellect. Indeed, it would violate the prin-ciple of historical continuity to suppose thatthere was any sudden change in the level ofmentality of the Roman world at the close ofthe classical period. We must assume, then,that the direction in which the great mindsturned was for some reason changed. New-ton is said to have alleged that he made hisdiscoveries by “intending” his mind in a cer-tain direction continuously. It is probable thatthe same explanation may be given of almostevery great scientific discovery. Anaxagorascould not have thought out the theory of themoon’s phases; Aristarchus could not havefound out the true mechanism of the solar sys-tem; Eratosthenes could not have developedhis plan for measuring the earth, had not eachof these investigators “intended” his mind per-sistently towards the problems in question.

Nor can we doubt that men lived in ev-ery generation of the dark age who were capa-ble of creative thought in the field of science,had they chosen similarly to “intend” theirminds in the right direction. The difficultywas that they did not so choose. Their mindshad a quite different bent. They were underthe spell of different ideals; all their mental


efforts were directed into different channels.What these different channels were cannotbe in doubt—they were the channels of ori-ental ecclesiasticism. One all-significant factspeaks volumes here. It is the fact that, asProfessor Robinson1 points out, from the timeof Boethius (died 524 or 525 A.D.) to that ofDante (1265-1321 A.D.) there was not a singlewriter of renown in western Europe who wasnot a professional churchman. All the learn-ing of the time, then, centred in the priest-hood. We know that the same condition ofthings pertained in Egypt, when science be-came static there. But, contrariwise, we haveseen that in Greece and early Rome the scien-tific workers were largely physicians or pro-fessional teachers; there was scarcely a pro-fessional theologian among them.

Similarly, as we shall see in the Arabicworld, where alone there was progress in themediæval epoch, the learned men were, forthe most part, physicians. Now the mean-ing of this must be self-evident. The physi-cian naturally “intends” his mind towards thepracticalities. His professional studies tend tomake him an investigator of the operationsof nature. He is usually a sceptic, with aspontaneous interest in practical science. But

1James Harvey Robinson, An Introduction to theHistory of Western Europe, New York, 1898, p. 330.


the theologian “intends” his mind away frompracticalities and towards mysticism. He is aprofessional believer in the supernatural; hediscounts the value of merely “natural” phe-nomena. His whole attitude of mind is un-scientific; the fundamental tenets of his faithare based on alleged occurrences which induc-tive science cannot admit—namely, miracles.And so the minds “intended” towards the su-pernatural achieved only the hazy mysticismof mediæval thought. Instead of investigat-ing natural laws, they paid heed (as, for ex-ample, Thomas Aquinas does in his SummaTheologia) to the “acts of angels,” the “speak-ing of angels,” the “subordination of angels,”the “deeds of guardian angels,” and the like.They disputed such important questions as,How many angels can stand upon the pointof a needle? They argued pro and con asto whether Christ were coeval with God, orwhether he had been merely created “in thebeginning,” perhaps ages before the creationof the world. How could it be expected that sci-ence should flourish when the greatest mindsof the age could concern themselves with prob-lems such as these?

Despite our preconceptions or prejudices,there can be but one answer to that ques-tion. Oriental superstition cast its blight uponthe fair field of science, whatever compensa-


tion it may or may not have brought in otherfields. But we must be on our guard lest weoverestimate or incorrectly estimate this in-fluence. Posterity, in glancing backward, isalways prone to stamp any given age of thepast with one idea, and to desire to charac-terize it with a single phrase; whereas in re-ality all ages are diversified, and any gen-eralization regarding an epoch is sure to dothat epoch something less or something morethan justice. We may be sure, then, that theideal of ecclesiasticism is not solely respon-sible for the scientific stasis of the dark age.Indeed, there was another influence of a to-tally different character that is too patent tobe overlooked—the influence, namely, of theeconomic condition of western Europe duringthis period. As I have elsewhere pointed out,2Italy, the centre of western civilization, wasat this time impoverished, and hence couldnot provide the monetary stimulus so essen-tial to artistic and scientific no less than tomaterial progress. There were no patrons ofscience and literature such as the Ptolemiesof that elder Alexandrian day. There were nogreat libraries; no colleges to supply opportu-

2Henry Smith Williams, “A Prefatory Characteriza-tion of The History of Italy,” in vol. IX. of The Histo-rians’ History of the World, 25 vols., London and NewYork, 1904.


nities and afford stimuli to the rising genera-tion. Worst of all, it became increasingly diffi-cult to secure books.

This phase of the subject is often over-looked. Yet a moment’s consideration willshow its importance. How should we fareto-day if no new scientific books were beingproduced, and if the records of former gen-erations were destroyed? That is what ac-tually happened in Europe during the Mid-dle Ages. At an earlier day books were madeand distributed much more abundantly thanis sometimes supposed. Bookmaking had, in-deed, been an important profession in Rome,the actual makers of books being slaves whoworked under the direction of a publisher. Itwas through the efforts of these workers thatthe classical works in Greek and Latin weremultiplied and disseminated. Unfortunatelythe climate of Europe does not conduce to theindefinite preservation of a book; hence veryfew remnants of classical works have comedown to us in the original from a remote pe-riod. The rare exceptions are certain papyrusfragments, found in Egypt, some of which areGreek manuscripts dating from the third cen-tury B.C. Even from these sources the outputis meagre; and the only other repository ofclassical books is a single room in the buriedcity of Herculaneum, which contained several


hundred manuscripts, mostly in a charredcondition, a considerable number of which,however, have been unrolled and found moreor less legible. This library in the buried citywas chiefly made up of philosophical works,some of which were quite unknown to themodern world until discovered there.

But this find, interesting as it was from anarchæological stand-point, had no very impor-tant bearing on our knowledge of the litera-ture of antiquity. Our chief dependence forour knowledge of that literature must still beplaced in such copies of books as were madein the successive generations. Comparativelyfew of the extant manuscripts are older thanthe tenth century of our era. It requiresbut a momentary consideration of the condi-tions under which ancient books were pro-duced to realize how slow and difficult the pro-cess was before the invention of printing. Thetaste of the book-buying public demanded aclearly written text, and in the Middle Agesit became customary to produce a richly orna-mented text as well. The script employed be-ing the prototype of the modern printed text,it will be obvious that a scribe could producebut a few pages at best in a day. A largework would therefore require the labor of ascribe for many months or even for severalyears. We may assume, then, that it would


be a very flourishing publisher who could pro-duce a hundred volumes all told per annum;and probably there were not many publishersat any given time, even in the period of Rome’sgreatest glory, who had anything like this out-put.

As there was a large number of authorsin every generation of the classical period, itfollows that most of these authors must havebeen obliged to content themselves with edi-tions numbering very few copies; and it goeswithout saying that the greater number ofbooks were never reproduced in what mightbe called a second edition. Even books thatretained their popularity for several genera-tions would presently fail to arouse sufficientinterest to be copied; and in due course suchworks would pass out of existence altogether.Doubtless many hundreds of books were thuslost before the close of the classical period,the names of their authors being quite forgot-ten, or preserved only through a chance ref-erence; and of course the work of eliminationwent on much more rapidly during the Mid-dle Ages, when the interest in classical litera-ture sank to so low an ebb in the West. Suchcollections of references and quotations as theGreek Anthology and the famous anthologiesof Stobæus and Athanasius and Eusebius giveus glimpses of a host of writers—more than


seven hundred are quoted by Stobæus—a verylarge proportion of whom are quite unknownexcept through these brief excerpts from theirlost works.

Quite naturally the scientific works suf-fered at least as largely as any others in anage given over to ecclesiastical dreamings. Yetin some regards there is matter for surpriseas to the works preserved. Thus, as we haveseen, the very extensive works of Aristotle onnatural history, and the equally extensive nat-ural history of Pliny, which were preservedthroughout this period, and are still extant,make up relatively bulky volumes. Theseworks seem to have interested the monks ofthe Middle Ages, while many much more im-portant scientific books were allowed to per-ish. A considerable bulk of scientific liter-ature was also preserved through the curi-ous channels of Arabic and Armenian transla-tions. Reference has already been made to theAlmagest of Ptolemy, which, as we have seen,was translated into Arabic, and which was ata later day brought by the Arabs into westernEurope and (at the instance of Frederick II.of Sicily) translated out of their language intomediæval Latin.

It remains to inquire, however, throughwhat channels the Greek works reached theArabs themselves. To gain an answer to this


question we must follow the stream of his-tory from its Roman course eastward to thenew seat of the Roman empire in Byzantium.Here civilization centred from about the fifthcentury A.D., and here the European came incontact with the civilization of the Syrians,the Persians, the Armenians, and finally ofthe Arabs. The Byzantines themselves, un-like the inhabitants of western Europe, didnot ignore the literature of old Greece; theGreek language became the regular speech ofthe Byzantine people, and their writers madea strenuous effort to perpetuate the idiom andstyle of the classical period. Naturally theyalso made transcriptions of the classical au-thors, and thus a great mass of literaturewas preserved, while the corresponding workswere quite forgotten in western Europe.

Meantime many of these works weretranslated into Syriac, Armenian, and Per-sian, and when later on the Byzantine civi-lization degenerated, many works that wereno longer to be had in the Greek originalscontinued to be widely circulated in Syriac,Persian, Armenian, and, ultimately, in Ara-bic translations. When the Arabs startedout in their conquests, which carried themthrough Egypt and along the southern coastof the Mediterranean, until they finally in-vaded Europe from the west by way of Gibral-


tar, they carried with them their translationsof many a Greek classical author, who was in-troduced anew to the western world throughthis strange channel.

We are told, for example, that Averrhoes,the famous commentator of Aristotle, wholived in Spain in the twelfth century, did notknow a word of Greek and was obliged to gainhis knowledge of the master through a Syr-iac translation; or, as others alleged (denyingthat he knew even Syriac), through an Arabicversion translated from the Syriac. We know,too, that the famous chronology of Eusebiuswas preserved through an Armenian transla-tion; and reference has more than once beenmade to the Arabic translation of Ptolemy’sgreat work, to which we still apply its Arabictitle of Almagest.

The familiar story that when the Arabsinvaded Egypt they burned the Alexandrianlibrary is now regarded as an invention oflater times. It seems much more probablethat the library had been largely scatteredbefore the coming of the Moslems. Indeed,it has even been suggested that the Chris-tians of an earlier day removed the recordsof pagan thought. Be that as it may, thefamous Alexandrian library had disappearedlong before the revival of interest in classi-cal learning. Meanwhile, as we have said,


the Arabs, far from destroying the western lit-erature, were its chief preservers. Partly atleast because of their regard for the recordsof the creative work of earlier generationsof alien peoples, the Arabs were enabled tooutstrip their contemporaries. For it cannotbe in doubt that, during that long stretch oftime when the western world was ignoringscience altogether or at most contenting it-self with the casual reading of Aristotle andPliny, the Arabs had the unique distinction ofattempting original investigations in science.To them were due all important progressivesteps which were made in any scientific fieldwhatever for about a thousand years after thetime of Ptolemy and Galen. The progressmade even by the Arabs during this long pe-riod seems meagre enough, yet it has somesignificant features. These will now demandour attention.

II. MEDIÆVALSCIENCE AMONGTHE ARABIANS

The successors of Mohammed showed them-selves curiously receptive of the ideas of thewestern people whom they conquered. Theycame in contact with the Greeks in westernAsia and in Egypt, and, as has been said, be-came their virtual successors in carrying for-ward the torch of learning. It must not beinferred, however, that the Arabian scholars,as a class, were comparable to their prede-cessors in creative genius. On the contrary,they retained much of the conservative orien-tal spirit. They were under the spell of tra-dition, and, in the main, what they acceptedfrom the Greeks they regarded as almost finalin its teaching. There were, however, a few no-table exceptions among their men of science,and to these must be ascribed several discov-

17


eries of some importance.The chief subjects that excited the inter-

est and exercised the ingenuity of the Ara-bian scholars were astronomy, mathematics,and medicine. The practical phases of allthese subjects were given particular atten-tion. Thus it is well known that our so-called Arabian numerals date from this pe-riod. The revolutionary effect of these charac-ters, as applied to practical mathematics, canhardly be overestimated; but it is generallyconsidered, and in fact was admitted by theArabs themselves, that these numerals werereally borrowed from the Hindoos, with whomthe Arabs came in contact on the east. Cer-tain of the Hindoo alphabets, notably that ofthe Battaks of Sumatra, give us clews to theoriginals of the numerals. It does not seemcertain, however, that the Hindoos employedthese characters according to the decimal sys-tem, which is the prime element of their im-portance. Knowledge is not forthcoming asto just when or by whom such applicationwas made. If this was an Arabic innovation,it was perhaps the most important one withwhich that nation is to be credited. Anothermathematical improvement was the introduc-tion into trigonometry of the sine—the half-chord of the double arc—instead of the chordof the arc itself which the Greek astronomers

II. ARABIAN MEDIÆVAL SCIENCE 19

had employed. This improvement was due tothe famous Albategnius, whose work in otherfields we shall examine in a moment.

Another evidence of practicality wasshown in the Arabian method of attemptingto advance upon Eratosthenes’ measurementof the earth. Instead of trusting to the mea-surement of angles, the Arabs decided to mea-sure directly a degree of the earth’s surface—or rather two degrees. Selecting a level plainin Mesopotamia for the experiment, one partyof the surveyors progressed northward, an-other party southward, from a given point tothe distance of one degree of arc, as deter-mined by astronomical observations. The re-sult found was fifty-six miles for the northerndegree, and fifty-six and two-third miles forthe southern. Unfortunately, we do not knowthe precise length of the mile in question, andtherefore cannot be assured as to the accuracyof the measurement. It is interesting to note,however, that the two degrees were found ofunequal lengths, suggesting that the earth isnot a perfect sphere—a suggestion the valid-ity of which was not to be put to the test of con-clusive measurements until about the close ofthe eighteenth century. The Arab measure-ment was made in the time of Caliph Abdal-lah al-Mamun, the son of the famous Harun-al-Rashid. Both father and son were famous


for their interest in science. Harun-al-Rashidwas, it will be recalled, the friend of Charle-magne. It is said that he sent that ruler, as atoken of friendship, a marvellous clock whichlet fall a metal ball to mark the hours. Thismechanism, which is alleged to have excitedgreat wonder in the West, furnishes yet an-other instance of Arabian practicality.

Perhaps the greatest of the Arabian as-tronomers was Mohammed ben Jabir Albateg-nius, or El-batani, who was born at Batan, inMesopotamia, about the year 850 A.D., anddied in 929. Albategnius was a student of thePtolemaic astronomy, but he was also a prac-tical observer. He made the important discov-ery of the motion of the solar apogee. That isto say, he found that the position of the sunamong the stars, at the time of its greatestdistance from the earth, was not what it hadbeen in the time of Ptolemy. The Greek as-tronomer placed the sun in longitude 65◦, butAlbategnius found it in longitude 82◦, a dis-tance too great to be accounted for by inaccu-racy of measurement. The modern inferencefrom this observation is that the solar systemis moving through space; but of course thisinference could not well be drawn while theearth was regarded as the fixed centre of theuniverse.

In the eleventh century another Arabian


discoverer, Arzachel, observing the sun to beless advanced than Albategnius had found it,inferred incorrectly that the sun had recededin the mean time. The modern explanationof this observation is that the measurementof Albategnius was somewhat in error, sincewe know that the sun’s motion is steadily pro-gressive. Arzachel, however, accepting themeasurement of his predecessor, drew thefalse inference of an oscillatory motion of thestars, the idea of the motion of the solar sys-tem not being permissible. This assumedphenomenon, which really has no existencein point of fact, was named the “trepidationof the fixed stars,” and was for centuries ac-cepted as an actual phenomenon. Arzachel ex-plained this supposed phenomenon by assum-ing that the equinoctial points, or the pointsof intersection of the equator and the ecliptic,revolve in circles of eight degrees’ radius. Thefirst points of Aries and Libra were supposedto describe the circumference of these circlesin about eight hundred years. All of whichillustrates how a difficult and false explana-tion may take the place of a simple and correctone. The observations of later generationshave shown conclusively that the sun’s shiftof position is regularly progressive, hence thatthere is no “trepidation” of the stars and norevolution of the equinoctial points.


If the Arabs were wrong as regards thissupposed motion of the fixed stars, they madeat least one correct observation as to the in-equality of motion of the moon. Two inequal-ities of the motion of this body were alreadyknown. A third, called the moon’s variation,was discovered by an Arabian astronomerwho lived at Cairo and observed at Bagdadin 975, and who bore the formidable nameof Mohammed Aboul Wefaal-Bouzdjani. Theinequality of motion in question, in virtue ofwhich the moon moves quickest when she is atnew or full, and slowest at the first and thirdquarter, was rediscovered by Tycho Brahe sixcenturies later; a fact which in itself evidencesthe neglect of the Arabian astronomer’s dis-covery by his immediate successors.

In the ninth and tenth centuries the Ara-bian city of Cordova, in Spain, was anotherimportant centre of scientific influence. Therewas a library of several hundred thousand vol-umes here, and a college where mathematicsand astronomy were taught. Granada, Toledo,and Salamanca were also important centres,to which students flocked from western Eu-rope. It was the proximity of these Arabiancentres that stimulated the scientific interestsof Alfonso X. of Castile, at whose instance thecelebrated Alfonsine tables were constructed.A familiar story records that Alfonso, ponder-


ing the complications of the Ptolemaic cyclesand epicycles, was led to remark that, hadhe been consulted at the time of creation, hecould have suggested a much better and sim-pler plan for the universe. Some centurieswere to elapse before Copernicus was to showthat it was not the plan of the universe, butman’s interpretation of it, that was at fault.

Another royal personage who came underArabian influence was Frederick II. of Sicily—the “Wonder of the World,” as he was called byhis contemporaries. The Almagest of Ptolemywas translated into Latin at his instance, be-ing introduced to the Western world throughthis curious channel. At this time it becamequite usual for the Italian and Spanish schol-ars to understand Arabic although they weretotally ignorant of Greek.

In the field of physical science one of themost important of the Arabian scientists wasAlhazen. His work, published about the year1100 A.D., had great celebrity throughout themediæval period. The original investigationsof Alhazen had to do largely with optics. Hemade particular studies of the eye itself, andthe names given by him to various parts of theeye, as the vitreous humor, the cornea, andthe retina, are still retained by anatomists.It is known that Ptolemy had studied the re-fraction of light, and that he, in common with


his immediate predecessors, was aware thatatmospheric refraction affects the apparentposition of stars near the horizon. Alhazencarried forward these studies, and was ledthrough them to make the first recorded sci-entific estimate of the phenomena of twilightand of the height of the atmosphere. The per-sistence of a glow in the atmosphere after thesun has disappeared beneath the horizon isso familiar a phenomenon that the ancientphilosophers seem not to have thought of itas requiring an explanation. Yet a moment’sconsideration makes it clear that, if light trav-els in straight lines and the rays of the sunwere in no wise deflected, the complete dark-ness of night should instantly succeed to daywhen the sun passes below the horizon. Thatthis sudden change does not occur, Alhazenexplained as due to the reflection of light bythe earth’s atmosphere.

Alhazen appears to have conceived the at-mosphere as a sharply defined layer, and, as-suming that twilight continues only so long asrays of the sun reflected from the outer sur-face of this layer can reach the spectator atany given point, he hit upon a means of mea-surement that seemed to solve the hithertoinscrutable problem as to the atmosphericdepth. Like the measurements of Aristarchusand Eratosthenes, this calculation of Alhazen


is simple enough in theory. Its defect con-sists largely in the difficulty of fixing its termswith precision, combined with the further factthat the rays of the sun, in taking the slantingcourse through the earth’s atmosphere, are re-ally deflected from a straight line in virtueof the constantly increasing density of the airnear the earth’s surface. Alhazen must havebeen aware of this latter fact, since it wasknown to the later Alexandrian astronomers,but he takes no account of it in the presentmeasurement. The diagram will make themethod of Alhazen clear.

His important premises are two: first, thewell-recognized fact that, when light is re-flected from any surface, the angle of inci-dence is equal to the angle of reflection; and,second, the much more doubtful observationthat twilight continues until such time as thesun, according to a simple calculation, is nine-teen degrees below the horizon. Referring tothe diagram, let the inner circle represent theearth’s surface, the outer circle the limits ofthe atmosphere, C being the earth’s centre,and RR radii of the earth. Then the observerat the point A will continue to receive the re-flected rays of the sun until that body reachesthe point S, which is, according to the hy-pothesis, nineteen degrees below the horizonline of the observer at A. This horizon line,


DIAGRAM TO ILLUSTRATE ALHAZEN’SMEASUREMENT OF THE HEIGHT OF THE

ATMOSPHERE

(For explanation refer to the text. It will be understood,of course, that the distorted, proportions make an an-gle very inaccurate. HMS, for example, as shown in thediagram, is obviously much greater than 19◦. Perhapsit should be added that the angle HMS would not atall serve the purpose to which it is here put were it notthat the distance of the sun makes the ray SM virtuallyparallel to the imaginary line SA, which latter definesthe actual angle of the sun’s position with regard to theobserver at A).


being represented by AH, and the sun’s rayby SM , the angle HMS is an angle of nine-teen degrees. The complementary angle SMAis, obviously, an angle of (180-19) one hun-dred and sixty-one degrees. But since M isthe reflecting surface and the angle of inci-dence equals the angle of reflection, the angleAMC is an angle of one-half of one hundredand sixty-one degrees, or eighty degrees andthirty minutes. Now this angle AMC, beingknown, the right-angled triangle MAC is eas-ily resolved, since the side AC of that triangle,being the radius of the earth, is a known di-mension. Resolution of this triangle gives usthe length of the hypotenuse MC, and the dif-ference between this and the radius (AC), orCD, is obviously the height of the atmosphere(h), which was the measurement desired. Ac-cording to the calculation of Alhazen, this h, orthe height of the atmosphere, represents fromtwenty to thirty miles. The modern compu-tation extends this to about fifty miles. But,considering the various ambiguities that nec-essarily attended the experiment, the resultwas a remarkably close approximation to thetruth.

Turning from physics to chemistry, we findas perhaps the greatest Arabian name that ofGeber, who taught in the College of Seville inthe first half of the eighth century. The most


important researches of this really remark-able experimenter had to do with the acids.The ancient world had had no knowledge ofany acid more powerful than acetic. Geber,however, vastly increased the possibilities ofchemical experiment by the discovery of sul-phuric, nitric, and nitromuriatic acids. Hemade use also of the processes of sublimationand filtration, and his works describe the wa-ter bath and the chemical oven. Among theimportant chemicals which he first differen-tiated is oxide of mercury, and his studies ofsulphur in its various compounds have pecu-liar interest. In particular is this true of hisobservation that, under certain conditions ofoxidation, the weight of a metal was lessened.

From the record of these studies in thefields of astronomy, physics, and chemistry, weturn to a somewhat extended survey of theArabian advances in the field of medicine.

ARABIAN MEDICINEThe influence of Arabian physicians restedchiefly upon their use of drugs rather thanupon anatomical knowledge. Like the mediæ-val Christians, they looked with horror on dis-section of the human body; yet there were al-ways among them investigators who turnedconstantly to nature herself for hidden truths,


and were ready to uphold the superiority ofactual observation to mere reading. Thus thephysician Abd el-Letif, while in Egypt, madecareful studies of a mound of bones containingmore than twenty thousand skeletons. Whileexamining these bones he discovered that thelower jaw consists of a single bone, not of two,as had been taught by Galen. He also dis-covered several other important mistakes inGalenic anatomy, and was so impressed withhis discoveries that he contemplated writinga work on anatomy which should correct thegreat classical authority’s mistakes.

It was the Arabs who invented the apothe-cary, and their pharmacopœia, issued fromthe hospital at Gondisapor, and elaboratedfrom time to time, formed the basis for West-ern pharmacopœias. Just how many drugsoriginated with them, and how many wereborrowed from the Hindoos, Jews, Syrians,and Persians, cannot be determined. It iscertain, however, that through them variousnew and useful drugs, such as senna, aconite,rhubarb, camphor, and mercury, were handeddown through the Middle Ages, and that theyare responsible for the introduction of alcoholin the field of therapeutics.

In mediæval Europe, Arabian sciencecame to be regarded with superstitious awe,and the works of certain Arabian physicians


were exalted to a position above all the an-cient writers. In modern times, however,there has been a reaction and a tendency todepreciation of their work. By some theyare held to be mere copyists or translatorsof Greek books, and in no sense original in-vestigators in medicine. Yet there can be lit-tle doubt that while the Arabians did copyand translate freely, they also originated andadded considerably to medical knowledge. Itis certain that in the time when Christianmonarchs in western Europe were payinglittle attention to science or education, thecaliphs and vizirs were encouraging physi-cians and philosophers, building schools, anderecting libraries and hospitals. They made atleast a creditable effort to uphold and advanceupon the scientific standards of an earlier age.

The first distinguished Arabian physicianwas Harets ben Kaladah, who received hiseducation in the Nestonian school at Gondis-apor, about the beginning of the seventh cen-tury. Notwithstanding the fact that Haretswas a Christian, he was chosen by Mo-hammed as his chief medical adviser, and rec-ommended as such to his successor, the CaliphAbu Bekr. Thus, at the very outset, the sci-ence of medicine was divorced from religionamong the Arabians; for if the prophet himselfcould employ the services of an unbeliever,


surely others might follow his example. Andthat this example was followed is shown inthe fact that many Christian physicians wereraised to honorable positions by succeedinggenerations of Arabian monarchs. This broad-minded view of medicine taken by the Arabsundoubtedly assisted as much as any one sin-gle factor in upbuilding the science, just as thenarrow and superstitious view taken by West-ern nations helped to destroy it.

The education of the Arabians made it nat-ural for them to associate medicine with thenatural sciences, rather than with religion.An Arabian savant was supposed to be equallywell educated in philosophy, jurisprudence,theology, mathematics, and medicine, andto practise law, theology, and medicine withequal skill upon occasion. It is easy to under-stand, therefore, why these religious fanat-ics were willing to employ unbelieving physi-cians, and their physicians themselves to turnto the scientific works of Hippocrates andGalen for medical instruction, rather than toreligious works. Even Mohammed himselfprofessed some knowledge of medicine, and of-ten relied upon this knowledge in treating ail-ments rather than upon prayers or incanta-tions. He is said, for example, to have recom-mended and applied the cautery in the caseof a friend who, when suffering from angina,


had sought his aid.The list of eminent Arabian physicians is

too long to be given here, but some of themare of such importance in their influence uponlater medicine that they cannot be entirely ig-nored. One of the first of these was Honainben Isaac (809-873 A.D.), a Christian Arab ofBagdad. He made translations of the works ofHippocrates, and practised the art along thelines indicated by his teachings and those ofGalen. He is considered the greatest transla-tor of the ninth century and one of the great-est philosophers of that period.

Another great Arabian physician, whosework was just beginning as Honain’s wasdrawing to a close, was Rhazes (850-923 A.D.),who during his life was no less noted as aphilosopher and musician than as a physician.He continued the work of Honain, and ad-vanced therapeutics by introducing more ex-tensive use of chemical remedies, such as mer-curial ointments, sulphuric acid, and aqua vi-tae. He is also credited with being the firstphysician to describe small-pox and measlesaccurately.

While Rhazes was still alive another Ara-bian, Haly Abbas (died about 994), was writ-ing his famous encyclopædia of medicine,called The Royal Book. But the names of allthese great physicians have been considerably


obscured by the reputation of Avicenna (980-1037), the Arabian “Prince of Physicians,” thegreatest name in Arabic medicine, and one ofthe most remarkable men in history. Leclercsays that “he was perhaps never surpassed byany man in brilliancy of intellect and indefati-gable activity.” His career was a most variedone. He was at all times a boisterous reveller,but whether flaunting gayly among the guestsof an emir or biding in some obscure apothe-cary cellar, his work of philosophical writ-ing was carried on steadily. When a friendlyemir was in power, he taught and wrote andcaroused at court; but between times, whensome unfriendly ruler was supreme, he washiding away obscurely, still pouring out hisgreat mass of manuscripts. In this way hisentire life was spent.

By his extensive writings he revived andkept alive the best of the teachings of theGreek physicians, adding to them such obser-vations as he had made in anatomy, physi-ology, and materia medica. Among his dis-coveries is that of the contagiousness of pul-monary tuberculosis. His works for severalcenturies continued to be looked upon as thehighest standard by physicians, and he shouldundoubtedly be credited with having at leastretarded the decline of mediæval medicine.

But it was not the Eastern Arabs alone


who were active in the field of medicine. Cor-dova, the capital of the western caliphate, be-came also a great centre of learning and pro-duced several great physicians. One of these,Albucasis (died in 1013 A.D.), is credited withhaving published the first illustrated work onsurgery, this book being remarkable in stillanother way, in that it was also the first book,since classical times, written from the prac-tical experience of the physician, and not amere compilation of ancient authors. A cen-tury after Albucasis came the great physicianAvenzoar (1113-1196), with whom he dividesabout equally the medical honors of the west-ern caliphate. Among Avenzoar’s discoverieswas that of the cause of “itch”—a little para-site, “so small that he is hardly visible.” Thediscovery of the cause of this common diseaseseems of minor importance now, but it is of in-terest in medical history because, had Aven-zoar’s discovery been remembered a hundredyears ago, “itch struck in” could hardly havebeen considered the cause of three-fourths ofall diseases, as it was by the famous Hahne-mann.

The illustrious pupil of Avenzoar, Aver-rhoes, who died in 1198 A.D., was the last ofthe great Arabian physicians who, by ratio-nal conception of medicine, attempted to stemthe flood of superstition that was overwhelm-


ing medicine. For a time he succeeded; but atlast the Moslem theologians prevailed, and hewas degraded and banished to a town inhab-ited only by the despised Jews.

ARABIAN HOSPITALSTo early Christians belong the credit of hav-ing established the first charitable institu-tions for caring for the sick; but their effortswere soon eclipsed by both Eastern and West-ern Mohammedans. As early as the eighthcentury the Arabs had begun building hospi-tals, but the flourishing time of hospital build-ing seems to have begun early in the tenthcentury. Lady Seidel, in 918 A.D., opened ahospital at Bagdad, endowed with an amountcorresponding to about three hundred poundssterling a month. Other similar hospitalswere erected in the years immediately follow-ing, and in 977 the Emir Adad-adaula estab-lished an enormous institution with a staff oftwenty-four medical officers. The great physi-cian Rhazes is said to have selected the sitefor one of these hospitals by hanging piecesof meat in various places about the city, se-lecting the site near the place at which pu-trefaction was slowest in making its appear-ance. By the middle of the twelfth centurythere were something like sixty medical in-


stitutions in Bagdad alone, and these institu-tions were free to all patients and supportedby official charity.

The Emir Nureddin, about the year 1160,founded a great hospital at Damascus, as athank-offering for his victories over the Cru-saders. This great institution completely over-shadowed all the earlier Moslem hospitals insize and in the completeness of its equipment.It was furnished with facilities for teaching,and was conducted for several centuries in alavish manner, regardless of expense. Butlittle over a century after its foundation thefame of its methods of treatment led to theestablishment of a larger and still more lux-urious institution—the Mansuri hospital atCairo. It seems that a certain sultan, havingbeen cured by medicines from the Damascenehospital, determined to build one of his ownat Cairo which should eclipse even the greatDamascene institution.

In a single year (1283-1284) this hospitalwas begun and completed. No efforts werespared in hurrying on the good work, and noone was exempt from performing labor on thebuilding if he chanced to pass one of the ad-joining streets. It was the order of the sul-tan that any person passing near could be im-pressed into the work, and this order was car-ried out to the letter, noblemen and beggars


alike being forced to lend a hand. Very natu-rally, the adjacent thoroughfares became un-popular and practically deserted, but still theholy work progressed rapidly and was shortlycompleted.

This immense structure is said to havecontained four courts, each having a fountainin the centre; lecture-halls, wards for isolat-ing certain diseases, and a department thatcorresponded to the modern hospital’s “out-patient” department. The yearly endowmentamounted to something like the equivalent ofone hundred and twenty-five thousand dol-lars. A novel feature was a hall where mu-sicians played day and night, and anotherwhere story-tellers were employed, so thatpersons troubled with insomnia were amusedand melancholiacs cheered. Those of a reli-gious turn of mind could listen to readings ofthe Koran, conducted continuously by a staffof some fifty chaplains. Each patient on leav-ing the hospital received some gold pieces,that he need not be obliged to attempt hardlabor at once.

In considering the astonishing tales ofthese sumptuous Arabian institutions, itshould be borne in mind that our accountsof them are, for the most part, from Mo-hammedan sources. Nevertheless, there canbe little question that they were enormous in-


stitutions, far surpassing any similar institu-tions in western Europe. The so-called hospi-tals in the West were, at this time, branches ofmonasteries under supervision of the monks,and did not compare favorably with the Ara-bian hospitals.

But while the medical science of the Mo-hammedans greatly overshadowed that of theChristians during this period, it did not com-pletely obliterate it. About the year 1000 A.D.came into prominence the Christian medi-cal school at Salerno, situated on the Italiancoast, some thirty miles southeast of Naples.Just how long this school had been in exis-tence, or by whom it was founded, cannot bedetermined, but its period of greatest influ-ence was the eleventh, twelfth, and thirteenthcenturies. The members of this school gradu-ally adopted Arabic medicine, making use ofmany drugs from the Arabic pharmacopœia,and this formed one of the stepping-stonesto the introduction of Arabian medicine allthrough western Europe.

It was not the adoption of Arabianmedicines, however, that has made the schoolat Salerno famous both in rhyme and prose,but rather the fact that women there prac-tised the healing art. Greatest among themwas Trotula, who lived in the eleventh cen-tury, and whose learning is reputed to have


equalled that of the greatest physicians of theday. She is accredited with a work on Diseasesof Women, still extant, and many of her writ-ings on general medical subjects were quotedthrough two succeeding centuries. If we mayjudge from these writings, she seemed to havehad many excellent ideas as to the propermethods of treating diseases, but it is diffi-cult to determine just which of the writingscredited to her are in reality hers. Indeed,the uncertainty is even greater than this im-plies, for, according to some writers, “Trotula”is merely the title of a book. Such an authorityas Malgaigne, however, believed that such awoman existed, and that the works accreditedto her are authentic. The truth of the mat-ter may perhaps never be fully established,but this at least is certain—the tradition inregard to Trotula could never have arisen hadnot women held a far different position amongthe Arabians of this period from that accordedthem in contemporary Christendom.

III. MEDIÆVALSCIENCE IN THEWEST

We have previously referred to the influence ofthe Byzantine civilization in transmitting thelearning of antiquity across the abysm of thedark age. It must be admitted, however, thatthe importance of that civilization did not ex-tend much beyond the task of the common car-rier. There were no great creative scientistsin the later Roman empire of the East anymore than in the corresponding empire of theWest. There was, however, one field in whichthe Byzantine made respectable progress andregarding which their efforts require a fewwords of special comment. This was the fieldof medicine.

The Byzantines of this time could boastof two great medical men, Aetius of Amida(about 502-575 A.D.) and Paul of Aegina

41


(about 620-690). The works of Aetius were ofvalue largely because they recorded the teach-ings of many of his eminent predecessors, buthe was not entirely lacking in originality, andwas perhaps the first physician to mentiondiphtheria, with an allusion to some obser-vations of the paralysis of the palate whichsometimes follows this disease.

Paul of Aegina, who came from the Alexan-drian school about a century later, was one ofthose remarkable men whose ideas are cen-turies ahead of their time. This was partic-ularly true of Paul in regard to surgery, andhis attitude towards the supernatural in thecausation and treatment of diseases. He wasessentially a surgeon, being particularly fa-miliar with military surgery, and some of hisdescriptions of complicated and difficult oper-ations have been little improved upon even inmodern times. In his books he describes suchoperations as the removal of foreign bodiesfrom the nose, ear, and esophagus; and he rec-ognizes foreign growths such as polypi in theair-passages, and gives the method of theirremoval. Such operations as tracheotomy,tonsellotomy, bronchotomy, staphylotomy, etc.,were performed by him, and he even advo-cated and described puncture of the abdomi-nal cavity, giving careful directions as to thelocation in which such punctures should be

III. WESTERN MEDIÆVAL SCIENCE 43

made. He advocated amputation of the breastfor the cure of cancer, and described extirpa-tion of the uterus. Just how successful thislast operation may have been as performedby him does not appear; but he would hardlyhave recommended it if it had not been some-times, at least, successful. That he mentionsit at all, however, is significant, as this diffi-cult operation is considered one of the greattriumphs of modern surgery.

But Paul of Aegina is a striking exceptionto the rule among Byzantine surgeons, and ashe was their greatest, so he was also their lastimportant surgeon. The energies of all Byzan-tium were so expended in religious controver-sies that medicine, like the other sciences, wassoon relegated to a place among the other su-perstitions, and the influence of the Byzantineschool was presently replaced by that of theconquering Arabians.

THIRTEENTH-CENTURYMEDICINEThe thirteenth century marks the beginningof a gradual change in medicine, and a ten-dency to leave the time-worn rut of super-stitious dogmas that so long retarded theprogress of science. It is thought that the


great epidemics which raged during the Mid-dle Ages acted powerfully in diverting themedical thought of the times into new andentirely different channels. It will be re-membered that the teachings of Galen werehanded through mediæval times as the high-est and best authority on the subject of all dis-eases. When, however, the great epidemicsmade their appearance, the medical men ap-pealed to the works of Galen in vain for en-lightenment, as these works, having beenwritten several centuries before the time ofthe plagues, naturally contained no informa-tion concerning them. It was evident, there-fore, that on this subject, at least, Galen wasnot infallible; and it would naturally followthat, one fallible point having been revealed,others would be sought for. In other words,scepticism in regard to accepted methodswould be aroused, and would lead naturally,as such scepticism usually does, to progress.The devastating effects of these plagues, de-spite prayers and incantations, would arousedoubt in the minds of many as to the effi-cacy of superstitious rites and ceremonies incuring diseases. They had seen thousandsand tens of thousands of their fellow-beingsswept away by these awful scourges. Theyhad seen the ravages of these epidemics con-tinue for months or even years, notwithstand-


ing the fact that multitudes of God-fearingpeople prayed hourly that such ravages mightbe checked. And they must have observed alsothat when even very simple rules of cleanli-ness and hygiene were followed there was adiminution in the ravages of the plague, evenwithout the aid of incantations. Such obser-vations as these would have a tendency toawaken a suspicion in the minds of many ofthe physicians that disease was not a man-ifestation of the supernatural, but a naturalphenomenon, to be treated by natural meth-ods.

But, be the causes what they may, it isa fact that the thirteenth century marks aturning-point, or the beginning of an attitudeof mind which resulted in bringing medicineto a much more rational position. Amongthe thirteenth-century physicians, two menare deserving of special mention. These areArnald of Villanova (1235-1312) and Peter ofAbano (1250-1315). Both these men sufferedpersecution for expressing their belief in nat-ural, as against the supernatural, causes ofdisease, and at one time Arnald was obligedto flee from Barcelona for declaring that the“bulls” of popes were human works, and that“acts of charity were dearer to God thanhecatombs.” He was also accused of alchemy.Fleeing from persecution, he finally perished


by shipwreck.Arnald was the first great representative

of the school of Montpellier. He devoted muchtime to the study of chemicals, and was ac-tive in attempting to re-establish the teach-ings of Hippocrates and Galen. He was oneof the first of a long line of alchemists who,for several succeeding centuries, expended somuch time and energy in attempting to findthe “elixir of life.” The Arab discovery of alco-hol first deluded him into the belief that the“elixir” had at last been found; but later hediscarded it and made extensive experimentswith brandy, employing it in the treatment ofcertain diseases—the first record of the ad-ministration of this liquor as a medicine. Ar-nald also revived the search for some anæs-thetic that would produce insensibility to painin surgical operations. This idea was notoriginal with him, for since very early timesphysicians had attempted to discover suchan anæsthetic, and even so early a writeras Herodotus tells how the Scythians, by in-halation of the vapors of some kind of hemp,produced complete insensibility. It may havebeen these writings that stimulated Arnald tosearch for such an anæsthetic. In a book usu-ally credited to him, medicines are named andmethods of administration described whichwill make the patient insensible to pain, so


that “he may be cut and feel nothing, asthough he were dead.” For this purpose a mix-ture of opium, mandragora, and henbane isto be used. This mixture was held at the pa-tient’s nostrils much as ether and chloroformare administered by the modern surgeon. Themethod was modified by Hugo of Lucca (diedin 1252 or 1268), who added certain other nar-cotics, such as hemlock, to the mixture, andboiled a new sponge in this decoction. Af-ter boiling for a certain time, this sponge wasdried, and when wanted for use was dipped inhot water and applied to the nostrils.

Just how frequently patients recoveredfrom the administration of such a combina-tion of powerful poisons does not appear, butthe percentage of deaths must have beenvery high, as the practice was generally con-demned. Insensibility could have been pro-duced only by swallowing large quantities ofthe liquid, which dripped into the nose andmouth when the sponge was applied, and alethal quantity might thus be swallowed. Themethod was revived, with various modifica-tions, from time to time, but as often fell intodisuse. As late as 1782 it was sometimes at-tempted, and in that year the King of Polandis said to have been completely anæsthetizedand to have recovered, after a painless ampu-tation had been performed by the surgeons.


Peter of Abano was one of the first greatmen produced by the University of Padua. Hisfate would have been even more tragic thanthat of the shipwrecked Arnald had he notcheated the purifying fagots of the church bydying opportunely on the eve of his executionfor heresy. But if his spirit had cheated the fa-natics, his body could not, and his bones wereburned for his heresy. He had dared to denythe existence of a devil, and had suggestedthat the case of a patient who lay in a trancefor three days might help to explain some mir-acles, like the raising of Lazarus.

His great work was Conciliator Differen-tiarum, an attempt to reconcile physiciansand philosophers. But his researches werenot confined to medicine, for he seems to havehad an inkling of the hitherto unknown factthat air possesses weight, and his calculationof the length of the year at three hundred andsixty-five days, six hours, and four minutes, isexceptionally accurate for the age in which helived. He was probably the first of the Westernwriters to teach that the brain is the sourceof the nerves, and the heart the source of thevessels. From this it is seen that he was grop-ing in the direction of an explanation of thecirculation of the blood, as demonstrated byHarvey three centuries later.

The work of Arnald and Peter of Abano


in “reviving” medicine was continued activelyby Mondino (1276-1326) of Bologna, the “re-storer of anatomy,” and by Guy of Chauliac:(born about 1300), the “restorer of surgery.”All through the early Middle Ages dissectionsof human bodies had been forbidden, andeven dissection of the lower animals gradu-ally fell into disrepute because physicians de-tected in such practices were sometimes ac-cused of sorcery. Before the close of the thir-teenth century, however, a reaction had be-gun, physicians were protected, and dissec-tions were occasionally sanctioned by the rul-ing monarch. Thus Emperor Frederick II.(1194-1250 A.D.)—whose services to sciencewe have already had occasion to mention—ordered that at least one human body shouldbe dissected by physicians in his kingdom ev-ery five years. By the time of Mondino dis-sections were becoming more frequent, andhe himself is known to have dissected anddemonstrated several bodies. His writings onanatomy have been called merely plagiarismsof Galen, but in all probability he made manydiscoveries independently, and on the whole,his work may be taken as more advanced thanGalen’s. His description of the heart is partic-ularly accurate, and he seems to have comenearer to determining the course of the bloodin its circulation than any of his predecessors.


In this quest he was greatly handicapped bythe prevailing belief in the idea that blood-vessels must contain air as well as blood, andthis led him to assume that one of the cav-ities of the heart contained “spirits,” or air.It is probable, however, that his accurate ob-servations, so far as they went, were helpfulstepping-stones to Harvey in his discovery ofthe circulation.

Guy of Chauliac, whose innovations insurgery reestablished that science on a firmbasis, was not only one of the most cultured,but also the most practical surgeon of histime. He had great reverence for the worksof Galen, Albucasis, and others of his notedpredecessors; but this reverence did not blindhim to their mistakes nor prevent him fromusing rational methods of treatment far inadvance of theirs. His practicality is shownin some of his simple but useful inventionsfor the sick-room, such as the device of arope, suspended from the ceiling over the bed,by which a patient may move himself aboutmore easily; and in some of his improve-ments in surgical dressings, such as stiffen-ing bandages by dipping them in the whiteof an egg so that they are held firmly. Hetreated broken limbs in the suspended cra-dle still in use, and introduced the method ofmaking “traction” on a broken limb by means


of a weight and pulley, to prevent deformitythrough shortening of the member. He wasone of the first physicians to recognize theutility of spectacles, and recommended themin cases not amenable to treatment with lo-tions and eye-waters. In some of his surgi-cal operations, such as trephining for fractureof the skull, his technique has been little im-proved upon even in modern times. In oneof these operations he successfully removed aportion of a man’s brain.

Surgery was undoubtedly stimulatedgreatly at this period by the constant wars.Lay physicians, as a class, had been lookeddown upon during the Dark Ages; but withthe beginning of the return to rationalism,the services of surgeons on the battle-field, toremove missiles from wounds, and to care forwounds and apply dressings, came to be morefully appreciated. In return for his labors thesurgeon was thus afforded better opportuni-ties for observing wounds and diseases, whichled naturally to a gradual improvement insurgical methods.


FIFTEENTH-CENTURYMEDICINEThe thirteenth and fourteenth centuries hadseen some slight advancement in the scienceof medicine; at least, certain surgeons andphysicians, if not the generality, had madeadvances; but it was not until the fifteenthcentury that the general revival of medicallearning became assured. In this movement,naturally, the printing-press played an all-important part. Medical books, hitherto prac-tically inaccessible to the great mass of physi-cians, now became common, and this outputof reprints of Greek and Arabic treatises re-vealed the fact that many of the supposed truecopies were spurious. These discoveries verynaturally aroused all manner of doubt andcriticism, which in turn helped in the devel-opment of independent thought.

A certain manuscript of the great Cor-nelius Celsus, the De Medicine, which hadbeen lost for many centuries, was found inthe church of St. Ambrose, at Milan, in 1443,and was at once put into print. The effect ofthe publication of this book, which had lainin hiding for so many centuries, was a rev-elation, showing the medical profession howfar most of their supposed true copies of Cel-sus had drifted away from the original. The


indisputable authenticity of this manuscript,discovered and vouched for by the man whoshortly after became Pope Nicholas V., madeits publication the more impressive. The out-put in book form of other authorities followedrapidly, and the manifest discrepancies be-tween such teachers as Celsus, Hippocrates,Galen, and Pliny heightened still more thegrowing spirit of criticism.

These doubts resulted in great controver-sies as to the proper treatment of certain dis-eases, some physicians following Hippocrates,others Galen or Celsus, still others the Ara-bian masters. One of the most bitter of thesecontests was over the question of “revulsion,”and “derivation”—that is, whether in cases ofpleurisy treated by bleeding, the venesectionshould be made at a point distant from theseat of the disease, as held by the “revulsion-ists,” or at a point nearer and on the sameside of the body, as practised by the “deriva-tionists.” That any great point for discussioncould be raised in the fifteenth or sixteenthcenturies on so simple a matter as it seemsto-day shows how necessary to the progressof medicine was the discovery of the circula-tion of the blood made by Harvey two cen-turies later. After Harvey’s discovery no suchdiscussion could have been possible, becausethis discovery made it evident that as far as


the general effect upon the circulation is con-cerned, it made little difference whether thebleeding was done near a diseased part or re-mote from it. But in the sixteenth centurythis question was the all-absorbing one amongthe doctors. At one time the faculty of Pariscondemned “derivation”; but the supporters ofthis method carried the war still higher, andEmperor Charles V. himself was appealed to.He reversed the decision of the Paris faculty,and decided in favor of “derivation.” His deci-sion was further supported by Pope ClementVII., although the discussion dragged on untilcut short by Harvey’s discovery.

But a new form of injury now claimedthe attention of the surgeons, something thatcould be decided by neither Greek nor Ara-bian authors, as the treatment of gun-shotwounds was, for obvious reasons, not givenin their writings. About this time, also, camethe great epidemics, “the sweating sickness”and scurvy; and upon these subjects, also, theGreeks and Arabians were silent. John ofVigo, in his book, the Practica Copiosa, pub-lished in 1514, and repeated in many editions,became the standard authority on all thesesubjects, and thus supplanted the works of theancient writers.

According to Vigo, gun-shot wounds dif-fered from the wounds made by ordinary


weapons—that is, spear, arrow, sword, oraxe—in that the bullet, being round, bruisedrather than cut its way through the tissues;it burned the flesh; and, worst of all, it poi-soned it. Vigo laid especial stress upon treat-ing this last condition, recommending the useof the cautery or the oil of elder, boiling hot.It is little wonder that gun-shot wounds wereso likely to prove fatal. Yet, after all, here wasthe germ of the idea of antisepsis.

NEW BEGINNINGS INGENERAL SCIENCEWe have dwelt thus at length on the subjectof medical science, because it was chiefly inthis field that progress was made in the West-ern world during the mediæval period, and be-cause these studies furnished the point of de-parture for the revival all along the line. Itwill be understood, however, from what wasstated in the preceding chapter, that the Ara-bian influences in particular were to some ex-tent making themselves felt along other lines.The opportunity afforded a portion of theWestern world—notably Spain and Sicily—togain access to the scientific ideas of antiquitythrough Arabic translations could not fail ofinfluence. Of like character, and perhaps even


more pronounced in degree, was the influ-ence wrought by the Byzantine refugees, who,when Constantinople began to be threatenedby the Turks, migrated to the West in consid-erable numbers, bringing with them a knowl-edge of Greek literature and a large number ofprecious works which for centuries had beenquite forgotten or absolutely ignored in Italy.Now Western scholars began to take an inter-est in the Greek language, which had been ut-terly neglected since the beginning of the Mid-dle Ages. Interesting stories are told of the ef-forts made by such men as Cosmo de’ Medicito gain possession of classical manuscripts.The revival of learning thus brought abouthad its first permanent influence in the fieldsof literature and art, but its effect on sci-ence could not be long delayed. Quite inde-pendently of the Byzantine influence, how-ever, the striving for better intellectual thingshad manifested itself in many ways before theclose of the thirteenth century. An illustrationof this is found in the almost simultaneousdevelopment of centres of teaching, which de-veloped into the universities of Italy, France,England, and, a little later, of Germany.

The regular list of studies that came to beadopted everywhere comprised seven nomi-nal branches, divided into two groups—the so-called quadrivium, comprising music, arith-


metic, geometry, and astronomy; and the triv-ium comprising grammar, rhetoric, and logic.The vagueness of implication of some of thesebranches gave opportunity to the teacher forthe promulgation of almost any knowledge ofwhich he might be possessed, but there canbe no doubt that, in general, science had butmeagre share in the curriculum. In so far as itwas given representation, its chief field musthave been Ptolemaic astronomy. The utterlack of scientific thought and scientific methodis illustrated most vividly in the works of thegreatest men of that period—such men as Al-bertus Magnus, Thomas Aquinas, Bonaven-tura, and the hosts of other scholastics oflesser rank. Yet the mental awakening im-plied in their efforts was sure to extend toother fields, and in point of fact there was atleast one contemporary of these great scholas-tics whose mind was intended towards sci-entific subjects, and who produced writingsstrangely at variance in tone and in contentwith the others. This anachronistic thinkerwas the English monk, Roger Bacon.

ROGER BACONBacon was born in 1214 and died in 1292.By some it is held that he was not appreci-ated in his own time because he was really


a modern scientist living in an age two cen-turies before modern science or methods ofmodern scientific thinking were known. Suchan estimate, however, is a manifest exaggera-tion of the facts, although there is probably agrain of truth in it withal. His learning cer-tainly brought him into contact with the greatthinkers of the time, and his writings causedhim to be imprisoned by his fellow-churchmenat different times, from which circumstanceswe may gather that he was advanced thinker,even if not a modern scientist.

Although Bacon was at various times indurance, or under surveillance, and forbid-den to write, he was nevertheless a marvel-lously prolific writer, as is shown by the nu-merous books and unpublished manuscriptsof his still extant. His master-production wasthe Opus Majus. In Part IV. of this work heattempts to show that all sciences rest ulti-mately on mathematics; but Part V., whichtreats of perspective, is of particular interestto modern scientists, because in this he dis-cusses reflection and refraction, and the prop-erties of mirrors and lenses. In this part, also,it is evident that he is making use of such Ara-bian writers as Alkindi and Alhazen, and thisis of especial interest, since it has been usedby his detractors, who accuse him of lack oforiginality, to prove that his seeming inven-


tions and discoveries were in reality adapta-tions of the Arab scientists. It is difficult to de-termine just how fully such criticisms are jus-tified. It is certain, however, that in this parthe describes the anatomy of the eye with greataccuracy, and discusses mirrors and lenses.

The magnifying power of the segment of aglass sphere had been noted by Alhazen, whohad observed also that the magnification wasincreased by increasing the size of the seg-ment used. Bacon took up the discussion ofthe comparative advantages of segments, andin this discussion seems to show that he un-derstood how to trace the progress of the raysof light through a spherical transparent body,and how to determine the place of the image.He also described a method of constructinga telescope, but it is by no means clear thathe had ever actually constructed such an in-strument. It is also a mooted question as towhether his instructions as to the construc-tion of such an instrument would have en-abled any one to construct one. The vagariesof the names of terms as he uses them allowsuch latitude in interpretation that modernscientists are not agreed as to the practicabil-ity of Bacon’s suggestions. For example, heconstantly refers to force under such namesas virtus, species, imago, agentis, and a scoreof other names, and this naturally gives rise


to the great differences in the interpretationsof his writings, with corresponding differencesin estimates of them.

The claim that Bacon originated the useof lenses, in the form of spectacles, cannot beproven. Smith has determined that as earlyas the opening years of the fourteenth centurysuch lenses were in use, but this proves noth-ing as regards Bacon’s connection with theirinvention. The knowledge of lenses seems tobe very ancient, if we may judge from the con-vex lens of rock crystal found by Layard in hisexcavations at Nimrud. There is nothing toshow, however, that the ancients ever thoughtof using them to correct defects of vision. Nei-ther, apparently, is it feasible to determinewhether the idea of such an application origi-nated with Bacon.

Another mechanical discovery about whichthere has been a great deal of discussion is Ba-con’s supposed invention of gunpowder. It ap-pears that in a certain passage of his work hedescribes the process of making a substancethat is, in effect, ordinary gunpowder; but itis more than doubtful whether he understoodthe properties of the substance he describes.It is fairly well established, however, that inBacon’s time gunpowder was known to theArabs, so that it should not be surprising tofind references made to it in Bacon’s work,


since there is reason to believe that he con-stantly consulted Arabian writings.

The great merit of Bacon’s work, however,depends on the principles taught as regardsexperiment and the observation of nature,rather than on any single invention. He hadthe all-important idea of breaking with tradi-tion. He championed unfettered inquiry in ev-ery field of thought. He had the instinct ofa scientific worker—a rare instinct indeed inthat age. Nor need we doubt that to the bestof his opportunities he was himself an originalinvestigator.

LEONARDO DA VINCIThe relative infertility of Bacon’s thought isshown by the fact that he founded no schooland left no trace of discipleship. The entirecentury after his death shows no single Eu-ropean name that need claim the attentionof the historian of science. In the latter partof the fifteenth century, however, there is evi-dence of a renaissance of science no less thanof art. The German Muller became famousunder the latinized named of Regio Montanus(1437-1472), although his actual scientific at-tainments would appear to have been impor-tant only in comparison with the utter igno-rance of his contemporaries. The most distin-


guished worker of the new era was the famousItalian Leonardo da Vinci—a man who hasbeen called by Hamerton the most universalgenius that ever lived. Leonardo’s position inthe history of art is known to every one. Withthat, of course, we have no present concern;but it is worth our while to inquire at somelength as to the famous painter’s accomplish-ments as a scientist.

From a passage in the works of Leonardo,first brought to light by Venturi,3 it wouldseem that the great painter anticipatedCopernicus in determining the movement ofthe earth. He made mathematical calcu-lations to prove this, and appears to havereached the definite conclusion that the earthdoes move—or what amounts to the samething, that the sun does not move. Muntz isauthority for the statement that in one of hiswritings he declares, “Il sole non si mouve”—the sun does not move.

Among his inventions is a dynamometerfor determining the traction power of ma-chines and animals, and his experiments withsteam have led some of his enthusiastic par-tisans to claim for him priority to Watt in theinvention of the steam-engine. In these ex-

3Etigene Muntz, Leonardo do Vinci, Artist, Thinker,and Man of Science, 2 vols., New York, 1892. Vol. II.,p. 73.


periments, however, Leonardo seems to haveadvanced little beyond Hero of Alexandriaand his steam toy. Hero’s steam-engine didnothing but rotate itself by virtue of escap-ing jets of steam forced from the bent tubes,while Leonardo’s “steam-engine” “drove a ballweighing one talent over a distance of six sta-dia.” In a manuscript now in the library ofthe Institut de France, Da Vinci describes thisengine minutely. The action of this machinewas due to the sudden conversion of smallquantities of water into steam (“smoke,” as hecalled it) by coming suddenly in contact witha heated surface in a proper receptacle, therapidly formed steam acting as a propulsiveforce after the manner of an explosive. It is re-ally a steam-gun, rather than a steam-engine,and it is not unlikely that the study of the ac-tion of gunpowder may have suggested it toLeonardo.

It is believed that Leonardo is the true dis-coverer of the camera-obscura, although theNeapolitan philosopher, Giambattista Porta,who was not born until some twenty years af-ter the death of Leonardo, is usually creditedwith first describing this device. There is littledoubt, however, that Da Vinci understood theprinciple of this mechanism, for he describeshow such a camera can be made by cuttinga small, round hole through the shutter of a


ROGER BACON


darkened room, the reversed image of objectsoutside being shown on the opposite wall.

Like other philosophers in all ages, he hadobserved a great number of facts which he wasunable to explain correctly. But such accumu-lations of scientific observations are alwaysinteresting, as showing how many centuriesof observation frequently precede correct ex-planation. He observed many facts aboutsounds, among others that blows struck upona bell produced sympathetic sounds in a bellof the same kind; and that striking the stringof a lute produced vibration in correspondingstrings of lutes strung to the same pitch. Heknew, also, that sounds could be heard at adistance at sea by listening at one end of atube, the other end of which was placed in thewater; and that the same expedient workedsuccessfully on land, the end of the tube beingplaced against the ground.

The knowledge of this great number of un-explained facts is often interpreted by the ad-mirers of Da Vinci, as showing an almost oc-cult insight into science many centuries in ad-vance of his time. Such interpretations, how-ever, are illusive. The observation, for exam-ple, that a tube placed against the ground en-ables one to hear movements on the earth at adistance, is not in itself evidence of anythingmore than acute scientific observation, as a


similar method is in use among almost everyrace of savages, notably the American Indi-ans. On the other hand, one is inclined to givecredence to almost any story of the breadth ofknowledge of the man who came so near an-ticipating Hutton, Lyell, and Darwin in hisinterpretation of the geological records as hefound them written on the rocks.

It is in this field of geology that Leonardois entitled to the greatest admiration by mod-ern scientists. He had observed the depositof fossil shells in various strata of rocks, evenon the tops of mountains, and he rejected oncefor all the theory that they had been depositedthere by the Deluge. He rightly interpretedtheir presence as evidence that they had oncebeen deposited at the bottom of the sea. Thisprocess he assumed had taken hundreds andthousands of centuries, thus tacitly rejectingthe biblical tradition as to the date of the cre-ation.

Notwithstanding the obvious interest thatattaches to the investigations of Leonardo, itmust be admitted that his work in science re-mained almost as infertile as that of his greatprecursor, Bacon. The really stimulative workof this generation was done by a man of af-fairs, who knew little of theoretical science ex-cept in one line, but who pursued that onepractical line until he achieved a wonderful


result. This man was Christopher Colum-bus. It is not necessary here to tell the tritestory of his accomplishment. Suffice it thathis practical demonstration of the rotundityof the earth is regarded by most modern writ-ers as marking an epoch in history. With theyear of his voyage the epoch of the MiddleAges is usually regarded as coming to an end.It must not be supposed that any very sud-den change came over the aspect of scholar-ship of the time, but the preliminaries of greatthings had been achieved, and when Colum-bus made his famous voyage in 1492, the manwas already alive who was to bring forwardthe first great vitalizing thought in the field ofpure science that the Western world had orig-inated for more than a thousand years. Thisman bore the name of Kopernik, or in its fa-miliar Anglicized form, Copernicus. His lifework and that of his disciples will claim ourattention in the succeeding chapter.

IV. THE NEWCOSMOLOGY—COPERNICUS TOKEPLER ANDGALILEO

We have seen that the Ptolemaic astronomy,which was the accepted doctrine throughoutthe Middle Ages, taught that the earth isround. Doubtless there was a popular opin-ion current which regarded the earth as flat,but it must be understood that this opinionhad no champions among men of science dur-ing the Middle Ages. When, in the year 1492,Columbus sailed out to the west on his mem-orable voyage, his expectation of reaching In-dia had full scientific warrant, however muchit may have been scouted by certain ecclesi-astics and by the average man of the period.

69


Nevertheless, we may well suppose that thesuccessful voyage of Columbus, and the stillmore demonstrative one made about thirtyyears later by Magellan, gave the theory ofthe earth’s rotundity a certainty it could neverpreviously have had. Alexandrian geogra-phers had measured the size of the earth, andhad not hesitated to assert that by sailingwestward one might reach India. But there isa wide gap between theory and practice, andit required the voyages of Columbus and hissuccessors to bridge that gap.

After the companions of Magellan com-pleted the circumnavigation of the globe, thegeneral shape of our earth would, obviously,never again be called in question. But demon-stration of the sphericity of the earth had, ofcourse, no direct bearing upon the question ofthe earth’s position in the universe. There-fore the voyage of Magellan served to fortify,rather than to dispute, the Ptolemaic theory.According to that theory, as we have seen, theearth was supposed to lie immovable at thecentre of the universe; the various heavenlybodies, including the sun, revolving about it ineccentric circles. We have seen that several ofthe ancient Greeks, notably Aristarchus, dis-puted this conception, declaring for the cen-tral position of the sun in the universe, andthe motion of the earth and other planets

IV. THE NEW COSMOLOGY 71

about that body. But this revolutionary the-ory seemed so opposed to the ordinary obser-vation that, having been discountenanced byHipparchus and Ptolemy, it did not find a sin-gle important champion for more than a thou-sand years after the time of the last greatAlexandrian astronomer.

The first man, seemingly, to hark back tothe Aristarchian conception in the new scien-tific era that was now dawning was the notedcardinal, Nikolaus of Cusa, who lived in thefirst half of the fifteenth century, and wasdistinguished as a philosophical writer andmathematician. His De Docta Ignorantia ex-pressly propounds the doctrine of the earth’smotion. No one, however, paid the slight-est attention to his suggestion, which, there-fore, merely serves to furnish us with anotherinteresting illustration of the futility of pro-pounding even a correct hypothesis before thetime is ripe to receive it—particularly if thehypothesis is not fully fortified by reasoningbased on experiment or observation.

The man who was destined to put forwardthe theory of the earth’s motion in a way tocommand attention was born in 1473, at thevillage of Thorn, in eastern Prussia. His namewas Nicholas Copernicus. There is no morefamous name in the entire annals of sciencethan this, yet posterity has never been able


fully to establish the lineage of the famous ex-positor of the true doctrine of the solar sys-tem. The city of Thorn lies in a province ofthat border territory which was then undercontrol of Poland, but which subsequently be-came a part of Prussia. It is claimed that theaspects of the city were essentially German,and it is admitted that the mother of Coper-nicus belonged to that race. The nationalityof the father is more in doubt, but it is urgedthat Copernicus used German as his mother-tongue. His great work was, of course, writ-ten in Latin, according to the custom of thetime; but it is said that, when not employ-ing that language, he always wrote in Ger-man. The disputed nationality of Coperni-cus strongly suggests that he came of a mixedracial lineage, and we are reminded again ofthe influences of those ethnical minglings towhich we have previously more than once re-ferred. The acknowledged centres of civiliza-tion towards the close of the fifteenth centurywere Italy and Spain. Therefore, the birth-place of Copernicus lay almost at the confinesof civilization, reminding us of that earlier pe-riod when Greece was the centre of culture,but when the great Greek thinkers were bornin Asia Minor and in Italy.

As a young man, Copernicus made hisway to Vienna to study medicine, and subse-


NICOLAUS COPERNICUS

(From the painting in possession of the Royal Society)


quently he journeyed into Italy and remainedthere many years, About the year 1500 heheld the chair of mathematics in a college atRome. Subsequently he returned to his nativeland and passed his remaining years there,dying at Domkerr, in Frauenburg, East Prus-sia, in the year 1543.

It would appear that Copernicus conceivedthe idea of the heliocentric system of the uni-verse while he was a comparatively youngman, since in the introduction to his greatwork, which he addressed to Pope Paul III.,he states that he has pondered his systemnot merely nine years, in accordance with themaxim of Horace, but well into the fourth pe-riod of nine years. Throughout a considerableportion of this period the great work of Coper-nicus was in manuscript, but it was not pub-lished until the year of his death. The rea-sons for the delay are not very fully estab-lished. Copernicus undoubtedly taught hissystem throughout the later decades of hislife. He himself tells us that he had even ques-tioned whether it were not better for him toconfine himself to such verbal teaching, fol-lowing thus the example of Pythagoras. Justas his life was drawing to a close, he decided topursue the opposite course, and the first copyof his work is said to have been placed in hishands as he lay on his deathbed.


The violent opposition which the new sys-tem met from ecclesiastical sources led sub-sequent commentators to suppose that Coper-nicus had delayed publication of his workthrough fear of the church authorities. Thereseems, however, to be no direct evidence forthis opinion. It has been thought signifi-cant that Copernicus addressed his work tothe pope. It is, of course, quite conceivablethat the aged astronomer might wish by thismeans to demonstrate that he wrote in nospirit of hostility to the church. His addressto the pope might have been considered as adesirable shield precisely because the authorrecognized that his work must needs meetwith ecclesiastical criticism. Be that as it may,Copernicus was removed by death from thedanger of attack, and it remained for his dis-ciples of a later generation to run the gauntletof criticism and suffer the charges of heresy.

The work of Copernicus, published thus inthe year 1543 at Nuremberg, bears the titleDe Orbium Cœlestium Revolutionibus.

It is not necessary to go into details as tothe cosmological system which Copernicus ad-vocated, since it is familiar to every one. Ina word, he supposed the sun to be the cen-tre of all the planetary motions, the earth tak-ing its place among the other planets, the listof which, as known at that time, comprised


Mercury, Venus, the Earth, Mars, Jupiter, andSaturn. The fixed stars were alleged to be sta-tionary, and it was necessary to suppose thatthey are almost infinitely distant, inasmuchas they showed to the observers of that timeno parallax; that is to say, they preserved thesame apparent position when viewed from theopposite points of the earth’s orbit.

But let us allow Copernicus to speak forhimself regarding his system, His expositionis full of interest. We quote first the introduc-tion just referred to, in which appeal is madedirectly to the pope.

“I can well believe, most holy fa-ther, that certain people, when theyhear of my attributing motion tothe earth in these books of mine,will at once declare that such anopinion ought to be rejected. Now,my own theories do not please meso much as not to consider whatothers may judge of them. Accord-ingly, when I began to reflect uponwhat those persons who accept thestability of the earth, as confirmedby the opinion of many centuries,would say when I claimed that theearth moves, I hesitated for a longtime as to whether I should pub-lish that which I have written to


demonstrate its motion, or whetherit would not be better to follow theexample of the Pythagoreans, whoused to hand down the secrets ofphilosophy to their relatives andfriends only in oral form. As I wellconsidered all this, I was almostimpelled to put the finished workwholly aside, through the scorn Ihad reason to anticipate on accountof the newness and apparent con-trariness to reason of my theory.

“My friends, however, dis-suaded me from such a courseand admonished me that I oughtto publish my book, which hadlain concealed in my possessionnot only nine years, but alreadyinto four times the ninth year.Not a few other distinguished andvery learned men asked me todo the same thing, and told methat I ought not, on account ofmy anxiety, to delay any longerin consecrating my work to thegeneral service of mathematicians.

“But your holiness will perhapsnot so much wonder that I havedared to bring the results of mynight labors to the light of day,


after having taken so much carein elaborating them, but is wait-ing instead to hear how it enteredmy mind to imagine that the earthmoved, contrary to the acceptedopinion of mathematicians—nay,almost contrary to ordinary humanunderstanding. Therefore I willnot conceal from your holiness thatwhat moved me to consider anotherway of reckoning the motions of theheavenly bodies was nothing elsethan the fact that the mathemati-cians do not agree with one an-other in their investigations. In thefirst place, they are so uncertainabout the motions of the sun andmoon that they cannot find out thelength of a full year. In the sec-ond place, they apply neither thesame laws of cause and effect, indetermining the motions of the sunand moon and of the five planets,nor the same proofs. Some employonly concentric circles, others useeccentric and epicyclic ones, withwhich, however, they do not fullyattain the desired end. They couldnot even discover nor compute themain thing—namely, the form of


the universe and the symmetry ofits parts. It was with them as ifsome should, from different places,take hands, feet, head, and otherparts of the body, which, althoughvery beautiful, were not drawn intheir proper relations, and, with-out making them in any way corre-spond, should construct a monsterinstead of a human being.

“Accordingly, when I had longreflected on this uncertainty ofmathematical tradition, I took thetrouble to read again the books ofall the philosophers I could get holdof, to see if some one of them hadnot once believed that there wereother motions of the heavenly bod-ies. First I found in Cicero thatNiceties had believed in the mo-tion of the earth. Afterwards Ifound in Plutarch, likewise, thatsome others had held the sameopinion. This induced me also tobegin to consider the movability ofthe earth, and, although the the-ory appeared contrary to reason, Idid so because I knew that othersbefore me had been allowed to as-sume rotary movements at will, in


order to explain the phenomena ofthese celestial bodies. I was of theopinion that I, too, might be per-mitted to see whether, by presup-posing motion in the earth, morereliable conclusions than hithertoreached could not be discovered forthe rotary motions of the spheres.And thus, acting on the hypothe-sis of the motion which, in the fol-lowing book, I ascribe to the earth,and by long and continued obser-vations, I have finally discoveredthat if the motion of the other plan-ets be carried over to the relationof the earth and this is made thebasis for the rotation of every star,not only will the phenomena of theplanets be explained thereby, butalso the laws and the size of thestars; all their spheres and theheavens themselves will appear soharmoniously connected that noth-ing could be changed in any partof them without confusion in theremaining parts and in the wholeuniverse. I do not doubt that cleverand learned men will agree withme if they are willing fully to com-prehend and to consider the proofs


which I advance in the book be-fore us. In order, however, thatboth the learned and the unlearnedmay see that I fear no man’s judg-ment, I wanted to dedicate these,my night labors, to your holiness,rather than to any one else, be-cause you, even in this remotecorner of the earth where I live,are held to be the greatest in dig-nity of station and in love for allsciences and for mathematics, sothat you, through your position andjudgment, can easily suppress thebites of slanderers, although theproverb says that there is no rem-edy against the bite of calumny.”

In chapter X. of book I., “On the Order ofthe Spheres,” occurs a more detailed presen-tation of the system, as follows:

“That which Martianus Capel-la, and a few other Latins, verywell knew, appears to me extremelynoteworthy. He believed thatVenus and Mercury revolve aboutthe sun as their centre and thatthey cannot go farther away fromit than the circles of their orbitspermit, since they do not revolve


about the earth like the other plan-ets. According to this theory, then,Mercury’s orbit would be includedwithin that of Venus, which is morethan twice as great, and would findroom enough within it for its revo-lution.

“If, acting upon this supposi-tion, we connect Saturn, Jupiter,and Mars with the same centre,keeping in mind the greater extentof their orbits, which include theearth’s sphere besides those of Mer-cury and Venus, we cannot fail tosee the explanation of the regularorder of their motions. He is cer-tain that Saturn, Jupiter, and Marsare always nearest the earth whenthey rise in the evening—that is,when they appear over against thesun, or the earth stands betweenthem and the sun—but that theyare farthest from the earth whenthey set in the evening—that is,when we have the sun betweenthem and the earth. This provessufficiently that their centre be-longs to the sun and is the sameabout which the orbits of Venusand Mercury circle. Since, how-


ever, all have one centre, it is nec-essary for the space intervening be-tween the orbits of Venus and Marsto include the earth with her ac-companying moon and all that isbeneath the moon; for the moon,which stands unquestionably near-est the earth, can in no way be sep-arated from her, especially as thereis sufficient room for the moon inthe aforesaid space. Hence we donot hesitate to claim that the wholesystem, which includes the moonwith the earth for its centre, makesthe round of that great circle be-tween the planets, in yearly mo-tion about the sun, and revolvesabout the centre of the universe,in which the sun rests motionless,and that all which looks like mo-tion in the sun is explained bythe motion of the earth. The ex-tent of the universe, however, is sogreat that, whereas the distance ofthe earth from the sun is consider-able in comparison with the size ofthe other planetary orbits, it dis-appears when compared with thesphere of the fixed stars. I holdthis to be more easily comprehen-


sible than when the mind is con-fused by an almost endless numberof circles, which is necessarily thecase with those who keep the earthin the middle of the universe. Al-though this may appear incompre-hensible and contrary to the opin-ion of many, I shall, if God wills,make it clearer than the sun, atleast to those who are not ignorantof mathematics.

“The order of the spheres is asfollows: The first and lightest ofall the spheres is that of the fixedstars, which includes itself and allothers, and hence is motionless asthe place in the universe to whichthe motion and position of all otherstars is referred.

“Then follows the outermostplanet, Saturn, which completes itsrevolution around the sun in thirtyyears; next comes Jupiter witha twelve years’ revolution; thenMars, which completes its course intwo years. The fourth one in or-der is the yearly revolution whichincludes the earth with the moon’sorbit as an epicycle. In the fifthplace is Venus with a revolution


of nine months. The sixth placeis taken by Mercury, which com-pletes its course in eighty days. Inthe middle of all stands the sun,and who could wish to place thelamp of this most beautiful templein another or better place. Thus, infact, the sun, seated upon the royalthrone, controls the family of thestars which circle around him. Wefind in their order a harmoniousconnection which cannot be foundelsewhere. Here the attentive ob-server can see why the waxing andwaning of Jupiter seems greaterthan with Saturn and smaller thanwith Mars, and again greater withVenus than with Mercury. Also,why Saturn, Jupiter, and Mars arenearer to the earth when they risein the evening than when they dis-appear in the rays of the sun. Moreprominently, however, is it seen inthe case of Mars, which when itappears in the heavens at night,seems to equal Jupiter in size, butsoon afterwards is found among thestars of second magnitude. All ofthis results from the same cause—namely, from the earth’s motion.


The fact that nothing of this is to beseen in the case of the fixed stars isa proof of their immeasurable dis-tance, which makes even the orbitof yearly motion or its counterpartinvisible to us.”4

The fact that the stars show no parallaxhad been regarded as an important argumentagainst the motion of the earth, and it wasstill so considered by the opponents of thesystem of Copernicus. It had, indeed, beennecessary for Aristarchus to explain the factas due to the extreme distance of the stars;a perfectly correct explanation, but one thatimplies distances that are altogether incon-ceivable. It remained for nineteenth-centuryastronomers to show, with the aid of instru-ments of greater precision, that certain of thestars have a parallax. But long before thisdemonstration had been brought forward, thesystem of Copernicus had been accepted as apart of common knowledge.

While Copernicus postulated a cosmicalscheme that was correct as to its main fea-tures, he did not altogether break away fromcertain defects of the Ptolemaic hypothesis.Indeed, he seems to have retained as much of

4Copernicus, Uber die Kreisbewegungen der Welfkor-per, trans. from Dannemann’s Geschichle du Naturwis-senschaften, 2 vols., Leipzig, 1896.


this as practicable, in deference to the preju-dice of his time. Thus he records the planetaryorbits as circular, and explains their eccentric-ities by resorting to the theory of epicycles,quite after the Ptolemaic method. But now, ofcourse, a much more simple mechanism suf-ficed to explain the planetary motions, sincethe orbits were correctly referred to the cen-tral sun and not to the earth.

Needless to say, the revolutionary concep-tion of Copernicus did not meet with imme-diate acceptance. A number of prominentastronomers, however, took it up almost atonce, among these being Rhaeticus, who wrotea commentary on the evolutions; ErasmusReinhold, the author of the Prutenic tables;Rothmann, astronomer to the Landgrave ofHesse, and Maestlin, the instructor of Ke-pler. The Prutenic tables, just referred to,so called because of their Prussian origin,were considered an improvement on the ta-bles of Copernicus, and were highly esteemedby the astronomers of the time. The com-mentary of Rhaeticus gives us the interest-ing information that it was the observation ofthe orbit of Mars and of the very great differ-ence between his apparent diameters at dif-ferent times which first led Copernicus to con-ceive the heliocentric idea. Of Reinhold it isrecorded that he considered the orbit of Mer-


cury elliptical, and that he advocated a theoryof the moon, according to which her epicyclerevolved on an elliptical orbit, thus in a mea-sure anticipating one of the great discoveriesof Kepler to which we shall refer presently.The Landgrave of Hesse was a practical as-tronomer, who produced a catalogue of fixedstars which has been compared with that ofTycho Brahe. He was assisted by Rothmannand by Justus Byrgius. Maestlin, the precep-tor of Kepler, is reputed to have been the firstmodern observer to give a correct explanationof the light seen on portions of the moon notdirectly illumined by the sun. He explainedthis as not due to any proper light of the moonitself, but as light reflected from the earth.Certain of the Greek philosophers, however,are said to have given the same explanation,and it is alleged also that Leonardo da Vincianticipated Maestlin in this regard.

While, various astronomers of some emi-nence thus gave support to the Copernicansystem, almost from the beginning, it unfor-tunately chanced that by far the most famousof the immediate successors of Copernicus de-clined to accept the theory of the earth’s mo-tion. This was Tycho Brahe, one of the great-est observing astronomers of any age. TychoBrahe was a Dane, born at Knudstrup in theyear 1546. He died in 1601 at Prague, in Bo-


hemia. During a considerable portion of hislife he found a patron in Frederick, King ofDenmark, who assisted him to build a splen-did observatory on the Island of Huene. Onthe death of his patron Tycho moved to Ger-many, where, as good luck would have it, hecame in contact with the youthful Kepler, andthus, no doubt, was instrumental in stimulat-ing the ambitions of one who in later yearswas to be known as a far greater theoristthan himself. As has been said, Tycho re-jected the Copernican theory of the earth’smotion. It should be added, however, thathe accepted that part of the Copernican the-ory which makes the sun the centre of all theplanetary motions, the earth being excepted.He thus developed a system of his own, whichwas in some sort a compromise between thePtolemaic and the Copernican systems. AsTycho conceived it, the sun revolves about theearth, carrying with it the planets-Mercury,Venus, Mars, Jupiter, and Saturn, which plan-ets have the sun and not the earth as the cen-tre of their orbits. This cosmical scheme, itshould be added, may be made to explain theobserved motions of the heavenly bodies, butit involves a much more complex mechanismthan is postulated by the Copernican theory.

Various explanations have been offered ofthe conservatism which held the great Danish


astronomer back from full acceptance of therelatively simple and, as we now know, cor-rect Copernican doctrine. From our latter-daypoint of view, it seems so much more naturalto accept than to reject the Copernican sys-tem, that we find it difficult to put ourselves inthe place of a sixteenth-century observer. Yetif we recall that the traditional view, havingwarrant of acceptance by nearly all thinkersof every age, recorded the earth as a fixed, im-movable body, we shall see that our surpriseshould be excited rather by the thinker whocan break away from this view than by the onewho still tends to cling to it.

Moreover, it is useless to attempt to dis-guise the fact that something more than amere vague tradition was supposed to supportthe idea of the earth’s overshadowing impor-tance in the cosmical scheme. The sixteenth-century mind was overmastered by the tenetsof ecclesiasticism, and it was a dangerousheresy to doubt that the Hebrew writings,upon which ecclesiasticism based its claim,contained the last word regarding matters ofscience. But the writers of the Hebrew texthad been under the influence of that Baby-lonian conception of the universe which ac-cepted the earth as unqualifiedly central—which, indeed, had never so much as con-ceived a contradictory hypothesis; and so the


Western world, which had come to acceptthese writings as actually supernatural in ori-gin, lay under the spell of Oriental ideas ofa pre-scientific era. In our own day, no onespeaking with authority thinks of these He-brew writings as having any scientific weightwhatever. Their interest in this regard ispurely antiquarian; hence from our changedpoint of view it seems scarcely credible thatTycho Brahe can have been in earnest whenhe quotes the Hebrew traditions as proof thatthe sun revolves about the earth. Yet we shallsee that for almost three centuries after thetime of Tycho, these same dreamings contin-ued to be cited in opposition to those scientificadvances which new observations made nec-essary; and this notwithstanding the fact thatthe Oriental phrasing is, for the most part, po-etically ambiguous and susceptible of shiftinginterpretations, as the criticism of successivegenerations has amply testified.

As we have said, Tycho Brahe, great ob-server as he was, could not shake himself freefrom the Oriental incubus. He began his ob-jections, then, to the Copernican system byquoting the adverse testimony of a Hebrewprophet who lived more than a thousand yearsB.C. All of this shows sufficiently that TychoBrahe was not a great theorist. He was essen-tially an observer, but in this regard he won a


secure place in the very first rank. Indeed, hewas easily the greatest observing astronomersince Hipparchus, between whom and him-self there were many points of resemblance.Hipparchus, it will be recalled, rejected theAristarchian conception of the universe justas Tycho rejected the conception of Coperni-cus.

But if Tycho propounded no great gener-alizations, the list of specific advances due tohim is a long one, and some of these wereto prove important aids in the hands of laterworkers to the secure demonstration of theCopernican idea. One of his most importantseries of studies had to do with comets. Re-garding these bodies there had been the great-est uncertainty in the minds of astronomers.The greatest variety of opinions regardingthem prevailed; they were thought on theone hand to be divine messengers, and onthe other to be merely igneous phenomenaof the earth’s atmosphere. Tycho Brahe de-clared that a comet which he observed in theyear 1577 had no parallax, proving its ex-treme distance. The observed course of thecomet intersected the planetary orbits, whichfact gave a quietus to the long-mooted ques-tion as to whether the Ptolemaic spheres weretransparent solids or merely imaginary; sincethe comet was seen to intersect these alleged


spheres, it was obvious that they could not bethe solid substance that they were commonlyimagined to be, and this fact in itself went fartowards discrediting the Ptolemaic system. Itshould be recalled, however, that this suppo-sition of tangible spheres for the various plan-etary and stellar orbits was a mediæval inter-pretation of Ptolemy’s theory rather than aninterpretation of Ptolemy himself, there be-ing nothing to show that the Alexandrian as-tronomer regarded his cycles and epicycles asother than theoretical.

An interesting practical discovery made byTycho was his method of determining the lat-itude of a place by means of two observationsmade at an interval of twelve hours. Hith-erto it had been necessary to observe the sun’sangle on the equinoctial days, a period of sixmonths being therefore required. Tycho mea-sured the angle of elevation of some star situ-ated near the pole, when on the meridian, andthen, twelve hours later, measured the angleof elevation of the same star when it againcame to the meridian at the opposite point ofits apparent circle about the polestar. Half thesum of these angles gives the latitude of theplace of observation.

As illustrating the accuracy of Tycho’s ob-servations, it may be noted that he rediscov-ered a third inequality of the moon’s motion at


TYCHO BRAHE’S QUADRANT

(From Dannemann’s Geschichte der Naturwis-senschaften.)


its variation, he, in common with other Euro-pean astronomers, being then quite unawarethat this inequality had been observed by anArabian astronomer. Tycho proved also thatthe angle of inclination of the moon’s orbit tothe ecliptic is subject to slight variation.

The very brilliant new star which shoneforth suddenly in the constellation of Cas-siopeia in the year 1572, was made the ob-ject of special studies by Tycho, who provedthat the star had no sensible parallax andconsequently was far beyond the planetaryregions. The appearance of a new star wasa phenomenon not unknown to the ancients,since Pliny records that Hipparchus was ledby such an appearance to make his cata-logue of the fixed stars. But the phenomenonis sufficiently uncommon to attract unusualattention. A similar phenomenon occurredin the year 1604, when the new star—inthis case appearing in the constellation ofSerpentarius—was explained by Kepler asprobably proceeding from a vast combustion.This explanation—in which Kepler is said tohave followed Tycho—is fully in accord withthe most recent theories on the subject, as weshall see in due course. It is surprising to hearTycho credited with so startling a theory, but,on the other hand, such an explanation is pre-cisely what should be expected from the other


astronomer named. For Johann Kepler, or, ashe was originally named, Johann von Kappel,was one of the most speculative astronomersof any age. He was forever theorizing, butsuch was the peculiar quality of his mind thathis theories never satisfied him for long unlesshe could put them to the test of observation.Thanks to this happy combination of quali-ties, Kepler became the discoverer of threefamous laws of planetary motion which lieat the very foundation of modern astronomy,and which were to be largely instrumental inguiding Newton to his still greater general-ization. These laws of planetary motion werevastly important as corroborating the Coper-nican theory of the universe, though their po-sition in this regard was not immediately rec-ognized by contemporary thinkers. Let us ex-amine with some detail into their discovery,meantime catching a glimpse of the life his-tory of the remarkable man whose name theybear.

JOHANN KEPLER ANDTHE LAWS OF PLANETARYMOTIONJohann Kepler was born the 27th of De-cember, 1571, in the little town of Weil, in


Wurtemburg. He was a weak, sickly child, fur-ther enfeebled by a severe attack of small-pox.It would seem paradoxical to assert that theparents of such a genius were mismated, buttheir home was not a happy one, the motherbeing of a nervous temperament, which per-haps in some measure accounted for the ge-nius of the child. The father led the life ofa soldier, and finally perished in the cam-paign against the Turks. Young Kepler’s stud-ies were directed with an eye to the ministry.After a preliminary training he attended theuniversity at Tubingen, where he came underthe influence of the celebrated Maestlin andbecame his life-long friend.

Curiously enough, it is recorded that atfirst Kepler had no taste for astronomy or formathematics. But the doors of the ministrybeing presently barred to him, he turned withenthusiasm to the study of astronomy, beingfrom the first an ardent advocate of the Coper-nican system. His teacher, Maestlin, acceptedthe same doctrine, though he was obliged, fortheological reasons, to teach the Ptolemaicsystem, as also to oppose the Gregorian re-form of the calendar.

The Gregorian calendar, it should be ex-plained, is so called because it was institutedby Pope Gregory XIII., who put it into ef-fect in the year 1582, up to which time the


so-called Julian calendar, as introduced byJulius Cæsar, had been everywhere acceptedin Christendom. This Julian calendar, as wehave seen, was a great improvement on pre-ceding ones, but still lacked something of per-fection inasmuch as its theoretical day dif-fered appreciably from the actual day. In thecourse of fifteen hundred years, since the timeof Cæsar, this defect amounted to a discrep-ancy of about eleven days. Pope Gregory pro-posed to correct this by omitting ten days fromthe calendar, which was done in September,1582. To prevent similar inaccuracies in thefuture, the Gregorian calendar provided thatonce in four centuries the additional day tomake a leap-year should be omitted, the dateselected for such omission being the last yearof every fourth century. Thus the years 1500,1900, and 2300, A.D., would not be leap-years.By this arrangement an approximate rectifi-cation of the calendar was effected, thougheven this does not make it absolutely exact.

Such a rectification as this was obviouslydesirable, but there was really no necessity forthe omission of the ten days from the calen-dar. The equinoctial day had shifted so thatin the year 1582 it fell on the 10th of Marchand September. There was no reason whyit should not have remained there. It wouldgreatly have simplified the task of future his-


torians had Gregory contented himself withproviding for the future stability of the calen-dar without making the needless shift in ques-tion. We are so accustomed to think of the 21stof March and 21st of September as the natu-ral periods of the equinox, that we are likely toforget that these are purely arbitrary dates forwhich the 10th might have been substitutedwithout any inconvenience or inconsistency.

But the opposition to the new calendar,to which reference has been made, was notbased on any such considerations as these. Itwas due, largely at any rate, to the fact thatGermany at this time was under sway of theLutheran revolt against the papacy. So effec-tive was the opposition that the Gregorian cal-endar did not come into vogue in Germany un-til the year 1699. It may be added that Eng-land, under stress of the same manner of prej-udice, held out against the new reckoning un-til the year 1751, while Russia does not acceptit even now.

As the Protestant leaders thus opposed thepapal attitude in a matter of so practical acharacter as the calendar, it might perhapshave been expected that the Lutherans wouldhave had a leaning towards the Copernicantheory of the universe, since this theory wasopposed by the papacy. Such, however, wasnot the case. Luther himself pointed out with


JOHANN KEPLER


great strenuousness, as a final and demon-strative argument, the fact that Joshua com-manded the sun and not the earth to standstill; and his followers were quite as intoler-ant towards the new teaching as were theirultramontane opponents. Kepler himself was,at various times, to feel the restraint of eccle-siastical opposition, though he was never sub-jected to direct persecution, as was his friendand contemporary, Galileo. At the very outsetof Kepler’s career there was, indeed, questionas to the publication of a work he had writ-ten, because that work took for granted thetruth of the Copernican doctrine. This workappeared, however, in the year 1596. It borethe title Mysterium Cosmographium, and itattempted to explain the positions of the vari-ous planetary bodies. Copernicus had devotedmuch time to observation of the planets withreference to measuring their distance, and hisefforts had been attended with considerablesuccess. He did not, indeed, know the actualdistance of the sun, and, therefore, was quiteunable to fix the distance of any planet; but,on the other hand, he determined the rela-tive distance of all the planets then known, asmeasured in terms of the sun’s distance, withremarkable accuracy.

With these measurements as a guide, Ke-pler was led to a very fanciful theory, ac-


cording to which the orbits of the five princi-pal planets sustain a peculiar relation to thefive regular solids of geometry. His theorywas this: “Around the orbit of the earth de-scribe a dodecahedron—the circle comprisingit will be that of Mars; around Mars describea tetrahedron—the circle comprising it willbe that of Jupiter; around Jupiter describe acube—the circle comprising it will be that ofSaturn; now within the earth’s orbit inscribean icosahedron—the inscribed circle will bethat of Venus; in the orbit of Venus inscribe anoctahedron—the circle inscribed will be thatof Mercury.”

Though this arrangement was a fancifulone, which no one would now recall had notthe theorizer obtained subsequent fame onmore substantial grounds, yet it evidenceda philosophical spirit on the part of the as-tronomer which, misdirected as it was in thisinstance, promised well for the future. TychoBrahe, to whom a copy of the work was sent,had the acumen to recognize it as a work ofgenius. He summoned the young astronomerto be his assistant at Prague, and no doubtthe association thus begun was instrumentalin determining the character of Kepler’s fu-ture work. It was precisely the training inminute observation that could avail most fora mind which, like Kepler’s, tended instinc-


tively to the formulation of theories. WhenTycho Brahe died, in 1601, Kepler became hissuccessor. In due time he secured access to allthe unpublished observations of his great pre-decessor, and these were of inestimable valueto him in the progress of his own studies.

Kepler was not only an ardent worker andan enthusiastic theorizer, but he was an inde-fatigable writer, and it pleased him to take thepublic fully into his confidence, not merely asto his successes, but as to his failures. Thushis works elaborate false theories as wellas correct ones, and detail the observationsthrough which the incorrect guesses were re-futed by their originator. Some of these ac-counts are highly interesting, but they mustnot detain us here. For our present purposeit must suffice to point out the three impor-tant theories, which, as culled from among ascore or so of incorrect ones, Kepler was ableto demonstrate to his own satisfaction andto that of subsequent observers. Stated in afew words, these theories, which have come tobear the name of Kepler’s Laws, are the fol-lowing:

1. That the planetary orbits are not circu-lar, but elliptical, the sun occupying one focusof the ellipses.

2. That the speed of planetary motionvaries in different parts of the orbit in such


KEPLER’S MECHANISM TO ILLUSTRATE HIS

(INCORRECT) EARLY THEORY AS TO THE ORBITS

OF THE PLANETARY BODIES


a way that an imaginary line drawn from thesun to the planet—that is to say, the radiusvector of the planet’s orbit—always sweepsthe same area in a given time.

These two laws Kepler published as earlyas 1609. Many years more of patient investi-gation were required before he found out thesecret of the relation between planetary dis-tances and times of revolution which his thirdlaw expresses. In 1618, however, he was ableto formulate this relation also, as follows:

3. The squares of the distance of the var-ious planets from the sun are proportional tothe cubes of their periods of revolution aboutthe sun.

All these laws, it will be observed, take forgranted the fact that the sun is the centre ofthe planetary orbits. It must be understood,too, that the earth is constantly regarded, inaccordance with the Copernican system, asbeing itself a member of the planetary sys-tem, subject to precisely the same laws asthe other planets. Long familiarity has madethese wonderful laws of Kepler seem such amatter of course that it is difficult now to ap-preciate them at their full value. Yet, as hasbeen already pointed out, it was the knowl-edge of these marvellously simple relationsbetween the planetary orbits that laid thefoundation for the Newtonian law of universal


gravitation. Contemporary judgment couldnot, of course, anticipate this culmination ofa later generation. What it could under-stand was that the first law of Kepler attackedone of the most time-honored of metaphysi-cal conceptions—namely, the Aristotelian ideathat the circle is the perfect figure, and hencethat the planetary orbits must be circular. Noteven Copernicus had doubted the validity ofthis assumption. That Kepler dared disputeso firmly fixed a belief, and one that seeminglyhad so sound a philosophical basis, evidencedthe iconoclastic nature of his genius. Thathe did not rest content until he had demon-strated the validity of his revolutionary as-sumption shows how truly this great theorizermade his hypotheses subservient to the mostrigid inductions.

GALILEO GALILEIWhile Kepler was solving these riddles ofplanetary motion, there was an even more fa-mous man in Italy whose championship of theCopernican doctrine was destined to give thegreatest possible publicity to the new ideas.This was Galileo Galilei, one of the most ex-traordinary scientific observers of any age.Galileo was born at Pisa, on the 18th of Febru-ary (old style), 1564. The day of his birth


is doubly memorable, since on the same daythe greatest Italian of the preceding epoch,Michael Angelo, breathed his last. Personsfond of symbolism have found in the coinci-dence a forecast of the transit from the artis-tic to the scientific epoch of the later Renais-sance. Galileo came of an impoverished no-ble family. He was educated for the professionof medicine, but did not progress far beforehis natural proclivities directed him towardsthe physical sciences. Meeting with opposi-tion in Pisa, he early accepted a call to thechair of natural philosophy in the Universityof Padua, and later in life he made his homeat Florence. The mechanical and physical dis-coveries of Galileo will claim our attention inanother chapter. Our present concern is withhis contribution to the Copernican theory.

Galileo himself records in a letter to Ke-pler that he became a convert to this theoryat an early day. He was not enabled, however,to make any marked contribution to the sub-ject, beyond the influence of his general teach-ings, until about the year 1610. The brilliantcontributions which he made were due largelyto a single discovery—namely, that of the tele-scope. Hitherto the astronomical observationshad been made with the unaided eye. Glasslenses had been known since the thirteenthcentury, but, until now, no one had thought


of their possible use as aids to distant vision.The question of priority of discovery has neverbeen settled. It is admitted, however, thatthe chief honors belong to the opticians of theNetherlands.

As early as the year 1590 the Dutch opti-cian Zacharias Jensen placed a concave and aconvex lens respectively at the ends of a tubeabout eighteen inches long, and used this in-strument for the purpose of magnifying smallobjects—producing, in short, a crude micro-scope. Some years later, Johannes Lipper-shey, of whom not much is known except thathe died in 1619, experimented with a some-what similar combination of lenses, and madethe startling observation that the weather-vane on a distant church-steeple seemed tobe brought much nearer when viewed throughthe lens. The combination of lenses he em-ployed is that still used in the constructionof opera-glasses; the Germans still call sucha combination a Dutch telescope.

Doubtless a large number of experi-menters took the matter up and the fame ofthe new instrument spread rapidly abroad.Galileo, down in Italy, heard rumors of thisremarkable contrivance, through the use ofwhich it was said “distant objects might beseen as clearly as those near at hand.” Heat once set to work to construct for himself a


GALILEO GALILEI


similar instrument, and his efforts were so farsuccessful that at first he “saw objects threetimes as near and nine times enlarged.” Con-tinuing his efforts, he presently so improvedhis glass that objects were enlarged almosta thousand times and made to appear thirtytimes nearer than when seen with the nakedeye. Naturally enough, Galileo turned thisfascinating instrument towards the skies, andhe was almost immediately rewarded by sev-eral startling discoveries. At the very out-set, his magnifying-glass brought to view avast number of stars that are invisible to thenaked eye, and enabled the observer to reachthe conclusion that the hazy light of the MilkyWay is merely due to the aggregation of a vastnumber of tiny stars.

Turning his telescope towards the moon,Galileo found that body rough and earth-likein contour, its surface covered with moun-tains, whose height could be approximatelymeasured through study of their shadows.This was disquieting, because the currentAristotelian doctrine supposed the moon, incommon with the planets, to be a perfectlyspherical, smooth body. The metaphysicalidea of a perfect universe was sure to bedisturbed by this seemingly rough workman-ship of the moon. Thus far, however, therewas nothing in the observations of Galileo to


bear directly upon the Copernican theory; butwhen an inspection was made of the planetsthe case was quite different. With the aid ofhis telescope, Galileo saw that Venus, for ex-ample, passes through phases precisely sim-ilar to those of the moon, due, of course, tothe same cause. Here, then, was demonstra-tive evidence that the planets are dark bodiesreflecting the light of the sun, and an expla-nation was given of the fact, hitherto urgedin opposition to the Copernican theory, thatthe inferior planets do not seem many timesbrighter when nearer the earth than whenin the most distant parts of their orbits; theexplanation being, of course, that when theplanets are between the earth and the sunonly a small portion of their illumined sur-faces is visible from the earth.

On inspecting the planet Jupiter, a stillmore striking revelation was made, as fourtiny stars were observed to occupy an equato-rial position near that planet, and were seen,when watched night after night, to be circlingabout the planet, precisely as the moon circlesabout the earth. Here, obviously, was a minia-ture solar system—a tangible object-lesson inthe Copernican theory. In honor of the rulingFlorentine house of the period, Galileo namedthese moons of Jupiter, Medicean stars.

Turning attention to the sun itself, Galileo


observed on the surface of that luminary aspot or blemish which gradually changed itsshape, suggesting that changes were takingplace in the substance of the sun—changesobviously incompatible with the perfect condi-tion demanded by the metaphysical theorists.But however disquieting for the conservative,the sun’s spots served a most useful purposein enabling Galileo to demonstrate that thesun itself revolves on its axis, since a givenspot was seen to pass across the disk and af-ter disappearing to reappear in due course.The period of rotation was found to be abouttwenty-four days.

It must be added that various observersdisputed priority of discovery of the sun’sspots with Galileo. Unquestionably a sun-spothad been seen by earlier observers, and bythem mistaken for the transit of an inferiorplanet. Kepler himself had made this mis-take. Before the day of the telescope, he hadviewed the image of the sun as thrown on ascreen in a camera-obscura, and had observeda spot on the disk which be interpreted as rep-resenting the planet Mercury, but which, as isnow known, must have been a sun-spot, sincethe planetary disk is too small to have been re-vealed by this method. Such observations asthese, however interesting, cannot be claimedas discoveries of the sun-spots. It is proba-


ble, however, that several discoverers (notablyJohann Fabricius) made the telescopic obser-vation of the spots, and recognized them ashaving to do with the sun’s surface, almostsimultaneously with Galileo. One of theseclaimants was a Jesuit named Scheiner, andthe jealousy of this man is said to have hada share in bringing about that persecution towhich we must now refer.

There is no more famous incident inthe history of science than the heresy trialthrough which Galileo was led to the nom-inal renunciation of his cherished doctrines.There is scarcely another incident that hasbeen commented upon so variously. Each suc-ceeding generation has put its own interpre-tation on it. The facts, however, have beenbut little questioned. It appears that in theyear 1616 the church became at last arousedto the implications of the heliocentric doctrineof the universe. Apparently it seemed clearto the church authorities that the authors ofthe Bible believed the world to be immovablyfixed at the centre of the universe. Such, in-deed, would seem to be the natural inferencefrom various familiar phrases of the Hebrewtext, and what we now know of the status ofOriental science in antiquity gives full war-rant to this interpretation. There is no rea-son to suppose that the conception of the sub-


ordinate place of the world in the solar sys-tem had ever so much as occurred, even asa vague speculation, to the authors of Gen-esis. In common with their contemporaries,they believed the earth to be the all-importantbody in the universe, and the sun a luminaryplaced in the sky for the sole purpose of givinglight to the earth. There is nothing strange,nothing anomalous, in this view; it merely re-flects the current notions of Oriental peoplesin antiquity. What is strange and anomalousis the fact that the Oriental dreamings thusexpressed could have been supposed to rep-resent the acme of scientific knowledge. Yetsuch a hold had these writings taken upon theWestern world that not even a Galileo daredcontradict them openly; and when the churchfathers gravely declared the heliocentric the-ory necessarily false, because contradictoryto Scripture, there were probably few peoplein Christendom whose mental attitude wouldpermit them justly to appreciate the humor ofsuch a pronouncement. And, indeed, if hereand there a man might have risen to such anappreciation, there were abundant reasons forthe repression of the impulse, for there wasnothing humorous about the response withwhich the authorities of the time were wont tomeet the expression of iconoclastic opinions.The burning at the stake of Giordano Bruno,


in the year 1600, was, for example, an object-lesson well calculated to restrain the enthusi-asm of other similarly minded teachers.

Doubtless it was such considerations thatexplained the relative silence of the cham-pions of the Copernican theory, accountingfor the otherwise inexplicable fact that abouteighty years elapsed after the death of Coper-nicus himself before a single text-book ex-pounded his theory. The text-book which thenappeared, under date of 1622, was written bythe famous Kepler, who perhaps was shieldedin a measure from the papal consequences ofsuch hardihood by the fact of residence in aProtestant country. Not that the Protestantsof the time favored the heliocentric doctrine—we have already quoted Luther in an adversesense—but of course it was characteristic ofthe Reformation temper to oppose any papalpronouncement, hence the ultramontane dec-laration of 1616 may indirectly have aided thedoctrine which it attacked, by making thatdoctrine less obnoxious to Lutheran eyes. Bethat as it may, the work of Kepler broughtits author into no direct conflict with the au-thorities. But the result was quite differentwhen, in 1632, Galileo at last broke silenceand gave the world, under cover of the form ofdialogue, an elaborate exposition of the Coper-nican theory. Galileo, it must be explained,


FRONTISPIECE OF GALILEO’S “SYSTEMA

COSMICUM”

(Published in 1641.)


had previously been warned to keep silent onthe subject, hence his publication doubly of-fended the authorities. To be sure, he couldreply that his dialogue introduced a championof the Ptolemaic system to dispute with theupholder of the opposite view, and that, bothviews being presented with full array of argu-ment, the reader was left to reach a verdictfor himself, the author having nowhere point-edly expressed an opinion. But such an argu-ment, of course, was specious, for no one whoread the dialogue could be in doubt as to theopinion of the author. Moreover, it was hintedthat Simplicio, the character who upheld thePtolemaic doctrine and who was everywhereworsted in the argument, was intended to rep-resent the pope himself—a suggestion whichprobably did no good to Galileo’s cause.

The character of Galileo’s artistic presen-tation may best be judged from an example, il-lustrating the vigorous assault of Salviati, thechampion of the new theory, and the feeble re-torts of his conservative antagonist:

“Salviati. Let us then beginour discussion with the consider-ation that, whatever motion maybe attributed to the earth, yet we,as dwellers upon it, and hence asparticipators in its motion, can-not possibly perceive anything of it,


presupposing that we are to con-sider only earthly things. On theother hand, it is just as necessarythat this same motion belong ap-parently to all other bodies and vis-ible objects, which, being separatedfrom the earth, do not take part inits motion. The correct method todiscover whether one can ascribemotion to the earth, and what kindof motion, is, therefore, to investi-gate and observe whether in bodiesoutside the earth a perceptible mo-tion may be discovered which be-longs to all alike. Because a move-ment which is perceptible only inthe moon, for instance, and hasnothing to do with Venus or Jupiteror other stars, cannot possibly bepeculiar to the earth, nor can itsseat be anywhere else than in themoon. Now there is one such uni-versal movement which controlsall others—namely, that which thesun, moon, the other planets, thefixed stars—in short, the wholeuniverse, with the single exceptionof the earth—appears to executefrom east to west in the space oftwenty-four hours. This now, as it


appears at the first glance anyway,might just as well be a motion ofthe earth alone as of all the restof the universe with the exceptionof the earth, for the same phenom-ena would result from either hy-pothesis. Beginning with the mostgeneral, I will enumerate the rea-sons which seem to speak in fa-vor of the earth’s motion. Whenwe merely consider the immensityof the starry sphere in comparisonwith the smallness of the terres-trial ball, which is contained manymillion times in the former, andthen think of the rapidity of themotion which completes a whole ro-tation in one day and night, I can-not persuade myself how any onecan hold it to be more reasonableand credible that it is the heav-enly sphere which rotates, whilethe earth stands still.

“Simplicio. I do not well un-derstand how that powerful motionmay be said to as good as not ex-ist for the sun, the moon, the otherplanets, and the innumerable hostof fixed stars. Do you call that noth-ing when the sun goes from one


meridian to another, rises up overthis horizon and sinks behind thatone, brings now day, and now night;when the moon goes through simi-lar changes, and the other planetsand fixed stars in the same way?

“Salviati. All the changes youmention are such only in respectto the earth. To convince yourselfof it, only imagine the earth outof existence. There would then beno rising and setting of the sun orof the moon, no horizon, no merid-ian, no day, no night—in short, thesaid motion causes no change ofany sort in the relation of the sunto the moon or to any of the otherheavenly bodies, be they planetsor fixed stars. All changes arerather in respect to the earth; theymay all be reduced to the simplefact that the sun is first visible inChina, then in Persia, afterwardsin Egypt, Greece, France, Spain,America, etc., and that the samething happens with the moon andthe other heavenly bodies. Ex-actly the same thing happens andin exactly the same way if, insteadof disturbing so large a part of


the universe, you let the earth re-volve about itself. The difficultyis, however, doubled, inasmuch asa second very important problempresents itself. If, namely, thatpowerful motion is ascribed to theheavens, it is absolutely necessaryto regard it as opposed to the in-dividual motion of all the planets,every one of which indubitably hasits own very leisurely and moder-ate movement from west to east. If,on the other hand, you let the earthmove about itself, this opposition ofmotion disappears.

“The improbability is tripled bythe complete overthrow of that or-der which rules all the heavenlybodies in which the revolving mo-tion is definitely established. Thegreater the sphere is in such a case,so much longer is the time requiredfor its revolution; the smaller thesphere the shorter the time. Sat-urn, whose orbit surpasses those ofall the planets in size, traverses itin thirty years. Jupiter completesits smaller course in twelve years,Mars in two; the moon performsits much smaller revolution within


a month. Just as clearly in theMedicean stars, we see that the onenearest Jupiter completes its revo-lution in a very short time—aboutforty-two hours; the next in aboutthree and one-half days, the thirdin seven, and the most distant onein sixteen days. This rule, whichis followed throughout, will still re-main if we ascribe the twenty-four-hourly motion to a rotation of theearth. If, however, the earth is leftmotionless, we must go first fromthe very short rule of the moonto ever greater ones—to the two-yearly rule of Mars, from that tothe twelve-yearly one of Jupiter,from here to the thirty-yearly oneof Saturn, and then suddenly toan incomparably greater sphere, towhich also we must ascribe a com-plete rotation in twenty-four hours.If, however, we assume a motion ofthe earth, the rapidity of the pe-riods is very well preserved; fromthe slowest sphere of Saturn wecome to the wholly motionless fixedstars. We also escape thereby afourth difficulty, which arises assoon as we assume that there is


motion in the sphere of the stars.I mean the great unevenness in themovement of these very stars, someof which would have to revolve withextraordinary rapidity in immensecircles, while others moved veryslowly in small circles, since someof them are at a greater, others at aless, distance from the pole. Thatis likewise an inconvenience, for,on the one hand, we see all thosestars, the motion of which is in-dubitable, revolve in great circles,while, on the other hand, thereseems to be little object in placingbodies, which are to move in circles,at an enormous distance from thecentre and then let them move invery small circles. And not only arethe size of the different circles andtherewith the rapidity of the move-ment very different in the differ-ent fixed stars, but the same starsalso change their orbits and theirrapidity of motion. Therein con-sists the fifth inconvenience. Thosestars, namely, which were at theequator two thousand years ago,and hence described great circlesin their revolutions, must to-day


move more slowly and in smallercircles, because they are many de-grees removed from it. It will evenhappen, after not so very long atime, that one of those which havehitherto been continually in mo-tion will finally coincide with thepole and stand still, but after a pe-riod of repose will again begin tomove. The other stars in the meanwhile, which unquestionably move,all have, as was said, a great cir-cle for an orbit and keep this un-changeably.

“The improbability is furtherincreased—this may be consideredthe sixth inconvenience—by thefact that it is impossible to conceivewhat degree of solidity those im-mense spheres must have, in thedepths of which so many stars arefixed so enduringly that they arekept revolving evenly in spite ofsuch difference of motion withoutchanging their respective positions.Or if, according to the much moreprobable theory, the heavens arefluid, and every star describes anorbit of its own, according to whatlaw then, or for what reason, are


their orbits so arranged that, whenlooked at from the earth, they ap-pear to be contained in one singlesphere? To attain this it seems tome much easier and more conve-nient to make them motionless in-stead of moving, just as the paving-stones on the market-place, for in-stance, remain in order more easilythan the swarms of children run-ning about on them.

“Finally, the seventh difficulty:If we attribute the daily rotationto the higher region of the heav-ens, we should have to endow itwith force and power sufficient tocarry with it the innumerable hostof the fixed stars—every one a bodyof very great compass and muchlarger than the earth—and all theplanets, although the latter, likethe earth, move naturally in an op-posite direction. In the midst ofall this the little earth, single andalone, would obstinately and wil-fully withstand such force—a sup-position which, it appears to me,has much against it. I could alsonot explain why the earth, a freelypoised body, balancing itself about


its centre, and surrounded on allsides by a fluid medium, should notbe affected by the universal rota-tion. Such difficulties, however, donot confront us if we attribute mo-tion to the earth—such a small, in-significant body in comparison withthe whole universe, and which forthat very reason cannot exerciseany power over the latter.

“Simplicio. You support your ar-guments throughout, it seems tome, on the greater ease and sim-plicity with which the said effectsare produced. You mean that as acause the motion of the earth aloneis just as satisfactory as the mo-tion of all the rest of the universewith the exception of the earth; youhold the actual event to be mucheasier in the former case than inthe latter. For the ruler of the uni-verse, however, whose might is in-finite, it is no less easy to move theuniverse than the earth or a strawbalm. But if his power is infinite,why should not a greater, ratherthan a very small, part of it be re-vealed to me?

“Salviati. If I had said that


the universe does not move on ac-count of the impotence of its ruler,I should have been wrong and yourrebuke would have been in order. Iadmit that it is just as easy for aninfinite power to move a hundredthousand as to move one. WhatI said, however, does not refer tohim who causes the motion, butto that which is moved. In an-swer to your remark that it is morefitting for an infinite power to re-veal a large part of itself ratherthan a little, I answer that, in rela-tion to the infinite, one part is notgreater than another, if both arefinite. Hence it is unallowable tosay that a hundred thousand is alarger part of an infinite numberthan two, although the former isfifty thousand times greater thanthe latter. If, therefore, we con-sider the moving bodies, we mustunquestionably regard the motionof the earth as a much simpler pro-cess than that of the universe; if,furthermore, we direct our atten-tion to so many other simplifica-tions which may be reached only bythis theory, the daily movement of


GALILEO BEFORE THE TRIBUNAL

the earth must appear much moreprobable than the motion of theuniverse without the earth, for, ac-cording to Aristotle’s just axiom,‘Frustra fit per plura, quod potestfieri per p auciora’ (It is vain to ex-pend many means where a few aresufficient).”5

The work was widely circulated, and itwas received with an interest which bespeaks

5Galileo, Dialogo dei due Massimi Systemi delMondo, trans. from Dannemann, op. cit.


a wide-spread undercurrent of belief in theCopernican doctrine. Naturally enough, it at-tracted immediate attention from the churchauthorities. Galileo was summoned to appearat Rome to defend his conduct. The philoso-pher, who was now in his seventieth year,pleaded age and infirmity. He had no desirefor personal experience of the tribunal of theInquisition; but the mandate was repeated,and Galileo went to Rome. There, as everyone knows, he disavowed any intention to op-pose the teachings of Scripture, and formallyrenounced the heretical doctrine of the earth’smotion. According to a tale which so longpassed current that every historian must stillrepeat it though no one now believes it au-thentic, Galileo qualified his renunciation bymuttering to himself, “E pur si muove” (It doesmove, none the less), as he rose to his feetand retired from the presence of his persecu-tors. The tale is one of those fictions which thedramatic sense of humanity is wont to imposeupon history, but, like most such fictions, itexpresses the spirit if not the letter of truth;for just as no one believes that Galileo’s lipsuttered the phrase, so no one doubts that therebellious words were in his mind.

After his formal renunciation, Galileo wasallowed to depart, but with the injunction thathe abstain in future from heretical teaching.


The remaining ten years of his life were de-voted chiefly to mechanics, where his exper-iments fortunately opposed the Aristotelianrather than the Hebrew teachings. Galileo’sdeath occurred in 1642, a hundred years afterthe death of Copernicus. Kepler had died thir-teen years before, and there remained no as-tronomer in the field who is conspicuous in thehistory of science as a champion of the Coper-nican doctrine. But in truth it might be saidthat the theory no longer needed a champion.The researches of Kepler and Galileo had pro-duced a mass of evidence for the Copernicantheory which amounted to demonstration. Ageneration or two might be required for thisevidence to make itself everywhere knownamong men of science, and of course the ec-clesiastical authorities must be expected tostand by their guns for a somewhat longer pe-riod. In point of fact, the ecclesiastical banwas not technically removed by the striking ofthe Copernican books from the list of the In-dex Expurgatorius until the year 1822, almosttwo hundred years after the date of Galileo’sdialogue. But this, of course, is in no sense aguide to the state of general opinion regard-ing the theory. We shall gain a true gauge asto this if we assume that the greater numberof important thinkers had accepted the helio-centric doctrine before the middle of the sev-


enteenth century, and that before the close ofthat century the old Ptolemaic idea had beenquite abandoned. A wonderful revolution inman’s estimate of the universe had thus beeneffected within about two centuries after thebirth of Copernicus.

V. GALILEO ANDTHE NEWPHYSICS

After Galileo had felt the strong hand of theInquisition, in 1632, he was careful to confinehis researches, or at least his publications, totopics that seemed free from theological impli-cations. In doing so he reverted to the field ofhis earliest studies—namely, the field of me-chanics; and the Dialoghi delle Nuove Scienze,which he finished in 1636, and which wasprinted two years later, attained a celebrityno less than that of the heretical dialogue thathad preceded it. The later work was free fromall apparent heresies, yet perhaps it did moretowards the establishment of the Copernicandoctrine, through the teaching of correct me-chanical principles, than the other work hadaccomplished by a more direct method.

Galileo’s astronomical discoveries were, as

133


we have seen, in a sense accidental; at least,they received their inception through the in-ventive genius of another. His mechanical dis-coveries, on the other hand, were the natu-ral output of his own creative genius. At thevery beginning of his career, while yet a veryyoung man, though a professor of mathemat-ics at Pisa, he had begun that onslaught uponthe old Aristotelian ideas which he was to con-tinue throughout his life. At the famous lean-ing tower in Pisa, the young iconoclast per-formed, in the year 1590, one of the most the-atrical demonstrations in the history of sci-ence. Assembling a multitude of championsof the old ideas, he proposed to demonstratethe falsity of the Aristotelian doctrine that thevelocity of falling bodies is proportionate totheir weight. There is perhaps no fact morestrongly illustrative of the temper of the Mid-dle Ages than the fact that this doctrine, astaught by the Aristotelian philosopher, shouldso long have gone unchallenged. Now, how-ever, it was put to the test; Galileo releaseda half-pound weight and a hundred-poundcannon-ball from near the top of the tower,and, needless to say, they reached the groundtogether. Of course, the spectators were butlittle pleased with what they saw. They couldnot doubt the evidence of their own sensesas to the particular experiment in question;

V. GALILEO AND THE NEW PHYSICS 135

they could suggest, however, that the exper-iment involved a violation of the laws of na-ture through the practice of magic. To contro-vert so firmly established an idea savored ofheresy. The young man guilty of such icono-clasm was naturally looked at askance by thescholarship of his time. Instead of being ap-plauded, he was hissed, and he found it expe-dient presently to retire from Pisa.

Fortunately, however, the new spirit ofprogress had made itself felt more effectivelyin some other portions of Italy, and so Galileofound a refuge and a following in Padua, andafterwards in Florence; and while, as we haveseen, he was obliged to curb his enthusiasmregarding the subject that was perhaps near-est his heart—the promulgation of the Coper-nican theory—yet he was permitted in themain to carry on his experimental observa-tions unrestrained. These experiments gavehim a place of unquestioned authority amonghis contemporaries, and they have transmit-ted his name to posterity as that of one ofthe greatest of experimenters and the virtualfounder of modern mechanical science. Theexperiments in question range over a widefield; but for the most part they have to dowith moving bodies and with questions offorce, or, as we should now say, of energy. Theexperiment at the leaning tower showed that


the velocity of falling bodies is independent ofthe weight of the bodies, provided the weightis sufficient to overcome the resistance of theatmosphere. Later experiments with fallingbodies led to the discovery of laws regardingthe accelerated velocity of fall. Such veloci-ties were found to bear a simple relation tothe period of time from the beginning of thefall. Other experiments, in which balls wereallowed to roll down inclined planes, corrob-orated the observation that the pull of grav-itation gave a velocity proportionate to thelength of fall, whether such fall were direct orin a slanting direction.

These studies were associated with ob-servations on projectiles, regarding whichGalileo was the first to entertain correct no-tions. According to the current idea, a projec-tile fired, for example, from a cannon, movedin a straight horizontal line until the propul-sive force was exhausted, and then fell to theground in a perpendicular line. Galileo taughtthat the projectile begins to fall at once onleaving the mouth of the cannon and traversesa parabolic course. According to his idea,which is now familiar to every one, a cannon-ball dropped from the level of the cannon’smuzzle will strike the ground simultaneouslywith a ball fired horizontally from the cannon.As to the paraboloid course pursued by the


projectile, the resistance of the air is a factorwhich Galileo could not accurately compute,and which interferes with the practical real-ization of his theory. But this is a minor con-sideration. The great importance of his ideaconsists in the recognition that such a force asthat of gravitation acts in precisely the sameway upon all unsupported bodies, whether ornot such bodies be at the same time actedupon by a force of translation.

Out of these studies of moving bodies wasgradually developed a correct notion of sev-eral important general laws of mechanics—laws a knowledge of which was absolutely es-sential to the progress of physical science. Thebelief in the rotation of the earth made neces-sary a clear conception that all bodies at thesurface of the earth partake of that motionquite independently of their various observedmotions in relation to one another. This ideawas hard to grasp, as an oft-repeated argu-ment shows. It was asserted again and againthat, if the earth rotates, a stone dropped fromthe top of a tower could not fall at the footof the tower, since the earth’s motion wouldsweep the tower far away from its original po-sition while the stone is in transit.

This was one of the stock argumentsagainst the earth’s motion, yet it was onethat could be refuted with the greatest ease


by reasoning from strictly analogous experi-ments. It might readily be observed, for ex-ample, that a stone dropped from a movingcart does not strike the ground directly belowthe point from which it is dropped, but par-takes of the forward motion of the cart. If anyone doubt this he has but to jump from a mov-ing cart to be given a practical demonstrationof the fact that his entire body was in someway influenced by the motion of translation.Similarly, the simple experiment of tossing aball from the deck of a moving ship will con-vince any one that the ball partakes of the mo-tion of the ship, so that it can be manipulatedprecisely as if the manipulator were standingon the earth. In short, every-day experiencegives us illustrations of what might be calledcompound motion, which makes it seem alto-gether plausible that, if the earth is in motion,objects at its surface will partake of that mo-tion in a way that does not interfere with anyother movements to which they may be sub-jected. As the Copernican doctrine made itsway, this idea of compound motion naturallyreceived more and more attention, and suchexperiments as those of Galileo prepared theway for a new interpretation of the mechani-cal principles involved.

The great difficulty was that the subjectof moving bodies had all along been contem-


plated from a wrong point of view. Since forcemust be applied to an object to put it in mo-tion, it was perhaps not unnaturally assumedthat similar force must continue to be appliedto keep the object in motion. When, for exam-ple, a stone is thrown from the hand, the di-rect force applied necessarily ceases as soon asthe projectile leaves the hand. The stone, nev-ertheless, flies on for a certain distance andthen falls to the ground. How is this flightof the stone to be explained? The ancientphilosophers puzzled more than a little overthis problem, and the Aristotelians reachedthe conclusion that the motion of the handhad imparted a propulsive motion to the air,and that this propulsive motion was transmit-ted to the stone, pushing it on. Just how theair took on this propulsive property was notexplained, and the vagueness of thought thatcharacterized the time did not demand an ex-planation. Possibly the dying away of ripplesin water may have furnished, by analogy, anexplanation of the gradual dying out of the im-pulse which propels the stone.

All of this was, of course, an unfortunatemaladjustment of the point of view. As ev-ery one nowadays knows, the air retards theprogress of the stone, enabling the pull ofgravitation to drag it to the earth earlier thanit otherwise could. Were the resistance of the


air and the pull of gravitation removed, thestone as projected from the hand would flyon in a straight line, at an unchanged veloc-ity, forever. But this fact, which is expressedin what we now term the first law of motion,was extremely difficult to grasp. The first im-portant step towards it was perhaps impliedin Galileo’s study of falling bodies. Thesestudies, as we have seen, demonstrated thata half-pound weight and a hundred-poundweight fall with the same velocity. It is, how-ever, matter of common experience that cer-tain bodies, as, for example, feathers, do notfall at the same rate of speed with these heav-ier bodies. This anomaly demands an expla-nation, and the explanation is found in theresistance offered the relatively light objectby the air. Once the idea that the air maythus act as an impeding force was grasped,the investigator of mechanical principles hadentered on a new and promising course.

Galileo could not demonstrate the retard-ing influence of air in the way which becamefamiliar a generation or two later; he couldnot put a feather and a coin in a vacuumtube and prove that the two would there fallwith equal velocity, because, in his day, theair-pump had not yet been invented. Theexperiment was made only a generation af-ter the time of Galileo, as we shall see; but,


meantime, the great Italian had fully graspedthe idea that atmospheric resistance playsa most important part in regard to the mo-tion of falling and projected bodies. Thankslargely to his own experiments, but partly alsoto the efforts of others, he had come, beforethe end of his life, pretty definitely to real-ize that the motion of a projectile, for exam-ple, must be thought of as inherent in theprojectile itself, and that the retardation orultimate cessation of that motion is due tothe action of antagonistic forces. In otherwords, he had come to grasp the meaning ofthe first law of motion. It remained, how-ever, for the great Frenchman Descartes togive precise expression to this law two yearsafter Galileo’s death. As Descartes expressedit in his Principia Philosophiae, published in1644, any body once in motion tends to go onin a straight line, at a uniform rate of speed,forever. Contrariwise, a stationary body willremain forever at rest unless acted on by somedisturbing force.

This all-important law, which lies at thevery foundation of all true conceptions of me-chanics, was thus worked out during the firsthalf of the seventeenth century, as the out-come of numberless experiments for whichGalileo’s experiments with failing bodies fur-nished the foundation. So numerous and so


gradual were the steps by which the rever-sal of view regarding moving bodies was ef-fected that it is impossible to trace them indetail. We must be content to reflect that atthe beginning of the Galilean epoch utterlyfalse notions regarding the subject were enter-tained by the very greatest philosophers—byGalileo himself, for example, and by Kepler—whereas at the close of that epoch the cor-rect and highly illuminative view had been at-tained.

We must now consider some other exper-iments of Galileo which led to scarcely less-important results. The experiments in ques-tion had to do with the movements of bodiespassing down an inclined plane, and with theallied subject of the motion of a pendulum.The elaborate experiments of Galileo regard-ing the former subject were made by measur-ing the velocity of a ball rolling down a planeinclined at various angles. He found that thevelocity acquired by a ball was proportionalto the height from which the ball descendedregardless of the steepness of the incline. Ex-periments were made also with a ball rollingdown a curved gutter, the curve representingthe are of a circle. These experiments ledto the study of the curvilinear motions of aweight suspended by a cord; in other words,of the pendulum.


Regarding the motion of the pendulum,some very curious facts were soon ascer-tained. Galileo found, for example, that a pen-dulum of a given length performs its oscilla-tions with the same frequency though the arcdescribed by the pendulum be varied greatly.6He found, also, that the rate of oscillation forpendulums of different lengths varies accord-ing to a simple law. In order that one pendu-lum shall oscillate one-half as fast as another,the length of the pendulums must be as four toone. Similarly, by lengthening the pendulumsnine times, the oscillation is reduced to one-third, In other words, the rate of oscillationof pendulums varies inversely as the squareof their length. Here, then, is a simple rela-tion between the motions of swinging bodieswhich suggests the relation which Kepler haddiscovered between the relative motions of theplanets. Every such discovery coming in thisage of the rejuvenation of experimental sci-ence had a peculiar force in teaching men theall-important lesson that simple laws lie backof most of the diverse phenomena of nature, ifonly these laws can be discovered.

Galileo further observed that his pendu-lum might be constructed of any weight suf-ficiently heavy readily to overcome the atmo-

6Rothmann, History of Astronomy (in the Library ofUseful Knowledge), London, 1834.


spheric resistance, and that, with this qual-ification, neither the weight nor the mate-rial had any influence upon the time of os-cillation, this being solely determined by thelength of the cord. Naturally, the practicalutility of these discoveries was not overlookedby Galileo. Since a pendulum of a given lengthoscillates with unvarying rapidity, here is anobvious means of measuring time. Galileo,however, appears not to have met with anygreat measure of success in putting this ideainto practice. It remained for the mechanicalingenuity of Huyghens to construct a satisfac-tory pendulum clock.

As a theoretical result of the studies ofrolling and oscillating bodies, there was de-veloped what is usually spoken of as the thirdlaw of motion—namely, the law that a givenforce operates upon a moving body with an ef-fect proportionate to its effect upon the samebody when at rest. Or, as Whewell states thelaw: “The dynamical effect of force is as thestatical effect; that is, the velocity which anyforce generates in a given time, when it putsthe body in motion, is proportional to the pres-sure which this same force produces in a bodyat rest.”7 According to the second law of mo-tion, each one of the different forces, operat-

7William Whewell, History of the Inductive Sciences,3 Vols., London, 1847, Vol. II., p. 48.


ing at the same time upon a moving body, pro-duces the same effect as if it operated uponthe body while at rest.

STEVINUS AND THE LAWOF EQUILIBRIUMIt appears, then, that the mechanical stud-ies of Galileo, taken as a whole, were nothingless than revolutionary. They constituted thefirst great advance upon the dynamic stud-ies of Archimedes, and then led to the securefoundation for one of the most important ofmodern sciences. We shall see that an impor-tant company of students entered the field im-mediately after the time of Galileo, and car-ried forward the work he had so well begun.But before passing on to the consideration oftheir labors, we must consider work in alliedfields of two men who were contemporariesof Galileo and whose original labors were insome respects scarcely less important than hisown. These men are the Dutchman Stevi-nus, who must always be remembered as aco-laborer with Galileo in the foundation ofthe science of dynamics, and the EnglishmanGilbert, to whom is due the unqualified praiseof first subjecting the phenomenon of mag-netism to a strictly scientific investigation.


Stevinus was born in the year 1548, anddied in 1620. He was a man of a practi-cal genius, and he attracted the attentionof his non-scientific contemporaries, amongother ways, by the construction of a curiousland-craft, which, mounted on wheels, was tobe propelled by sails like a boat. Not only didhe write a book on this curious horseless car-riage, but he put his idea into practical ap-plication, producing a vehicle which actuallytraversed the distance between Scheveningenand Petton, with no fewer than twenty-sevenpassengers, one of them being Prince Mau-rice of Orange. This demonstration was madeabout the year 1600. It does not appear, how-ever, that any important use was made of thestrange vehicle; but the man who inventedit put his mechanical ingenuity to other usewith better effect. It was he who solved theproblem of oblique forces, and who discov-ered the important hydrostatic principle thatthe pressure of fluids is proportionate to theirdepth, without regard to the shape of the in-cluding vessel.

The study of oblique forces was made byStevinus with the aid of inclined planes. Hismost demonstrative experiment was a verysimple one, in which a chain of balls of equalweight was hung from a triangle; the trianglebeing so constructed as to rest on a horizon-


tal base, the oblique sides bearing the relationto each other of two to one. Stevinus foundthat his chain of balls just balanced when fourballs were on the longer side and two on theshorter and steeper side. The balancing offorce thus brought about constituted a stableequilibrium, Stevinus being the first to dis-criminate between such a condition and theunbalanced condition called unstable equilib-rium. By this simple experiment was laid thefoundation of the science of statics. Stevinushad a full grasp of the principle which his ex-periment involved, and he applied it to the so-lution of oblique forces in all directions. Ear-lier investigations of Stevinus were publishedin 1608. His collected works were publishedat Leyden in 1634.

This study of the equilibrium of pressureof bodies at rest led Stevinus, not unnaturally,to consider the allied subject of the pressure ofliquids. He is to be credited with the explana-tion of the so-called hydrostatic paradox. Thefamiliar modern experiment which illustratesthis paradox is made by inserting a long per-pendicular tube of small caliber into the top ofa tight barrel. On filling the barrel and tubewith water, it is possible to produce a pres-sure which will burst the barrel, though it bea strong one, and though the actual weight ofwater in the tube is comparatively insignifi-


cant. This illustrates the fact that the pres-sure at the bottom of a column of liquid is pro-portionate to the height of the column, and notto its bulk, this being the hydrostatic para-dox in question. The explanation is that anenclosed fluid under pressure exerts an equalforce upon all parts of the circumscribing wall;the aggregate pressure may, therefore, be in-creased indefinitely by increasing the surface.It is this principle, of course, which is utilizedin the familiar hydrostatic press. Theoreticalexplanations of the pressure of liquids weresupplied a generation or two later by numer-ous investigators, including Newton, but thepractical refoundation of the science of hydro-statics in modern times dates from the exper-iments of Stevinus.

GALILEO AND THEEQUILIBRIUM OF FLUIDSExperiments of an allied character, having todo with the equilibrium of fluids, exercisedthe ingenuity of Galileo. Some of his mostinteresting experiments have to do with thesubject of floating bodies. It will be recalledthat Archimedes, away back in the Alexan-drian epoch, had solved the most importantproblems of hydrostatic equilibrium. Now,


however, his experiments were overlooked orforgotten, and Galileo was obliged to makeexperiments anew, and to combat fallaciousviews that ought long since to have been aban-doned. Perhaps the most illuminative view ofthe spirit of the times can be gained by quot-ing at length a paper of Galileo’s, in which hedetails his own experiments with floating bod-ies and controverts the views of his opponents.The paper has further value as illustratingGalileo’s methods both as experimenter andas speculative reasoner.

The current view, which Galileo here un-dertakes to refute, asserts that water offersresistance to penetration, and that this resis-tance is instrumental in determining whethera body placed in water will float or sink.Galileo contends that water is non-resistant,and that bodies float or sink in virtue of theirrespective weights. This, of course, is merelya restatement of the law of Archimedes. Butit remains to explain the fact that bodies ofa certain shape will float, while bodies of thesame material and weight, but of a differentshape, will sink. We shall see what explana-tion Galileo finds of this anomaly as we pro-ceed.

In the first place, Galileo makes a cone ofwood or of wax, and shows that when it floatswith either its point or its base in the water, it


displaces exactly the same amount of fluid, al-though the apex is by its shape better adaptedto overcome the resistance of the water, if thatwere the cause of buoyancy. Again, the exper-iment may be varied by tempering the waxwith filings of lead till it sinks in the water,when it will be found that in any figure thesame quantity of cork must be added to it toraise the surface.

“But,” says Galileo, “this si-lences not my antagonists; theysay that all the discourse hithertomade by me imports little to them,and that it serves their turn; thatthey have demonstrated in one in-stance, and in such manner and fig-ure as pleases them best—namely,in a board and in a ball of ebony—that one when put into the wa-ter sinks to the bottom, and thatthe other stays to swim on the top;and the matter being the same,and the two bodies differing innothing but in figure, they affirmthat with all perspicuity they havedemonstrated and sensibly mani-fested what they undertook. Nev-ertheless, I believe, and think I canprove, that this very experimentproves nothing against my theory.


And first, it is false that the ballsinks and the board not; for theboard will sink, too, if you do toboth the figures as the words ofour question require; that is, if youput them both in the water; forto be in the water implies to beplaced in the water, and by Aris-totle’s own definition of place, tobe placed imports to be environedby the surface of the ambient body;but when my antagonists show thefloating board of ebony, they put itnot into the water, but upon thewater; where, being detained by acertain impediment (of which moreanon), it is surrounded, partly withwater, partly with air, which is con-trary to our agreement, for thatwas that bodies should be in thewater, and not part in the water,part in the air.

“I will not omit another reason,founded also upon experience, and,if I deceive not myself, conclusiveagainst the notion that figure, andthe resistance of the water to pen-etration, have anything to do withthe buoyancy of bodies. Choose apiece of wood or other matter, as,


for instance, walnut-wood, of whicha ball rises from the bottom of thewater to the surface more slowlythan a ball of ebony of the samesize sinks, so that, clearly, the ballof ebony divides the water morereadily in sinking than the ball ofwood does in rising. Then take aboard of walnut-tree equal to andlike the floating one of my antag-onists; and if it be true that thislatter floats by reason of the figurebeing unable to penetrate the wa-ter, the other of walnut-tree, with-out a question, if thrust to the bot-tom, ought to stay there, as havingthe same impeding figure, and be-ing less apt to overcome the saidresistance of the water. But if wefind by experience that not only thethin board, but every other figureof the same walnut-tree, will re-turn to float, as unquestionably weshall, then I must desire my op-ponents to forbear to attribute thefloating of the ebony to the figureof the board, since the resistance ofthe water is the same in rising as insinking, and the force of ascensionof the walnut-tree is less than the


ebony’s force for going to the bot-tom.

“Now let us return to the thinplate of gold or silver, or the thinboard of ebony, and let us lay itlightly upon the water, so thatit may stay there without sink-ing, and carefully observe the ef-fect. It will appear clearly thatthe plates are a considerable mat-ter lower than the surface of thewater, which rises up and makesa kind of rampart round them onevery side. But if it has alreadypenetrated and overcome the con-tinuity of the water, and is of itsown nature heavier than the wa-ter, why does it not continue tosink, but stop and suspend itselfin that little dimple that its weighthas made in the water? My answeris, because in sinking till its sur-face is below the water, which risesup in a bank round it, it draws af-ter and carries along with it the airabove it, so that that which, in thiscase, descends in the water is notonly the board of ebony or the plateof iron, but a compound of ebonyand air, from which composition re-


sults a solid no longer specificallyheavier than the water, as was theebony or gold alone. But, gentle-men, we want the same matter; youare to alter nothing but the shape,and, therefore, have the goodnessto remove this air, which may bedone simply by washing the surfaceof the board, for the water havingonce got between the board and theair will run together, and the ebonywill go to the bottom; and if it doesnot, you have won the day.

“But methinks I hear some ofmy antagonists cunningly oppos-ing this, and telling me that theywill not on any account allow theirboards to be wetted, because theweight of the water so added, bymaking it heavier than it was be-fore, draws it to the bottom, andthat the addition of new weight iscontrary to our agreement, whichwas that the matter should be thesame.

“To this I answer, first, that no-body can suppose bodies to be putinto the water without their be-ing wet, nor do I wish to do moreto the board than you may do to


the ball. Moreover, it is not truethat the board sinks on account ofthe weight of the water added inthe washing; for I will put ten ortwenty drops on the floating board,and so long as they stand separateit shall not sink; but if the board betaken out and all that water wipedoff, and the whole surface bathedwith one single drop, and put itagain upon the water, there is noquestion but it will sink, the otherwater running to cover it, beingno longer hindered by the air. Inthe next place, it is altogether falsethat water can in any way increasethe weight of bodies immersed init, for water has no weight in wa-ter, since it does not sink. Now justas he who should say that brassby its own nature sinks, but thatwhen formed into the shape of akettle it acquires from that figurethe virtue of lying in water withoutsinking, would say what is false,because that is not purely brasswhich then is put into the water,but a compound of brass and air;so is it neither more nor less falsethat a thin plate of brass or ebony


swims by virtue of its dilated andbroad figure. Also, I cannot omitto tell my opponents that this con-ceit of refusing to bathe the surfaceof the board might beget an opin-ion in a third person of a poverty ofargument on their side, especiallyas the conversation began aboutflakes of ice, in which it would besimple to require that the surfacesshould be kept dry; not to men-tion that such pieces of ice, whetherwet or dry, always float, and so myantagonists say, because of theirshape.

“Some may wonder that I af-firm this power to be in the airof keeping plate of brass or sil-ver above water, as if in a certainsense I would attribute to the aira kind of magnetic virtue for sus-taining heavy bodies with which itis in contact. To satisfy all thesedoubts I have contrived the follow-ing experiment to demonstrate howtruly the air does support thesebodies; for I have found, when oneof these bodies which floats whenplaced lightly on the water is thor-oughly bathed and sunk to the bot-


tom, that by carrying down to it alittle air without otherwise touch-ing it in the least, I am able toraise and carry it back to the top,where it floats as before. To thiseffect, I take a ball of wax, andwith a little lead make it just heavyenough to sink very slowly to thebottom, taking care that its surfacebe quite smooth and even. This,if put gently into the water, sub-merges almost entirely, there re-maining visible only a little of thevery top, which, so long as it isjoined to the air, keeps the ballafloat; but if we take away the con-tact of the air by wetting this top,the ball sinks to the bottom andremains there. Now to make itreturn to the surface by virtue ofthe air which before sustained it,thrust into the water a glass withthe mouth downward, which willcarry with it the air it contains,and move this down towards theball until you see, by the trans-parency of the glass, that the airhas reached the top of it; then gen-tly draw the glass upward, and youwill see the ball rise, and after-


wards stay on the top of the water,if you carefully part the glass andwater without too much disturbingit.”8

It will be seen that Galileo, while holdingin the main to a correct thesis, yet mingleswith it some false ideas. At the very outset,of course, it is not true that water has no re-sistance to penetration; it is true, however, inthe sense in which Galileo uses the term—that is to say, the resistance of the water topenetration is not the determining factor or-dinarily in deciding whether a body sinks orfloats. Yet in the case of the flat body it isnot altogether inappropriate to say that thewater resists penetration and thus supportsthe body. The modern physicist explains thephenomenon as due to surface-tension of thefluid. Of course, Galileo’s disquisition on themixing of air with the floating body is utterlyfanciful. His experiments were beautifully ex-act; his theorizing from them was, in this in-stance, altogether fallacious. Thus, as alreadyintimated, his paper is admirably adapted toconvey a double lesson to the student of sci-ence.

8The Lives of Eminent Persons, by Biot, Jardine,Bethune, etc., London, 1833.


WILLIAM GILBERT ANDTHE STUDY OFMAGNETISMIt will be observed that the studies of Galileoand Stevinus were chiefly concerned with theforce of gravitation. Meanwhile, there was anEnglish philosopher of corresponding genius,whose attention was directed towards investi-gation of the equally mysterious force of ter-restrial magnetism. With the doubtful excep-tion of Bacon, Gilbert was the most distin-guished man of science in England during thereign of Queen Elizabeth. He was for manyyears court physician, and Queen Elizabethultimately settled upon him a pension that en-abled him to continue his researches in purescience.

His investigations in chemistry, althoughsupposed to be of great importance, are mostlylost; but his great work, De Magnete, on whichhe labored for upwards of eighteen years, isa work of sufficient importance, as Hallamsays, “to raise a lasting reputation for its au-thor.” From its first appearance it created aprofound impression upon the learned men ofthe continent, although in England Gilbert’stheories seem to have been somewhat less fa-vorably received. Galileo freely expressed his


admiration for the work and its author; Ba-con, who admired the author, did not expressthe same admiration for his theories; but Dr.Priestley, later, declared him to be “the fatherof modern electricity.”

Strangely enough, Gilbert’s book hadnever been translated into English, or appar-ently into any other language, until recentyears, although at the time of its publicationcertain learned men, unable to read the bookin the original, had asked that it should be.By this neglect, or oversight, a great numberof general readers as well as many scientists,through succeeding centuries, have been de-prived of the benefit of writings that containeda good share of the fundamental facts aboutmagnetism as known to-day.

Gilbert was the first to discover that theearth is a great magnet, and he not onlygave the name of “pole” to the extremities ofthe magnetic needle, but also spoke of these“poles” as north and south pole, although heused these names in the opposite sense fromthat in which we now use them, his south polebeing the extremity which pointed towardsthe north, and vice versa. He was also firstto make use of the terms “electric force,” “elec-tric emanations,” and “electric attractions.”

It is hardly necessary to say that some ofthe views taken by Gilbert, many of his the-


ories, and the accuracy of some of his exper-iments have in recent times been found tobe erroneous. As a pioneer in an unexploredfield of science, however, his work is remark-ably accurate. “On the whole,” says Dr. JohnRobinson, “this performance contains morereal information than any writing of the agein which he lived, and is scarcely exceeded byany that has appeared since.”9

In the preface to his work Gilbert says:“Since in the discovery of secret things, andin the investigation of hidden causes, strongerreasons are obtained from sure experimentsand demonstrated arguments than from prob-able conjectures and the opinions of philo-sophical speculators of the common sort,therefore, to the end of that noble substanceof that great loadstone, our common mother(the earth), still quite unknown, and also thatthe forces extraordinary and exalted of thisglobe may the better be understood, we havedecided, first, to begin with the common stonyand ferruginous matter, and magnetic bodies,and the part of the earth that we may han-dle and may perceive with senses, and then toproceed with plain magnetic experiments, and

9William Gilbert, De Magnete, translated by P.Fleury Motteley, London, 1893. In the biographicalmemoir, p. xvi.


to penetrate to the inner parts of the earth.”10

Before taking up the demonstration thatthe earth is simply a giant loadstone, Gilbertdemonstrated in an ingenious way that everyloadstone, of whatever size, has definite andfixed poles. He did this by placing the stone ina metal lathe and converting it into a sphere,and upon this sphere demonstrated how thepoles can be found. To this round loadstone hegave the name of terrella—that is, little earth.

“To find, then, poles answering to theearth,” he says, “take in your hand the roundstone, and lay on it a needle or a piece of ironwire: the ends of the wire move round theirmiddle point, and suddenly come to a stand-still. Now, with ochre or with chalk, markwhere the wire lies still and sticks. Thenmove the middle or centre of the wire to an-other spot, and so to a third and fourth, al-ways marking the stone along the length ofthe wire where it stands still; the lines somarked will exhibit meridian circles, or circleslike meridians, on the stone or terrella; andmanifestly they will all come together at thepoles of the stone. The circle being continuedin this way, the poles appear, both the northand the south, and betwixt these, midway, wemay draw a large circle for an equator, as isdone by the astronomer in the heavens and

10Gilbert, op. cit., p. xlvii.


on his spheres, and by the geographer on theterrestrial globe.”11

Gilbert had tried the familiar experimentof placing the loadstone on a float in water,and observed that the poles always revolveduntil they pointed north and south, which heexplained as due to the earth’s magnetic at-traction. In this same connection he noticedthat a piece of wrought iron mounted on acork float was attracted by other metals to aslight degree, and he observed also that anordinary iron bar, if suspended horizontallyby a thread, assumes invariably a north andsouth direction. These, with many other ex-periments of a similar nature, convinced himthat the earth “is a magnet and a loadstone,”which he says is a “new and till now unheard-of view of the earth.”

Fully to appreciate Gilbert’s revolutionaryviews concerning the earth as a magnet, itshould be remembered that numberless theo-ries to explain the action of the electric needlehad been advanced. Columbus and Paracel-sus, for example, believed that the magnetwas attracted by some point in the heavens,such as a magnetic star. Gilbert himself tellsof some of the beliefs that had been held by hispredecessors, many of whom he declares “wil-fully falsify.” One of his first steps was to re-

11Gilbert, op. cit., p. 24.


fute by experiment such assertions as that ofCardan, that “a wound by a magnetized nee-dle was painless”; and also the assertion ofFracastoni that loadstone attracts silver; orthat of Scalinger, that the diamond will at-tract iron; and the statement of Matthiolusthat “iron rubbed with garlic is no longer at-tracted to the loadstone.”

Gilbert made extensive experiments to ex-plain the dipping of the needle, which hadbeen first noticed by William Norman. Hisdeduction as to this phenomenon led him tobelieve that this was also explained by themagnetic attraction of the earth, and to pre-dict where the vertical dip would be found.These deductions seem the more wonderfulbecause at the time he made them the dip hadjust been discovered, and had not been stud-ied except at London. His theory of the dipwas, therefore, a scientific prediction, basedon a preconceived hypothesis. Gilbert foundthe dip to be 72◦ at London; eight years laterHudson found the dip at 75◦ 22’ north latitudeto be 89◦ 30’; but it was not until over two hun-dred years later, in 1831, that the vertical dipwas first observed by Sir James Ross at about70◦ 5’ north latitude, and 96◦ 43’ west longi-tude. This was not the exact point assumed byGilbert, and his scientific predictions, there-fore, were not quite correct; but such compar-


atively slight and excusable errors mar but lit-tle the excellence of his work as a whole.

A brief epitome of some of his other im-portant discoveries suffices to show that theexalted position in science accorded him bycontemporaries, as well as succeeding gener-ations of scientists, was well merited. Hewas first to distinguish between magnetismand electricity, giving the latter its name. Hediscovered also the “electrical charge,” andpointed the way to the discovery of insula-tion by showing that the charge could be re-tained some time in the excited body by cov-ering it with some non-conducting substance,such as silk; although, of course, electricalconduction can hardly be said to have beenmore than vaguely surmised, if understoodat all by him. The first electrical instrumentever made, and known as such, was inventedby him, as was also the first magnetometer,and the first electrical indicating device. Al-though three centuries have elapsed since hisdeath, the method of magnetizing iron first in-troduced by him is in common use to-day.

He made exhaustive experiments with aneedle balanced on a pivot to see how manysubstances he could find which, like amber,on being rubbed affected the needle. In thisway he discovered that light substances wereattracted by alum, mica, arsenic, sealing-


wax, lac sulphur, slags, beryl, amethyst, rock-crystal, sapphire, jet, carbuncle, diamond,opal, Bristol stone, glass, glass of antimony,gum-mastic, hard resin, rock-salt, and, ofcourse, amber. He discovered also that at-mospheric conditions affected the productionof electricity, dryness being unfavorable andmoisture favorable.

Galileo’s estimate of this first electrician isthe verdict of succeeding generations. “I ex-tremely admire and envy this author,” he said.“I think him worthy of the greatest praise forthe many new and true observations which hehas made, to the disgrace of so many vain andfabling authors.”

STUDIES OF LIGHT, HEAT,AND ATMOSPHERICPRESSUREWe have seen that Gilbert was by no meanslacking in versatility, yet the investigationsupon which his fame is founded were all pur-sued along one line, so that the father of mag-netism may be considered one of the earliestof specialists in physical science. Most work-ers of the time, on the other band, extendedtheir investigations in many directions. Thesum total of scientific knowledge of that day


had not bulked so large as to exclude thepossibility that one man might master it all.So we find a Galileo, for example, makingrevolutionary discoveries in astronomy, andperforming fundamental experiments in var-ious fields of physics. Galileo’s great contem-porary, Kepler, was almost equally versatile,though his astronomical studies were of suchpre-eminent importance that his other inves-tigations sink into relative insignificance. Yethe performed some notable experiments in atleast one department of physics. These exper-iments had to do with the refraction of light, asubject which Kepler was led to investigate, inpart at least, through his interest in the tele-scope.

We have seen that Ptolemy in the Alexan-drian time, and Alhazen, the Arab, madestudies of refraction. Kepler repeated theirexperiments, and, striving as always to gen-eralize his observations, he attempted to findthe law that governed the observed changeof direction which a ray of light assumes inpassing from one medium to another. Keplermeasured the angle of refraction by means ofa simple yet ingenious trough-like apparatuswhich enabled him to compare readily the di-rect and refracted rays. He discovered thatwhen a ray of light passes through a glassplate, if it strikes the farther surface of the


glass at an angle greater than 45◦ it will be to-tally refracted instead of passing through intothe air. He could not well fail to know that dif-ferent mediums refract light differently, andthat for the same medium the amount of lightvaries with the change in the angle of inci-dence. He was not able, however, to gener-alize his observations as he desired, and tothe last the law that governs refraction es-caped him. It remained for Willebrord Snell,a Dutchman, about the year 1621, to discoverthe law in question, and for Descartes, a lit-tle later, to formulate it. Descartes, indeed,has sometimes been supposed to be the dis-coverer of the law. There is reason to believethat he based his generalizations on the ex-periment of Snell, though he did not openlyacknowledge his indebtedness. The law, asDescartes expressed it, states that the sineof the angle of incidence bears a fixed ratioto the sine of the angle of refraction for anygiven medium. Here, then, was another illus-tration of the fact that almost infinitely variedphenomena may be brought within the scopeof a simple law. Once the law had been ex-pressed, it could be tested and verified withthe greatest ease; and, as usual, the discov-ery being made, it seems surprising that ear-lier investigators—in particular so sagaciousa guesser as Kepler—should have missed it.


Galileo himself must have been to someextent a student of light, since, as we haveseen, he made such notable contributions topractical optics through perfecting the tele-scope; but he seems not to have added any-thing to the theory of light. The subject ofheat, however, attracted his attention in asomewhat different way, and he was led tothe invention of the first contrivance for mea-suring temperatures. His thermometer wasbased on the afterwards familiar principle ofthe expansion of a liquid under the influenceof heat; but as a practical means of measur-ing temperature it was a very crude affair,because the tube that contained the measur-ing liquid was exposed to the air, hence baro-metric changes of pressure vitiated the experi-ment. It remained for Galileo’s Italian succes-sors of the Accademia del Cimento of Florenceto improve upon the apparatus, after the ex-periments of Torricelli—to which we shall re-fer in a moment—had thrown new light on thequestion of atmospheric pressure. Still laterthe celebrated Huygens hit upon the idea ofusing the melting and the boiling point of wa-ter as fixed points in a scale of measurements,which first gave definiteness to thermometrictests.


TORRICELLIIn the closing years of his life Galileo tookinto his family, as his adopted disciple inscience, a young man, Evangelista Torricelli(1608-1647), who proved himself, during hisshort lifetime, to be a worthy follower of hisgreat master. Not only worthy on account ofhis great scientific discoveries, but grateful aswell, for when he had made the great dis-covery that the “suction” made by a vacuumwas really nothing but air pressure, and notsuction at all, he regretted that so importanta step in science might not have been madeby his great teacher, Galileo, instead of byhimself. “This generosity of Torricelli,” saysPlayfair, “was, perhaps, rarer than his genius:there are more who might have discovered thesuspension of mercury in the barometer thanwho would have been willing to part with thehonor of the discovery to a master or a friend.”

Torricelli’s discovery was made in 1643,less than two years after the death of his mas-ter. Galileo had observed that water will notrise in an exhausted tube, such as a pump,to a height greater than thirty-three feet, buthe was never able to offer a satisfactory ex-planation of the principle. Torricelli was ableto demonstrate that the height at which thewater stood depended upon nothing but its


weight as compared with the weight of air. Ifthis be true, it is evident that any fluid will besupported at a definite height, according to itsrelative weight as compared with air. Thusmercury, which is about thirteen times moredense than water, should only rise to one-thirteenth the height of a column of water—that is, about thirty inches. Reasoning in thisway, Torricelli proceeded to prove that his the-ory was correct. Filling a long tube, closedat one end, with mercury, he inverted thetube with its open orifice in a vessel of mer-cury. The column of mercury fell at once, butat a height of about thirty inches it stoppedand remained stationary, the pressure of theair on the mercury in the vessel maintain-ing it at that height. This discovery was ashattering blow to the old theory that haddominated that field of physics for so manycenturies. It was completely revolutionaryto prove that, instead of a mysterious some-thing within the tube being responsible forthe suspension of liquids at certain heights,it was simply the ordinary atmospheric pres-sure mysterious enough, it is true—pushingupon them from without. The pressure ex-erted by the atmosphere was but little under-stood at that time, but Torricelli’s discoveryaided materially in solving the mystery. Thewhole class of similar phenomena of air pres-


sure, which had been held in the trammel oflong-established but false doctrines, was nowreduced to one simple law, and the door to asolution of a host of unsolved problems thrownopen.

It had long been suspected and believedthat the density of the atmosphere varies atcertain times. That the air is sometimes“heavy” and at other times “light” is appar-ent to the senses without scientific appara-tus for demonstration. It is evident, then,that Torricelli’s column of mercury should riseand fall just in proportion to the lightness orheaviness of the air. A short series of ob-servations proved that it did so, and withthose observations went naturally the obser-vations as to changes in the weather. It wasonly necessary, therefore, to scratch a scaleon the glass tube, indicating relative atmo-spheric pressures, and the Torricellian barom-eter was complete.

Such a revolutionary theory and such animportant discovery were, of course, not to beaccepted without controversy, but the feeblearguments of the opponents showed how un-tenable the old theory had become. In 1648Pascal suggested that if the theory of the pres-sure of air upon the mercury was correct, itcould be demonstrated by ascending a moun-tain with the mercury tube. As the air was


known to get progressively lighter from baseto summit, the height of the column shouldbe progressively lessened as the ascent wasmade, and increase again on the descent intothe denser air. The experiment was made onthe mountain called the Puy-de-Dome, in Au-vergne, and the column of mercury fell androse progressively through a space of aboutthree inches as the ascent and descent weremade.

This experiment practically sealed the ver-dict on the new theory, but it also suggestedsomething more. If the mercury descended toa certain mark on the scale on a mountain-topwhose height was known, why was not this ameans of measuring the heights of all otherelevations? And so the beginning was madewhich, with certain modifications and correc-tions in details, is now the basis of barometri-cal measurements of heights.

In hydraulics, also, Torricelli seems tohave taken one of the first steps. He did thisby showing that the water which issues from ahole in the side or bottom of a vessel does so atthe same velocity as that which a body wouldacquire by falling from the level of the surfaceof the water to that of the orifice. This discov-ery was of the greatest importance to a correctunderstanding of the science of the motions offluids. He also discovered the valuable me-


BLAISE PASCAL

(From the painting by Philippe de Champagne.)


chanical principle that if any number of bod-ies be connected so that by their motion thereis neither ascent nor descent of their centre ofgravity, these bodies are in equilibrium.

Besides making these discoveries, hegreatly improved the microscope and the tele-scope, and invented a simple microscope madeof a globule of glass. In 1644 he published atract on the properties of the cycloid in whichhe suggested a solution of the problem of itsquadrature. As soon as this pamphlet ap-peared its author was accused by Gilles Rober-val (1602-1675) of having appropriated a solu-tion already offered by him. This led to a longdebate, during which Torricelli was seizedwith a fever, from the effects of which he died,in Florence, October 25, 1647. There is reasonto believe, however, that while Roberval’s dis-covery was made before Torricelli’s, the latterreached his conclusions independently.

VI. TWO PSEUDO-SCIENCES—ALCHEMY ANDASTROLOGY

In recent chapters we have seen science comeforward with tremendous strides. A new erais obviously at hand. But we shall misconceivethe spirit of the times if we fail to understandthat in the midst of all this progress therewas still room for mediæval superstition andfor the pursuit of fallacious ideals. Two formsof pseudo-science were peculiarly prevalent—alchemy and astrology. Neither of these canwith full propriety be called a science, yet bothwere pursued by many of the greatest scien-tific workers of the period. Moreover, the stud-ies of the alchemist may with some proprietybe said to have laid the foundation for thelatter-day science of chemistry; while astrol-

177


ogy was closely allied to astronomy, though itsrelations to that science are not as intimate ashas sometimes been supposed.

Just when the study of alchemy began isundetermined. It was certainly of very an-cient origin, perhaps Egyptian, but its mostflourishing time was from about the eighthcentury A.D. to the eighteenth century. Thestories of the Old Testament formed a basisfor some of the strange beliefs regarding theproperties of the magic “elixir,” or “philoso-pher’s stone.” Alchemists believed that mostof the antediluvians, perhaps all of them, pos-sessed a knowledge of this stone. How, oth-erwise, could they have prolonged their livesto nine and a half centuries? And Moses wassurely a first-rate alchemist, as is proved bythe story of the Golden Calf.12 After Aaronhad made the calf of gold, Moses performedthe much more difficult task of grinding itto powder and “strewing it upon the waters,”thus showing that he had transmuted it intosome lighter substance.

But antediluvians and Biblical characterswere not the only persons who were thoughtto have discovered the coveted “elixir.” Hun-dreds of aged mediæval chemists were cred-ited with having made the discovery, and werethought to be living on through the centuries

12Exodus xxxii, 20.

VI. TWO PSEUDO-SCIENCES 179

by its means. Alaies de Lisle, for example,who died in 1298, at the age of 110, was al-leged to have been at the point of death at theage of fifty, but just at this time he made thefortunate discovery of the magic stone, and socontinued to live in health and affluence forsixty years more. And De Lisle was but onecase among hundreds.

An aged and wealthy alchemist couldclaim with seeming plausibility that he wasprolonging his life by his magic; whereas ayounger man might assert that, knowing thegreat secret, he was keeping himself youngthrough the centuries. In either case sucha statement, or rumor, about a learned andwealthy alchemist was likely to be believed,particularly among strangers; and as such aman would, of course, be the object of muchattention, the claim was frequently made bypersons seeking notoriety. One of the mostcelebrated of these impostors was a certainCount de Saint-Germain, who was connectedwith the court of Louis XV. His statementscarried the more weight because, having ap-parently no means of maintenance, he contin-ued to live in affluence year after year—fortwo thousand years, as he himself admitted—by means of the magic stone. If at any timehis statements were doubted, he was in thehabit of referring to his valet for confirmation,


this valet being also under the influence of theelixir of life.

“Upon one occasion his master wastelling a party of ladies and gen-tlemen, at dinner, some conversa-tion he had had in Palestine, withKing Richard I., of England, whomhe described as a very particularfriend of his. Signs of astonishmentand incredulity were visible on thefaces of the company, upon whichSaint-Germain very coolly turnedto his servant, who stood behindhis chair, and asked him if he hadnot spoken the truth. ‘I really can-not say,’ replied the man, withoutmoving a muscle; ‘you forget, sir, Ihave been only five hundred yearsin your service.’ ‘Ah, true,’ said hismaster, ‘I remember now; it was alittle before your time!”’13

In the time of Saint-Germain, only a littleover a century ago, belief in alchemy had al-most disappeared, and his extraordinary taleswere probably regarded in the light of amus-ing stories. Still there was undoubtedly a lin-gering suspicion in the minds of many that

13Charles Mackay, Popular Delusions, 3 vols., Lon-don, 1850. Vol. II., p. 280.


this man possessed some peculiar secret. Afew centuries earlier his tales would hardlyhave been questioned, for at that time the be-lief in the existence of this magic somethingwas so strong that the search for it became al-most a form of mania; and once a man wasseized with it, he gambled away health, po-sition, and life itself in pursuing the covetedstake. An example of this is seen in Alber-tus Magnus, one of the most learned men ofhis time, who it is said resigned his positionas bishop of Ratisbon in order that he mightpursue his researches in alchemy.

If self-sacrifice was not sufficient to securethe prize, crime would naturally follow, forthere could be no limit to the price of thestakes in this game. The notorious Marechalde Reys, failing to find the coveted stone byordinary methods of laboratory research, waspersuaded by an impostor that if he wouldpropitiate the friendship of the devil the se-cret would be revealed. To this end De Reysbegan secretly capturing young children asthey passed his castle and murdering them.When he was at last brought to justice it wasproved that he had murdered something likea hundred children within a period of threeyears. So, at least, runs one version of thestory of this perverted being.

Naturally monarchs, constantly in need of


funds, were interested in these alchemists.Even sober England did not escape, and Ray-mond Lully, one of the most famous of thethirteenth and fourteenth century alchemists,is said to have been secretly invited by KingEdward I. (or II.) to leave Milan and set-tle in England. According to some accounts,apartments were assigned to his use in theTower of London, where he is alleged to havemade some six million pounds sterling forthe monarch, out of iron, mercury, lead, andpewter.

Pope John XXII., a friend and pupil of thealchemist Arnold de Villeneuve, is reportedto have learned the secrets of alchemy fromhis master. Later he issued two bulls against“pretenders” in the art, which, far from show-ing his disbelief, were cited by alchemists asproving that he recognized pretenders as dis-tinct from true masters of magic.

To moderns the attitude of mind of the al-chemist is difficult to comprehend. It is, per-haps, possible to conceive of animals or plantspossessing souls, but the early alchemist at-tributed the same thing—or something kinto it—to metals also. Furthermore, just asplants germinated from seeds, so metals weresupposed to germinate also, and hence a con-stant growth of metals in the ground. To provethis the alchemist cited cases where previ-


ously exhausted gold-mines were found, af-ter a lapse of time, to contain fresh quanti-ties of gold. The “seed” of the remaining parti-cles of gold had multiplied and increased. Butthis germinating process could only take placeunder favorable conditions, just as the seedof a plant must have its proper surroundingsbefore germinating; and it was believed thatthe action of the philosopher’s stone was tohasten this process, as man may hasten thegrowth of plants by artificial means. Goldwas looked upon as the most perfect metal,and all other metals imperfect, because notyet “purified.” By some alchemists they wereregarded as lepers, who, when cured of theirleprosy, would become gold. And since na-ture intended that all things should be per-fect, it was the aim of the alchemist to assisther in this purifying process, and incidentallyto gain wealth and prolong his life.

By other alchemists the process of tran-sition from baser metals into gold was con-ceived to be like a process of ripening fruit.The ripened product was gold, while the greenfruit, in various stages of maturity, was repre-sented by the base metals. Silver, for exam-ple, was more nearly ripe than lead; but thedifference was only one of “digestion,” and itwas thought that by further “digestion” leadmight first become silver and eventually gold.


In other words, Nature had not completed herwork, and was wofully slow at it at best; butman, with his superior faculties, was to has-ten the process in his laboratories—if he couldbut hit upon the right method of doing so.

It should not be inferred that the alchemistset about his task of assisting nature in ahaphazard way, and without training in thevarious alchemic laboratory methods. On thecontrary, he usually served a long apprentice-ship in the rudiments of his calling. He wasobliged to learn, in a general way, many of thesame things that must be understood in eitherchemical or alchemical laboratories. The gen-eral knowledge that certain liquids vaporizeat lower temperatures than others, and thatthe melting-points of metals differ greatly, forexample, was just as necessary to alchemyas to chemistry. The knowledge of the grossstructure, or nature, of materials was muchthe same to the alchemist as to the chemist,and, for that matter, many of the experimentsin calcining, distilling, etc., were practicallyidentical.

To the alchemist there were threeprinciples—salt, sulphur, and mercury—and the sources of these principles werethe four elements—earth, water, fire, andair. These four elements were accountablefor every substance in nature. Some of the


experiments to prove this were so illusive,and yet apparently so simple, that one isnot surprised that it took centuries to dis-prove them. That water was composed ofearth and air seemed easily proven by thesimple process of boiling it in a tea-kettle,for the residue left was obviously an earthysubstance, whereas the steam driven off wassupposed to be air. The fact that pure waterleaves no residue was not demonstrated untilafter alchemy had practically ceased to exist.It was possible also to demonstrate thatwater could be turned into fire by thrustinga red-hot poker under a bellglass containinga dish of water. Not only did the quantity ofwater diminish, but, if a lighted candle wasthrust under the glass, the contents ignitedand burned, proving, apparently, that waterhad been converted into fire. These, andscores of other similar experiments, seemedso easily explained, and to accord so wellwith the “four elements” theory, that theywere seldom questioned until a later age ofinductive science.

But there was one experiment to which thealchemist pinned his faith in showing thatmetals could be “killed” and “revived,” whenproper means were employed. It had beenknown for many centuries that if any metal,other than gold or silver, were calcined in an


open crucible, it turned, after a time, into apeculiar kind of ash. This ash was thoughtby the alchemist to represent the death of themetal. But if to this same ash a few grainsof wheat were added and heat again appliedto the crucible, the metal was seen to “risefrom its ashes” and resume its original form—a well-known phenomenon of reducing met-als from oxides by the use of carbon, in theform of wheat, or, for that matter, any othercarbonaceous substance. Wheat was, there-fore, made the symbol of the resurrection ofthe life eternal. Oats, corn, or a piece ofcharcoal would have “revived” the metals fromthe ashes equally well, but the mediæval al-chemist seems not to have known this. How-ever, in this experiment the metal seemed ac-tually to be destroyed and revivified, and, asscience had not as yet explained this strik-ing phenomenon, it is little wonder that it de-ceived the alchemist.

Since the alchemists pursued their searchof the magic stone in such a methodical way, itwould seem that they must have some idea ofthe appearance of the substance they sought.Probably they did, each according to his ownmental bias; but, if so, they seldom commit-ted themselves to writing, confining their dis-courses largely to speculations as to the prop-erties of this illusive substance. Furthermore,


the desire for secrecy would prevent themfrom expressing so important a piece of infor-mation. But on the subject of the properties,if not on the appearance of the “essence,” theywere voluminous writers. It was supposed tobe the only perfect substance in existence, andto be confined in various substances, in quan-tities proportionate to the state of perfectionof the substance. Thus, gold being most nearlyperfect would contain more, silver less, leadstill less, and so on. The “essence” containedin the more nearly perfect metals was thoughtto be more potent, a very small quantity of itbeing capable of creating large quantities ofgold and of prolonging life indefinitely.

It would appear from many of the writ-ings of the alchemists that their conceptionof nature and the supernatural was so con-fused and entangled in an inexplicable philos-ophy that they themselves did not really un-derstand the meaning of what they were at-tempting to convey. But it should not be for-gotten that alchemy was kept as much as pos-sible from the ignorant general public, and thealchemists themselves had knowledge of se-cret words and expressions which conveyed adefinite meaning to one of their number, butwhich would appear a meaningless jumble toan outsider. Some of these writers declaredopenly that their writings were intended to


convey an entirely erroneous impression, andwere sent out only for that purpose.

However, while it may have been true thatthe vagaries of their writings were made pur-posely, the case is probably more correctlyexplained by saying that the very nature ofthe art made definite statements impossible.They were dealing with something that didnot exist—could not exist. Their attempteddescriptions became, therefore, the languageof romance rather than the language of sci-ence.

But if the alchemists themselves were usu-ally silent as to the appearance of the actualsubstance of the philosopher’s stone, therewere numberless other writers who were lessreticent. By some it was supposed to be astone, by others a liquid or elixir, but morecommonly it was described as a black pow-der. It also possessed different degrees of ef-ficiency according to its degrees of purity, cer-tain forms only possessing the power of turn-ing base metals into gold, while others gaveeternal youth and life or different degrees ofhealth. Thus an alchemist, who had madea partial discovery of this substance, couldprolong life a certain number of years only,or, possessing only a small and inadequateamount of the magic powder, he was obliged togive up the ghost when the effect of this small


quantity had passed away.This belief in the supernatural power of

the philosopher’s stone to prolong life andheal diseases was probably a later phase ofalchemy, possibly developed by attempts toconnect the power of the mysterious essencewith Biblical teachings. The early Roman al-chemists, who claimed to be able to transmutemetals, seem not to have made other claimsfor their magic stone.

By the fifteenth century the belief in thephilosopher’s stone had become so fixed thatgovernments began to be alarmed lest somelucky possessor of the secret should flood thecountry with gold, thus rendering the existingcoin of little value. Some little consolation wasfound in the thought that in case all the basermetals were converted into gold iron wouldthen become the “precious metal,” and wouldremain so until some new philosopher’s stonewas found to convert gold back into iron—a much more difficult feat, it was thought.However, to be on the safe side, the EnglishParliament, in 1404, saw fit to pass an actdeclaring the making of gold and silver to bea felony. Nevertheless, in 1455, King HenryVI. granted permission to several “knights,citizens of London, chemists, and monks” tofind the philosopher’s stone, or elixir, that thecrown might thus be enabled to pay off its


debts. The monks and ecclesiastics were sup-posed to be most likely to discover the secretprocess, since “they were such good artists intransubstantiating bread and wine.”

In Germany the emperors Maximilian I.,Rudolf II., and Frederick II. gave consider-able attention to the search, and the examplethey set was followed by thousands of theirsubjects. It is said that some noblemen de-veloped the unpleasant custom of inviting totheir courts men who were reputed to havefound the stone, and then imprisoning thepoor alchemists until they had made a cer-tain quantity of gold, stimulating their activ-ity with tortures of the most atrocious kinds.Thus this danger of being imprisoned andheld for ransom until some fabulous amountof gold should be made became the constantmenace of the alchemist. It was useless for analchemist to plead poverty once it was noisedabout that he had learned the secret. Forhow could such a man be poor when, with apiece of metal and a few grains of magic pow-der, he was able to provide himself with gold?It was, therefore, a reckless alchemist indeedwho dared boast that he had made the coveteddiscovery.

The fate of a certain indiscreet alchemist,supposed by many to have been Seton, aScotchman, was not an uncommon one. Word


having been brought to the elector of Saxonythat this alchemist was in Dresden and boast-ing of his powers, the elector caused him to bearrested and imprisoned. Forty guards werestationed to see that he did not escape andthat no one visited him save the elector him-self. For some time the elector tried by ar-gument and persuasion to penetrate his se-cret or to induce him to make a certain quan-tity of gold; but as Seton steadily refused, therack was tried, and for several months he suf-fered torture, until finally, reduced to a mereskeleton, he was rescued by a rival candidateof the elector, a Pole named Michael Sendivo-gins, who drugged the guards. However, be-fore Seton could be “persuaded” by his newcaptor, he died of his injuries.

But Sendivogins was also ambitious inalchemy, and, since Seton was beyond hisreach, he took the next best step and marriedhis widow. From her, as the story goes, he re-ceived an ounce of black powder—the verita-ble philosopher’s stone. With this he manu-factured great quantities of gold, even invit-ing Emperor Rudolf II. to see him work themiracle. That monarch was so impressed thathe caused a tablet to be inserted in the wall ofthe room in which he had seen the gold made.

Sendivogins had learned discretion fromthe misfortune of Seton, so that he took the


precaution of concealing most of the preciouspowder in a secret chamber of his carriagewhen he travelled, having only a small quan-tity carried by his steward in a gold box. Inparticularly dangerous places, he is said tohave exchanged clothes with his coachman,making the servant take his place in the car-riage while he mounted the box.

About the middle of the seventeenth cen-tury alchemy took such firm root in the re-ligious field that it became the basis of thesect known as the Rosicrucians. The namewas derived from the teaching of a Germanphilosopher, Rosenkreutz, who, having beenhealed of a dangerous illness by an Arabiansupposed to possess the philosopher’s stone,returned home and gathered about him a cho-sen band of friends, to whom he imparted thesecret. This sect came rapidly into promi-nence, and for a short time at least createda sensation in Europe, and at the time werecredited with having “refined and spiritual-ized” alchemy. But by the end of the seven-teenth century their number had dwindled toa mere handful, and henceforth they exertedlittle influence.

Another and earlier religious sect was theAureacrucians, founded by Jacob Bohme, ashoemaker, born in Prussia in 1575. Accord-ing to his teachings the philosopher’s stone


could be discovered by a diligent search ofthe Old and the New Testaments, and moreparticularly the Apocalypse, which containedall the secrets of alchemy. This sect foundquite a number of followers during the life ofBohme, but gradually died out after his death;not, however, until many of its members hadbeen tortured for heresy, and one at least,Kuhlmann, of Moscow, burned as a sorcerer.

The names of the different substances thatat various times were thought to contain thelarge quantities of the “essence” during themany centuries of searching for it, form a listof practically all substances that were known,discovered, or invented during the period.Some believed that acids contained the sub-stance; others sought it in minerals or in an-imal or vegetable products; while still otherslooked to find it among the distilled “spirits”—the alcoholic liquors and distilled products.On the introduction of alcohol by the Arabsthat substance became of all-absorbing inter-est, and for a long time allured the alchemistinto believing that through it they were soonto be rewarded. They rectified and refined ituntil “sometimes it was so strong that it brokethe vessels containing it,” but still it failedin its magic power. Later, brandy was sub-stituted for it, and this in turn discarded formore recent discoveries.


There were always, of course, two classesof alchemists: serious investigators whosehonesty could not be questioned, and cleverimpostors whose legerdemain was probablylargely responsible for the extended beliefin the existence of the philosopher’s stone.Sometimes an alchemist practised both, us-ing the profits of his sleight-of-hand to pro-cure the means of carrying on his serious al-chemical researches. The impostures of someof these jugglers deceived even the most in-telligent and learned men of the time, andso kept the flame of hope constantly burn-ing. The age of cold investigation had not ar-rived, and it is easy to understand how anunscrupulous mediæval Hermann or Kellarmight completely deceive even the most in-telligent and thoughtful scholars. In scoffingat the credulity of such an age, it should notbe forgotten that the “Keely motor” was a latenineteenth-century illusion.

But long before the belief in the philoso-pher’s stone had died out, the methods ofthe legerdemain alchemist had been inves-tigated and reported upon officially by bod-ies of men appointed to make such investi-gations, although it took several generationscompletely to overthrow a superstition thathad been handed down through several thou-sand years. In April of 1772 Monsieur Ge-


offroy made a report to the Royal Academyof Sciences, at Paris, on the alchemic cheatsprincipally of the sixteenth and seventeenthcenturies. In this report he explains manyof the seemingly marvellous feats of the un-scrupulous alchemists. A very common formof deception was the use of a double-bottomedcrucible. A copper or brass crucible was cov-ered on the inside with a layer of wax, clev-erly painted so as to resemble the ordinarymetal. Between this layer of wax and thebottom of the crucible, however, was a layerof gold dust or silver. When the alchemistwished to demonstrate his power, he had butto place some mercury or whatever substancehe chose in the crucible, heat it, throw in agrain or two of some mysterious powder, pro-nounce a few equally mysterious phrases toimpress his audience, and, behold, a lump ofprecious metal would be found in the bottomof his pot. This was the favorite method ofmediocre performers, but was, of course, eas-ily detected.

An equally successful but more difficultway was to insert surreptitiously a lump ofmetal into the mixture, using an ordinary cru-cible. This required great dexterity, but wasfacilitated by the use of many mysterious cer-emonies on the part of the operator while per-forming, just as the modern vaudeville per-


former diverts the attention of the audience tohis right hand while his left is engaged in thetrick. Such ceremonies were not questioned,for it was the common belief that the wholeprocess “lay in the spirit as much as in thesubstance,” many, as we have seen, regardingthe whole process as a divine manifestation.

Sometimes a hollow rod was used for stir-ring the mixture in the crucible, this rod con-taining gold dust, and having the end pluggedeither with wax or soft metal that was eas-ily melted. Again, pieces of lead were usedwhich had been plugged with lumps of goldcarefully covered over; and a very simple andimpressive demonstration was making use ofa nugget of gold that had been coated overwith quicksilver and tarnished so as to re-semble lead or some base metal. When thiswas thrown into acid the coating was removedby chemical action, leaving the shining metalin the bottom of the vessel. In order to per-form some of these tricks, it is obvious thatthe alchemist must have been well suppliedwith gold, as some of them, when performingbefore a royal audience, gave the products totheir visitors. But it was always a paying in-vestment, for once his reputation was estab-lished the gold-maker found an endless vari-ety of ways of turning his alleged knowledgeto account, frequently amassing great wealth.


Some of the cleverest of the charlatans of-ten invited royal or other distinguished gueststo bring with them iron nails to be turned intogold ones. They were transmuted in the al-chemist’s crucible before the eyes of the vis-itors, the juggler adroitly extracting the ironnail and inserting a gold one without detec-tion. It mattered little if the converted goldnail differed in size and shape from the orig-inal, for this change in shape could be laid tothe process of transmutation; and even thevery critical were hardly likely to find faultwith the exchange thus made. Furthermore,it was believed that gold possessed the prop-erty of changing its bulk under certain con-ditions, some of the more conservative al-chemists maintaining that gold was only in-creased in bulk, not necessarily created, bycertain forms of the magic stone. Thus a veryproficient operator was thought to be able toincrease a grain of gold into a pound of puremetal, while one less expert could only dou-ble, or possibly treble, its original weight.

The actual number of useful discoveriesresulting from the efforts of the alchemistsis considerable, some of them of incalcula-ble value. Roger Bacon, who lived in thethirteenth century, while devoting much ofhis time to alchemy, made such valuable dis-coveries as the theory, at least, of the tele-


scope, and probably gunpowder. Of this lat-ter we cannot be sure that the discovery washis own and that he had not learned of itthrough the source of old manuscripts. Butit is not impossible nor improbable that hemay have hit upon the mixture that makesthe explosives while searching for the philoso-pher’s stone in his laboratory. “Von Helmont,in the same pursuit, discoverd the propertiesof gas,” says Mackay; “Geber made discoveriesin chemistry, which were equally important;and Paracelsus, amid his perpetual visions ofthe transmutation of metals, found that mer-cury was a remedy for one of the most odiousand excruciating of all the diseases that af-flict humanity.”14 As we shall see a little far-ther on, alchemy finally evolved into modernchemistry, but not until it had passed throughseveral important transitional stages.

ASTROLOGYIn a general way modern astronomy may beconsidered as the outgrowth of astrology, justas modern chemistry is the result of alchemy.It is quite possible, however, that astronomy isthe older of the two; but astrology must havedeveloped very shortly after. The primitive

14Mackay, op. cit., Vol. II., p. 289.


astronomer, having acquired enough knowl-edge from his observations of the heavenlybodies to make correct predictions, such as thetime of the coming of the new moon, wouldbe led, naturally, to believe that certain pre-dictions other than purely astronomical onescould be made by studying the heavens. Evenif the astronomer himself did not believe this,some of his superstitious admirers would; forto the unscientific mind predictions of earthlyevents would surely seem no more miraculousthan correct predictions as to the future move-ments of the sun, moon, and stars. When as-tronomy had reached a stage of developmentso that such things as eclipses could be pre-dicted with anything like accuracy, the oc-cult knowledge of the astronomer would beunquestioned. Turning this apparently oc-cult knowledge to account in a mercenary waywould then be the inevitable result, althoughit cannot be doubted that many of the as-trologers, in all ages, were sincere in their be-liefs.

Later, as the business of astrology becamea profitable one, sincere astronomers wouldfind it expedient to practise astrology as ameans of gaining a livelihood. Such a philoso-pher as Kepler freely admitted that he prac-tised astrology “to keep from starving,” al-though he confessed no faith in such predic-


tions. “Ye otherwise philosophers,” he said,“ye censure this daughter of astronomy be-yond her deserts; know ye not that she mustsupport her mother by her charms.”

Once astrology had become an establishedpractice, any considerable knowledge of as-tronomy was unnecessary, for as it was atbest but a system of good guessing as tofuture events, clever impostors could thriveequally well without troubling to study as-tronomy. The celebrated astrologers, however,were usually astronomers as well, and un-doubtedly based many of their predictions onthe position and movements of the heavenlybodies. Thus, the casting of a horoscope—that is, the methods by which the astrologersascertained the relative position of the heav-enly bodies at the time of a birth—was a sim-ple but fairly exact procedure. Its basis wasthe zodiac, or the path traced by the sun inhis yearly course through certain constella-tions. At the moment of the birth of a child,the first care of the astrologer was to note theparticular part of the zodiac that appearedon the horizon. The zodiac was then dividedinto “houses”—that is, into twelve spaces—ona chart. In these houses were inserted theplaces of the planets, sun, and moon, with ref-erence to the zodiac. When this chart wascompleted it made a fairly correct diagram


of the heavens and the position of the heav-enly bodies as they would appear to a personstanding at the place of birth at a certain time.

Up to this point the process was a sim-ple one of astronomy. But the next step—the really important one—that of interpret-ing this chart, was the one which called forththe skill and imagination of the astrologer. Inthis interpretation, not in his mere observa-tions, lay the secret of his success. Nor didhis task cease with simply foretelling futureevents that were to happen in the life of thenewly born infant. He must not only pointout the dangers, but show the means wherebythey could be averted, and his prophylacticmeasures, like his predictions, were alleged tobe based on his reading of the stars.

But casting a horoscope at the time ofbirths was, of course, only a small part of theastrologer’s duty. His offices were sought bypersons of all ages for predictions as to theirfutures, the movements of an enemy, whereto find stolen goods, and a host of everyday oc-currences. In such cases it is more than proba-ble that the astrologers did very little consult-ing of the stars in making their predictions.They became expert physiognomists and ex-cellent judges of human nature, and were thusable to foretell futures with the same shrewd-ness and by the same methods as the mod-


ern “mediums,” palmists, and fortune-tellers.To strengthen belief in their powers, it be-came a common thing for some supposedlylost document of the astrologer to be myste-riously discovered after an important event,this document purporting to foretell this veryevent. It was also a common practice withastrologers to retain, or have access to, theiroriginal charts, cleverly altering them fromtime to time to fit conditions.

The dangers attendant upon astrologywere of such a nature that the lot of the as-trologer was likely to prove anything but anenviable one. As in the case of the alchemist,the greater the reputation of an astrologer thegreater dangers he was likely to fall into. Ifhe became so famous that he was employedby kings or noblemen, his too true or toofalse prophecies were likely to bring him intodisrepute—even to endanger his life.

Throughout the dark age the astrologersflourished, but the sixteenth and seventeenthcenturies were the golden age of these impos-tors. A skilful astrologer was as much an es-sential to the government as the highest offi-cial, and it would have been a bold monarch,indeed, who would undertake any expeditionof importance unless sanctioned by the gov-erning stars as interpreted by these officials.

It should not be understood, however, that


belief in astrology died with the advent ofthe Copernican doctrine. It did become sep-arated from astronomy very shortly after, tobe sure, and undoubtedly among the scien-tists it lost much of its prestige. But it cannotbe considered as entirely passed away, evento-day, and even if we leave out of consider-ation street-corner “astrologers” and fortune-tellers, whose signs may be seen in every largecity, there still remains quite a large classof relatively intelligent people who believe inwhat they call “the science of astrology.” Need-less to say, such people are not found amongthe scientific thinkers; but it is significantthat scarcely a year passes that some book orpamphlet is not published by some ardent be-liever in astrology, attempting to prove by theillogical dogmas characteristic of unscientificthinkers that astrology is a science. The argu-ments contained in these pamphlets are verymuch the same as those of the astrologersthree hundred years ago, except that they lackthe quaint form of wording which is one of thefeatures that lends interest to the older docu-ments. These pamphlets need not be takenseriously, but they are interesting as exem-plifying how difficult it is, even in an age ofscience, to entirely stamp out firmly estab-lished superstitions. Here are some of thearguments advanced in defence of astrology,


taken from a little brochure entitled “Astrol-ogy Vindicated,” published in 1898: “It will befound that a person born when the Sun is intwenty degrees Scorpio has the left ear as hisexceptional feature and the nose (Sagittarius)bent towards the left ear. A person born whenthe Sun is in any of the latter degrees of Tau-rus, say the twenty-fifth degree, will have asmall, sharp, weak chin, curved up towardsGemini, the two vertical lines on the upperlip.”15 The time was when science went outof its way to prove that such statements wereuntrue; but that time is past, and such writ-ers are usually classed among those energeticbut misguided persons who are unable to dis-tinguish between logic and sophistry.

In England, from the time of Elizabeth tothe reign of William and Mary, judicial astrol-ogy was at its height. After the great Lon-don fire, in 1666, a committee of the House ofCommons publicly summoned the famous as-trologer, Lilly, to come before Parliament andreport to them on his alleged prediction of thecalamity that had befallen the city. Lilly, forsome reason best known to himself, deniedhaving made such a prediction, being, as heexplained, “more interested in determining af-fairs of much more importance to the future

15John B. Schmalz, Astrology Vindicated, New York,1898.


welfare of the country.” Some of the explana-tions of his interpretations will suffice to showtheir absurdities, which, however, were by nomeans regarded as absurdities at that time,for Lilly was one of the greatest astrologers ofhis day. He said that in 1588 a prophecy hadbeen printed in Greek characters which fore-told exactly the troubles of England betweenthe years 1641 and 1660. “And after him shallcome a dreadful dead man,” ran the prophecy,“and with him a royal G of the best blood inthe world, and he shall have the crown andshall set England on the right way and putout all heresies.” His interpretation of thiswas that, “Monkery being extinguished aboveeighty or ninety years, and the Lord General’sname being Monk, is the dead man. The royalG or C (it is gamma in the Greek, intendingC in the Latin, being the third letter in thealphabet) is Charles II., who, for his extrac-tion, may be said to be of the best blood of theworld.”16

This may be taken as a fair sample ofLilly’s interpretations of astrological proph-esies, but many of his own writings, whilesomewhat more definite and direct, are stillleft sufficiently vague to allow his skilful in-terpretations to set right an apparent mis-

16William Lilly, The Starry Messenger, London, 1645,p. 63.


take. One of his famous documents was “TheStarry Messenger,” a little pamphlet purport-ing to explain the phenomenon of a “strangeapparition of three suns” that were seen inLondon on November 19, 1644—-the anniver-sary of the birth of Charles I., then the reign-ing monarch. This phenomenon caused agreat stir among the English astrologers, com-ing, as it did, at a time of great political distur-bance. Prophecies were numerous, and Lilly’sbrochure is only one of many that appeared atthat time, most of which, however, have beenlost. Lilly, in his preface, says: “If there be anyof so prevaricate a judgment as to think thatthe apparition of these three Suns doth inti-mate no Novelle thing to happen in our ownClimate, where they were manifestly visible, Ishall lament their indisposition, and conceivetheir brains to be shallow, and voyde of under-standing humanity, or notice of common His-tory.”

Having thus forgiven his few doubtingreaders, who were by no means in the ma-jority in his day, he takes up in review therecords of the various appearances of threesuns as they have occurred during the Chris-tian era, showing how such phenomena havegoverned certain human events in a very defi-nite manner. Some of these are worth record-ing.


“Anno 66. A comet was seen, and also threeSuns: In which yeer, Florus President of theJews was by them slain. Paul writes to Tim-othy. The Christians are warned by a divineOracle, and depart out of Jerusalem. Boadicea British Queen, killeth seventy thousand Ro-mans. The Nazareni, a scurvie Sect, begun,that boasted much of Revelations and Visions.About a year after Nero was proclaimed en-emy to the State of Rome.”

Again, “Anno 1157, in September, therewere seen three Suns together, in as clearweather as could be: And a few days after,in the same month, three Moons, and, in theMoon that stood in the middle, a white Crosse.Sueno, King of Denmark, at a great Feast, kil-leth Canutus: Sueno is himself slain, in pur-suit of Waldemar. The Order of Eremites, ac-cording to the rule of Saint Augustine, begunthis year; and in the next, the Pope submitsto the Emperour: (was not this miraculous?)Lombardy was also adjudged to the Emper-our.”

Continuing this list of peculiar phenomenahe comes down to within a few years of hisown time.

“Anno 1622, three Suns appeared at Hei-delberg. The woful Calamities that have eversince fallen upon the Palatinate, we are allsensible of, and of the loss of it, for any thing


I see, for ever, from the right Heir. Osman thegreat Turk is strangled that year; and Spinolabesiegeth Bergen up Zoom, etc.”

Fortified by the enumeration of these pastevents, he then proceeds to make his deduc-tions. “Only this I must tell thee,” he writes,“that the interpretation I write is, I con-ceive, grounded upon probable foundations;and who lives to see a few years over his head,will easily perceive I have unfolded as muchas was fit to discover, and that my judgmentwas not a mile and a half from truth.”

There is a great significance in this “asmuch as was fit to discover”—a mysterioussomething that Lilly thinks it expedient not todivulge. But, nevertheless, one would imag-ine that he was about to make some definiteprediction about Charles I., since these threesuns appeared upon his birthday and surelymust portend something concerning him. Butafter rambling on through many pages of dis-sertations upon planets and prophecies, he fi-nally makes his own indefinite prediction.

“O all you Emperors, Kings, Princes,Rulers and Magistrates of Europe, this un-accustomed Apparition is like the Handwrit-ing in Daniel to some of you; it premon-isheth you, above all other people, to makeyour peace with God in time. You shallevery one of you smart, and every one of


you taste (none excepted) the heavie handof God, who will strengthen your subjectswith invincible courage to suppress your mis-governments and Oppressions in Church orCommon-wealth;. . . Those words are gen-eral: a word for my own country of Eng-land. . . . Look to yourselves; here’s some mon-strous death towards you. But to whom? wiltthou say. Herein we consider the Signe, Lordthereof, and the House; The Sun signifies inthat Royal Signe, great ones; the House signi-fies captivity, poison, Treachery: From whichis derived thus much, That some very greatman, what King, Prince, Duke, or the like, Ireally affirm I perfectly know not, shall, I say,come to some such untimely end.”17

Here is shown a typical example of astro-logical prophecy, which seems to tell some-thing or nothing, according to the point ofview of the reader. According to a believerin astrology, after the execution of Charles I.,five years later, this could be made to seema direct and exact prophecy. For example,he says: “You Kings, Princes, etc., . . . it pre-monisheth you . . . to make your peace withGod. . . . Look to yourselves; here’s some mon-strous death towards you. . . . That some verygreat man, what King, Prince, shall, I say,come to such untimely end.”

17Lilly, op. cit., p. 70.


But by the doubter the complete prophecycould be shown to be absolutely indefinite, andapplicable as much to the king of France orSpain as to Charles I., or to any king in thefuture, since no definite time is stated. Fur-thermore, Lilly distinctly states, “What King,Prince, Duke, or the like, I really affirm I per-fectly know not”—which last, at least, wasa most truthful statement. The same inge-nuity that made “Gen. Monk” the “dreadfuldead man,” could easily make such a predic-tion apply to the execution of Charles I. Sucha definite statement that, on such and such aday a certain number of years in the future,the monarch of England would be beheaded—such an exact statement can scarcely be foundin any of the works on astrology. It shouldbe borne in mind, also, that Lilly was of theCromwell party and opposed to the king.

After the death of Charles I., Lilly ad-mitted that the monarch had given him athousand pounds to cast his horoscope. “Iadvised him,” says Lilly, “to proceed east-wards; he went west, and all the world knowsthe result.” It is an unfortunate thing forthe cause of astrology that Lilly failed tomention this until after the downfall of themonarch. In fact, the sudden death, or declinein power, of any monarch, even to-day, bringsout the perennial post-mortem predictions of


astrologers.We see how Lilly, an opponent of the king,

made his so-called prophecy of the disaster ofthe king and his army. At the same time an-other celebrated astrologer and rival of Lilly,George Wharton, also made some predictionsabout the outcome of the eventful march fromOxford. Wharton, unlike Lilly, was a followerof the king’s party, but that, of course, shouldhave had no influence in his “scientific” read-ing of the stars. Wharton’s predictions aremuch less verbose than Lilly’s, much moreexplicit, and, incidentally, much more incor-rect in this particular instance. “The MoonLady of the 12,” he wrote, “and moving be-twixt the 8 degree, 34 min., and 21 degree,26 min. of Aquarius, gives us to understandthat His Majesty shall receive much content-ment by certain Messages brought him fromforeign parts; and that he shall receive somesudden and unexpected supply of . . . by themeans of some that assimilate the conditionof his Enemies: And withal this comfort; thatHis Majesty shall be exceeding successful inBesieging Towns, Castles, or Forts, and in per-suing the enemy.

“Mars his Sextile to the Sun, Lord ofthe Ascendant (which happeneth the 18 dayof May) will encourage our Soldiers to ad-vance with much alacrity and cheerfulness of


spirit; to show themselves gallant in the mostdangerous attempt. . . . And now to sum upall: It is most apparent to every impartialand ingenuous judgment; That although HisMajesty cannot expect to be secured from ev-ery trivial disaster that may befall his army,either by the too much Presumption, Igno-rance, or Negligence of some particular Per-sons (which is frequently incident and un-avoidable in the best of Armies), yet the sev-eral positions of the Heavens duly consideredand compared among themselves, as well inthe prefixed Scheme as at the Quarterly In-gresses, do generally render His Majesty andhis whole Army unexpectedly victorious andsuccessful in all his designs; Believe it (Lon-don), thy Miseries approach, they are like tobe many, great, and grievous, and not to bediverted, unless thou seasonably crave Par-don of God for being Nurse to this presentRebellion, and speedily submit to thy Prince’sMercy; Which shall be the daily Prayer of Geo.Wharton.”18

In the light of after events, it is probablethat Wharton’s stock as an astrologer was notgreatly enhanced by this document, at leastamong members of the Royal family. Lilly’s

18George Wharton, An Astrological jugement uponHis Majesty’s Present March begun from Oxford, May7, 1645, pp. 7-10.


book, on the other hand, became a favoritewith the Parliamentary army.

After the downfall and death of Napoleonthere were unearthed many alleged authen-tic astrological documents foretelling his ruin.And on the death of George IV., in 1830, thereappeared a document (unknown, as usual, un-til that time) purporting to foretell the deathof the monarch to the day, and this withoutthe astrologer knowing that his horoscope wasbeing cast for a monarch. A full account of thisprophecy is told, with full belief, by Roback, anineteenth-century astrologer. He says:

“In the year 1828, a stranger ofnoble mien, advanced in life, butpossessing the most bland man-ners, arrived at the abode of a cele-brated astrologer in London,” ask-ing that the learned man foretellhis future. “The astrologer com-plied with the request of the myste-rious visitor, drew forth his tables,consulted his ephemeris, and castthe horoscope or celestial map forthe hour and the moment of the in-quiry, according to the establishedrules of his art.

“The elements of his calcula-tion were adverse, and a feelingof gloom cast a shade of serious


thought, if not dejection, over hiscountenance.

“‘You are of high rank,’ said theastrologer, as he calculated andlooked on the stranger, ‘and of il-lustrious title.’ The stranger madea graceful inclination of the headin token of acknowledgment of thecomplimentary remarks, and theastrologer proceeded with his mis-sion.

“The celestial signs were omi-nous of calamity to the stranger,who, probably observing a suddenchange in the countenance of theastrologer, eagerly inquired whatevil or good fortune had been as-signed him by the celestial orbs.

“‘To the first part of your in-quiry,’ said the astrologer, ‘I canreadily reply. You have been a fa-vorite of fortune; her smiles on youhave been abundant, her frownsbut few; you have had, perhapsnow possess, wealth and power; theimpossibility of their accomplish-ment is the only limit to the fulfil-ment of your desires.”’

“‘You have spoken truly of thepast,’ said the stranger. ‘I have full


faith in your revelations of the fu-ture: what say you of my pilgrim-age in this life—is it short or long?’

“‘I regret,’ replied the astrologer,in answer to this inquiry, ‘to be theherald of ill, though true, fortune;your sojourn on earth will be short.’

“‘How short?’ eagerly inquiredthe excited and anxious stranger.

“‘Give me a momentary truce,’said the astrologer; ‘I will con-sult the horoscope, and may pos-sibly find some mitigating circum-stances.’

“Having cast his eyes over thecelestial map, and paused for somemoments, he surveyed the counte-nance of the stranger with greatsympathy, and said, ‘I am sorrythat I can find no planetary influ-ences that oppose your destiny—your death will take place in twoyears.’

“The event justified the astro-logic prediction: George IV. died onMay 18, 1830, exactly two yearsfrom the day on which he had vis-ited the astrologer.”19

19C. W. Roback, The Mysteries of Astrology, Boston,1854, p. 29.


This makes a very pretty story, but ithardly seems like occult insight that an as-trologer should have been able to predict anearly death of a man nearly seventy years old,or to have guessed that his well-groomed vis-itor “had, perhaps now possesses, wealth andpower.” Here again, however, the point of viewof each individual plays the governing part indetermining the importance of such a docu-ment. To the scientist it proves nothing; tothe believer in astrology, everything. The sig-nificant thing is that it appeared shortly afterthe death of the monarch.

On the Continent astrologers were evenmore in favor than in England. Charle-magne, and some of his immediate successors,to be sure, attempted to exterminate them,but such rulers as Louis XI. and Catherinede’ Medici patronized and encouraged them,and it was many years after the time ofCopernicus before their influence was entirelystamped out even in official life. There can beno question that what gave the color of truthto many of the predictions was the fact thatso many of the prophecies of sudden deathsand great conflagrations were known to havecome true—in many instances were made tocome true by the astrologer himself. And so ithappened that when the prediction of a greatconflagration at a certain time culminated in


such a conflagration, many times a second butless-important burning took place, in whichthe ambitious astrologer, or his followers, tooka central part about a stake, being convictedof incendiarism, which they had committed inorder that their prophecies might be fulfilled.

But, on the other hand, these predictionswere sometimes turned to account by inter-ested friends to warn certain persons of ap-proaching dangers.

For example, a certain astrologer foretoldthe death of Prince Alexander de’ Medici. Henot only foretold the death, but described sominutely the circumstances that would attendit, and gave such a correct description of theassassin who should murder the prince, thathe was at once suspected of having a handin the assassination. It developed later, how-ever, that such was probably not the case; butthat some friend of Prince Alexander, know-ing of the plot to take his life, had induced theastrologer to foretell the event in order thatthe prince might have timely warning and soelude the conspirators.

The cause of the decline of astrology wasthe growing prevalence of the new spirit ofexperimental science. Doubtless the most di-rect blow was dealt by the Copernican theory.So soon as this was established, the recogni-tion of the earth’s subordinate place in the


universe must have made it difficult for as-tronomers to be longer deceived by such co-incidences as had sufficed to convince the ob-servers of a more credulous generation. Ty-cho Brahe was, perhaps, the last astronomerof prominence who was a conscientious prac-tiser of the art of the astrologer.

VII. FROMPARACELSUS TOHARVEY

PARACELSUSIn the year 1526 there appeared a new lec-turer on the platform at the University atBasel—a small, beardless, effeminate-lookingperson—who had already inflamed all Chris-tendom with his peculiar philosophy, his rev-olutionary methods of treating diseases, andhis unparalleled success in curing them. Aman who was to be remembered in after-timeby some as the father of modern chemistryand the founder of modern medicine; by oth-ers as madman, charlatan, impostor; and bystill others as a combination of all these. Thissoft-cheeked, effeminate, woman-hating man,whose very sex has been questioned, was

219


Theophrastus von Hohenheim, better knownas Paracelsus (1493-1541).

To appreciate his work, something mustbe known of the life of the man. He wasborn near Maria-Einsiedeln, in Switzerland,the son of a poor physician of the place. He be-gan the study of medicine under the instruc-tion of his father, and later on came under theinstruction of several learned churchmen. Atthe age of sixteen he entered the University ofBasel, but, soon becoming disgusted with thephilosophical teachings of the time, he quit-ted the scholarly world of dogmas and theoriesand went to live among the miners in the Ty-rol, in order that he might study nature andmen at first hand. Ordinary methods of studywere thrown aside, and he devoted his time topersonal observation—the only true means ofgaining useful knowledge, as he preached andpractised ever after. Here he became familiarwith the art of mining, learned the physicalproperties of minerals, ores, and metals, andacquired some knowledge of mineral waters.More important still, he came in contact withsuch diseases, wounds, and injuries as minersare subject to, and he tried his hand at thepractical treatment of these conditions, un-trammelled by the traditions of a professionin which his training had been so scant.

Having acquired some empirical skill in

VII. FROM PARACELSUS TO HARVEY 221

treating diseases, Paracelsus set out wan-dering from place to place all over Europe,gathering practical information as he went,and learning more and more of the medicinalvirtues of plants and minerals. His wander-ings covered a period of about ten years, atthe end of which time he returned to Basel,where he was soon invited to give a course oflectures in the university.

These lectures were revolutionary in tworespects—they were given in German insteadof time-honored Latin, and they were basedupon personal experience rather than uponthe works of such writers as Galen and Avi-cenna. Indeed, the iconoclastic teacher spokewith open disparagement of these reveredmasters, and openly upbraided his fellow-practitioners for following their tenets. Nat-urally such teaching raised a storm of oppo-sition among the older physicians, but for atime the unparalleled success of Paracelsus incuring diseases more than offset his unpopu-larity. Gradually, however, his bitter tongueand his coarse personality rendered him sounpopular, even among his patients, that, fi-nally, his liberty and life being jeopardized,he was obliged to flee from Basel, and be-came a wanderer. He lived for brief periodsin Colmar, Nuremberg, Appenzell, Zurich, Pf-effers, Augsburg, and several other cities, un-


til finally at Salzburg his eventful life cameto a close in 1541. His enemies said that hehad died in a tavern from the effects of a pro-tracted debauch; his supporters maintainedthat he had been murdered at the instigationof rival physicians and apothecaries.

But the effects of his teachings had takenfirm root, and continued to spread after hisdeath. He had shown the fallibility of many ofthe teachings of the hitherto standard meth-ods of treating diseases, and had demon-strated the advantages of independent rea-soning based on observation. In his Mag-icum he gives his reasons for breaking withtradition. “I did,” he says, “embrace at thebeginning these doctrines, as my adversaries(followers of Galen) have done, but since Isaw that from their procedures nothing re-sulted but death, murder, stranglings, an-chylosed limbs, paralysis, and so forth, thatthey held most diseases incurable . . . there-fore have I quitted this wretched art, andsought for truth in any other direction. Iasked myself if there were no such thing asa teacher in medicine, where could I learnthis art best? Nowhere better than the openbook of nature, written with God’s own fin-ger.” We shall see, however, that this “book ofnature” taught Paracelsus some very strangelessons. Modesty was not one of these. “Now


at this time,” he declares, “I, TheophrastusParacelsus, Bombast, Monarch of the Arcana,was endowed by God with special gifts for thisend, that every searcher after this supremephilosopher’s work may be forced to imitateand to follow me, be he Italian, Pole, Gaul,German, or whatsoever or whosoever he be.Come hither after me, all ye philosophers, as-tronomers, and spagirists. . . . I will show andopen to you . . . this corporeal regeneration.”20

Paracelsus based his medical teachingson four “pillars”—philosophy, astronomy,alchemy, and virtue of the physician—astrange-enough equipment surely, and yet,properly interpreted, not quite so anomalousas it seems at first blush. Philosophy was the“gate of medicine,” whereby the physician en-tered rightly upon the true course of learn-ing; astronomy, the study of the stars, wasall-important because “they (the stars) causeddisease by their exhalations, as, for instance,the sun by excessive heat”; alchemy, as he in-terpreted it, meant the improvement of natu-ral substances for man’s benefit; while virtuein the physician was necessary since “only thevirtuous are permitted to penetrate into theinnermost nature of man and the universe.”

All his writings aim to promote progress20A. E. Waite, The Hermetic and Alchemical Writings

of Paracelsus, 2 vols., London, 1894. Vol. I., p. 21.


in medicine, and to hold before the physiciana grand ideal of his profession. In this hisviews are wide and far-reaching, based on therelationship which man bears to nature asa whole; but in his sweeping condemnationshe not only rejected Galenic therapeutics andGalenic anatomy, but condemned dissectionsof any kind. He laid the cause of all diseasesat the door of the three mystic elements—salt,sulphur, and mercury. In health he supposedthese to be mingled in the body so as to beindistinguishable; a slight separation of themproduced disease; and death he supposed to bethe result of their complete separation. Thespiritual agencies of diseases, he said, hadnothing to do with either angels or devils, butwere the spirits of human beings.

He believed that all food contained poi-sons, and that the function of digestion wasto separate the poisonous from the nutritious.In the stomach was an archæus, or alchemist,whose duty was to make this separation. Indigestive disorders the archæus failed to dothis, and the poisons thus gaining access tothe system were “coagulated” and deposited inthe joints and various other parts of the body.Thus the deposits in the kidneys and tartar onthe teeth were formed; and the stony depositsof gout were particularly familiar examples ofthis. All this is visionary enough, yet it shows


at least a groping after rational explanationsof vital phenomena.

Like most others of his time, Paracel-sus believed firmly in the doctrine of“signatures”—a belief that every organ andpart of the body had a corresponding form innature, whose function was to heal diseasesof the organ it resembled. The vagaries ofthis peculiar doctrine are too numerous andcomplicated for lengthy discussion, and var-ied greatly from generation to generation. Ingeneral, however, the theory may be summedup in the words of Paracelsus: “As a womanis known by her shape, so are the medicines.”Hence the physicians were constantly search-ing for some object of corresponding shape toan organ of the body. The most natural ap-plication of this doctrine would be the use ofthe organs of the lower animals for the treat-ment of the corresponding diseased organs inman. Thus diseases of the heart were to betreated with the hearts of animals, liver dis-orders with livers, and so on. But this ap-parently simple form of treatment had end-less modifications and restrictions, for not allanimals were useful. For example, it was use-less to give the stomach of an ox in gastric dis-eases when the indication in such cases wasreally for the stomach of a rat. Nor were theorgans of animals the only “signatures” in na-


ture. Plants also played a very important role,and the herb-doctors devoted endless labor tosearching for such plants. Thus the blood-root, with its red juice, was supposed to beuseful in blood diseases, in stopping hemor-rhage, or in subduing the redness of an in-flammation.

Paracelsus’s system of signatures, how-ever, was so complicated by his theories ofastronomy and alchemy that it is practicallybeyond comprehension. It is possible that hehimself may have understood it, but it is im-probable that any one else did—as shown bythe endless discussions that have taken placeabout it. But with all the vagaries of his the-ories he was still rational in his applications,and he attacked to good purpose the compli-cated “shot-gun” prescriptions of his contem-poraries, advocating more simple methods oftreatment.

The ever-fascinating subject of electricity,or, more specifically, “magnetism,” found greatfavor with him, and with properly adjustedmagnets he claimed to be able to cure manydiseases. In epilepsy and lockjaw, for exam-ple, one had but to fasten magnets to the fourextremities of the body, and then, “when theproper medicines were given,” the cure wouldbe effected. The easy loop-hole for excusingfailure on the ground of improper medicines


is obvious, but Paracelsus declares that thisone prescription is of more value than “all thehumoralists have ever written or taught.”

Since Paracelsus condemned the study ofanatomy as useless, he quite naturally re-garded surgery in the same light. In thishe would have done far better to have stud-ied some of his predecessors, such as Galen,Paul of Aegina, and Avicenna. But insteadof “cutting men to pieces,” he taught that sur-geons would gain more by devoting their timeto searching for the universal panacea whichwould cure all diseases, surgical as well asmedical. In this we detect a taint of the pop-ular belief in the philosopher’s stone and themagic elixir of life, his belief in which havebeen stoutly denied by some of his followers.He did admit, however, that one operationalone was perhaps permissible—lithotomy, orthe “cutting for stone.”

His influence upon medicine rests un-doubtedly upon his revolutionary attitude,rather than on any great or new discover-ies made by him. It is claimed by manythat he brought prominently into use opiumand mercury, and if this were indisputablyproven his services to medicine could hardlybe overestimated. Unfortunately, however,there are good grounds for doubting that hewas particularly influential in reintroducing


these medicines. His chief influence may per-haps be summed up in a single phrase—heoverthrew old traditions.

To Paracelsus’s endeavors, however, if notto the actual products of his work, is due thecredit of setting in motion the chain of thoughtthat developed finally into scientific chem-istry. Nor can the ultimate aim of the modernchemist seek a higher object than that of thissixteenth-century alchemist, who taught that“true alchemy has but one aim and object, toextract the quintessence of things, and to pre-pare arcana, tinctures, and elixirs which mayrestore to man the health and soundness hehas lost.”

THE GREAT ANATOMISTSAbout the beginning of the sixteenth century,while Paracelsus was scoffing at the study ofanatomy as useless, and using his influenceagainst it, there had already come upon thescene the first of the great anatomists whosework was to make the century conspicuous inthat branch of medicine.

The young anatomist Charles Etienne(1503-1564) made one of the first noteworthydiscoveries, pointing out for the first time thatthe spinal cord contains a canal, continuousthroughout its length. He also made other mi-


nor discoveries of some importance, but his re-searches were completely overshadowed andobscured by the work of a young Fleming whocame upon the scene a few years later, andwho shone with such brilliancy in the medicalworld that he obscured completely the workof his contemporary until many years later.This young physician, who was destined tolead such an eventful career and meet suchan untimely end as a martyr to science, wasAndrew Vesalius (1514-1564), who is calledthe “greatest of anatomists.” At the time hecame into the field medicine was strugglingagainst the dominating Galenic teachings andthe theories of Paracelsus, but perhaps mostof all against the superstitions of the time. InFrance human dissections were attended withsuch dangers that the young Vesalius trans-ferred his field of labors to Italy, where suchinvestigations were covertly permitted, if notopenly countenanced.

From the very start the young Fleminglooked askance at the accepted teachings ofthe day, and began a series of independent in-vestigations based upon his own observations.The results of these investigations he gave ina treatise on the subject which is regarded asthe first comprehensive and systematic workon human anatomy. This remarkable workwas published in the author’s twenty-eighth


or twenty-ninth year. Soon after this Vesal-ius was invited as imperial physician to thecourt of Emperor Charles V. He continued toact in the same capacity at the court of PhilipII., after the abdication of his patron. Butin spite of this royal favor there was at worka factor more powerful than the influence ofthe monarch himself—an instrument that didso much to retard scientific progress, and bywhich so many lives were brought to a prema-ture close.

Vesalius had received permission from thekinsmen of a certain grandee to performan autopsy. While making his observationsthe heart of the outraged body was seen topalpitate—so at least it was reported. Thiswas brought immediately to the attention ofthe Inquisition, and it was only by the inter-vention of the king himself that the anatomistescaped the usual fate of those accused by thattribunal. As it was, he was obliged to performa pilgrimage to the Holy Land. While return-ing from this he was shipwrecked, and per-ished from hunger and exposure on the islandof Zante.

At the very time when the anatomicalwritings of Vesalius were startling the medi-cal world, there was living and working con-temporaneously another great anatomist, Eu-stachius (died 1574), whose records of his


anatomical investigations were ready for pub-lication only nine years after the publicationof the work of Vesalius. Owing to the unfor-tunate circumstances of the anatomist, how-ever, they were never published during hislifetime—not, in fact, until 1714. When atlast they were given to the world as Anatomi-cal Engravings, they showed conclusively thatEustachius was equal, if not superior to Vesal-ius in his knowledge of anatomy. It has beensaid of this remarkable collection of engrav-ings that if they had been published whenthey were made in the sixteenth century,anatomy would have been advanced by atleast two centuries. But be this as it may, theycertainly show that their author was a mostcareful dissector and observer.

Eustachius described accurately for thefirst time certain structures of the middle ear,and rediscovered the tube leading from theear to the throat that bears his name. Healso made careful studies of the teeth and thephenomena of first and second dentition. Hewas not baffled by the minuteness of struc-tures and where he was unable to study themwith the naked eye he used glasses for thepurpose, and resorted to macerations and in-jections for the study of certain complicatedstructures. But while the fruit of his pen andpencil were lost for more than a century af-


ter his death, the effects of his teachings werenot; and his two pupils, Fallopius and Colum-bus, are almost as well known to-day as theirillustrious teacher. Columbus (1490-1559) didmuch in correcting the mistakes made in theanatomy of the bones as described by Vesal-ius. He also added much to the science by giv-ing correct accounts of the shape and cavitiesof the heart, and made many other discoveriesof minor importance. Fallopius (1523-1562)added considerably to the general knowledgeof anatomy, made several discoveries in theanatomy of the ear, and also several organsin the abdominal cavity.

At this time a most vitally important con-troversy was in progress as to whether or notthe veins of the bodies were supplied withvalves, many anatomists being unable to findthem. Etienne had first described these struc-tures, and Vesalius had confirmed his obser-vations. It would seem as if there could beno difficulty in settling the question as to thefact of such valves being present in the ves-sels, for the demonstration is so simple thatit is now made daily by medical students inall physiological laboratories and dissecting-rooms. But many of the great anatomists ofthe sixteenth century were unable to makethis demonstration, even when it had beenbrought to their attention by such an author-


ity as Vesalius. Fallopius, writing to Vesal-ius on the subject in 1562, declared that hewas unable to find such valves. Others, how-ever, such as Eustachius and Fabricius (1537-1619), were more successful, and found anddescribed these structures. But the purposeserved by these valves was entirely misinter-preted. That they act in preventing the back-ward flow of the blood in the veins on its wayto the heart, just as the valves of the heartitself prevent regurgitation, has been knownsince the time of Harvey; but the best inter-pretation that could be given at that time,even by such a man as Fabricius, was thatthey acted in retarding the flow of the bloodas it comes from the heart, and thus preventits too rapid distribution throughout the body.The fact that the blood might have been goingtowards the heart, instead of coming from it,seems never to have been considered seriouslyuntil demonstrated so conclusively by Harvey.

Of this important and remarkable contro-versy over the valves in veins, Withington hasthis to say: “This is truly a marvellous story.A great Galenic anatomist is first to give a fulland correct description of the valves and theirfunction, but fails to see that any modificationof the old view as to the motion of the bloodis required. Two able dissectors carefully testtheir action by experiment, and come to a re-


sult the exact reverse of the truth. Urged bythem, the two foremost anatomists of the agemake a special search for valves and fail tofind them. Finally, passing over lesser pe-culiarities, an aged and honorable professor,who has lived through all this, calmly assertsthat no anatomist, ancient or modern, hasever mentioned valves in veins till he discov-ered them in 1574!”21

Among the anatomists who probably dis-covered these valves was Michael Servetus(1511-1553); but if this is somewhat in doubt,it is certain that he discovered and describedthe pulmonary circulation, and had a veryclear idea of the process of respiration as car-ried on in the lungs. The description was con-tained in a famous document sent to Calvin in1545—a document which the reformer care-fully kept for seven years in order that hemight make use of some of the heretical state-ments it contained to accomplish his desire ofbringing its writer to the stake. The awful fateof Servetus, the interesting character of theman, and the fact that he came so near to an-ticipating the discoveries of Harvey make himone of the most interesting figures in medicalhistory.

In this document which was sent to Calvin,21E. T. Withington, Medical History from the Earliest

Times, London, 1894, p. 278.


Servetus rejected the doctrine of natural, vi-tal, and animal spirits, as contained in theveins, arteries, and nerves respectively, andmade the all-important statement that thefluids contained in veins and arteries are thesame. He showed also that the blood is“purged from fume” and purified by respira-tion in the lungs, and declared that there isa new vessel in the lungs, “formed out of veinand artery.” Even at the present day there islittle to add to or change in this description ofServetus’s.

By keeping this document, pregnant withadvanced scientific views, from the world, andin the end only using it as a means of destroy-ing its author, the great reformer showed thesame jealousy in retarding scientific progressas had his arch-enemies of the Inquisition, atwhose dictates Vesalius became a martyr toscience, and in whose dungeons Etienne per-ished.

THE COMING OF HARVEYThe time was ripe for the culminating dis-covery of the circulation of the blood; but asyet no one had determined the all-importantfact that there are two currents of blood inthe body, one going to the heart, one comingfrom it. The valves in the veins would seem


to show conclusively that the venous currentdid not come from the heart, and surgeonsmust have observed thousands of times theevery-day phenomenon of congested veins atthe distal extremity of a limb around which aligature or constriction of any kind had beenplaced, and the simultaneous depletion of thevessels at the proximal points above the liga-ture. But it should be remembered that induc-tive science was in its infancy. This was thesixteenth, not the nineteenth century, and fewmen had learned to put implicit confidence intheir observations and convictions when op-posed to existing doctrines. The time was athand, however, when such a man was to makehis appearance, and, as in the case of so manyrevolutionary doctrines in science, this manwas an Englishman. It remained for WilliamHarvey (1578-1657) to solve the great mysterywhich had puzzled the medical world since thebeginning of history; not only to solve it, butto prove his case so conclusively and so sim-ply that for all time his little booklet must hehanded down as one of the great masterpiecesof lucid and almost faultless demonstration.

Harvey, the son of a prosperous Kentishyeoman, was born at Folkestone. His educa-tion was begun at the grammar-school of Can-terbury, and later he became a pensioner ofCaius College, Cambridge. Soon after taking


his degree of B.A., at the age of nineteen, hedecided upon the profession of medicine, andwent to Padua as a pupil of Fabricius andCasserius. Returning to England at the ageof twenty-four, he soon after (1609) obtainedthe reversion of the post of physician to St.Bartholomew’s Hospital, his application be-ing supported by James I. himself. Even atthis time he was a popular physician, count-ing among his patients such men as FrancisBacon. In 1618 he was appointed physicianextraordinary to the king, and, a little later,physician in ordinary. He was in attendanceupon Charles I. at the battle of Edgehill, in1642, where, with the young Prince of Walesand the Duke of York, after seeking shelterunder a hedge, he drew a book out of hispocket and, forgetful of the battle, became ab-sorbed in study, until finally the cannon-ballsfrom the enemy’s artillery made him seek amore sheltered position.

On the fall of Charles I. he retired frompractice, and lived in retirement with hisbrother. He was then well along in years, butstill pursued his scientific researches with thesame vigor as before, directing his attentionchiefly to the study of embryology. On June 3,1657, he was attacked by paralysis and died,in his eightieth year. He had lived to seehis theory of the circulation accepted, several


years before, by all the eminent anatomists ofthe civilized world.

A keenness in the observation of facts,characteristic of the mind of the man, hadled Harvey to doubt the truth of existing doc-trines as to the phenomena of the circula-tion. Galen had taught that “the arteriesare filled, like bellows, because they are ex-panded,” but Harvey thought that the actionof spurting blood from a severed vessel dis-proved this. For the spurting was remit-tant, “now with greater, now with less im-petus,” and its greater force always corre-sponded to the expansion (diastole), not thecontraction (systole) of the vessel. Further-more, it was evident that contraction of theheart and the arteries was not simultaneous,as was commonly taught, because in that casethere would be no marked propulsion of theblood in any direction; and there was no gain-saying the fact that the blood was forcibly pro-pelled in a definite direction, and that direc-tion away from the heart.

Harvey’s investigations led him to doubtalso the accepted theory that there was aporosity in the septum of tissue that dividesthe two ventricles of the heart. It seemed un-reasonable to suppose that a thick fluid likethe blood could find its way through pores sosmall that they could not be demonstrated by


WILLIAM HARVEY


any means devised by man. In evidence thatthere could be no such openings he pointed outthat, since the two ventricles contract at thesame time, this process would impede ratherthan facilitate such an intra-ventricular pas-sage of blood. But what seemed the most con-clusive proof of all was the fact that in the fœ-tus there existed a demonstrable opening be-tween the two ventricles, and yet this is closedin the fully developed heart. Why should Na-ture, if she intended that blood should passbetween the two cavities, choose to close thisopening and substitute microscopic openingsin place of it? It would surely seem more rea-sonable to have the small perforations in thethin, easily permeable membrane of the fœ-tus, and the opening in the adult heart, ratherthan the reverse. From all this Harvey drewhis correct conclusions, declaring earnestly,“By Hercules, there are no such porosities,and they cannot be demonstrated.”

Having convinced himself that no intra-ventricular opening existed, he proceeded tostudy the action of the heart itself, untram-melled by too much faith in established theo-ries, and, as yet, with no theory of his own.He soon discovered that the commonly ac-cepted theory of the heart striking againstthe chest-wall during the period of relaxationwas entirely wrong, and that its action was


exactly the reverse of this, the heart strik-ing the chest-wall during contraction. Havingthus disproved the accepted theory concern-ing the heart’s action, he took up the subjectof the action of arteries, and soon was able todemonstrate by vivisection that the contrac-tion of the arteries was not simultaneous withcontractions of the heart. His experimentsdemonstrated that these vessels were sim-ply elastic tubes whose pulsations were “noth-ing else than the impulse of the blood withinthem.” The reason that the arterial pulsationwas not simultaneous with the heart-beat hefound to be because of the time required tocarry the impulse along the tube,

By a series of further careful examinationsand experiments, which are too extended to begiven here, he was soon able further to demon-strate the action and course of the blood dur-ing the contractions of the heart. His expla-nations were practically the same as thosegiven to-day—first the contraction of the auri-cle, sending blood into the ventricle; then ven-tricular contraction, making the pulse, andsending the blood into the arteries. He hadthus demonstrated what had not been gener-ally accepted before, that the heart was anorgan for the propulsion of blood. To makesuch a statement to-day seems not unlike thesober announcement that the earth is round


or that the sun does not revolve about it. Be-fore Harvey’s time, however, it was consideredas an organ that was “in some mysterious waythe source of vitality and warmth, as an ani-mated crucible for the concoction of blood andthe generation of vital spirits.”22

In watching the rapid and ceaseless con-tractions of the heart, Harvey was impressedwith the fact that, even if a very small amountof blood was sent out at each pulsation, anenormous quantity must pass through the or-gan in a day, or even in an hour. Estimat-ing the size of the cavities of the heart, andnoting that at least a drachm must be sentout with each pulsation, it was evident thatthe two thousand beats given by a very slowhuman heart in an hour must send out someforty pounds of blood—more than twice theamount in the entire body. The question was,what became of it all? For it should be re-membered that the return of the blood by theveins was unknown, and nothing like a “circu-lation” more than vaguely conceived even byHarvey himself. Once it could be shown thatthe veins were constantly returning blood tothe heart, the discovery that the blood in someway passes from the arteries to the veins wasonly a short step. Harvey, by resorting to vivi-

22John Dalton, Doctrines of the Circulation, Philadel-phia, 1884, p. 179.


sections of lower animals and reptiles, soondemonstrated beyond question the fact thatthe veins do carry the return blood. “But this,in particular, can be shown clearer than day-light,” says Harvey. “The vena cava enters theheart at an inferior portion, while the arterypasses out above. Now if the vena cava betaken up with forceps or the thumb and fin-ger, and the course of the blood interceptedfor some distance below the heart, you will atonce see it almost emptied between the fingersand the heart, the blood being exhausted bythe heart’s pulsation, the heart at the sametime becoming much paler even in its dilata-tion, smaller in size, owing to the deficiencyof blood, and at length languid in pulsation,as if about to die. On the other hand, whenyou release the vein the heart immediately re-gains its color and dimensions. After that, ifyou leave the vein free and tie and compressthe arteries at some distance from the heart,you will see, on the contrary, their includedportion grow excessively turgid, the heart be-coming so beyond measure, assuming a dark-red color, even to lividity, and at length sooverloaded with blood as to seem in dangerof suffocation; but when the obstruction is re-moved it returns to its normal condition, insize, color, and movement.”23

23William Harvey, De Motu Cordis et Sanguinis, Lon-


This conclusive demonstration that theveins return the blood to the heart must havebeen most impressive to Harvey, who hadbeen taught to believe that the blood currentin the veins pursued an opposite course, andmust have tended to shake his faith in all ex-isting doctrines of the day.

His next step was the natural one ofdemonstrating that the blood passes from thearteries to the veins. He demonstrated con-clusively that this did occur, but for once hisrejection of the ancient writers and one mod-ern one was a mistake. For Galen had taught,and had attempted to demonstrate, that thereare sets of minute vessels connecting the ar-teries and the veins; and Servetus had shownthat there must be such vessels, at least in thelungs.

However, the little flaw in the otherwisecomplete demonstration of Harvey detractsnothing from the main issue at stake. It wasfor others who followed to show just how thesesmall vessels acted in effecting the transferof the blood from artery to vein, and thegrand general statement that such a trans-fer does take place was, after all, the all-important one, and the exact method of howit takes place a detail. Harvey’s experimentsto demonstrate that the blood passes from the

don, 1803, chap. X.


arteries to the veins are so simply and con-cisely stated that they may best be given inhis own words.

“I have here to cite certain ex-periments,” he wrote, “from whichit seems obvious that the blood en-ters a limb by the arteries, and re-turns from it by the veins; thatthe arteries are the vessels carry-ing the blood from the heart, andthe veins the returning channelsof the blood to the heart; that inthe limbs and extreme parts ofthe body the blood passes eitherby anastomosis from the arteriesinto the veins, or immediately bythe pores of the flesh, or in bothways, as has already been said inspeaking of the passage of the bloodthrough the lungs; whence it ap-pears manifest that in the circuitthe blood moves from thence hither,and hence thither; from the centreto the extremities, to wit, and fromthe extreme parts back again to thecentre. Finally, upon grounds of cir-culation, with the same elementsas before, it will be obvious that thequantity can neither be accountedfor by the ingesta, nor yet be held


necessary to nutrition.“Now let any one make an ex-

periment on the arm of a man, ei-ther using such a fillet as is em-ployed in blood-letting or graspingthe limb tightly with his hand, thebest subject for it being one whois lean, and who has large veins,and the best time after exercise,when the body is warm, the pulse isfull, and the blood carried in largequantities to the extremities, forall then is more conspicuous; undersuch circumstances let a ligaturebe thrown about the extremity anddrawn as tightly as can be borne: itwill first be perceived that beyondthe ligature neither in the wristnor anywhere else do the arteriespulsate, that at the same time im-mediately above the ligature theartery begins to rise higher at eachdiastole, to throb more violently,and to swell in its vicinity with akind of tide, as if it strove to breakthrough and overcome the obsta-cle to its current; the artery here,in short, appears as if it were per-manently full. The hand undersuch circumstances retains its nat-


ural color and appearances; in thecourse of time it begins to fall some-what in temperature, indeed, butnothing is drawn into it.

“After the bandage has beenkept on some short time in thisway, let it be slackened a little,brought to the state or term of mid-dling tightness which is used inbleeding, and it will be seen thatthe whole hand and arm will in-stantly become deeply suffused anddistended, injected, gorged withblood, drawn, as it is said, by thismiddling ligature, without pain, orheat, or any horror of a vacuum, orany other cause yet indicated.

“As we have noted, in connec-tion with the tight ligature, thatthe artery above the bandage wasdistended and pulsated, not belowit, so, in the case of the moderatelytight bandage, on the contrary, dowe find that the veins below, neverabove, the fillet swell and becomedilated, while the arteries shrink;and such is the degree of distentionof the veins here that it is only verystrong pressure that will force theblood beyond the fillet and cause


any of the veins in the upper partof the arm to rise.

“From these facts it is easy forany careful observer to learn thatthe blood enters an extremity bythe arteries; for when they areeffectively compressed nothing isdrawn to the member; the handpreserves its color; nothing flowsinto it, neither is it distended; butwhen the pressure is diminished,as it is with the bleeding fillet, it ismanifest that the blood is instantlythrown in with force, for then thehand begins to swell; which is asmuch as to say that when the ar-teries pulsate the blood is flow-ing through them, as it is whenthe moderately tight ligature is ap-plied; but when they do not pul-sate, or when a tight ligature isused, they cease from transmittinganything; they are only distendedabove the part where the ligatureis applied. The veins again be-ing compressed, nothing can flowthrough them; the certain indica-tion of which is that below the lig-ature they are much more tumidthan above it, and than they usu-


ally appear when there is no ban-dage upon the arm.

“It therefore plainly appearsthat the ligature prevents the re-turn of the blood through the veinsto the parts above it, and maintainsthose beneath it in a state of per-manent distention. But the arter-ies, in spite of the pressure, andunder the force and impulse of theheart, send on the blood from theinternal parts of the body to theparts beyond the bandage.”24

This use of ligatures is very significant, be-cause, as shown, a very tight ligature stopscirculation in both arteries and veins, while aloose one, while checking the circulation in theveins, which lie nearer the surface and are notso directly influenced by the force of the heart,does not stop the passage of blood in the arter-ies, which are usually deeply imbedded in thetissues, and not so easily influenced by pres-sure from without.

The last step of Harvey’s demonstrationwas to prove that the blood does flow alongthe veins to the heart, aided by the valves thathad been the cause of so much discussion and

24The Works of William Harvey, translated by RobertWillis, London, 1847, p. 56.


dispute between the great sixteenth-centuryanatomists. Harvey not only demonstratedthe presence of these valves, but showed con-clusively, by simple experiments, what theirfunction was, thus completing his demonstra-tion of the phenomena of the circulation.

The final ocular demonstration of the pas-sage of the blood from the arteries to the veinswas not to be made until four years after Har-vey’s death. This process, which can be ob-served easily in the web of a frog’s foot bythe aid of a low-power lens, was first demon-strated by Marcello Malpighi (1628-1694) in1661. By the aid of a lens he first saw thesmall “capillary” vessels connecting the veinsand arteries in a piece of dried lung. Tak-ing his cue from this, he examined the lungof a turtle, and was able to see in it the pas-sage of the corpuscles through these minutevessels, making their way along these pre-viously unknown channels from the arteriesinto the veins on their journey back to theheart. Thus the work of Harvey, all but com-plete, was made absolutely entire by the greatItalian. And all this in a single generation.


LEEUWENHOEKDISCOVERS BACTERIAThe seventeenth century was not to close,however, without another discovery in sci-ence, which, when applied to the causationof disease almost two centuries later, revo-lutionized therapeutics more completely thanany one discovery. This was the discoveryof microbes, by Antonius von Leeuwenhoek(1632-1723), in 1683. Von Leeuwenhoek dis-covered that “in the white matter betweenhis teeth” there were millions of microscopic“animals”—more, in fact, than “there were hu-man beings in the united Netherlands,” andall “moving in the most delightful manner.”There can be no question that he saw them,for we can recognize in his descriptions ofthese various forms of little “animals” the fourprincipal forms of microbes—the long andshort rods of bacilli and bacteria, the spheresof micrococci, and the corkscrew spirillum.

The presence of these microbes in hismouth greatly annoyed Antonius, and he triedvarious methods of getting rid of them, suchas using vinegar and hot coffee. In doing thishe little suspected that he was anticipatingmodern antiseptic surgery by a century andthree-quarters, and to be attempting what an-tiseptic surgery is now able to accomplish. For


the fundamental principle of antisepsis is theuse of medicines for ridding wounds of sim-ilar microscopic organisms. Von Leenwen-hoek was only temporarily successful in hisattempts, however, and took occasion to com-municate his discovery to the Royal Societyof England, hoping that they would be “in-terested in this novelty.” Probably they were,but not sufficiently so for any member to pur-sue any protracted investigations or reach anysatisfactory conclusions, and the whole mat-ter was practically forgotten until the middleof the nineteenth century.

VIII. MEDICINE INTHE SIXTEENTHANDSEVENTEENTHCENTURIES

Of the half-dozen surgeons who were promi-nent in the sixteenth century, AmbroisePare (1517-1590), called the father of Frenchsurgery, is perhaps the most widely known.He rose from the position of a common bar-ber to that of surgeon to three French monar-chs, Henry II., Francis II., and Charles IX.Some of his mottoes are still first principlesof the medical man. Among others are: “Hewho becomes a surgeon for the sake of money,and not for the sake of knowledge, will ac-complish nothing”; and “A tried remedy is bet-ter than a newly invented.” On his statue is

253


his modest estimate of his work in caring forthe wounded, “Je le pansay, Dieu le guarit”—Idressed him, God cured him.

It was in this dressing of wounds onthe battlefield that he accidentally discov-ered how useless and harmful was the terri-bly painful treatment of applying boiling oilto gunshot wounds as advocated by John ofVigo. It happened that after a certain battle,where there was an unusually large numberof casualties, Pare found, to his horror, thatno more boiling oil was available for the sur-geons, and that he should be obliged to dressthe wounded by other simpler methods. To hisamazement the results proved entirely satis-factory, and from that day he discarded thehot-oil treatment.

As Pare did not understand Latin he wrotehis treatises in French, thus inaugurating acustom in France that was begun by Paracel-sus in Germany half a century before. Hereintroduced the use of the ligature in con-trolling hemorrhage, introduced the “figureof eight” suture in the operation for hare-lip,improved many of the medico-legal doctrines,and advanced the practice of surgery gener-ally. He is credited with having successfullyperformed the operation for strangulated her-nia, but he probably borrowed it from Pe-ter Franco (1505-1570), who published an ac-

VIII. 16–17TH CENTURY MEDICINE 255

count of this operation in 1556. As this opera-tion is considered by some the most importantoperation in surgery, its discoverer is entitledto more than passing notice, although he wasdespised and ignored by the surgeons of histime.

Franco was an illiterate travelling lith-otomist—a class of itinerant physicians whowere very generally frowned down by the reg-ular practitioners of medicine. But Francopossessed such skill as an operator, and ap-pears to have been so earnest in the pursuit ofwhat he considered a legitimate calling, thathe finally overcame the popular prejudice andbecame one of the salaried surgeons of the re-public of Bern. He was the first surgeon toperform the suprapubic lithotomy operation—the removal of stone through the abdomen in-stead of through the perineum. His works,while written in an illiterate style, give theclearest descriptions of any of the early mod-ern writers.

As the fame of Franco rests upon his oper-ation for prolonging human life, so the fameof his Italian contemporary, Gaspar Taglia-cozzi (1545-1599), rests upon his operation forincreasing human comfort and happiness byrestoring amputated noses. At the time inwhich he lived amputation of the nose wasvery common, partly from disease, but also


because a certain pope had fixed the amputa-tion of that member as the penalty for larceny.Tagliacozzi probably borrowed his operationfrom the East; but he was the first Westernsurgeon to perform it and describe it. So greatwas the fame of his operations that patientsflocked to him from all over Europe, and each“went away with as many noses as he liked.”Naturally, the man who directed his efforts torestoring structures that had been removedby order of the Church was regarded in thelight of a heretic by many theologians; andthough he succeeded in cheating the stake ordungeon, and died a natural death, his bodywas finally cast out of the church in which ithad been buried.

In the sixteenth century Germany pro-duced a surgeon, Fabricius Hildanes (1560-1639), whose work compares favorably withthat of Pare, and whose name would undoubt-edly have been much better known had notthe circumstances of the time in which helived tended to obscure his merits. The blindfollowers of Paracelsus could see nothing out-side the pale of their master’s teachings, andthe disastrous Thirty Years’ War tended to ob-scure and retard all scientific advances in Ger-many. Unlike many of his fellow-surgeons,Hildanes was well versed in Latin and Greek;and, contrary to the teachings of Paracelsus,


he laid particular stress upon the necessityof the surgeon having a thorough knowledgeof anatomy. He had a helpmate in his wife,who was also something of a surgeon, and sheis credited with having first made use of themagnet in removing particles of metal fromthe eye. Hildanes tells of a certain man whohad been injured by a small piece of steel inthe cornea, which resisted all his efforts toremove it. After observing Hildanes’ fruit-less efforts for a time, it suddenly occurredto his wife to attempt to make the extractionwith a piece of loadstone. While the physicianheld open the two lids, his wife attempted towithdraw the steel with the magnet held closeto the cornea, and after several efforts shewas successful—which Hildanes enumeratesas one of the advantages of being a marriedman.

Hildanes was particularly happy in hisinventions of surgical instruments, many ofwhich were designed for locating and remov-ing the various missiles recently introduced inwarfare.

The seventeenth century, which was sucha flourishing one for anatomy and physiology,was not as productive of great surgeons or ad-vances in surgery as the sixteenth had been orthe eighteenth was to be. There was a grad-ual improvement all along the line, however,


and much of the work begun by such surgeonsas Pare and Hildanes was perfected or im-proved. Perhaps the most progressive surgeonof the century was an Englishman, RichardWiseman (1625-1686), who, like Harvey, en-joyed royal favor, being in the service of allthe Stuart kings. He was the first surgeonto advocate primary amputation, in gunshotwounds, of the limbs, and also to introduce thetreatment of aneurisms by compression; buthe is generally rated as a conservative opera-tor, who favored medication rather than radi-cal operations, where possible.

In Italy, Marcus Aurelius Severinus (1580-1656) and Peter Marchettis (1589-1675) werethe leading surgeons of their nation. Likemany of his predecessors in Europe, Severi-nus ran amuck with the Holy Inquisition andfled from Naples. But the waning of the pow-erful arm of the Church is shown by the factthat he was brought back by the unanimousvoice of the grateful citizens, and lived insafety despite the frowns of the theologians.

The sixteenth century cannot be said tohave added much of importance in the fieldof practical medicine, and, as in the preced-ing and succeeding centuries, was at bestonly struggling along in the wake of anatomy,physiology, and surgery. In the seventeenthcentury, however, at least one discovery in


therapeutics was made that has been an in-estimable boon to humanity ever since. Thiswas the introduction of cinchona bark (fromwhich quinine is obtained) in 1640. But thiscentury was productive of many medical sys-tems, and could boast of many great namesamong the medical profession, and, on thewhole, made considerably more progress thanthe preceding century.

Of the founders of medical systems, oneof the most widely known is Jan Baptistavan Helmont (1578-1644), an eccentric geniuswho constructed a system of medicine of hisown and for a time exerted considerable in-fluence. But in the end his system was des-tined to pass out of existence, not very longafter the death of its author. Van Helmontwas not only a physician, but was master ofall the other branches of learning of the time,taking up the study of medicine and chem-istry as an after-thought, but devoting himselfto them with the greatest enthusiasm oncehe had begun his investigations. His atti-tude towards existing doctrines was as rev-olutionary as that of Paracelsus, and he re-jected the teachings of Galen and all the an-cient writers, although retaining some of theviews of Paracelsus. He modified the archæusof Paracelsus, and added many complicationsto it. He believed the whole body to be con-


trolled by an archæus influus, the soul by thearchæi insiti, and these in turn controlled bythe central archæus. His system is too elabo-rate and complicated for full explanation, butits chief service to medicine was in introduc-ing new chemical methods in the preparationof drugs. In this way he was indirectly con-nected with the establishment of the Iatro-chemical school. It was he who first used theword “gas”—a word coined by him, along withmany others that soon fell into disuse.

The principles of the Iatrochemical schoolwere the use of chemical medicines, and a the-ory of pathology different from the prevail-ing “humoral” pathology. The founder of thisschool was Sylvius (Franz de le Boe, 1614-1672), professor of medicine at Leyden. Heattempted to establish a permanent system ofmedicine based on the newly discovered the-ory of the circulation and the new chemistry,but his name is remembered by medical menbecause of the fissure in the brain (fissure ofSylvius) that bears it. He laid great stress onthe cause of fevers and other diseases as orig-inating in the disturbances of the process offermentation in the stomach. The doctrines ofSylvius spread widely over the continent, butwere not generally accepted in England untilmodified by Thomas Willis (1622-1675), whosename, like that of Sylvius, is perpetuated by a


structure in the brain named after him, thecircle of Willis. Willis’s descriptions of certainnervous diseases, and an account of diabetes,are the first recorded, and added materially toscientific medicine. These schools of medicinelasted until the end of the seventeenth cen-tury, when they were finally overthrown bySydenham.

The Iatrophysical school (also called ia-tromathematical, iatromechanical, or physi-atric) was founded on theories of physiology,probably by Borelli, of Naples (1608-1679), al-though Sanctorius, a professor at Padua, wasa precursor, if not directly interested in estab-lishing it. Sanctorius discovered the fact thatan “insensible perspiration” is being given offby the body continually, and was amazed tofind that loss of weight in this way far ex-ceeded the loss of weight by all other excre-tions of the body combined. He made thisdiscovery by means of a peculiar weighing-machine to which a chair was attached, andin which he spent most of his time. Very natu-rally he overestimated the importance of thisdiscovery, but it was, nevertheless, of greatvalue in pointing out the hygienic importanceof the care of the skin. He also introduced athermometer which he advocated as valuablein cases of fever, but the instrument was prob-ably not his own invention, but borrowed from


his friend Galileo.Harvey’s discovery of the circulation of the

blood laid the foundation of the Iatrophysicalschool by showing that this vital process wascomparable to a hydraulic system. In his Onthe Motive of Animals, Borelli first attemptedto account for the phenomena of life and dis-eases on these principles. The iatromechan-ics held that the great cause of disease is dueto different states of elasticity of the solidsof the body interfering with the movementsof the fluids, which are themselves subject tochanges in density, one or both of these con-ditions continuing to cause stagnation or con-gestion. The school thus founded by Borelliwas the outcome of the unbounded enthusi-asm, with its accompanying exaggeration ofcertain phenomena with the correspondingbelittling of others that naturally follows sucha revolutionary discovery as that of Harvey.Having such a founder as the brilliant ItalianBorelli, it was given a sufficient impetus byhis writings to carry it some distance beforeit finally collapsed. Some of the exaggeratedmathematical calculations of Borelli himselfare worth noting. Each heart-beat, as he cal-culated it, overcomes a resistance equal toone hundred and eighty thousand pounds;—the modern physiologist estimates its force atfrom five to nine ounces!


THOMAS SYDENHAMBut while the Continent was struggling withthese illusive “systems,” and dabbling in mys-tic theories that were to scarcely outlive themen who conceived them, there appeared inEngland—the “land of common-sense,” as aGerman scientist has called it—“a cool, clear,and unprejudiced spirit,” who in the goldenage of systems declined “to be like the manwho builds the chambers of the upper storyof his house before he had laid securely thefoundation walls.”25 This man was ThomasSydenham (1624-1689), who, while the greatHarvey was serving the king as surgeon,was fighting as a captain in the parliamen-tary army. Sydenham took for his guide theteachings of Hippocrates, modified to suit theadvances that had been made in scientificknowledge since the days of the great Greek,and established, as a standard, observationand experience. He cared little for theory un-less confirmed by practice, but took the Hip-pocratic view that nature cured diseases, as-sisted by the physician. He gave due credit,however, to the importance of the part playedby the assistant. As he saw it, medicine couldbe advanced in three ways: (1) “By accurate

25Hermann Baas, History of Medicine, translated byH. E. Henderson, New York, 1894, p. 504.


descriptions or natural histories of diseases;(2) by establishing a fixed principle or methodof treatment, founded upon experience; (3)by searching for specific remedies, which hebelieves must exist in considerable numbers,though he admits that the only one yet discov-ered is Peruvian bark.”26 As it happened, an-other equally specific remedy, mercury, whenused in certain diseases, was already knownto him, but he evidently did not recognize itas such.

The influence on future medicine of Syden-ham’s teachings was most pronounced, duemostly to his teaching of careful observation.To most physicians, however, he is now re-membered chiefly for his introduction of theuse of laudanum, still considered one of themost valuable remedies of modern pharma-copœias. The German gives the honor of in-troducing this preparation to Paracelsus, butthe English-speaking world will always be-lieve that the credit should be given to Syden-ham.

26E. T. Withington, Medical History from the EarliestTimes, London, 1894, p. 320.

IX.PHILOSOPHER-SCIENTISTS ANDNEWINSTITUTIONS OFLEARNING

We saw that in the old Greek days there wasno sharp line of demarcation between the fieldof the philosopher and that of the scientist. Inthe Hellenistic epoch, however, knowledge be-came more specialized, and our recent chap-ters have shown us scientific investigatorswhose efforts were far enough removed fromthe intangibilities of the philosopher. It mustnot be overlooked, however, that even in thepresent epoch there were men whose intellec-tual efforts were primarily directed towards

265


the subtleties of philosophy, yet who had alsoa penchant for strictly scientific imaginings, ifnot indeed for practical scientific experiments.At least three of these men were of sufficientimportance in the history of the developmentof science to demand more than passing no-tice. These three are the Englishman Fran-cis Bacon (1561-1626), the Frenchman ReneDescartes (1596-1650); and the German Got-tfried Leibnitz (1646-1716). Bacon, as the ear-liest path-breaker, showed the way, theoret-ically at least, in which the sciences shouldbe studied; Descartes, pursuing the methodspointed out by Bacon, carried the same lineof abstract reason into practice as well; whileLeibnitz, coming some years later, and hav-ing the advantage of the wisdom of his twogreat predecessors, was naturally influencedby both in his views of abstract scientific prin-ciples.

Bacon’s career as a statesman and hisfaults and misfortunes as a man do not con-cern us here. Our interest in him begins withhis entrance into Trinity College, Cambridge,where he took up the study of all the sciencestaught there at that time. During the threeyears he became more and more convincedthat science was not being studied in a prof-itable manner, until at last, at the end of hiscollege course, he made ready to renounce the

IX. PHILOSOPHER-SCIENTISTS 267

old Aristotelian methods of study and advancehis theory of inductive study. For although hewas a great admirer of Aristotle’s work, he be-came convinced that his methods of approach-ing study were entirely wrong.

“The opinion of Aristotle,” he says, in hisDe Argumentum Scientiarum, “seemeth to mea negligent opinion, that of those things whichexist by nature nothing can be changed bycustom; using for example, that if a stonebe thrown ten thousand times up it will notlearn to ascend; and that by often seeing orhearing we do not learn to see or hear bet-ter. For though this principle be true inthings wherein nature is peremptory (the rea-son whereof we cannot now stand to discuss),yet it is otherwise in things wherein natureadmitteth a latitude. For he might see that astraight glove will come more easily on withuse; and that a wand will by use bend other-wise than it grew; and that by use of the voicewe speak louder and stronger; and that byuse of enduring heat or cold we endure it thebetter, and the like; which latter sort have anearer resemblance unto that subject of man-ners he handleth than those instances whichhe allegeth.”27

These were his opinions, formed while a27George L. Craik, Bacon and His Writings and Phi-

losophy, 2 vols., London, 1846. Vol. II., p. 121.


FRANCIS BACON


young man in college, repeated at intervalsthrough his maturer years, and reiterated andemphasized in his old age. Masses of factswere to be obtained by observing nature atfirst hand, and from such accumulations offacts deductions were to be made. In short,reasoning was to be from the specific to thegeneral, and not vice versa.

It was by his teachings alone that Baconthus contributed to the foundation of modernscience; and, while he was constantly think-ing and writing on scientific subjects, he con-tributed little in the way of actual discoveries.“I only sound the clarion,” he said, “but I enternot the battle.”

The case of Descartes, however, is differ-ent. He both sounded the clarion and enteredinto the fight. He himself freely acknowledgeshis debt to Bacon for his teachings of induc-tive methods of study, but modern criticismplaces his work on the same plane as thatof the great Englishman. “If you lay hold ofany characteristic product of modern ways ofthinking,” says Huxley, “either in the regionof philosophy or in that of science, you findthe spirit of that thought, if not its form, hasbeen present in the mind of the great French-man.”28

28From Huxley’s address “On Descartes’s DiscourseTouching the Method of Using One’s Reason Rightly


Descartes, the son of a noble family ofFrance, was educated by Jesuit teachers. LikeBacon, he very early conceived the idea thatthe methods of teaching and studying sciencewere wrong, but be pondered the matter wellinto middle life before putting into writinghis ideas of philosophy and science. Then, inhis Discourse Touching the Method of UsingOne’s Reason Rightly and of Seeking ScientificTruth, he pointed out the way of seeking aftertruth. His central idea in this was to empha-size the importance of doubt, and avoidanceof accepting as truth anything that does notadmit of absolute and unqualified proof. Inreaching these conclusions he had before himthe striking examples of scientific deductionsby Galileo, and more recently the discovery ofthe circulation of the blood by Harvey. Thislast came as a revelation to scientists, reduc-ing this seemingly occult process, as it did, tothe field of mechanical phenomena. The samemechanical laws that governed the heavenlybodies, as shown by Galileo, governed the ac-tion of the human heart, and, for aught anyone knew, every part of the body, and even themind itself.

Having once conceived this idea, Descartesbegan a series of dissections and experimentsupon the lower animals, to find, if possible,

and of Seeking Scientific Truth.”


RENÉ DESCARTES

(From the painting by Franz Hals, in the gallery of theLouvre.)


further proof of this general law. To him thehuman body was simply a machine, a compli-cated mechanism, whose functions were con-trolled just as any other piece of machinery.He compared the human body to complicatedmachinery run by water-falls and complicatedpipes. “The nerves of the machine which Iam describing,” he says, “may very well becompared to the pipes of these waterworks;its muscles and its tendons to the other var-ious engines and springs which seem to movethem; its animal spirits to the water whichimpels them, of which the heart is the foun-tain; while the cavities of the brain are thecentral office. Moreover, respiration and othersuch actions as are natural and usual in thebody, and which depend on the course of thespirits, are like the movements of a clock, ora mill, which may be kept up by the ordinaryflow of water.”29

In such passages as these Descartes antic-ipates the ideas of physiology of the presenttime. He believed that the functions are per-formed by the various organs of the bodies ofanimals and men as a mechanism, to which inman was added the soul. This soul he locatedin the pineal gland, a degenerate and presum-ably functionless little organ in the brain. For

29Rene Descartes, Traite de l’Homme (Cousins’s edi-tion. in 2 vols.), Paris, 1824. Vol. VI., p. 347.


years Descartes’s idea of the function of thisgland was held by many physiologists, andit was only the introduction of modern high-power microscopy that reduced this also to amere mechanism, and showed that it is ap-parently the remains of a Cyclopean eye oncecommon to man’s remote ancestors.

Descartes was the originator of a the-ory of the movements of the universe by amechanical process—the Cartesian theory ofvortices—which for several decades after itspromulgation reigned supreme in science. Itis the ingenuity of this theory, not the truth ofits assertions, that still excites admiration, forit has long since been supplanted. It was cer-tainly the best hitherto advanced—the best“that the observations of the age admitted,”according to D’Alembert.

According to this theory the infinite uni-verse is full of matter, there being no suchthing as a vacuum. Matter, as Descartes be-lieved, is uniform in character throughout theentire universe, and since motion cannot takeplace in any part of a space completely filled,without simultaneous movement in all otherparts, there are constant more or less circu-lar movements, vortices, or whirlpools of par-ticles, varying, of course, in size and velocity.As a result of this circular movement the par-ticles of matter tend to become globular from


contact with one another. Two species of mat-ter are thus formed, one larger and globular,which continue their circular motion with aconstant tendency to fly from the centre ofthe axis of rotation, the other composed of theclippings resulting from the grinding process.These smaller “filings” from the main bodies,becoming smaller and smaller, gradually losetheir velocity and accumulate in the centreof the vortex. This collection of the smallermatter in the centre of the vortex constitutesthe sun or star, while the spherical particlespropelled in straight lines from the centre to-wards the circumference of the vortex producethe phenomenon of light radiating from thecentral star. Thus this matter becomes theatmosphere revolving around the accumula-tion at the centre. But the small particles be-ing constantly worn away from the revolvingspherical particles in the vortex, become en-tangled in their passage, and when they reachthe edge of the inner strata of solar dust theysettle upon it and form what we call sun-spots.These are constantly dissolved and reformed,until sometimes they form a crust round thecentral nucleus.

As the expansive force of the star dimin-ishes in the course of time, it is encroachedupon by neighboring vortices. If the partof the encroaching star be of a less velocity


GOTTFRIED WILHELM VON LEIBNITZ


than the star which it has swept up, it willpresently lose its hold, and the smaller starpass out of range, becoming a comet. But ifthe velocity of the vortex into which the in-crusted star settles be equivalent to that ofthe surrounded vortex, it will hold it as a cap-tive, still revolving and “wrapt in its own fir-mament.” Thus the several planets of our so-lar system have been captured and held by thesun-vortex, as have the moon and other satel-lites.

But although these new theories at firstcreated great enthusiasm among all classesof philosophers and scientists, they soon cameunder the ban of the Church. While no actualharm came to Descartes himself, his writingswere condemned by the Catholic and Protes-tant churches alike. The spirit of philosophi-cal inquiry he had engendered, however, livedon, and is largely responsible for modern phi-losophy.

In many ways the life and works ofLeibnitz remind us of Bacon rather thanDescartes. His life was spent in filling highpolitical positions, and his philosophical andscientific writings were by-paths of his fer-tile mind. He was a theoretical rather thana practical scientist, his contributions to sci-ence being in the nature of philosophical rea-sonings rather than practical demonstrations.


Had he been able to withdraw from publiclife and devote himself to science alone, asDescartes did, he would undoubtedly haveproved himself equally great as a practicalworker. But during the time of his great-est activity in philosophical fields, betweenthe years 1690 and 1716, he was all the timeperforming extraordinary active duties in en-tirely foreign fields. His work may be re-garded, perhaps, as doing for Germany in par-ticular what Bacon’s did for England and therest of the world in general.

Only a comparatively small part of hisphilosophical writings concern us here. Ac-cording to his theory of the ultimate elementsof the universe, the entire universe is com-posed of individual centres, or monads. Tothese monads he ascribed numberless quali-ties by which every phase of nature may beaccounted. They were supposed by him to bepercipient, self-acting beings, not under arbi-trary control of the deity, and yet God him-self was the original monad from which all therest are generated. With this conception asa basis, Leibnitz deduced his doctrine of pre-established harmony, whereby the numerousindependent substances composing the worldare made to form one universe. He believedthat by virtue of an inward energy monadsdevelop themselves spontaneously, each being


independent of every other. In short, eachmonad is a kind of deity in itself—a micro-cosm representing all the great features of themacrocosm.

It would be impossible clearly to estimatethe precise value of the stimulative influ-ence of these philosophers upon the scientificthought of their time. There was one way,however, in which their influence was madevery tangible—namely, in the incentive theygave to the foundation of scientific societies.

SCIENTIFIC SOCIETIESAt the present time, when the elements oftime and distance are practically eliminatedin the propagation of news, and when cheapprinting has minimized the difficulties of pub-lishing scientific discoveries, it is difficult tounderstand the isolated position of the scien-tific investigation of the ages that precededsteam and electricity. Shut off from theworld and completely out of touch with fellow-laborers perhaps only a few miles away, theinvestigators were naturally seriously handi-capped; and inventions and discoveries werenot made with the same rapidity that theywould undoubtedly have been had the samemen been receiving daily, weekly, or monthlycommunications from fellow-laborers all over


the world, as they do to-day. Neither did theyhave the advantage of public or semi-publiclaboratories, where they were brought intocontact with other men, from whom to gatherfresh trains of thought and receive the stimu-lus of their successes or failures. In the nat-ural course of events, however, neighbors whowere interested in somewhat similar pursuits,not of the character of the rivalry of trade orcommerce, would meet more or less frequentlyand discuss their progress. The mutual ad-vantages of such intercourse would be at onceappreciated; and it would be but a short stepfrom the casual meeting of two neighborlyscientists to the establishment of “societies,”meeting at fixed times, and composed of mem-bers living within reasonable travelling dis-tance. There would, perhaps, be the weeklyor monthly meetings of men in a limited area;and as the natural outgrowth of these littlelocal societies, with frequent meetings, wouldcome the formation of larger societies, meet-ing less often, where members travelled a con-siderable distance to attend. And, finally,with increased facilities for communicationand travel, the great international societiesof to-day would be produced—the natural out-come of the neighborly meetings of the primi-tive mediæval investigators.

In Italy, at about the time of Galileo, sev-


eral small societies were formed. One of themost important of these was the Lyncean So-ciety, founded about the year 1611, Galileohimself being a member. This society was suc-ceeded by the Accademia del Cimento, at Flo-rence, in 1657, which for a time flourished,with such a famous scientist as Torricelli asone of its members.

In England an impetus seems to have beengiven by Sir Francis Bacon’s writings in criti-cism and censure of the systern of teaching incolleges. It is supposed that his suggestionsas to what should be the aims of a scientificsociety led eventually to the establishment ofthe Royal Society. He pointed out how littlehad really been accomplished by the existinginstitutions of learning in advancing science,and asserted that little good could ever comefrom them while their methods of teaching re-mained unchanged. He contended that thesystem which made the lectures and exercisesof such a nature that no deviation from theestablished routine could be thought of waspernicious. But he showed that if any teacherhad the temerity to turn from the traditionalpaths, the daring pioneer was likely to find in-surmountable obstacles placed in the way ofhis advancement. The studies were “impris-oned” within the limits of a certain set of au-thors, and originality in thought or teaching


was to be neither contemplated nor tolerated.The words of Bacon, given in strong and

unsparing terms of censure and condemna-tion, but nevertheless with perfect justifica-tion, soon bore fruit. As early as the year1645 a small company of scientists had beenin the habit of meeting at some place in Lon-don to discuss philosophical and scientific sub-jects for mental advancement. In 1648, ow-ing to the political disturbances of the time,some of the members of these meetings re-moved to Oxford, among them Boyle, Wallis,and Wren, where the meetings were contin-ued, as were also the meetings of those leftin London. In 1662, however, when the polit-ical situation had become more settled, thesetwo bodies of men were united under a char-ter from Charles II., and Bacon’s ideas werepractically expressed in that learned body, theRoyal Society of London. And it matters lit-tle that in some respects Bacon’s views werenot followed in the practical workings of thesociety, or that the division of labor in theearly stages was somewhat different than atpresent. The aim of the society has alwaysbeen one for the advancement of learning; andif Bacon himself could look over its records, hewould surely have little fault to find with theaid it has given in carrying out his ideas forthe promulgation of useful knowledge.


Ten years after the charter was grantedto the Royal Society of London, Lord Bacon’swords took practical effect in Germany, withthe result that the Academia Naturae Cu-riosorum was founded, under the leadershipof Professor J. C. Sturm. The early laborsof this society were devoted to a repetitionof the most notable experiments of the time,and the work of the embryo society was pub-lished in two volumes, in 1672 and 1685 re-spectively, which were practically text-booksof the physics of the period. It was not un-til 1700 that Frederick I. founded the RoyalAcademy of Sciences at Berlin, after the elab-orate plan of Leibnitz, who was himself thefirst president.

Perhaps the nearest realization of Bacon’sideal, however, is in the Royal Academy of Sci-ences at Paris, which was founded in 1666 un-der the administration of Colbert, during thereign of Louis XIV. This institution not onlyrecognized independent members, but hadbesides twenty pensionnaires who receivedsalaries from the government. In this way aselect body of scientists were enabled to pur-sue their investigations without being obligedto “give thought to the morrow” for their sus-tenance. In return they were to furnish themeetings with scientific memoirs, and once ayear give an account of the work they were


engaged upon. Thus a certain number of thebrightest minds were encouraged to devotetheir entire time to scientific research, “deliv-ered alike from the temptations of wealth orthe embarrassments of poverty.” That sucha plan works well is amply attested by theresults emanating from the French academy.Pensionnaires in various branches of science,however, either paid by the state or by learnedsocieties, are no longer confined to France.

Among the other early scientific societieswas the Imperial Academy of Sciences at St.Petersburg, projected by Peter the Great, andestablished by his widow, Catharine I., in1725; and also the Royal Swedish Academy,incorporated in 1781, and counting among itsearly members such men as the celebratedLinnæus. But after the first impulse had re-sulted in a few learned societies, their mani-fest advantage was so evident that additionalnumbers increased rapidly, until at presentalmost every branch of every science is repre-sented by more or less important bodies; andthese are, individually and collectively, addingto knowledge and stimulating interest in themany fields of science, thus vindicating LordBacon’s asseverations that knowledge couldbe satisfactorily promulgated in this manner.

X. THESUCCESSORS OFGALILEO INPHYSICALSCIENCE

We have now to witness the diversified ef-forts of a company of men who, working forthe most part independently, greatly added tothe data of the physical sciences—such menas Boyle, Huygens, Von Gericke, and Hooke.It will be found that the studies of these mencovered the whole field of physical sciences asthen understood—the field of so-called natu-ral philosophy. We shall best treat these suc-cessors of Galileo and precursors of Newtonsomewhat biographically, pointing out the cor-respondences and differences between theirvarious accomplishments as we proceed. It

285


will be noted in due course that the workof some of them was anticipatory of greatachievements of a later century.

ROBERT BOYLE(1627-1691)Some of Robert Boyle’s views as to the possi-ble structure of atmospheric air will be con-sidered a little farther on in this chapter, butfor the moment we will take up the consid-eration of some of his experiments upon thatas well as other gases. Boyle was alwaysmuch interested in alchemy, and carried onextensive experiments in attempting to ac-complish the transmutation of metals; but hedid not confine himself to these experiments,devoting himself to researches in all the fieldsof natural philosophy. He was associated atOxford with a company of scientists, includ-ing Wallis and Wren, who held meetings andmade experiments together, these gatheringsbeing the beginning, as mentioned a momentago, of what finally became the Royal Society.It was during this residence at Oxford thatmany of his valuable researches upon air weremade, and during this time be invented hisair-pump, now exhibited in the Royal Society

X. THE SUCCESSORS OF GALILEO 287

rooms at Burlington House.30

His experiments to prove the atmosphericpressure are most interesting and conclusive.“Having three small, round glass bubbles,blown at the flame of a lamp, about the sizeof hazel-nuts,” he says, “each of them with ashort, slender stem, by means whereof theywere so exactly poised in water that a verysmall change of weight would make them ei-ther emerge or sink; at a time when the atmo-sphere was of convenient weight, I put theminto a wide-mouthed glass of common water,and leaving them in a quiet place, where theywere frequently in my eye, I observed thatsometimes they would be at the top of the wa-ter, and remain there for several days, or per-haps weeks, together, and sometimes fall tothe bottom, and after having continued therefor some time rise again. And sometimes theywould rise or fall as the air was hot or cold.”31

It was in the course of these experimentsthat the observations made by Boyle led tothe invention of his “statical barometer,” themercurial barometer having been invented,as we have seen, by Torricelli, in 1643. Indescribing this invention he says: “Makingchoice of a large, thin, and light glass bubble,

30See The Phlogiston Theory, Vol. IV.31Robert Boyle, Philosophical Works, 3 vols., London,

1738. Vol. III., p. 41.


blown at the flame of a lamp, I counterpoisedit with a metallic weight, in a pair of scalesthat were suspended in a frame, that wouldturn with the thirtieth part of a grain. Boththe frame and the balance were then placednear a good barometer, whence I might learnthe present weight of the atmosphere; when,though the scales were unable to show allthe variations that appeared in the mercurialbarometer, yet they gave notice of those thataltered the height of the mercury half a quar-ter of an inch.”32 A fairly sensitive barometer,after all. This statical barometer suggestedseveral useful applications to the fertile imag-ination of its inventor, among others the mea-suring of mountain-peaks, as with the mercu-rial barometer, the rarefication of the air atthe top giving a definite ratio to the more con-densed air in the valley.

Another of his experiments was madeto discover the atmospheric pressure to thesquare inch. After considerable difficulty hedetermined that the relative weight of a cu-bic inch of water and mercury was about oneto fourteen, and computing from other knownweights he determined that “when a columnof quicksilver thirty inches high is sustainedin the barometer, as it frequently happens,a column of air that presses upon an inch

32Ibid., Vol. III., p. 47.


VIEW IN THE LIBRARY OF THE ROYAL SOCIETY

On the desk in the foreground is Boyle’s air-pump on theleft. Priestly’s electric machine on the right.

square near the surface of the earth mustweigh about fifteen avoirdupois pounds.”33 Asthe pressure of air at the sea-level is now es-timated at 14.7304 pounds to the square inch,it will be seen that Boyle’s calculation was notfar wrong.

From his numerous experiments upon theair, Boyle was led to believe that there weremany “latent qualities” due to substances con-tained in it that science had as yet been un-able to fathom, believing that there is “not a

33Ibid., Vol. II., p. 92.


more heterogeneous body in the world.” Hebelieved that contagious diseases were carriedby the air, and suggested that eruptions of theearth, such as those made by earthquakes,might send up “venomous exhalations” thatproduced diseases. He suggested also that theair might play an important part in some pro-cesses of calcination, which, as we shall see,was proved to be true by Lavoisier late in theeighteenth century. Boyle’s notions of the ex-act chemical action in these phenomena wereof course vague and indefinite, but he had ob-served that some part was played by the air,and he was right in supposing that the air“may have a great share in varying the saltsobtainable from calcined vitriol.”34

Although he was himself such a painstak-ing observer of facts, he had the fault of hisage of placing too much faith in hear-say ev-idence of untrained observers. Thus, fromthe numerous stories he heard concerningthe growth of metals in previously exhaustedmines, he believed that the air was respon-sible for producing this growth—in which heundoubtedly believed. The story of a tin-miner that, in his own time, after a lapse ofonly twenty-five years, a heap of earth previ-ously exhausted of its ore became again evenmore richly impregnated than before by ly-

34Ibid., Vol. II., p. 2.


ing exposed to the air, seems to have been be-lieved by the philosopher.

As Boyle was an alchemist, and undoubt-edly believed in the alchemic theory that met-als have “spirits” and various other qualitiesthat do not exist, it is not surprising that hewas credulous in the matter of beliefs concern-ing peculiar phenomena exhibited by them.Furthermore, he undoubtedly fell into the er-ror common to “specialists,” or persons work-ing for long periods of time on one subject—the error of over-enthusiasm in his subject.He had discovered so many remarkable qual-ities in the air that it is not surprising to findthat he attributed to it many more that hecould not demonstrate.

Boyle’s work upon colors, although proba-bly of less importance than his experimentsand deductions upon air, show that he was inthe van as far as the science of his day wasconcerned. As he points out, the schools ofhis time generally taught that “color is a pene-trating quality, reaching to the innermost partof the substance,” and, as an example of this,sealing-wax was cited, which could be brokeninto minute bits, each particle retaining thesame color as its fellows or the original mass.To refute this theory, and to show instancesto the contrary, Boyle, among other things,shows that various colors—blue, red, yellow—


may be produced upon tempered steel, and yetthe metal within “a hair’s-breadth of its sur-face” have none of these colors. Therefore, hewas led to believe that color, in opaque bodiesat least, is superficial.

“But before we descend to a more particu-lar consideration of our subject,” he says, “’tisproper to observe that colors may be regardedeither as a quality residing in bodies to modifylight after a particular manner, or else as lightitself so modified as to strike upon the organsof sight, and cause the sensation we call color;and that this latter is the more proper accep-tation of the word color will appear hereafter.And indeed it is the light itself, which after acertain manner, either mixed with shades orother-wise, strikes our eyes and immediatelyproduces that motion in the organ which givesus the color of an object.”35

In examining smooth and rough surfacesto determine the cause of their color, he madeuse of the microscope, and pointed out thevery obvious example of the difference in colorof a rough and a polished piece of the sameblock of stone. He used some striking illustra-tions of the effect of light and the position ofthe eye upon colors. “Thus the color of plush orvelvet will appear various if you stroke part ofit one way and part another, the posture of the

35Ibid., Vol. I., p. 8.


particular threads in regard to the light, orthe eye, being thereby varied. And ’tis observ-able that in a field of ripe corn, blown upon bythe wind, there will appear waves of a colordifferent from that of the rest of the corn, be-cause the wind, by depressing some of the earsmore than others, causes one to reflect morelight from the lateral and strawy parts thananother.”36 His work upon color, however, asupon light, was entirely overshadowed by thework of his great fellow-countryman Newton.

Boyle’s work on electricity was a continu-ation of Gilbert’s, to which he added severalnew facts. He added several substances toGilbert’s list of “electrics,” experimented onsmooth and rough surfaces in exciting of elec-tricity, and made the important discovery thatamber retained its attractive virtue after thefriction that excited it had ceased. “For theattrition having caused an intestine motion inits parts,” he says, “the heat thereby excitedought not to cease as soon as ever the rubbingis over, but to continue capable of emittingeffluvia for some time afterwards, longer orshorter according to the goodness of the elec-tric and the degree of the commotion made; allwhich, joined together, may sometimes makethe effect considerable; and by this means, ona warm day, I, with a certain body not big-

36Ibid., vol. III., p. 508.


ger than a pea, but very vigorously attrac-tive, moved a steel needle, freely poised, aboutthree minutes after I had left off rubbing it.”37

MARIOTTE AND VONGUERICKEWorking contemporaneously with Boyle, anda man whose name is usually associated withhis as the propounder of the law of density ofgases, was Edme Mariotte (died 1684), a na-tive of Burgundy. Mariotte demonstrated thatbut for the resistance of the atmosphere, allbodies, whether light or heavy, dense or thin,would fall with equal rapidity, and he provedthis by the well-known “guinea-and-feather”experiment. Having exhausted the air from along glass tube in which a guinea piece anda feather had been placed, he showed that inthe vacuum thus formed they fell with equalrapidity as often as the tube was reversed.From his various experiments as to the pres-sure of the atmosphere he deduced the lawthat the density and elasticity of the atmo-sphere are precisely proportional to the com-pressing force (the law of Boyle and Mariotte).He also ascertained that air existed in a stateof mechanical mixture with liquids, “existing

37Ibid., Vol. III. p. 361.


between their particles in a state of condensa-tion.” He made many other experiments, es-pecially on the collision of bodies, but his mostimportant work was upon the atmosphere.

But meanwhile another contemporary ofBoyle and Mariotte was interesting himself inthe study of the atmosphere, and had madea wonderful invention and a most strikingdemonstration. This was Otto von Guer-icke (1602-1686), Burgomaster of Magdeburg,and councillor to his “most serene and potentHighness” the elector of that place. Whennot engrossed with the duties of public office,he devoted his time to the study of the sci-ences, particularly pneumatics and electric-ity, both then in their infancy. The discov-eries of Galileo, Pascal, and Torricelli incitedhim to solve the problem of the creation of avacuum—a desideratum since before the daysof Aristotle. His first experiments were witha wooden pump and a barrel of water, but hesoon found that with such porous material aswood a vacuum could not be created or main-tained. He therefore made use of a globe ofcopper, with pump and stop-cock; and withthis he was able to pump out air almost aseasily as water. Thus, in 1650, the air-pumpwas invented. Continuing his experimentsupon vacuums and atmospheric pressure withhis newly discovered pump, he made some


startling discoveries as to the enormous pres-sure exerted by the air.

It was not his intention, however, todemonstrate his newly acquired knowledgeby words or theories alone, nor by mere lab-oratory experiments; but he chose insteadan open field, to which were invited Em-peror Ferdinand III., and all the princes ofthe Diet at Ratisbon. When they were as-sembled he produced two hollow brass hemi-spheres about two feet in diameter, and plac-ing their exactly fitting surfaces together, pro-ceeded to pump out the air from their hollowinterior, thus causing them to stick togetherfirmly in a most remarkable way, apparentlywithout anything holding them. This of it-self was strange enough; but now the wor-thy burgomaster produced teams of horses,and harnessing them to either side of thehemispheres, attempted to pull the adheringbrasses apart. Five, ten, fifteen teams—thirtyhorses, in all—were attached; but pull andtug as they would they could not separate thefirmly clasped hemispheres. The enormouspressure of the atmosphere had been moststrikingly demonstrated.

But it is one thing to demonstrate, an-other to convince; and many of the goodpeople of Magdeburg shook their heads overthis “devil’s contrivance,” and predicted that


Heaven would punish the Herr Burgomaster,as indeed it had once by striking his housewith lightning and injuring some of his infer-nal contrivances. They predicted his futurepunishment, but they did not molest him, forto his fellow-citizens, who talked and laughed,drank and smoked with him, and knew himfor the honest citizen that he was, he did notseem bewitched at all. And so he lived andworked and added other facts to science, andhis brass hemispheres were not destroyed byfanatical Inquisitors, but are still preserved inthe royal library at Berlin.

In his experiments with his air-pump hediscovered many things regarding the actionof gases, among others that animals cannotlive in a vacuum. He invented the anemoscopeand the air-balance, and being thus enabledto weigh the air and note the changes thatpreceded storms and calms, he was able stillfurther to dumfound his wondering fellow-Magdeburgers by more or less accurate pre-dictions about the weather.

Von Guericke did not accept Gilbert’s the-ory that the earth was a great magnet, but inhis experiments along lines similar to thosepursued by Gilbert, he not only invented thefirst electrical machine, but discovered elec-trical attraction and repulsion. The electri-cal machine which he invented consisted of a


VON GUERICKE’S AIR-PUMP

(From Dannemann’s Geschichte der Naturwis-senschaften.)


sphere of sulphur mounted on an iron axis toimitate the rotation of the earth, and which,when rubbed, manifested electrical reactions.When this globe was revolved and strokedwith the dry hand it was found that it at-tached to it “all sorts of little fragments, likeleaves of gold, silver, paper, etc.” “Thus thisglobe,” he says, “when brought rather neardrops of water causes them to swell and puffup. It likewise attracts air, smoke, etc.”38 Be-fore the time of Guericke’s demonstrations,Cabæus had noted that chaff leaped back froman “electric,” but he did not interpret the phe-nomenon as electrical repulsion. Von Gu-ericke, however, recognized it as such, andrefers to it as what he calls “expulsive virtue.”“Even expulsive virtue is seen in this globe,”he says, “for it not only attracts, but alsorepels again from itself little bodies of thissort, nor does it receive them until they havetouched something else.” It will be observedfrom this that he was very close to discoveringthe discharge of the electrification of attractedbodies by contact with some other object, afterwhich they are reattracted by the electric.

He performed a most interesting experi-ment with his sulphur globe and a feather,

38Otto von Guericke, in the Philosophical Transac-tions of the Royal Society of London, No. 88, for 1672,p. 5103.


and in doing so came near anticipating Ben-jamin Franklin in his discovery of the effectsof pointed conductors in drawing off the dis-charge. Having revolved and stroked his globeuntil it repelled a bit of down, he removedthe globe from its rack and advancing it to-wards the now repellent down, drove it be-fore him about the room. In this chase heobserved that the down preferred to alightagainst “the points of any object whatsoever.”He noticed that should the down chance to bedriven within a few inches of a lighted can-dle, its attitude towards the globe suddenlychanged, and instead of running away from it,it now “flew to it for protection”—the chargeon the down having been dissipated by the hotair. He also noted that if one face of a featherhad been first attracted and then repelled bythe sulphur ball, that the surface so affectedwas always turned towards the globe; so thatif the positions of the two were reversed, thesides of the feather reversed also.

Still another important discovery, that ofelectrical conduction, was made by Von Guer-icke. Until his discovery no one had observedthe transference of electricity from one body toanother, although Gilbert had some time be-fore noted that a rod rendered magnetic at oneend became so at the other. Von Guericke’sexperiments were made upon a linen thread


with his sulphur globe, which, he says, “hav-ing been previously excited by rubbing, canexercise likewise its virtue through a linenthread an ell or more long, and there at-tract something.” But this discovery, and hisequally important one that the sulphur ballbecomes luminous when rubbed, were prac-tically forgotten until again brought to no-tice by the discoveries of Francis Hauksbeeand Stephen Gray early in the eighteenth cen-tury. From this we may gather that Von Guer-icke himself did not realize the import of hisdiscoveries, for otherwise he would certainlyhave carried his investigations still further.But as it was he turned his attention to otherfields of research.

ROBERT HOOKEA slender, crooked, shrivelled-limbed, cantan-kerous little man, with dishevelled hair andhaggard countenance, bad-tempered and irri-table, penurious and dishonest, at least in hisclaims for priority in discoveries—this is thepicture usually drawn, alike by friends andenemies, of Robert Hooke (1635-1703), a manwith an almost unparalleled genius for scien-tific discoveries in almost all branches of sci-ence. History gives few examples so strikingof a man whose really great achievements in


science would alone have made his name im-mortal, and yet who had the pusillanimousspirit of a charlatan—an almost insane ma-nia, as it seems—for claiming the credit of dis-coveries made by others. This attitude of mindcan hardly be explained except as a mania:it is certainly more charitable so to regard it.For his own discoveries and inventions wereso numerous that a few more or less wouldhardly have added to his fame, as his repu-tation as a philosopher was well established.Admiration for his ability and his philosophi-cal knowledge must always be marred by therecollection of his arrogant claims to the dis-coveries of other philosophers.

It seems pretty definitely determined thatHooke should be credited with the inventionof the balance-spring for regulating watches;but for a long time a heated controversywas waged between Hooke and Huygens asto who was the real inventor. It appearsthat Hooke conceived the idea of the balance-spring, while to Huygens belongs the credit ofhaving adapted the coiled spring in a work-ing model. He thus made practical Hooke’sconception, which is without value except asapplied by the coiled spring; but, neverthe-less, the inventor, as well as the perfector,should receive credit. In this controversy, un-like many others, the blame cannot be laid at


Hooke’s door.Hooke was the first curator of the Royal

Society, and when anything was to be inves-tigated, usually invented the mechanical de-vices for doing so. Astronomical apparatus,instruments for measuring specific weights,clocks and chronometers, methods of measur-ing the velocity of falling bodies, freezing andboiling points, strength of gunpowder, mag-netic instruments—in short, all kinds of in-genious mechanical devices in all branches ofscience and mechanics. It was he who madethe famous air-pump of Robert Boyle, basedon Boyle’s plans. Incidentally, Hooke claimedto be the inventor of the first air-pump him-self, although this claim is now entirely dis-credited.

Within a period of two years he devised noless than thirty different methods of flying,all of which, of course, came to nothing, butgo to show the fertile imagination of the man,and his tireless energy. He experimented withelectricity and made some novel suggestionsupon the difference between the electric sparkand the glow, although on the whole his con-tributions in this field are unimportant. Healso first pointed out that the motions of theheavenly bodies must be looked upon as amechanical problem, and was almost withingrasping distance of the exact theory of grav-


REPRODUCTION OF A PLATE IN HOOKE’S“MICROSCOPICAL OBSERVATIONS”

Showing the points of a needle (Fig. 1), a printed dot(Fig. 2), and the edge of a razor (Fig. 3), as magnifiedby Hooke’s microscope.


itation, himself originating the idea of mak-ing use of the pendulum in measuring grav-ity. Likewise, he first proposed the wave the-ory of light; although it was Huygens who es-tablished it on its present foundation.

Hooke published, among other things, abook of plates and descriptions of his Micro-scopical Observations, which gives an idea ofthe advance that had already been made inmicroscopy in his time. Two of these platesare given here, which, even in this age of mi-croscopy, are both interesting and instructive.These plates are made from prints of Hooke’soriginal copper plates, and show that excel-lent lenses were made even at that time. Theyillustrate, also, how much might have beenaccomplished in the field of medicine if moreattention had been given to microscopy byphysicians. Even a century later, had physi-cians made better use of their microscopes,they could hardly have overlooked such aneasily found parasite as the itch mite, whichis quite as easily detected as the cheese mite,pictured in Hooke’s book.

In justice to Hooke, and in extenuationof his otherwise inexcusable peculiarities ofmind, it should be remembered that for manyyears he suffered from a painful and wast-ing disease. This may have affected his men-tal equilibrium, without appreciably affecting


his ingenuity. In his own time this conditionwould hardly have been considered a disease;but to-day, with our advanced ideas as to men-tal diseases, we should be more inclined toascribe his unfortunate attitude of mind toa pathological condition, rather than to anymanifestation of normal mentality. From thispoint of view his mental deformity seems notunlike that of Cavendish’s, later, except thatin the case of Cavendish it manifested itself asan abnormal sensitiveness instead of an ab-normal irritability.

CHRISTIAN HUYGENSIf for nothing else, the world is indebted tothe man who invented the pendulum clock,Christian Huygens (1629-1695), of the Hague,inventor, mathematician, mechanician, as-tronomer, and physicist. Huygens was the de-scendant of a noble and distinguished family,his father, Sir Constantine Huygens, being awell-known poet and diplomatist. Early in lifeyoung Huygens began his career in the legalprofession, completing his education in the ju-ridical school at Breda; but his taste for math-ematics soon led him to neglect his legal stud-ies, and his aptitude for scientific researcheswas so marked that Descartes predicted greatthings of him even while he was a mere tyro


in the field of scientific investigation.One of his first endeavors in science

was to attempt an improvement of the tele-scope. Reflecting upon the process of mak-ing lenses then in vogue, young Huygensand his brother Constantine attempted a newmethod of grinding and polishing, wherebythey overcame a great deal of the sphericaland chromatic aberration. With this new tele-scope a much clearer field of vision was ob-tained, so much so that Huygens was ableto detect, among other things, a hitherto un-known satellite of Saturn. It was these as-tronomical researches that led him to applythe pendulum to regulate the movements ofclocks. The need for some more exact methodof measuring time in his observations of thestars was keenly felt by the young astronomer,and after several experiments along differentlines, Huygens hit upon the use of a swing-ing weight; and in 1656 made his invention ofthe pendulum clock. The year following, hisclock was presented to the states-general. Ac-curacy as to time is absolutely essential in as-tronomy, but until the invention of Huygens’sclock there was no precise, nor even approxi-mately precise, means of measuring short in-tervals.

Huygens was one of the first to adapt themicrometer to the telescope—a mechanical


ROBERT HOOKE’S MICROSCOPE


device on which all the nice determinationof minute distances depends. He also tookup the controversy against Hooke as to thesuperiority of telescopic over plain sights toquadrants, Hooke contending in favor of theplain. In this controversy, the subject of whichattracted wide attention, Huygens was com-pletely victorious; and Hooke, being unable torefute Huygens’s arguments, exhibited suchirritability that he increased his already gen-eral unpopularity. All of the arguments forand against the telescope sight are too numer-ous to be given here. In contending in its favorHuygens pointed out that the unaided eye isunable to appreciate an angular space in thesky less than about thirty seconds. Even inthe best quadrant with a plain sight, there-fore, the altitude must be uncertain by thatquantity. If in place of the plain sight a tele-scope is substituted, even if it magnify onlythirty times, it will enable the observer to fixthe position to one second, with progressivelyincreased accuracy as the magnifying powerof the telescope is increased. This was onlyone of the many telling arguments advancedby Huygens.

In the field of optics, also, Huygens hasadded considerably to science, and his work,Dioptrics, is said to have been a favorite bookwith Newton. During the later part of his life,


however, Huygens again devoted himself toinventing and constructing telescopes, grind-ing the lenses, and devising, if not actuallymaking, the frame for holding them. Thesetelescopes were of enormous lengths, three ofhis object-glasses, now in possession of theRoyal Society, being of 123, 180, and 210 feetfocal length respectively. Such instruments, ifconstructed in the ordinary form of the longtube, were very unmanageable, and to ob-viate this Huygens adopted the plan of dis-pensing with the tube altogether, mountinghis lenses on long poles manipulated by ma-chinery. Even these were unwieldy enough,but the difficulties of manipulation were fullycompensated by the results obtained.

It had been discovered, among otherthings, that in oblique refraction light is sep-arated into colors. Therefore, any small por-tion of the convex lens of the telescope, being aprism, the rays proceed to the focus, separatedinto prismatic colors, which make the imagethus formed edged with a fringe of color andindistinct. But, fortunately for the early tele-scope makers, the degree of this aberration isindependent of the focal length of the lens; sothat, by increasing this focal length and us-ing the appropriate eye-piece, the image canbe greatly magnified, while the fringe of colorsremains about the same as when a less power-


ful lens is used. Hence the advantage of Huy-gens’s long telescope. He did not confine hisefforts to simply lengthening the focal lengthof his telescopes, however, but also added totheir efficiency by inventing an almost perfectachromatic eye-piece.

In 1663 he was elected a fellow of the RoyalSociety of London, and in 1669 he gave to thatbody a concise statement of the laws govern-ing the collision of elastic bodies. Althoughthe same views had been given by Wallis andWren a few weeks earlier, there is no doubtthat Huygens’s views were reached indepen-dently; and it is probable that he had arrivedat his conclusions several years before. Inthe Philosophical Transactions for 1669 it isrecorded that the society being interested inthe laws of the principles of motion, a requestwas made that M. Huygens, Dr. Wallis, andSir Christopher Wren submit their views onthe subject. Wallis submitted his paper first,November 15, 1668. A month later, December17th, Wren imparted to the society his laws asto the nature of the collision of bodies. And afew days later, January 5, 1669, Huygens sentin his “Rules Concerning the Motion of Bodiesafter Mutual Impulse.” Although Huygens’sreport was received last, he was anticipatedby such a brief space of time, and his views areso clearly stated—on the whole rather more


so than those of the other two—that we givethem in part here:

“1. If a hard body should strike against abody equally hard at rest, after contact theformer will rest and the latter acquire a ve-locity equal to that of the moving body.

“2. But if that other equal body be likewisein motion, and moving in the same direction,after contact they will move with reciprocalvelocities.

“3. A body, however great, is moved by abody however small impelled with any veloc-ity whatsoever.

“5. The quantity of motion of two bod-ies may be either increased or diminished bytheir shock; but the same quantity towardsthe same part remains, after subtracting thequantity of the contrary motion.

“6. The sum of the products arising frommultiplying the mass of any hard body intothe squares of its velocity is the same both be-fore and after the stroke.

“7. A hard body at rest will receive agreater quantity of motion from another hardbody, either greater or less than itself, bythe interposition of any third body of a meanquantity, than if it was immediately struck bythe body itself; and if the interposing body bea mean proportional between the other two,its action upon the quiescent body will be the


greatest of all.”39

This was only one of several interestingand important communications sent to theRoyal Society during his lifetime. One of thesewas a report on what he calls “PneumaticalExperiments.” “Upon including in a vacuuman insect resembling a beetle, but somewhatlarger,” he says, “when it seemed to be dead,the air was readmitted, and soon after it re-vived; putting it again in the vacuum, andleaving it for an hour, after which the air wasreadmitted, it was observed that the insect re-quired a longer time to recover; including itthe third time for two days, after which theair was admitted, it was ten hours before it be-gan to stir; but, putting it in a fourth time, foreight days, it never afterwards recovered. . . .Several birds, rats, mice, rabbits, and catswere killed in a vacuum, but if the air was ad-mitted before the engine was quite exhaustedsome of them would recover; yet none revivedthat had been in a perfect vacuum. . . . Uponputting the weight of eighteen grains of pow-der with a gauge into a receiver that held sev-eral pounds of water, and firing the powder, itraised the mercury an inch and a half; fromwhich it appears that there is one-fifth of airin gunpowder, upon the supposition that air is

39Von Guericke, Phil. Trans. for 1669, Vol. I., pp. 173,174.


HUYGENS’S CLOCK

(Side view, showing the pendulum mechanism.)


about one thousand times lighter than water;for in this experiment the mercury rose to theeighteenth part of the height at which the aircommonly sustains it, and consequently theweight of eighteen grains of powder yieldedair enough to fill the eighteenth part of areceiver that contained seven pounds of wa-ter; now this eighteenth part contains forty-nine drachms of water; wherefore the air, thattakes up an equal space, being a thousandtimes lighter, weighs one-thousandth part offorty-nine drachms, which is more than threegrains and a half; it follows, therefore, thatthe weight of eighteen grains of powder con-tains more than three and a half of air, whichis about one-fifth of eighteen grains. . . .”

From 1665 to 1681, accepting the tempt-ing offer made him through Colbert, by LouisXIV., Huygens pursued his studies at theBibliotheque du Roi as a resident of France.Here he published his Horologium Oscilla-torium, dedicated to the king, containing,among other things, his solution of the prob-lem of the “centre of oscillation.” This in it-self was an important step in the history ofmechanics. Assuming as true that the cen-tre of gravity of any number of interdependentbodies cannot rise higher than the point fromwhich it falls, he reached correct conclusionsas to the general principle of the conserva-


tion of vis viva, although he did not actuallyprove his conclusions. This was the first at-tempt to deal with the dynamics of a system.In this work, also, was the true determinationof the relation between the length of a pendu-lum and the time of its oscillation.

In 1681 he returned to Holland, influ-enced, it is believed, by the attitude that wasbeing taken in France against his religion.Here he continued his investigations, built hisimmense telescopes, and, among other things,discovered “polarization,” which is recorded inTraite de la Lumiere, published at Leyden in1690. Five years later he died, bequeathinghis manuscripts to the University of Leyden.It is interesting to note that he never acceptedNewton’s theory of gravitation as a universalproperty of matter.

XI. NEWTON ANDTHECOMPOSITION OFLIGHT

Galileo, that giant in physical science of theearly seventeenth century, died in 1642. OnChristmas day of the same year there wasborn in England another intellectual giantwho was destined to carry forward the workof Copernicus, Kepler, and Galileo to a mar-vellous consummation through the discoveryof the great unifying law in accordance withwhich the planetary motions are performed.We refer, of course, to the greatest of Englishphysical scientists, Isaac Newton, the Shake-speare of the scientific world. Born thus be-fore the middle of the seventeenth century,Newton lived beyond the first quarter of theeighteenth (1727). For the last forty years of

317


that period his was the dominating scientificpersonality of the world. With full proprietythat time has been spoken of as the “Age ofNewton.”

Yet the man who was to achieve such dis-tinction gave no early premonition of futuregreatness. He was a sickly child from birth,and a boy of little seeming promise. He wasan indifferent student, yet, on the other hand,he cared little for the common amusements ofboyhood. He early exhibited, however, a tastefor mechanical contrivances, and spent muchtime in devising windmills, water-clocks, sun-dials, and kites. While other boys were in-terested only in having kites that would fly,Newton—at least so the stories of a later timewould have us understand—cared more forthe investigation of the seeming principles in-volved, or for testing the best methods of at-taching the strings, or the best materials tobe used in construction.

Meanwhile the future philosopher was ac-quiring a taste for reading and study, delv-ing into old volumes whenever he found anopportunity. These habits convinced his rel-atives that it was useless to attempt to makea farmer of the youth, as had been their in-tention. He was therefore sent back to school,and in the summer of 1661 he matriculatedat Trinity College, Cambridge. Even at col-

XI. THE COMPOSITION OF LIGHT 319

lege Newton seems to have shown no unusualmental capacity, and in 1664, when examinedfor a scholarship by Dr. Barrow, that gentle-man is said to have formed a poor opinionof the applicant. It is said that the knowl-edge of the estimate placed upon his abilitiesby his instructor piqued Newton, and led himto take up in earnest the mathematical stud-ies in which he afterwards attained such dis-tinction. The study of Euclid and Descartes’s“Geometry” roused in him a latent interest inmathematics, and from that time forward hisinvestigations were carried on with enthusi-asm. In 1667 he was elected Fellow of TrinityCollege, taking the degree of M.A. the follow-ing spring.

It will thus appear that Newton’s boy-hood and early manhood were passed duringthat troublous time in British political annalswhich saw the overthrow of Charles I., the au-tocracy of Cromwell, and the eventual restora-tion of the Stuarts. His maturer years wit-nessed the overthrow of the last Stuart andthe reign of the Dutchman, William of Or-ange. In his old age he saw the first of theHanoverians mount the throne of England.Within a decade of his death such scientificpath-finders as Cavendish, Black, and Priest-ley were born—men who lived on to the closeof the eighteenth century. In a full sense,


then, the age of Newton bridges the gap fromthat early time of scientific awakening underKepler and Galileo to the time which we of thetwentieth century think of as essentially mod-ern.

THE COMPOSITION OFWHITE LIGHTIn December, 1672, Newton was elected a Fel-low of the Royal Society, and at this meetinga paper describing his invention of the reflect-ing telescope was read. A few days later hewrote to the secretary, making some inquiriesas to the weekly meetings of the society, andintimating that he had an account of an inter-esting discovery that he wished to lay beforethe society. When this communication wasmade public, it proved to be an explanationof the discovery of the composition of whitelight. We have seen that the question as tothe nature of color had commanded the at-tention of such investigators as Huygens, butthat no very satisfactory solution of the ques-tion had been attained. Newton proved bydemonstrative experiments that white light iscomposed of the blending of the rays of diversecolors, and that the color that we ascribe toany object is merely due to the fact that the


object in question reflects rays of that color,absorbing the rest. That white light is reallymade up of many colors blended would seemincredible had not the experiments by whichthis composition is demonstrated become fa-miliar to every one. The experiments wereabsolutely novel when Newton brought themforward, and his demonstration of the compo-sition of light was one of the most striking ex-positions ever brought to the attention of theRoyal Society. It is hardly necessary to addthat, notwithstanding the conclusive charac-ter of Newton’s work, his explanations did notfor a long time meet with general acceptance.

Newton was led to his discovery by someexperiments made with an ordinary glassprism applied to a hole in the shutter of adarkened room, the refracted rays of the sun-light being received upon the opposite walland forming there the familiar spectrum.

“It was a very pleasing di-version,” he wrote, “to view thevivid and intense colors producedthereby; and after a time, applyingmyself to consider them very cir-cumspectly, I became surprised tosee them in varying form, which,according to the received laws ofrefraction, I expected should havebeen circular. They were termi-


nated at the sides with straightlines, but at the ends the decay oflight was so gradual that it was dif-ficult to determine justly what wastheir figure, yet they seemed semi-circular.

“Comparing the length of thiscolored spectrum with its breadth,I found it almost five times greater;a disproportion so extravagant thatit excited me to a more than or-dinary curiosity of examining fromwhence it might proceed. I couldscarce think that the various thick-nesses of the glass, or the termi-nation with shadow or darkness,could have any influence on lightto produce such an effect; yet Ithought it not amiss, first, to ex-amine those circumstances, andso tried what would happen bytransmitting light through parts ofthe glass of divers thickness, orthrough holes in the window ofdivers bigness, or by setting theprism without so that the lightmight pass through it and be re-fracted before it was transmittedthrough the hole; but I found noneof those circumstances material.


The fashion of the colors was in allthese cases the same.

“Then I suspected whether byany unevenness of the glass orother contingent irregularity thesecolors might be thus dilated. Andto try this I took another prism likethe former, and so placed it that thelight, passing through them both,might be refracted contrary ways,and so by the latter returned intothat course from which the formerdiverted it. For, by this means, Ithought, the regular effects of thefirst prism would be destroyed bythe second prism, but the irregularones more augmented by the mul-tiplicity of refractions. The eventwas that the light, which by thefirst prism was diffused into an ob-long form, was by the second re-duced into an orbicular one withas much regularity as when it didnot all pass through them. So that,whatever was the cause of thatlength, ’twas not any contingent ir-regularity.

“I then proceeded to examinemore critically what might be ef-fected by the difference of the in-


cidence of rays coming from diversparts of the sun; and to that endmeasured the several lines and an-gles belonging to the image. Itsdistance from the hole or prismwas 22 feet; its utmost length 131

4

inches; its breadth 258; the diame-

ter of the hole 14

of an inch; the an-gle which the rays, tending towardsthe middle of the image, made withthose lines, in which they wouldhave proceeded without refraction,was 44◦ 56’; and the vertical an-gle of the prism, 63◦ 12’. Alsothe refractions on both sides of theprism—that is, of the incident andemergent rays—were, as near as Icould make them, equal, and con-sequently about 54◦ 4’; and therays fell perpendicularly upon thewall. Now, subducting the diam-eter of the hole from the lengthand breadth of the image, there re-mains 13 inches the length, and23

8the breadth, comprehended by

those rays, which, passing throughthe centre of the said hole, whichthat breadth subtended, was about31’, answerable to the sun’s diame-ter; but the angle which its length


subtended was more than five suchdiameters, namely 2◦ 49’.

“Having made these observa-tions, I first computed from themthe refractive power of the glass,and found it measured by the ra-tio of the sines 20 to 31. And then,by that ratio, I computed the re-fractions of two rays flowing fromopposite parts of the sun’s discus,so as to differ 31’ in their obliquityof incidence, and found that theemergent rays should have compre-hended an angle of 31’, as they did,before they were incident.

“But because this computationwas founded on the hypothesis ofthe proportionality of the sinesof incidence and refraction, whichthough by my own experience Icould not imagine to be so erro-neous as to make that angle but31’, which in reality was 2◦ 49’,yet my curiosity caused me againto make my prism. And havingplaced it at my window, as before,I observed that by turning it a lit-tle about its axis to and fro, so asto vary its obliquity to the lightmore than an angle of 4◦ or 5◦,


the colors were not thereby sensi-bly translated from their place onthe wall, and consequently by thatvariation of incidence the quantityof refraction was not sensibly var-ied. By this experiment, therefore,as well as by the former computa-tion, it was evident that the differ-ence of the incidence of rays flowingfrom divers parts of the sun couldnot make them after decussationdiverge at a sensibly greater an-gle than that at which they beforeconverged; which being, at most,but about 31’ or 32’, there stillremained some other cause to befound out, from whence it could be2◦ 49’.”

All this caused Newton to suspect that therays, after their trajection through the prism,moved in curved rather than in straight lines,thus tending to be cast upon the wall at dif-ferent places according to the amount of thiscurve. His suspicions were increased, also, byhappening to recall that a tennis-ball some-times describes such a curve when “cut” by atennis-racket striking the ball obliquely.

“For a circular as well as aprogressive motion being commu-nicated to it by the stroke,” he says,


“its parts on that side where themotions conspire must press andbeat the contiguous air more vio-lently than on the other, and thereexcite a reluctancy and reactionof the air proportionately greater.And for the same reason, if the raysof light should possibly be globu-lar bodies, and by their oblique pas-sage out of one medium into an-other acquire a circulating motion,they ought to feel the greater re-sistance from the ambient ether onthat side where the motions con-spire, and thence be continuallybowed to the other. But notwith-standing this plausible ground ofsuspicion, when I came to examineit I could observe no such curvityin them. And, besides (which wasenough for my purpose), I observedthat the difference ’twixt the lengthof the image and diameter of thehole through which the light wastransmitted was proportionable totheir distance.

“The gradual removal of thesesuspicions at length led me to theexperimentum crucis, which wasthis: I took two boards, and, plac-


ing one of them close behind theprism at the window, so that thelight must pass through a smallhole, made in it for the purpose,and fall on the other board, whichI placed at about twelve feet dis-tance, having first made a smallhole in it also, for some of the in-cident light to pass through. ThenI placed another prism behind thissecond board, so that the lighttrajected through both the boardsmight pass through that also, andbe again refracted before it arrivedat the wall. This done, I tookthe first prism in my hands andturned it to and fro slowly aboutits axis, so much as to make theseveral parts of the image, caston the second board, successivelypass through the hole in it, thatI might observe to what places onthe wall the second prism wouldrefract them. And I saw by thevariation of these places that thelight, tending to that end of the im-age towards which the refractionof the first prism was made, didin the second prism suffer a re-fraction considerably greater than


the light tending to the other end.And so the true cause of the lengthof that image was detected to beno other than that light consists ofrays differently refrangible, which,without any respect to a differencein their incidence, were, accordingto their degrees of refrangibility,transmitted towards divers parts ofthe wall.”40

THE NATURE OF COLORHaving thus proved the composition of light,Newton took up an exhaustive discussion asto colors, which cannot be entered into atlength here. Some of his remarks on thesubject of compound colors, however, may bestated in part. Newton’s views are of par-ticular interest in this connection, since, aswe have already pointed out, the question asto what constituted color could not be agreedupon by the philosophers. Some held thatcolor was an integral part of the substance;others maintained that it was simply a reflec-tion from the surface; and no scientific expla-nation had been generally accepted. Newton

40Phil. Trans. of Royal Soc. of London, No. 80, 1672,pp. 3076-3079.


concludes his paper as follows:

“I might add more instances of thisnature, but I shall conclude withthe general one that the colors ofall natural bodies have no otherorigin than this, that they are var-iously qualified to reflect one sortof light in greater plenty than an-other. And this I have experi-mented in a dark room by illumi-nating those bodies with uncom-pounded light of divers colors. Forby that means any body may bemade to appear of any color. Theyhave there no appropriate color,but ever appear of the color ofthe light cast upon them, but yetwith this difference, that they aremost brisk and vivid in the light oftheir own daylight color. Miniumappeareth there of any color in-differently with which ’tis illus-trated, but yet most luminous inred; and so Bise appeareth indif-ferently of any color with which’tis illustrated, but yet most lu-minous in blue. And thereforeMinium reflecteth rays of any color,but most copiously those induedwith red; and consequently, when


illustrated with daylight—that is,with all sorts of rays promiscuouslyblended—those qualified with redshall abound most in the reflectedlight, and by their prevalence causeit to appear of that color. Andfor the same reason, Bise, reflect-ing blue most copiously, shall ap-pear blue by the excess of thoserays in its reflected light; and thelike of other bodies. And that thisis the entire and adequate causeof their colors is manifest, becausethey have no power to change or al-ter the colors of any sort of rays in-cident apart, but put on all colorsindifferently with which they areenlightened.”41

This epoch-making paper aroused a stormof opposition. Some of Newton’s opponentscriticised his methods, others even doubtedthe truth of his experiments. There wasone slight mistake in Newton’s belief that allprisms would give a spectrum of exactly thesame length, and it was some time before hecorrected this error. Meanwhile he patientlymet and answered the arguments of his op-ponents until he began to feel that patience

41Ibid., pp. 3084, 3085.


was no longer a virtue. At one time he evenwent so far as to declare that, once he was“free of this business,” he would renounce sci-entific research forever, at least in a publicway. Fortunately for the world, however, hedid not adhere to this determination, but wenton to even greater discoveries—which, it maybe added, involved still greater controversies.

In commenting on Newton’s discovery ofthe composition of light, Voltaire said: “SirIsaac Newton has demonstrated to the eye,by the bare assistance of a prism, that lightis a composition of colored rays, which, beingunited, form white color. A single ray is byhim divided into seven, which all fall upon apiece of linen or a sheet of white paper, in theirorder one above the other, and at equal dis-tances. The first is red, the second orange, thethird yellow, the fourth green, the fifth blue,the sixth indigo, the seventh a violet purple.Each of these rays transmitted afterwards bya hundred other prisms will never change thecolor it bears; in like manner as gold, whencompletely purged from its dross, will neverchange afterwards in the crucible.”42

42Voltaire, Letters Concerning the English Nation,London, 1811.

XII. NEWTON ANDTHE LAW OFGRAVITATION

We come now to the story of what is by com-mon consent the greatest of scientific achieve-ments. The law of universal gravitation is themost far-reaching principle as yet discovered.It has application equally to the minutest par-ticle of matter and to the most distant suns inthe universe, yet it is amazing in its very sim-plicity. As usually phrased, the law is this:That every particle of matter in the universeattracts every other particle with a force thatvaries directly with the mass of the particlesand inversely as the squares of their mutualdistance. Newton did not vault at once to thefull expression of this law, though he had for-mulated it fully before he gave the results ofhis investigations to the world. We have nowto follow the steps by which he reached this

333


culminating achievement.At the very beginning we must understand

that the idea of universal gravitation wasnot absolutely original with Newton. Awayback in the old Greek days, as we have seen,Anaxagoras conceived and clearly expressedthe idea that the force which holds the heav-enly bodies in their orbits may be the samethat operates upon substances at the sur-face of the earth. With Anaxagoras this wasscarcely more than a guess. After his daythe idea seems not to have been expressedby any one until the seventeenth century’sawakening of science. Then the considera-tion of Kepler’s Third Law of planetary mo-tion suggested to many minds perhaps inde-pendently the probability that the force hith-erto mentioned merely as centripetal, throughthe operation of which the planets are held intheir orbits is a force varying inversely as thesquare of the distance from the sun. This ideahad come to Robert Hooke, to Wren, and per-haps to Halley, as well as to Newton; but asyet no one had conceived a method by whichthe validity of the suggestion might be tested.It was claimed later on by Hooke that hehad discovered a method demonstrating thetruth of the theory of inverse squares, andafter the full announcement of Newton’s dis-covery a heated controversy was precipitated

XII. THE LAW OF GRAVITATION 335

in which Hooke put forward his claims withaccustomed acrimony. Hooke, however, neverproduced his demonstration, and it may wellbe doubted whether he had found a methodwhich did more than vaguely suggest the lawwhich the observations of Kepler had partiallyrevealed. Newton’s great merit lay not somuch in conceiving the law of inverse squaresas in the demonstration of the law. He wasled to this demonstration through consider-ing the orbital motion of the moon. Accordingto the familiar story, which has become oneof the classic myths of science, Newton wasled to take up the problem through observ-ing the fall of an apple. Voltaire is responsi-ble for the story, which serves as well as an-other; its truth or falsity need not in the leastconcern us. Suffice it that through ponder-ing on the familiar fact of terrestrial gravita-tion, Newton was led to question whether thisforce which operates so tangibly here at theearth’s surface may not extend its influenceout into the depths of space, so as to include,for example, the moon. Obviously some forcepulls the moon constantly towards the earth;otherwise that body would fly off at a tan-gent and never return. May not this so-calledcentripetal force be identical with terrestrialgravitation? Such was Newton’s query. Prob-ably many another man since Anaxagoras had


asked the same question, but assuredly New-ton was the first man to find an answer.

The thought that suggested itself to New-ton’s mind was this: If we make a diagram il-lustrating the orbital course of the moon forany given period, say one minute, we shallfind that the course of the moon departs froma straight line during that period by a mea-surable distance—that: is to say, the moonhas been virtually pulled towards the earthby an amount that is represented by the dif-ference between its actual position at the endof the minute under observation and the posi-tion it would occupy had its course been tan-gential, as, according to the first law of mo-tion, it must have been had not some force de-flected it towards the earth. Measuring thedeflection in question—which is equivalent tothe so-called versed sine of the arc traversed—we have a basis for determining the strengthof the deflecting force. Newton constructedsuch a diagram, and, measuring the amountof the moon’s departure from a tangential rec-tilinear course in one minute, determined thisto be, by his calculation, thirteen feet. Obvi-ously, then, the force acting upon the moon isone that would cause that body to fall towardsthe earth to the distance of thirteen feet inthe first minute of its fall. Would such be theforce of gravitation acting at the distance of


the moon if the power of gravitation varies in-versely as the square of the distance? Thatwas the tangible form in which the problempresented itself to Newton. The mathematicalsolution of the problem was simple enough. Itis based on a comparison of the moon’s dis-tance with the length of the earth’s radius. Onmaking this calculation, Newton found thatthe pull of gravitation—if that were really theforce that controls the moon—gives that bodya fall of slightly over fifteen feet in the firstminute, instead of thirteen feet. Here wassurely a suggestive approximation, yet, on theother band, the discrepancy seemed to be toogreat to warrant him in the supposition thathe had found the true solution. He thereforedismissed the matter from his mind for thetime being, nor did he return to it definitelyfor some years.

It was to appear in due time that New-ton’s hypothesis was perfectly valid and thathis method of attempted demonstration wasequally so. The difficulty was that the earth’sproper dimensions were not at that timeknown. A wrong estimate of the earth’s sizevitiated all the other calculations involved,since the measurement of the moon’s distancedepends upon the observation of the paral-lax, which cannot lead to a correct computa-tion unless the length of the earth’s radius


NEWTON’S LAW OF GRAVITATION

E represents the earth and A the moon. Were the earth’spull on the moon to cease, the moon’s inertia wouldcause it to take the tangential course, AB. On the otherhand, were the moon’s motion to be stopped for an in-stant, the moon would fall directly towards the earth,along the line AD. The moon’s actual orbit, resultingfrom these component forces, is AC. Let AC representthe actual flight of the moon in one minute. Then BC,which is obviously equal to AD, represents the distancewhich the moon virtually falls towards the earth in oneminute. Actual computation, based on measurements ofthe moon’s orbit, showed this distance to be about fif-teen feet. Another computation showed that this is thedistance that the moon would fall towards the earth un-der the influence of gravity, on the supposition that theforce of gravity decreases inversely with the square ofthe distance; the basis of comparison being furnishedby falling bodies at the surface of the earth. Theory andobservations thus coinciding, Newton was justified indeclaring that the force that pulls the moon towards theearth and keeps it in its orbit, is the familiar force ofgravity, and that this varies inversely as the square ofthe distance.


is accurately known. Newton’s first calcula-tion was made as early as 1666, and it wasnot until 1682 that his attention was called toa new and apparently accurate measurementof a degree of the earth’s meridian made bythe French astronomer Picard. The new mea-surement made a degree of the earth’s surface69.10 miles, instead of sixty miles.

Learning of this materially altered calcu-lation as to the earth’s size, Newton was ledto take up again his problem of the fallingmoon. As he proceeded with his computa-tion, it became more and more certain thatthis time the result was to harmonize withthe observed facts. As the story goes, hewas so completely overwhelmed with emotionthat he was forced to ask a friend to com-plete the simple calculation. That story maywell be true, for, simple though the compu-tation was, its result was perhaps the mostwonderful demonstration hitherto achieved inthe entire field of science. Now at last it wasknown that the force of gravitation operatesat the distance of the moon, and holds thatbody in its elliptical orbit, and it requiredbut a slight effort of the imagination to as-sume that the force which operates throughsuch a reach of space extends its influenceyet more widely. That such is really the casewas demonstrated presently through calcula-


tions as to the moons of Jupiter and by sim-ilar computations regarding the orbital mo-tions of the various planets. All results har-monizing, Newton was justified in reachingthe conclusion that gravitation is a universalproperty of matter. It remained, as we shallsee, for nineteenth-century scientists to provethat the same force actually operates uponthe stars, though it should be added that thisdemonstration merely fortified a belief thathad already found full acceptance.

Having thus epitomized Newton’s discov-ery, we must now take up the steps of hisprogress somewhat in detail, and state histheories and their demonstration in his ownwords. Proposition IV., theorem 4, of his Prin-cipia is as follows:

“That the moon gravitates to-wards the earth and by the forceof gravity is continually drawn offfrom a rectilinear motion and re-tained in its orbit.

“The mean distance of the moonfrom the earth, in the syzygiesin semi-diameters of the earth,is, according to Ptolemy and mostastronomers, 59; according toVendelin and Huygens, 60; toCopernicus, 601

3; to Street, 602

3;

and to Tycho, 5612. But Tycho, and


all that follow his tables of refrac-tions, making the refractions of thesun and moon (altogether againstthe nature of light) to exceed therefractions of the fixed stars, andthat by four or five minutes nearthe horizon, did thereby increasethe moon’s horizontal parallax bya like number of minutes, that is,by a twelfth or fifteenth part of thewhole parallax. Correct this errorand the distance will become about601

2semi-diameters of the earth,

near to what others have assigned.Let us assume the mean distanceof 60 diameters in the syzygies;and suppose one revolution of themoon, in respect to the fixed stars,to be completed in 27d. 7h. 43’, asastronomers have determined; andthe circumference of the earth toamount to 123,249,600 Paris feet,as the French have found by men-suration. And now, if we imaginethe moon, deprived of all motion,to be let go, so as to descend to-wards the earth with the impulseof all that force by which (by Cor.Prop. iii.) it is retained in its orb, itwill in the space of one minute of


time describe in its fall 15 112

Parisfeet. For the versed sine of that arcwhich the moon, in the space of oneminute of time, would by its meanmotion describe at the distance ofsixty semi-diameters of the earth,is nearly 15 1

12Paris feet, or more

accurately 15 feet, 1 inch, 1 line49. Wherefore, since that force, in

approaching the earth, increases inthe reciprocal-duplicate proportionof the distance, and upon that ac-count, at the surface of the earth,is 60×60 times greater than at themoon, a body in our regions, fallingwith that force, ought in the spaceof one minute of time to describe60×60×15 1

12Paris feet; and in the

space of one second of time, to de-scribe 15 1

12of those feet, or more

accurately, 15 feet, 1 inch, 1 line49. And with this very force we ac-

tually find that bodies here uponearth do really descend; for a pen-dulum oscillating seconds in thelatitude of Paris will be 3 Paris feet,and 8 lines 1

2in length, as Mr. Huy-

gens has observed. And the spacewhich a heavy body describes byfalling in one second of time is to


half the length of the pendulum inthe duplicate ratio of the circum-ference of a circle to its diameter(as Mr. Huygens has also shown),and is therefore 15 Paris feet, 1inch, 1 line 4

9. And therefore the

force by which the moon is retainedin its orbit is that very same forcewhich we commonly call gravity;for, were gravity another force dif-ferent from that, then bodies de-scending to the earth with the jointimpulse of both forces would fallwith a double velocity, and in thespace of one second of time woulddescribe 301

6Paris feet; altogether

against experience.”43

All this is beautifully clear, and its validityhas never in recent generations been calledin question; yet it should be explained thatthe argument does not amount to an actu-ally indisputable demonstration. It is at leastpossible that the coincidence between the ob-served and computed motion of the moon maybe a mere coincidence and nothing more. Thisprobability, however, is so remote that Newtonis fully justified in disregarding it, and, as has

43Sir Isaac Newton, Principia, translated by AndrewMotte, New York, 1848, pp. 391, 392.


been said, all subsequent generations have ac-cepted the computation as demonstrative.

Let us produce now Newton’s further com-putations as to the other planetary bodies,passing on to his final conclusion that gravityis a universal force.

“PROPOSITION V., THEOREM V.“That the circumjovial planets

gravitate towards Jupiter; the cir-cumsaturnal towards Saturn; thecircumsolar towards the sun; andby the forces of their gravity aredrawn off from rectilinear motions,and retained in curvilinear orbits.

“For the revolutions of the cir-cumjovial planets about Jupiter,of the circumsaturnal about Sat-urn, and of Mercury and Venusand the other circumsolar planetsabout the sun, are appearances ofthe same sort with the revolutionof the moon about the earth; andtherefore, by Rule II., must be ow-ing to the same sort of causes; es-pecially since it has been demon-strated that the forces upon whichthose revolutions depend tend tothe centres of Jupiter, of Saturn,and of the sun; and that thoseforces, in receding from Jupiter,


from Saturn, and from the sun, de-crease in the same proportion, andaccording to the same law, as theforce of gravity does in recedingfrom the earth.

“Cor. 1.—There is, therefore, apower of gravity tending to all theplanets; for doubtless Venus, Mer-cury, and the rest are bodies of thesame sort with Jupiter and Saturn.And since all attraction (by LawIII.) is mutual, Jupiter will there-fore gravitate towards all his ownsatellites, Saturn towards his, theearth towards the moon, and thesun towards all the primary plan-ets.

“Cor. 2.—The force of gravitywhich tends to any one planet is re-ciprocally as the square of the dis-tance of places from the planet’scentre.

“Cor. 3.—All the planets do mu-tually gravitate towards one an-other, by Cor. 1 and 2, and henceit is that Jupiter and Saturn, whennear their conjunction, by theirmutual attractions sensibly disturbeach other’s motions. So the sundisturbs the motions of the moon;


and both sun and moon disturb oursea, as we shall hereafter explain.

“SCHOLIUM“The force which retains the ce-

lestial bodies in their orbits hasbeen hitherto called centripetalforce; but it being now made plainthat it can be no other than a gravi-tating force, we shall hereafter callit gravity. For the cause of thecentripetal force which retains themoon in its orbit will extend itselfto all the planets by Rules I., II.,and III.“PROPOSITION VI., THEOREM VI.

“That all bodies gravitate to-wards every planet; and that theweights of the bodies towards anythe same planet, at equal distancesfrom the centre of the planet, areproportional to the quantities ofmatter which they severally con-tain.

“It has been now a long timeobserved by others that all sortsof heavy bodies (allowance beingmade for the inability of retar-dation which they suffer from asmall power of resistance in theair) descend to the earth from equal


heights in equal times; and thatequality of times we may distin-guish to a great accuracy by helpof pendulums. I tried the thingin gold, silver, lead, glass, sand,common salt, wood, water, andwheat. I provided two woodenboxes, round and equal: I filledthe one with wood, and suspendedan equal weight of gold (as exactlyas I could) in the centre of oscilla-tion of the other. The boxes hang-ing by eleven feet, made a cou-ple of pendulums exactly equal inweight and figure, and equally re-ceiving the resistance of the air.And, placing the one by the other,I observed them to play togetherforward and backward, for a longtime, with equal vibrations. Andtherefore the quantity of matter ingold was to the quantity of matterin the wood as the action of the mo-tive force (or vis motrix) upon allthe gold to the action of the sameupon all the wood—that is, as theweight of the one to the weight ofthe other: and the like happenedin the other bodies. By these ex-periments, in bodies of the same


weight, I could manifestly have dis-covered a difference of matter lessthan the thousandth part of thewhole, had any such been. But,without all doubt, the nature ofgravity towards the planets is thesame as towards the earth. For,should we imagine our terrestrialbodies removed to the orb of themoon, and there, together with themoon, deprived of all motion, to belet go, so as to fall together towardsthe earth, it is certain, from whatwe have demonstrated before, that,in equal times, they would describeequal spaces with the moon, andof consequence are to the moon,in quantity and matter, as theirweights to its weight.

“Moreover, since the satellitesof Jupiter perform their revo-lutions in times which observethe sesquiplicate proportion oftheir distances from Jupiter’s cen-tre, their accelerative gravitiestowards Jupiter will be recip-rocally as the square of theirdistances from Jupiter’s centre—that is, equal, at equal distances.And, therefore, these satellites, if


supposed to fall towards Jupiterfrom equal heights, would describeequal spaces in equal times, inlike manner as heavy bodies do onour earth. And, by the same ar-gument, if the circumsolar plan-ets were supposed to be let fall atequal distances from the sun, theywould, in their descent towards thesun, describe equal spaces in equaltimes. But forces which equallyaccelerate unequal bodies must beas those bodies—that is to say, theweights of the planets (towards thesun) must be as their quantities ofmatter. Further, that the weightsof Jupiter and his satellites to-wards the sun are proportional tothe several quantities of their mat-ter, appears from the exceedinglyregular motions of the satellites.For if some of these bodies weremore strongly attracted to the sunin proportion to their quantity ofmatter than others, the motions ofthe satellites would be disturbed bythat inequality of attraction. If atequal distances from the sun anysatellite, in proportion to the quan-tity of its matter, did gravitate to-


wards the sun with a force greaterthan Jupiter in proportion to his,according to any given proportion,suppose d to e; then the distancebetween the centres of the sun andof the satellite’s orbit would be al-ways greater than the distance be-tween the centres of the sun andof Jupiter nearly in the subdupli-cate of that proportion: as by somecomputations I have found. And ifthe satellite did gravitate towardsthe sun with a force, lesser in theproportion of e to d, the distance ofthe centre of the satellite’s orb fromthe sun would be less than the dis-tance of the centre of Jupiter fromthe sun in the subduplicate of thesame proportion. Therefore, if atequal distances from the sun, theaccelerative gravity of any satellitetowards the sun were greater orless than the accelerative gravityof Jupiter towards the sun by one-one-thousandth part of the wholegravity, the distance of the centreof the satellite’s orbit from the sunwould be greater or less than thedistance of Jupiter from the sun byone one-two-thousandth part of the


whole distance—that is, by a fifthpart of the distance of the utmostsatellite from the centre of Jupiter;an eccentricity of the orbit whichwould be very sensible. But the or-bits of the satellites are concentricto Jupiter, and therefore the accel-erative gravities of Jupiter and ofall its satellites towards the sun, atequal distances from the sun, areas their several quantities of mat-ter; and the weights of the moonand of the earth towards the sunare either none, or accurately pro-portional to the masses of matterwhich they contain.

“Cor. 5.—The power of gravityis of a different nature from thepower of magnetism; for the mag-netic attraction is not as the mat-ter attracted. Some bodies are at-tracted more by the magnet; oth-ers less; most bodies not at all. Thepower of magnetism in one and thesame body may be increased anddiminished; and is sometimes farstronger, for the quantity of mat-ter, than the power of gravity; andin receding from the magnet de-creases not in the duplicate, but al-


most in the triplicate proportion ofthe distance, as nearly as I couldjudge from some rude observations.

“PROP. VII., THEOREM VII.“That there is a power of gravity

tending to all bodies, proportionalto the several quantities of matterwhich they contain. That all theplanets mutually gravitate one to-wards another we have proved be-fore; as well as that the force ofgravity towards every one of themconsidered apart, is reciprocally asthe square of the distance of placesfrom the centre of the planet. Andthence it follows, that the gravitytending towards all the planets isproportional to the matter whichthey contain.

“Moreover, since all the partsof any planet A gravitates towardsany other planet B; and the gravityof every part is to the gravity of thewhole as the matter of the part is tothe matter of the whole; and to ev-ery action corresponds a reaction;therefore the planet B will, on theother hand, gravitate towards allthe parts of planet A, and its grav-ity towards any one part will be to


the gravity towards the whole asthe matter of the part to the mat-ter of the whole. Q.E.D.

“Hence it would appear that theforce of the whole must arise fromthe force of the component parts.”

Newton closes this remarkable Book III.with the following words:

“Hitherto we have explained thephenomena of the heavens and ofour sea by the power of gravity, buthave not yet assigned the cause ofthis power. This is certain, thatit must proceed from a cause thatpenetrates to the very centre of thesun and planets, without sufferingthe least diminution of its force;that operates not according to thequantity of the surfaces of the par-ticles upon which it acts (as me-chanical causes used to do), butaccording to the quantity of solidmatter which they contain, andpropagates its virtue on all sides toimmense distances, decreasing al-ways in the duplicate proportionsof the distances. Gravitation to-wards the sun is made up out ofthe gravitations towards the sev-eral particles of which the body of


the sun is composed; and in reced-ing from the sun decreases accu-rately in the duplicate proportionof the distances as far as the orb ofSaturn, as evidently appears fromthe quiescence of the aphelions ofthe planets; nay, and even to theremotest aphelions of the comets,if those aphelions are also quies-cent. But hitherto I have not beenable to discover the cause of thoseproperties of gravity from phenom-ena, and I frame no hypothesis; forwhatever is not deduced from thephenomena is to be called an hy-pothesis; and hypotheses, whethermetaphysical or physical, whetherof occult qualities or mechanical,have no place in experimental phi-losophy. . . . And to us it is enoughthat gravity does really exist, andact according to the laws whichwe have explained, and abundantlyserves to account for all the mo-tions of the celestial bodies and ofour sea.”44

The very magnitude of the importance ofthe theory of universal gravitation made its

44Newton op. cit., pp. 506, 507.


general acceptance a matter of considerabletime after the actual discovery. This opposi-tion had of course been foreseen by Newton,and, much as be dreaded controversy, he wasprepared to face it and combat it to the bit-ter end. He knew that his theory was right; itremained for him to convince the world of itstruth. He knew that some of his contemporaryphilosophers would accept it at once; otherswould at first doubt, question, and dispute,but finally accept; while still others woulddoubt and dispute until the end of their days.This had been the history of other great dis-coveries; and this will probably be the historyof most great discoveries for all time. But inthis case the discoverer lived to see his theoryaccepted by practically all the great minds ofhis time.

Delambre is authority for the following es-timate of Newton by Lagrange. “The cele-brated Lagrange,” he says, “who frequentlyasserted that Newton was the greatest geniusthat ever existed, used to add—‘and the mostfortunate, for we cannot find more than oncea system of the world to establish.”’ With par-donable exaggeration the admiring followersof the great generalizer pronounced this epi-taph:


“Nature and Nature’s laws lay hid in night;God said ‘Let Newton be!’and all was light.”

XIII.INSTRUMENTS OFPRECISION INTHE AGE OFNEWTON

During the Newtonian epoch there were nu-merous important inventions of scientific in-struments, as well as many improvementsmade upon the older ones. Some of these dis-coveries have been referred to briefly in otherplaces, but their importance in promoting sci-entific investigation warrants a fuller treat-ment of some of the more significant.

Many of the errors that had arisen in var-ious scientific calculations before the seven-teenth century may be ascribed to the crude-ness and inaccuracy in the construction ofmost scientific instruments. Scientists had

357


not as yet learned that an approach to abso-lute accuracy was necessary in every investi-gation in the field of science, and that suchaccuracy must be extended to the construc-tion of the instruments used in these inves-tigations and observations. In astronomy itis obvious that instruments of delicate exact-ness are most essential; yet Tycho Brahe, wholived in the sixteenth century, is credited withbeing the first astronomer whose instrumentsshow extreme care in construction.

It seems practically settled that the firsttelescope was invented in Holland in 1608;but three men, Hans Lippershey, JamesMetius, and Zacharias Jansen, have beengiven the credit of the invention at differenttimes. It would seem from certain papers,now in the library of the University of Leyden,and included in Huygens’s papers, that Lip-pershey was probably the first to invent a tele-scope and to describe his invention. The storyis told that Lippershey, who was a spectacle-maker, stumbled by accident upon the discov-ery that when two lenses are held at a cer-tain distance apart, objects at a distance ap-pear nearer and larger. Having made this dis-covery, be fitted two lenses with a tube so asto maintain them at the proper distance, andthus constructed the first telescope.

It was Galileo, however, as referred to in

XIII. INSTRUMENTS OF PRECISION 359

a preceding chapter, who first constructed atelescope based on his knowledge of the lawsof refraction. In 1609, having heard that aninstrument had been invented, consisting oftwo lenses fixed in a tube, whereby objectswere made to appear larger and nearer, he setabout constructing such an instrument thatshould follow out the known effects of refrac-tion. His first telescope, made of two lensesfixed in a lead pipe, was soon followed by oth-ers of improved types, Galileo devoting muchtime and labor to perfecting lenses and cor-recting errors. In fact, his work in develop-ing the instrument was so important that thetelescope came gradually to be known as the“Galilean telescope.”

In the construction of his telescope Galileomade use of a convex and a concave lens; butshortly after this Kepler invented an instru-ment in which both the lenses used were con-vex. This telescope gave a much larger fieldof view than the Galilean telescope, but didnot give as clear an image, and in consequencedid not come into general use until the middleof the seventeenth century. The first power-ful telescope of this type was made by Huy-gens and his brother. It was of twelve feet fo-cal length, and enabled Huygens to discover anew satellite of Saturn, and to determine alsothe true explanation of Saturn’s ring.


It was Huygens, together with Malvasiaand Auzout, who first applied the microme-ter to the telescope, although the inventor ofthe first micrometer was William Gascoigne,of Yorkshire, about 1636. The micrometeras used in telescopes enables the observer tomeasure accurately small angular distances.Before the invention of the telescope suchmeasurements were limited to the angle thatcould be distinguished by the naked eye, andwere, of course, only approximately accurate.Even very careful observers, such as TychoBrahe, were able to obtain only fairly accurateresults. But by applying Gascoigne’s inven-tion to the telescope almost absolute accuracybecame at once possible. The principle of Gas-coigne’s micrometer was that of two pointerslying parallel, and in this position pointing tozero. These were arranged so that the turningof a single screw separated or approximatedthem at will, and the angle thus formed couldbe determined with absolute accuracy.

Huygens’s micrometer was a slip of metalof variable breadth inserted at the focus ofthe telescope. By observing at what point thisexactly covered an object under examination,and knowing the focal length of the telescopeand the width of the metal, he could then de-duce the apparent angular breadth of the ob-ject. Huygens discovered also that an object


placed in the common focus of the two lensesof a Kepler telescope appears distinct andclearly defined. The micrometers of Malvasia,and later of Auzout and Picard, are the devel-opment of this discovery. Malvasia’s microm-eter, which he described in 1662, consisted offine silver wires placed at right-angles at thefocus of his telescope.

As telescopes increased in power, however,it was found that even the finest wire, or silkfilaments, were much too thick for astronom-ical observations, as they obliterated the im-age, and so, finally, the spider-web came intouse and is still used in micrometers and othersimilar instruments. Before that time, how-ever, the fine crossed wires had revolutionizedastronomical observations. “We may judgehow great was the improvement which thesecontrivances introduced into the art of observ-ing,” says Whewell, “by finding that Heveliusrefused to adopt them because they wouldmake all the old observations of no value. Hehad spent a laborious and active life in the ex-ercise of the old methods, and could not bearto think that all the treasures which he hadaccumulated had lost their worth by the dis-covery of a new mine of richer ones.” Until thetime of Newton, all the telescopes in use wereeither of the Galilean or Keplerian type, thatis, refractors. But about the year 1670 New-


ton constructed his first reflecting telescope,which was greatly superior to, although muchsmaller than, the telescopes then in use. Hewas led to this invention by his experimentswith light and colors. In 1671 he presentedto the Royal Society a second and somewhatlarger telescope, which he had made; and thistype of instrument was little improved uponuntil the introduction of the achromatic tele-scope, invented by Chester Moor Hall in 1733.

As is generally known, the element of ac-curate measurements of time plays an impor-tant part in the measurements of the move-ments of the heavenly bodies. In fact, one wasscarcely possible without the other, and as ithappened it was the same man, Huygens, whoperfected Kepler’s telescope and invented thependulum clock. The general idea had beensuggested by Galileo; or, better perhaps, theequal time occupied by the successive oscilla-tions of the pendulum had been noted by him.He had not been able, however, to put thisdiscovery to practical account. But in 1656Huygens invented the necessary machineryfor maintaining the motion of the pendulumand perfected several accurate clocks. Theseclocks were of invaluable assistance to the as-tronomers, affording as they did a means ofkeeping time “more accurate than the sun it-self.” When Picard had corrected the varia-


tion caused by heat and cold acting upon thependulum rod by combining metals of differ-ent degrees of expansibility, a high degree ofaccuracy was possible.

But while the pendulum clock was an un-equalled stationary time-piece, it was use-less in such unstable situations as, for exam-ple, on shipboard. But here again Huygensplayed a prominent part by first applying thecoiled balance-spring for regulating watchesand marine clocks. The idea of applying aspring to the balance-wheel was not originalwith Huygens, however, as it had been firstconceived by Robert Hooke; but Huygens’sapplication made practical Hooke’s idea. InEngland the importance of securing accuratewatches or marine clocks was so fully appre-ciated that a reward of £20,000 sterling wasoffered by Parliament as a stimulus to the in-ventor of such a time-piece. The immediate in-centive for this offer was the obvious fact thatwith such an instrument the determination ofthe longitude of places would be much sim-plified. Encouraged by these offers, a certaincarpenter named Harrison turned his atten-tion to the subject of watch-making, and, aftermany years of labor, in 1758 produced a springtime-keeper which, during a sea-voyage occu-pying one hundred and sixty-one days, var-ied only one minute and five seconds. This


gained for Harrison a reward of £5000 ster-ling at once, and a little later £10,000 more,from Parliament.

While inventors were busy with the prob-lem of accurate chronometers, however, an-other instrument for taking longitude at seahad been invented. This was the reflectingquadrant, or sextant, as the improved instru-ment is now called, invented by John Hadleyin 1731, and independently by Thomas God-frey, a poor glazier of Philadelphia, in 1730.Godfrey’s invention, which was constructed onthe same principle as that of the Hadley in-strument, was not generally recognized un-til two years after Hadley’s discovery, al-though the instrument was finished and ac-tually in use on a sea-voyage some months be-fore Hadley reported his invention. The prin-ciple of the sextant, however, seems to havebeen known to Newton, who constructed aninstrument not very unlike that of Hadley;but this invention was lost sight of until sev-eral years after the philosopher’s death andsome time after Hadley’s invention.

The introduction of the sextant greatlysimplified taking reckonings at sea as well asfacilitating taking the correct longitude of dis-tant places. Before that time the mariner wasobliged to depend upon his compass, a cross-staff, or an astrolabe, a table of the sun’s dec-


lination and a correction for the altitude ofthe polestar, and very inadequate and incor-rect charts. Such were the instruments usedby Columbus and Vasco da Gama and theirimmediate successors.

During the Newtonian period the mi-croscopes generally in use were those con-structed of simple lenses, for although com-pound microscopes were known, the difficul-ties of correcting aberration had not beensurmounted, and a much clearer field wasgiven by the simple instrument. The re-sults obtained by the use of such instru-ments, however, were very satisfactory inmany ways. By referring to certain platesin this volume, which reproduce illustrationsfrom Robert Hooke’s work on the microscope,it will be seen that quite a high degree of ef-fectiveness had been attained. And it shouldbe recalled that Antony von Leeuwenhoek,whose death took place shortly before New-ton’s, had discovered such micro-organisms asbacteria, had seen the blood corpuscles in cir-culation, and examined and described othermicroscopic structures of the body.

XIV. PROGRESS INELECTRICITYFROM GILBERTAND VONGUERICKE TOFRANKLIN

We have seen how Gilbert, by his experimentswith magnets, gave an impetus to the studyof magnetism and electricity. Gilbert himselfdemonstrated some facts and advanced sometheories, but the system of general laws was tocome later. To this end the discovery of elec-trical repulsion, as well as attraction, by VonGuericke, with his sulphur ball, was a stepforward; but something like a century passedafter Gilbert’s beginning before anything ofmuch importance was done in the field of elec-

367


tricity.In 1705, however, Francis Hauksbee began

a series of experiments that resulted in somestartling demonstrations. For many years ithad been observed that a peculiar light wasseen sometimes in the mercurial barometer,but Hauksbee and the other scientific inves-tigators supposed the radiance to be due tothe mercury in a vacuum, brought about, per-haps, by some agitation. That this light mighthave any connection with electricity did not,at first, occur to Hauksbee any more than ithad to his predecessors. The problem thatinterested him was whether the vacuum inthe tube of the barometer was essential to thelight; and in experimenting to determine this,he invented his “mercurial fountain.” Hav-ing exhausted the air in a receiver contain-ing some mercury, he found that by allowingair to rush through the mercury the metalbecame a jet thrown in all directions againstthe sides of the vessel, making a great, flam-ing shower, “like flashes of lightning,” as hesaid. But it seemed to him that there wasa difference between this light and the glownoted in the barometer. This was a brightlight, whereas the barometer light was onlya glow. Pondering over this, Hauksbee triedvarious experiments, revolving pieces of am-ber, flint, steel, and other substances in his ex-

XIV. PROGRESS IN ELECTRICITY 369

hausted air-pump receiver, with negative, orunsatisfactory, results. Finally, it occurred tohim to revolve an exhausted glass tube itself.Mounting such a globe of glass on an axis sothat it could be revolved rapidly by a belt run-ning on a large wheel, he found that by hold-ing his fingers against the whirling globe apurplish glow appeared, giving sufficient lightso that coarse print could be read, and thewalls of a dark room sensibly lightened sev-eral feet away. As air was admitted to theglobe the light gradually diminished, and itseemed to him that this diminished glow wasvery similar in appearance to the pale lightseen in the mercurial barometer. Could it bethat it was the glass, and not the mercury,that caused it? Going to a barometer he pro-ceeded to rub the glass above the column ofmercury over the vacuum, without disturbingthe mercury, when, to his astonishment, thesame faint light, to all appearances identicalwith the glow seen in the whirling globe, wasproduced.

Turning these demonstrations over in hismind, he recalled the well-known fact thatrubbed glass attracted bits of paper, leaf-brass, and other light substances, and thatthis phenomenon was supposed to be electri-cal. This led him finally to determine the hith-erto unsuspected fact, that the glow in the


barometer was electrical as was also the glowseen in his whirling globe. Continuing hisinvestigations, he soon discovered that solidglass rods when rubbed produced the same ef-fects as the tube. By mere chance, happeningto hold a rubbed tube to his cheek, he felt theeffect of electricity upon the skin like “a num-ber of fine, limber hairs,” and this suggestedto him that, since the mysterious manifesta-tion was so plain, it could be made to show itseffects upon various substances. Suspendingsome woollen threads over the whirling glasscylinder, he found that as soon as he touchedthe glass with his hands the threads, whichwere waved about by the wind of the revolu-tion, suddenly straightened themselves in apeculiar manner, and stood in a radical posi-tion, pointing to the axis of the cylinder.

Encouraged by these successes, he con-tinued his experiments with breathless ex-pectancy, and soon made another importantdiscovery, that of “induction,” although thereal significance of this discovery was notappreciated by him or, for that matter, byany one else for several generations following.This discovery was made by placing two re-volving cylinders within an inch of each other,one with the air exhausted and the other un-exhausted. Placing his hand on the unex-hausted tube caused the light to appear not


only upon it, but on the other tube as well. Alittle later he discovered that it is not neces-sary to whirl the exhausted tube to producethis effect, but simply to place it in close prox-imity to the other whirling cylinder.

These demonstrations of Hauksbee at-tracted wide attention and gave an impetus toinvestigators in the field of electricity; but stillno great advance was made for something likea quarter of a century. Possibly the energies ofthe scientists were exhausted for the momentin exploring the new fields thrown open to in-vestigation by the colossal work of Newton.

THE EXPERIMENTS OFSTEPHEN GRAYIn 1729 Stephen Gray (died in 1736), aneccentric and irascible old pensioner of theCharter House in London, undertook someinvestigations along lines similar to those ofHauksbee. While experimenting with a glasstube for producing electricity, as Hauksbeehad done, he noticed that the corks with whichhe had stopped the ends of the tube to excludethe dust, seemed to attract bits of paper andleaf-brass as well as the glass itself. He sur-mised at once that this mysterious electricity,or “virtue,” as it was called, might be trans-


mitted through other substances as it seemedto be through glass.

“Having by me an ivory ball ofabout one and three-tenths of aninch in diameter,” he writes, “witha hole through it, this I fixedupon a fir-stick about four incheslong, thrusting the other end intothe cork, and upon rubbing thetube found that the ball attractedand repelled the feather with morevigor than the cork had done, re-peating its attractions and repul-sions for many times together. Ithen fixed the ball on longer sticks,first upon one of eight inches, andafterwards upon one of twenty-fourinches long, and found the effectthe same. Then I made use of iron,and then brass wire, to fix the ballon, inserting the other end of thewire in the cork, as before, andfound that the attraction was thesame as when the fir-sticks weremade use of, and that when thefeather was held over against anypart of the wire it was attracted byit; but though it was then nearerthe tube, yet its attraction was notso strong as that of the ball. When


the wire of two or three feet longwas used, its vibrations, caused bythe rubbing of the tube, made itsomewhat troublesome to be man-aged. This put me to thinkingwhether, if the ball was hung bya pack-thread and suspended bya loop on the tube, the electric-ity would not be carried down theline to the ball; I found it to suc-ceed accordingly; for upon suspend-ing the ball on the tube by a pack-thread about three feet long, whenthe tube had been excited by rub-bing, the ivory ball attracted andrepelled the leaf-brass over whichit was held as freely as it had donewhen it was suspended on sticks orwire, as did also a ball of cork, andanother of lead that weighed onepound and a quarter.”

Gray next attempted to determine whatother bodies would attract the bits of paper,and for this purpose he tried coins, pieces ofmetal, and even a tea-kettle, “both empty andfilled with hot or cold water”; but he foundthat the attractive power appeared to be thesame regardless of the substance used.

“I next proceeded,” he continues,“to try at what greater distances


the electric virtues might be car-ried, and having by me a hollowwalking-cane, which I suppose waspart of a fishing-rod, two feet seveninches long, I cut the great end of itto fit into the bore of the tube, intowhich it went about five inches;then when the cane was put intothe end of the tube, and this ex-cited, the cane drew the leaf-brassto the height of more than twoinches, as did also the ivory ball,when by a cork and stick it hadbeen fixed to the end of the cane. . . .With several pieces of Spanish caneand fir-sticks I afterwards made arod, which, together with the tube,was somewhat more than eighteenfeet long, which was the greatestlength I could conveniently use inmy chamber, and found the attrac-tion very nearly, if not altogether,as strong as when the ball wasplaced on the shorter rods.”

This experiment exhausted the capacity ofhis small room, but on going to the country alittle later he was able to continue his experi-ments.

“To a pole of eighteen feet therewas tied a line of thirty-four feet


in length, so that the pole and linetogether were fifty-two feet. Withthe pole and tube I stood in thebalcony, the assistant below in thecourt, where he held the board withthe leaf-brass on it. Then the tubebeing excited, as usual, the electricvirtue passed from the tube up thepole and down the line to the ivoryball, which attracted the leaf-brass,and as the ball passed over it inits vibrations the leaf-brass wouldfollow it till it was carried off theboard.”

Gray next attempted to send the electric-ity over a line suspended horizontally. To dothis he suspended the pack-thread by piecesof string looped over nails driven into beamsfor that purpose. But when thus suspended hefound that the ivory ball no longer excited theleaf-brass, and he guessed correctly that theexplanation of this lay in the fact that “whenthe electric virtue came to the loop that wassuspended on the beam it went up the sameto the beam,” none of it reaching the ball. Aswe shall see from what follows, however, Grayhad not as yet determined that certain sub-stances will conduct electricity while otherswill not. But by a lucky accident he made thediscovery that silk, for example, was a poor


conductor, and could be turned to account ininsulating the conducting-cord.

A certain Mr. Wheler had become much in-terested in the old pensioner and his work,and, as a guest at the Wheler house, Grayhad been repeating some of his former exper-iments with the fishing-rod, line, and ivoryball. He had finally exhausted the heightsfrom which these experiments could be madeby climbing to the clock-tower and excitingbits of leaf-brass on the ground below.

“As we had no greater heightshere,” he says, “Mr. Wheler was de-sirous to try whether we could notcarry the electric virtue horizon-tally. I then told him of the at-tempt I had made with that design,but without success, telling him themethod and materials made use of,as mentioned above. He then pro-posed a silk line to support the lineby which the electric virtue was topass. I told him it might do bet-ter upon account of its smallness;so that there would be less virtuecarried from the line of communi-cation.

“The first experiment was madein the matted gallery, July 2, 1729,about ten in the morning. About


four feet from the end of the gallerythere was a cross line that wasfixed by its ends to each side ofthe gallery by two nails; the mid-dle part of the line was silk, therest at each end pack-thread; thenthe line to which the ivory ballwas hung and by which the elec-tric virtue was to be conveyed toit from the tube, being eighty andone-half feet in length, was laidon the cross silk line, so that theball hung about nine feet below it.Then the other end of the line wasby a loop suspended on the glasscane, and the leaf-brass held underthe ball on a piece of white paper;when, the tube being rubbed, theball attracted the leaf-brass, andkept it suspended on it for sometime.”

This experiment succeeded so well that thestring was lengthened until it was some twohundred and ninety-three feet long; and stillthe attractive force continued, apparently asstrong as ever. On lengthening the string stillmore, however, the extra weight proved toomuch for the strength of the silk suspending-thread.

“Upon this,” says Gray, “having


brought with me both brass andiron wire, instead of the silk weput up small iron wire; but thiswas too weak to bear the weightof the line. We then took brasswire of a somewhat larger size thanthat of iron. This supported ourline of communication; but thoughthe tube was well rubbed, yet therewas not the least motion or attrac-tion given by the ball, neither withthe great tube, which we made useof when we found the small solidcane to be ineffectual; by which wewere now convinced that the suc-cess we had before depended uponthe lines that supported the line ofcommunication being silk, and notupon their being small, as beforetrial I had imagined it might be;the same effect happening here asit did when the line that is to con-vey the electric virtue is supportedby pack-thread.”

Soon after this Gray and his host sus-pended a pack-thread six hundred and sixty-six feet long on poles across a field, thesepoles being slightly inclined so that the threadcould be suspended from the top by small silkcords, thus securing the necessary insulation.


This pack-thread line, suspended upon polesalong which Gray was able to transmit theelectricity, is very suggestive of the moderntelegraph, but the idea of signalling or makinguse of it for communicating in any way seemsnot to have occurred to any one at that time.Even the successors of Gray who constructedlines some thousands of feet long made no at-tempt to use them for anything but experi-mental purposes—simply to test the distancesthat the current could be sent. Nevertheless,Gray should probably be credited with the dis-covery of two of the most important propertiesof electricity—that it can be conducted and in-sulated, although, as we have seen, Gilbertand Von Guericke had an inkling of both theseproperties.

EXPERIMENTS OFCISTERNAY DUFAYSo far England had produced the two foremostworkers in electricity. It was now France’sturn to take a hand, and, through the effortsof Charles Francois de Cisternay Dufay, toadvance the science of electricity very mate-rially. Dufay was a highly educated savant,who had been soldier and diplomat betimes,but whose versatility and ability as a scien-


tist is shown by the fact that he was the onlyman who had ever contributed to the annalsof the academy investigations in every one ofthe six subjects admitted by that institutionas worthy of recognition. Dufay upheld hisreputation in this new field of science, makingmany discoveries and correcting many mis-takes of former observers. In this work alsohe proved himself a great diplomat by remain-ing on terms of intimate friendship with Dr.Gray—a thing that few people were able to do.

Almost his first step was to overthrow thebelief that certain bodies are “electrics” andothers “non-electrics”—that is, that some sub-stances when rubbed show certain peculiar-ities in attracting pieces of paper and foilwhich others do not. Dufay proved that allbodies possess this quality in a certain degree.

“I have found that all bodies(metallic, soft, or fluid ones ex-cepted),” he says, “may be madeelectric by first heating them moreor less and then rubbing them onany sort of cloth. So that all kindsof stones, as well precious as com-mon, all kinds of wood, and, in gen-eral, everything that I have madetrial of, became electric by beat-ing and rubbing, except such bodiesas grow soft by beat, as the gums,


which dissolve in water, glue, andsuch like substances. ’Tis also to beremarked that the hardest stonesor marbles require more chafing orheating than others, and that thesame rule obtains with regard tothe woods; so that box, lignum vi-tae, and such others must be chafedalmost to the degree of browning,whereas fir, lime-tree, and cork re-quire but a moderate heat.

“Having read in one of Mr.Gray’s letters that water may bemade electrical by holding the ex-cited glass tube near it (a dish ofwater being fixed to a stand andthat set on a plate of glass, oron the brim of a drinking-glass,previously chafed, or otherwisewarmed), I have found, upon trial,that the same thing happened to allbodies without exception, whethersolid or fluid, and that for that pur-pose ’twas sufficient to set themon a glass stand slightly warmed,or only dried, and then by bring-ing the tube near them they imme-diately became electrical. I madethis experiment with ice, with alighted wood-coal, and with every-


thing that came into my mind;and I constantly remarked thatsuch bodies of themselves as wereleast electrical had the greatest de-gree of electricity communicated tothem at the approval of the glasstube.”

His next important discovery was that col-ors had nothing to do with the conduction ofelectricity.

“Mr. Gray says, towards the end ofone of his letters,” he writes, “thatbodies attract more or less accord-ing to their colors. This led me tomake several very singular exper-iments. I took nine silk ribbonsof equal size, one white, one black,and the other seven of the sevenprimitive colors, and having hungthem all in order in the same line,and then bringing the tube nearthem, the black one was first at-tracted, the white one next, andothers in order successively to thered one, which was attracted least,and the last of them all. I after-wards cut out nine square pieces ofgauze of the same colors with theribbons, and having put them one


after another on a hoop of wood,with leaf-gold under them, the leaf-gold was attracted through all thecolored pieces of gauze, but notthrough the white or black. This in-clined me first to think that colorscontribute much to electricity, butthree experiments convinced me tothe contrary. The first, that bywarming the pieces of gauze nei-ther the black nor white pieces ob-structed the action of the electri-cal tube more than those of theother colors. In like manner, theribbons being warmed, the blackand white are not more stronglyattracted than the rest. The sec-ond is, the gauzes and ribbons be-ing wetted, the ribbons are all at-tracted equally, and all the pieces ofgauze equally intercept the actionof electric bodies. The third is, thatthe colors of a prism being thrownon a white gauze, there appear nodifferences of attraction. Whenceit proceeds that this difference pro-ceeds, not from the color, as a color,but from the substances that areemployed in the dyeing. For whenI colored ribbons by rubbing them


with charcoal, carmine, and suchother substances, the differencesno longer proved the same.”

In connection with his experiments withhis thread suspended on glass poles, Dufaynoted that a certain amount of the current islost, being given off to the surrounding air.He recommended, therefore, that the cordsexperimented with be wrapped with somenon-conductor—that it should be “insulated”(“isolee”), as he said, first making use of thisterm.

DUFAY DISCOVERSVITREOUS ANDRESINOUS ELECTRICITYIt has been shown in an earlier chapter howVon Guericke discovered that light substanceslike feathers, after being attracted to thesulphur-ball electric-machine, were repelledby it until they touched some object. Von Gu-ericke noted this, but failed to explain it sat-isfactorily. Dufay, repeating Von Guericke’sexperiments, found that if, while the excitedtube or sulphur ball is driving the repelledfeather before it, the ball be touched or rubbedanew, the feather comes to it again, and is re-


pelled alternately, as, the hand touches theball, or is withdrawn. From this he concludedthat electrified bodies first attract bodies notelectrified, “charge” them with electricity, andthen repel them, the body so charged not be-ing attracted again until it has discharged itselectricity by touching something.

“On making the experiment re-lated by Otto von Guericke,” hesays, “which consists in making aball of sulphur rendered electricalto repel a down feather, I perceivedthat the same effects were pro-duced not only by the tube, but byall electric bodies whatsoever, and Idiscovered that which accounts fora great part of the irregularitiesand, if I may use the term, of thecaprices that seem to accompanymost of the experiments on electric-ity. This principle is that electricbodies attract all that are not so,and repel them as soon as they arebecome electric by the vicinity orcontact of the electric body. Thusgold-leaf is first attracted by thetube, and acquires an electricity byapproaching it, and of consequenceis immediately repelled by it. Noris it reattracted while it retains


its electric quality. But if whileit is thus sustained in the air itchance to light on some other body,it straightway loses its electricity,and in consequence is reattractedby the tube, which, after havinggiven it a new electricity, repelsit a second time, which continuesas long as the tube keeps its elec-tricity. Upon applying this princi-ple to the various experiments ofelectricity, one will be surprised atthe number of obscure and puz-zling facts that it clears up. ForMr. Hauksbee’s famous experimentof the glass globe, in which silkthreads are put, is a necessary con-sequence of it. When these threadsare arranged in the form of raysby the electricity of the sides of theglobe, if the finger be put near theoutside of the globe the silk threadswithin fly from it, as is well known,which happens only because thefinger or any other body appliednear the glass globe is thereby ren-dered electrical, and consequentlyrepels the silk threads which areendowed with the same quality.With a little reflection we may in


the same manner account for mostof the other phenomena, and whichseem inexplicable without attend-ing to this principle.

“Chance has thrown in my wayanother principle, more universaland remarkable than the preced-ing one, and which throws a newlight on the subject of electricity.This principle is that there aretwo distinct electricities, very dif-ferent from each other, one of whichI call vitreous electricity and theother resinous electricity. The firstis that of glass, rock-crystal, pre-cious stones, hair of animals, wool,and many other bodies. The sec-ond is that of amber, copal, gum-sack, silk thread, paper, and anumber of other substances. Thecharacteristic of these two electric-ities is that a body of the vitre-ous electricity, for example, repelsall such as are of the same elec-tricity, and on the contrary attractsall those of the resinous electric-ity; so that the tube, made electri-cal, will repel glass, crystal, hair ofanimals, etc., when rendered elec-tric, and will attract silk thread,


paper, etc., though rendered elec-trical likewise. Amber, on the con-trary, will attract electric glass andother substances of the same class,and will repel gum-sack, copal,silk thread, etc. Two silk ribbonsrendered electrical will repel eachother; two woollen threads will dothe like; but a woollen thread and asilken thread will mutually attracteach other. This principle very nat-urally explains why the ends ofthreads of silk or wool recede fromeach other, in the form of pencil orbroom, when they have acquired anelectric quality. From this principleone may with the same ease deducethe explanation of a great numberof other phenomena; and it is prob-able that this truth will lead us tothe further discovery of many otherthings.

“In order to know immediatelyto which of the two classes ofelectrics belongs any body whatso-ever, one need only render electrica silk thread, which is known to beof the resinuous electricity, and seewhether that body, rendered elec-trical, attracts or repels it. If it


attracts it, it is certainly of thekind of electricity which I call vit-reous; if, on the contrary, it repelsit, it is of the same kind of elec-tricity with the silk—that is, of theresinous. I have likewise observedthat communicated electricity re-tains the same properties; for if aball of ivory or wood be set on aglass stand, and this ball be ren-dered electric by the tube, it willrepel such substances as the tuberepels; but if it be rendered elec-tric by applying a cylinder of gum-sack near it, it will produce quitecontrary effects—namely, preciselythe same as gum-sack would pro-duce. In order to succeed in theseexperiments, it is requisite that thetwo bodies which are put near eachother, to find out the nature of theirelectricity, be rendered as electricalas possible, for if one of them wasnot at all or but weakly electrical,it would be attracted by the other,though it be of that sort that shouldnaturally be repelled by it. Butthe experiment will always succeedperfectly well if both bodies are suf-


ficiently electrical.”45

As we now know, Dufay was wrong in sup-posing that there were two different kindsof electricity, vitreous and resinous. A littlelater the matter was explained by calling one“positive” electricity and the other “negative,”and it was believed that certain substancesproduced only the one kind peculiar to thatparticular substance. We shall see presently,however, that some twenty years later an En-glish scientist dispelled this illusion by pro-ducing both positive (or vitreous) and nega-tive (or resinous) electricity on the same tubeof glass at the same time.

After the death of Dufay his work was con-tinued by his fellow-countryman Dr. JosephDesaguliers, who was the first experimenterto electrify running water, and who was prob-ably the first to suggest that clouds mightbe electrified bodies. But about this time—that is, just before the middle of the eigh-teenth century—the field of greatest experi-mental activity was transferred to Germany,although both England and France were stillactive. The two German philosophers who ac-complished most at this time were ChristianAugust Hansen and George Matthias Bose,

45A letter from M. Dufay, F.R.S. and of the RoyalAcademy of Sciences at Paris, etc., in the Phil. Trans.of the Royal Soc., vol. XXXVIII., pp. 258-265.


both professors in Leipsic. Both seem to haveconceived the idea, simultaneously and inde-pendently, of generating electricity by revolv-ing globes run by belt and wheel in much thesame manner as the apparatus of Hauksbee.

With such machines it was possible to gen-erate a much greater amount of electricitythan Dufay had been able to do with therubbed tube, and so equipped, the two Ger-man professors were able to generate electricsparks and jets of fire in a most startling man-ner. Bose in particular had a love for the spec-tacular, which he turned to account with hisnew electrical machine upon many occasions.On one of these occasions he prepared an elab-orate dinner, to which a large number of dis-tinguished guests were invited. Before the ar-rival of the company, however, Bose insulatedthe great banquet-table on cakes of pitch, andthen connected it with a huge electrical ma-chine concealed in another room. All beingready, and the guests in their places about tobe seated, Bose gave a secret signal for start-ing this machine, when, to the astonishmentof the party, flames of fire shot from flowers,dishes, and viands, giving a most startling butbeautiful display.

To add still further to the astonishment ofhis guests, Bose then presented a beautifulyoung lady, to whom each of the young men


of the party was introduced. In some mys-terious manner she was insulated and con-nected with the concealed electrical machine,so that as each gallant touched her fingertipshe received an electric shock that “made himreel.” Not content with this, the host invitedthe young men to kiss the beautiful maid. Butthose who were bold enough to attempt it re-ceived an electric shock that nearly “knockedtheir teeth out,” as the professor tells it.

LUDOLFF’S EXPERIMENTWITH THE ELECTRICSPARKBut Bose was only one of several Germanscientists who were making elaborate exper-iments. While Bose was constructing and ex-perimenting with his huge machine, anotherGerman, Christian Friedrich Ludolff, demon-strated that electric sparks are actual fire—a fact long suspected but hitherto unproved.Ludolff ’s discovery, as it chanced, was made inthe lecture-hall of the reorganized Academy ofSciences at Berlin, before an audience of sci-entists and great personages, at the openinglecture in 1744.

In the course of this lecture on electricity,during which some of the well-known mani-


festations of electricity were being shown, itoccurred to Ludolff to attempt to ignite someinflammable fluid by projecting an electricspark upon its surface with a glass rod. Thisidea was suggested to him while performingthe familiar experiment of producing a sparkon the surface of a bowl of water by touchingit with a charged glass rod. He announcedto his audience the experiment he was aboutto attempt, and having warmed a spoonful ofsulphuric ether, he touched its surface withthe glass rod, causing it to burst into flame.This experiment left no room for doubt thatthe electric spark was actual fire.

As soon as this experiment of Ludolff ’s wasmade known to Bose, he immediately claimedthat he had previously made similar demon-strations on various inflammable substances,both liquid and solid; and it seems highlyprobable that he had done so, as he was con-stantly experimenting with the sparks, andmust almost certainly have set certain sub-stances ablaze by accident, if not by intent.At all events, he carried on a series of ex-periments along this line to good purpose,finally succeeding in exploding gun-powder,and so making the first forerunner of the elec-tric fuses now so universally used in blast-ing, firing cannon, and other similar purposes.It was Bose also who, observing some of the


peculiar manifestations in electrified tubes,and noticing their resemblance to “northernlights,” was one of the first, if not the first, tosuggest that the aurora borealis is of electricorigin.

These spectacular demonstrations had theeffect of calling public attention to the factthat electricity is a most wonderful and mys-terious thing, to say the least, and kept bothscientists and laymen agog with expectancy.Bose himself was aflame with excitement,and so determined in his efforts to producestill stronger electric currents, that he sacri-ficed the tube of his twenty-foot telescope forthe construction of a mammoth electrical ma-chine. With this great machine a discharge ofelectricity was generated powerful enough towound the skin when it happened to strike it.

Until this time electricity had been littlemore than a plaything of the scientists—or,at least, no practical use had been made ofit. As it was a practising physician, Gilbert,who first laid the foundation for experiment-ing with the new substance, so again it wasa medical man who first attempted to putit to practical use, and that in the field ofhis profession. Gottlieb Kruger, a professorof medicine at Halle in 1743, suggested thatelectricity might be of use in some branchesof medicine; and the year following Chris-


tian Gottlieb Kratzenstein made a first exper-iment to determine the effects of electricityupon the body. He found that “the action ofthe heart was accelerated, the circulation in-creased, and that muscles were made to con-tract by the discharge”: and he began at onceadministering electricity in the treatment ofcertain diseases. He found that it acted ben-eficially in rheumatic affections, and that itwas particularly useful in certain nervous dis-eases, such as palsies. This was over a cen-tury ago, and to-day about the most impor-tant use made of the particular kind of elec-tricity with which he experimented (the static,or frictional) is for the treatment of diseasesaffecting the nervous system.

By the middle of the century a perfect ma-nia for making electrical machines had spreadover Europe, and the whirling, hand-rubbedglobes were gradually replaced by great cylin-ders rubbed by woollen cloths or pads, andgenerating an “enormous power of electric-ity.” These cylinders were run by belts andfoot-treadles, and gave a more powerful, con-stant, and satisfactory current than knownheretofore. While making experiments withone of these machines, Johann Heinrichs Win-kler attempted to measure the speed at whichelectricity travels. To do this he extended acord suspended on silk threads, with the end


attached to the machine and the end whichwas to attract the bits of gold-leaf near enoughtogether so that the operator could watch andmeasure the interval of time that elapsed be-tween the starting of the current along thecord and its attracting the gold-leaf. Thelength of the cord used in this experimentwas only a little over a hundred feet, and thiswas, of course, entirely inadequate, the cur-rent travelling that space apparently instan-taneously.

The improved method of generating elec-tricity that had come into general use madeseveral of the scientists again turn their at-tention more particularly to attempt puttingit to some practical account. They were stim-ulated to these efforts by the constant re-proaches that were beginning to be heard onall sides that electricity was merely a “philoso-pher’s plaything.” One of the first to suc-ceed in inventing something that approacheda practical mechanical contrivance was An-drew Gordon, a Scotch Benedictine monk. Heinvented an electric bell which would ring au-tomatically, and a little “motor,” if it may be socalled. And while neither of these inventionswere of any practical importance in them-selves, they were attempts in the right direc-tion, and were the first ancestors of modernelectric bells and motors, although the princi-


ple upon which they worked was entirely dif-ferent from modern electrical machines. Themotor was simply a wheel with several pro-truding metal points around its rim. Thesepoints were arranged to receive an electricaldischarge from a frictional machine, the dis-charge causing the wheel to rotate. There wasvery little force given to this rotation, how-ever, not enough, in fact, to make it possi-ble to more than barely turn the wheel it-self. Two more great discoveries, galvanismand electro-magnetic induction, were neces-sary before the practical motor became possi-ble.

The sober Gordon had a taste for the spec-tacular almost equal to that of Bose. It washe who ignited a bowl of alcohol by turning astream of electrified water upon it, thus pre-senting the seeming paradox of fire producedby a stream of water. Gordon also demon-strated the power of the electrical dischargeby killing small birds and animals at a dis-tance of two hundred ells, the electricity beingconveyed that distance through small wires.


THE LEYDEN JARDISCOVEREDAs yet no one had discovered that electric-ity could be stored, or generated in any wayother than by some friction device. But verysoon two experimenters, Dean von Kleist, ofCamin, Pomerania, and Pieter van Musschen-broek, the famous teacher of Leyden, appar-ently independently, made the discovery ofwhat has been known ever since as the Ley-den jar. And although Musschenbroek issometimes credited with being the discoverer,there can be no doubt that Von Kleist’s discov-ery antedated his by a few months at least.

Von Kleist found that by a device made ofa narrow-necked bottle containing alcohol ormercury, into which an iron nail was inserted,be was able to retain the charge of electric-ity, after electrifying this apparatus with thefrictional machine. He made also a similardevice, more closely resembling the modernLeyden jar, from a thermometer tube partlyfilled with water and a wire tipped with a ballof lead. With these devices he found that hecould retain the charge of electricity for sev-eral hours, and could produce the usual elec-trical manifestations, even to igniting spirits,quite as well as with the frictional machine.These experiments were first made in Octo-


ber, 1745, and after a month of further ex-perimenting, Von Kleist sent the following ac-count of them to several of the leading scien-tists, among others, Dr. Lieberkuhn, in Berlin,and Dr. Kruger, of Halle.

“When a nail, or a piece of thickbrass wire, is put into a smallapothecary’s phial and electrified,remarkable effects follow; but thephial must be very dry, or warm.I commonly rub it over beforehandwith a finger on which I put somepounded chalk. If a little mer-cury or a few drops of spirit ofwine be put into it, the experimentsucceeds better. As soon as thisphial and nail are removed fromthe electrifying-glass, or the primeconductor, to which it has been ex-posed, is taken away, it throws outa pencil of flame so long that, withthis burning machine in my hand,I have taken above sixty steps inwalking about my room. When itis electrified strongly, I can take itinto another room and there firespirits of wine with it. If while itis electrifying I put my finger, ora piece of gold which I hold in myhand, to the nail, I receive a shock


which stuns my arms and shoul-ders.

“A tin tube, or a man, placedupon electrics, is electrified muchstronger by this means than in thecommon way. When I present thisphial and nail to a tin tube, which Ihave, fifteen feet long, nothing butexperience can make a person be-lieve how strongly it is electrified.I am persuaded,” he adds, “thatin this manner Mr. Bose wouldnot have taken a second electri-cal kiss. Two thin glasses havebeen broken by the shock of it. Itappears to me very extraordinary,that when this phial and nail arein contact with either conducting ornon-conducting matter, the strongshock does not follow. I have ce-mented it to wood, metal, glass,sealing-wax, etc., when I have elec-trified without any great effect.The human body, therefore, mustcontribute something to it. Thisopinion is confirmed by my observ-ing that unless I hold the phialin my hand I cannot fire spirits ofwine with it.”46

46Dean von Kleist, in the Danzick Memoirs, Vol. I.,


But it seems that none of the men who sawthis account were able to repeat the experi-ment and produce the effects claimed by VonKleist, and probably for this reason the dis-covery of the obscure Pomeranian was for atime lost sight of.

Musschenbroek’s discovery was madewithin a short time after Von Kleist’s—infact, only a matter of about two months later.But the difference in the reputations of thetwo discoverers insured a very different recep-tion for their discoveries. Musschenbroek wasone of the foremost teachers of Europe, andso widely known that the great universitiesvied with each other, and kings were bidding,for his services. Naturally, any discoverymade by such a famous person would soon beheralded from one end of Europe to the other.And so when this professor of Leyden madehis discovery, the apparatus came to be calledthe “Leyden jar,” for want of a better name.There can be little doubt that Musschenbroekmade his discovery entirely independentlyof any knowledge of Von Kleist’s, or, for thatmatter, without ever having heard of thePomeranian, and his actions in the matterare entirely honorable.

His discovery was the result of an acci-

p. 407. From Joseph Priestley’s History of Electricity,London, 1775, pp. 83, 84.


dent. While experimenting to determine thestrength of electricity he suspended a gun-barrel, which he charged with electricity froma revolving glass globe. From the end ofthe gun-barrel opposite the globe was a brasswire, which extended into a glass jar partlyfilled with water. Musschenbroek held in onehand this jar, while with the other he at-tempted to draw sparks from the barrel. Sud-denly he received a shock in the hand holdingthe jar, that “shook him like a stroke of light-ning,” and for a moment made him believethat “he was done for.” Continuing his ex-periments, nevertheless, he found that if thejar were placed on a piece of metal on the ta-ble, a shock would be received by touching thispiece of metal with one hand and touching thewire with the other—that is, a path was madefor the electrical discharge through the body.This was practically the same experiment asmade by Von Kleist with his bottle and nail,but carried one step farther, as it showed thatthe “jar” need not necessarily be held in thehand, as believed by Von Kleist. Further ex-periments, continued by many philosophers atthe time, revealed what Von Kleist had al-ready pointed out, that the electrified jar re-mained charged for some time.

Soon after this Daniel Gralath, wishing toobtain stronger discharges than could be had


from a single Leyden jar, conceived the idea ofcombining several jars, thus for the first timegrouping the generators in a “battery” whichproduced a discharge strong enough to killbirds and small animals. He also attemptedto measure the strength of the discharges, butsoon gave it up in despair, and the solutionof this problem was left for late nineteenth-century scientists.

The advent of the Leyden jar, which madeit possible to produce strong electrical dis-charges from a small and comparatively sim-ple device, was followed by more spectaculardemonstrations of various kinds all over Eu-rope. These exhibitions aroused the interestof the kings and noblemen, so that electric-ity no longer remained a “plaything of thephilosophers” alone, but of kings as well. A fa-vorite demonstration was that of sending theelectrical discharge through long lines of sol-diers linked together by pieces of wire, the dis-charge causing them to “spring into the air si-multaneously” in a most astonishing manner.A certain monk in Paris prepared a most elab-orate series of demonstrations for the amuse-ment of the king, among other things link-ing together an entire regiment of nine hun-dred men, causing them to perform simul-taneous springs and contortions in a man-ner most amusing to the royal guests. But


not all the experiments being made were ofa purely spectacular character, although mostof them accomplished little except in a nega-tive way. The famous Abbe Nollet, for exam-ple, combined useful experiments with spec-tacular demonstrations, thus keeping up pop-ular interest while aiding the cause of scien-tific electricity.

WILLIAM WATSONNaturally, the new discoveries made neces-sary a new nomenclature, new words and elec-trical terms being constantly employed by thevarious writers of that day. Among these writ-ers was the English scientist William Watson,who was not only a most prolific writer buta tireless investigator. Many of the wordscoined by him are now obsolete, but one atleast, “circuit,” still remains in use.

In 1746, a French scientist, Louis Guil-laume le Monnier, had made a circuit includ-ing metal and water by laying a chain half-way around the edge of a pond, a man at ei-ther end holding it. One of these men dippedhis free hand in the water, the other present-ing a Leyden jar to a rod suspended on acork float on the water, both men receiving ashock simultaneously. Watson, a year later,attempted the same experiment on a larger


scale. He laid a wire about twelve hundredfeet long across Westminster Bridge over theThames, bringing the ends to the water’s edgeon the opposite banks, a man at one end hold-ing the wire and touching the water. A secondman on the opposite side held the wire and aLeyden jar; and a third touched the jar withone hand, while with the other he grasped awire that extended into the river. In this waythey not only received the shock, but fired al-cohol as readily across the stream as couldbe done in the laboratory. In this experimentWatson discovered the superiority of wire overchain as a conductor, rightly ascribing this su-periority to the continuity of the metal.

Watson continued making similar experi-ments over longer watercourses, some of themas long as eight thousand feet, and while en-gaged in making one of these he made the dis-covery so essential to later inventions, thatthe earth could be used as part of the cir-cuit in the same manner as bodies of water.Lengthening his wires he continued his exper-iments until a circuit of four miles was made,and still the electricity seemed to traverse thecourse instantaneously, and with apparentlyundiminished force, if the insulation was per-fect.


BENJAMIN FRANKLINWatson’s writings now carried the field of ac-tive discovery across the Atlantic, and for thefirst time an American scientist appeared—a scientist who not only rivalled, but ex-celled, his European contemporaries. Ben-jamin Franklin, of Philadelphia, coming intopossession of some of Watson’s books, becameso interested in the experiments describedin them that he began at once experiment-ing with electricity. In Watson’s book weregiven directions for making various exper-iments, and these assisted Franklin in re-peating the old experiments, and eventuallyadding new ones. Associated with Franklin,and equally interested and enthusiastic, if notequally successful in making discoveries, werethree other men, Thomas Hopkinson, PhilipSing, and Ebenezer Kinnersley. These menworked together constantly, although it ap-pears to have been Franklin who made inde-pendently the important discoveries, and for-mulated the famous Franklinian theory.

Working steadily, and keeping constantlyin touch with the progress of the European in-vestigators, Franklin soon made some exper-iments which he thought demonstrated somehitherto unknown phases of electrical mani-festation. This was the effect of pointed bodies


BENJAMIN FRANKLIN


“in drawing off and throwing off the electricalfire.” In his description of this phenomenon,Franklin writes:

“Place an iron shot of three orfour inches diameter on the mouthof a clean, dry, glass bottle. By afine silken thread from the ceilingright over the mouth of the bottle,suspend a small cork ball, aboutthe bigness of a marble; the threadof such a length that the cork ballmay rest against the side of theshot. Electrify the shot, and theball will be repelled to the distanceof four or five inches, more or less,according to the quantity of elec-tricity. When in this state, if youpresent to the shot the point of along, slender shaft-bodkin, at sixor eight inches distance, the repel-lency is instantly destroyed, andthe cork flies to the shot. A bluntbody must be brought within aninch, and draw a spark, to producethe same effect.

“To prove that the electrical fireis drawn off by the point, if youtake the blade of the bodkin outof the wooden handle and fix it ina stick of sealing-wax, and then


present it at the distance aforesaid,or if you bring it very near, no sucheffect follows; but sliding one fin-ger along the wax till you touchthe blade, and the ball flies to theshot immediately. If you presentthe point in the dark you will see,sometimes at a foot distance, andmore, a light gather upon it likethat of a fire-fly or glow-worm; theless sharp the point, the nearer youmust bring it to observe the light;and at whatever distance you seethe light, you may draw off the elec-trical fire and destroy the repel-lency. If a cork ball so suspended berepelled by the tube, and a point bepresented quick to it, though at aconsiderable distance, ’tis surpris-ing to see how suddenly it flies backto the tube. Points of wood will doas well as those of iron, providedthe wood is not dry; for perfectlydry wood will no more conduct elec-tricity than sealing-wax.

“To show that points will throwoff as well as draw off the electricalfire, lay a long, sharp needle uponthe shot, and you cannot electrifythe shot so as to make it repel the


cork ball. Or fix a needle to the endof a suspended gun-barrel or ironrod, so as to point beyond it like alittle bayonet, and while it remainsthere, the gun-barrel or rod cannot,by applying the tube to the otherend, be electrified so as to give aspark, the fire continually runningout silently at the point. In thedark you may see it make the sameappearance as it does in the casebefore mentioned.”47

Von Guericke, Hauksbee, and Gray hadnoticed that pointed bodies attracted electric-ity in a peculiar manner, but this demonstra-tion of the “drawing off” of “electrical fire” wasoriginal with Franklin. Original also was thetheory that he now suggested, which had atleast the merit of being thinkable even by non-philosophical minds. It assumes that electric-ity is like a fluid, that will flow along con-ductors and accumulate in proper receptacles,very much as ordinary fluids do. This concep-tion is probably entirely incorrect, but never-theless it is likely to remain a popular one, atleast outside of scientific circles, or until some-thing equally tangible is substituted.

47Benjamin Franklin, New Experiments and Obser-vations on Electricity, London, 1760, pp. 107, 108.


FRANKLIN’S THEORY OFELECTRICITYAccording to Franklin’s theory, electricity ex-ists in all bodies as a “common stock,” andtends to seek and remain in a state of equi-librium, just as fluids naturally tend to seeka level. But it may, nevertheless, be raisedor lowered, and this equilibrium be thus dis-turbed. If a body has more electricity than itsnormal amount it is said to be positively elec-trified; but if it has less, it is negatively electri-fied. An over-electrified or “plus” body tends togive its surplus stock to a body containing thenormal amount; while the “minus” or under-electrified body will draw electricity from onecontaining the normal amount.

Working along lines suggested by this the-ory, Franklin attempted to show that electric-ity is not created by friction, but simply col-lected from its diversified state, the rubbedglass globe attracting a certain quantity of“electrical fire,” but ever ready to give it upto any body that has less. He explained thecharged Leyden jar by showing that the in-ner coating of tin-foil received more than theordinary quantity of electricity, and in conse-quence is positively electrified, while the outercoating, having the ordinary quantity of elec-tricity diminished, is electrified negatively.


These studies of the Leyden jar, and thestudies of pieces of glass coated with sheetmetal, led Franklin to invent his battery, con-structed of eleven large glass plates coatedwith sheets of lead. With this machine, afterovercoming some defects, he was able to pro-duce electrical manifestations of great force—a force that “knew no bounds,” as he declared(“except in the matter of expense and of la-bor”), and which could be made to exceed “thegreatest known effects of common lightning.”

This reference to lightning would seem toshow Franklin’s belief, even at that time, thatlightning is electricity. Many eminent ob-servers, such as Hauksbee, Wall, Gray, andNollet, had noticed the resemblance betweenelectric sparks and lightning, but none ofthese had more than surmised that the twomight be identical. In 1746, the surgeon, JohnFreke, also asserted his belief in this identity.Winkler, shortly after this time, expressed thesame belief, and, assuming that they were thesame, declared that “there is no proof thatthey are of different natures”; and still he didnot prove that they were the same nature.


FRANKLIN INVENTS THELIGHTNING-RODEven before Franklin proved conclusively thenature of lightning, his experiments in draw-ing off the electric charge with points led tosome practical suggestions which resulted inthe invention of the lightning-rod. In the let-ter of July, 1750, which he wrote on the sub-ject, he gave careful instructions as to the wayin which these rods might be constructed. Inpart Franklin wrote:

“May not the knowledge ofthis power of points be of useto mankind in preserving houses,churches, ships, etc., from thestroke of lightning by directing usto fix on the highest parts of theedifices upright rods of iron madesharp as a needle, and gilt to pre-vent rusting, and from the foot ofthese rods a wire down the outsideof the building into the grounds,or down round one of the shroudsof a ship and down her side tillit reaches the water? Would notthese pointed rods probably drawthe electrical fire silently out of acloud before it came nigh enough to


strike, and thereby secure us fromthat most sudden and terrible mis-chief?

“To determine this question,whether the clouds that contain thelightning are electrified or not, Ipropose an experiment to be triedwhere it may be done conveniently.On the top of some high tower orsteeple, place a kind of sentry-box,big enough to contain a man andan electrical stand. From the mid-dle of the stand let an iron rodrise and pass, bending out of thedoor, and then upright twenty orthirty feet, pointed very sharp atthe end. If the electrical stand bekept clean and dry, a man stand-ing on it when such clouds are pass-ing low might be electrified and af-ford sparks, the rod drawing fire tohim from a cloud. If any danger tothe man be apprehended (though Ithink there would be none), let himstand on the floor of his box andnow and then bring near to the rodthe loop of a wire that has one endfastened to the leads, he holdingit by a wax handle; so the sparks,if the rod is electrified, will strike


from the rod to the wire and not ef-fect him.”48

Not satisfied with all the evidence thathe had collected pointing to the identity oflightning and electricity, he adds one morestriking and very suggestive piece of evidence.Lightning was known sometimes to strike per-sons blind without killing them. In experi-menting on pigeons and pullets with his elec-trical machine, Franklin found that a fowl,when not killed outright, was sometimes ren-dered blind. The report of these experimentswere incorporated in this famous letter of thePhiladelphia philosopher.

The attitude of the Royal Society towardsthis clearly stated letter, with its useful sug-gestions, must always remain as a blot onthe record of this usually very receptive andliberal-minded body. Far from publishingit or receiving it at all, they derided thewhole matter as too visionary for discussionby the society. How was it possible that anygreat scientific discovery could be made by aself-educated colonial newspaper editor, whoknew nothing of European science except byhearsay, when all the great scientific minds ofEurope had failed to make the discovery? Howindeed! And yet it would seem that if any of

48Franklin, op. cit., pp. 62, 63.


the influential members of the learned societyhad taken the trouble to read over Franklin’sclearly stated letter, they could hardly havefailed to see that his suggestions were worthyof consideration. But at all events, whetherthey did or did not matters little. The fact re-mains that they refused to consider the paperseriously at the time; and later on, when itstrue value became known, were obliged to ac-knowledge their error by a tardy report on thealready well-known document.

But if English scientists were cold in theirreception of Franklin’s theory and sugges-tions, the French scientists were not. Buf-fon, perceiving at once the importance ofsome of Franklin’s experiments, took steps tohave the famous letter translated into French,and soon not only the savants, but membersof the court and the king himself were in-tensely interested. Two scientists, De Lorand D’Alibard, undertook to test the truthof Franklin’s suggestions as to pointed rods“drawing off lightning.” In a garden nearParis, the latter erected a pointed iron rodfifty feet high and an inch in diameter. As nothunder-clouds appeared for several days, aguard was stationed, armed with an insulatedbrass wire, who was directed to test the ironrods with it in case a storm came on duringD’Alibard’s absence. The storm did come on,


and the guard, not waiting for his employer’sarrival, seized the wire and touched the rod.Instantly there was a report. Sparks flewand the guard received such a shock that hethought his time had come. Believing from hisoutcry that he was mortally hurt, his friendsrushed for a spiritual adviser, who came run-ning through rain and hail to administer thelast rites; but when he found the guard stillalive and uninjured, he turned his visit to ac-count by testing the rod himself several times,and later writing a report of his experimentsto M. d’Alibard. This scientist at once re-ported the affair to the French Academy, re-marking that “Franklin’s idea was no longer aconjecture, but a reality.”

FRANKLIN PROVES THATLIGHTNING ISELECTRICITYEurope, hitherto somewhat sceptical ofFranklin’s views, was by this time convincedof the identity of lightning and electricity.It was now Franklin’s turn to be sceptical.To him the fact that a rod, one hundred feethigh, became electrified during a storm didnot necessarily prove that the storm-cloudswere electrified. A rod of that length was


not really projected into the cloud, for evena very low thunder-cloud was more than ahundred feet above the ground. Irrefutableproof could only be had, as he saw it, by“extracting” the lightning with somethingactually sent up into the storm-cloud; andto accomplish this Franklin made his silkkite, with which he finally demonstrated tohis own and the world’s satisfaction that histheory was correct.

Taking his kite out into an open commonon the approach of a thunder-storm, he flew itwell up into the threatening clouds, and then,touching, the suspended key with his knuckle,received the electric spark; and a little laterhe charged a Leyden jar from the electricitydrawn from the clouds with his kite.

In a brief but direct letter, he sent an ac-count of his kite and his experiment to Eng-land:

“Make a small cross of two lightstrips of cedar,” he wrote, “the armsso long as to reach to the four cor-ners of a large, thin, silk handker-chief when extended; tie the cor-ners of the handkerchief to the ex-tremities of the cross so you havethe body of a kite; which beingproperly accommodated with a tail,loop, and string, will rise in the


air like those made of paper; butthis being of silk is fitter to bearthe wind and wet of a thunder-gustwithout tearing. To the top of theupright stick of the cross is to befixed a very sharp-pointed wire, ris-ing a foot or more above the wood.To the end of the twine, next thehand, is to be tied a silk ribbon;where the silk and twine join akey may be fastened. This kite isto be raised when a thunder-gustappears to be coming on, and theperson who holds the string muststand within a door or window orunder some cover, so that the silkribbon may not be wet; and caremust be taken that the twine doesnot touch the frame of the door orwindow. As soon as any of thethunder-clouds come over the kite,the pointed wire will draw the elec-tric fire from them, and the kite,with all the twine, will be electri-fied and the loose filaments willstand out everywhere and be at-tracted by the approaching finger,and when the rain has wet the kiteand twine so that it can conduct theelectric fire freely, you will find it


stream out plentifully from the keyon the approach of your knuckle,and with this key the phial maybe charged; and from electric firethus obtained spirits may be kin-dled and all other electric exper-iments performed which are usu-ally done by the help of a rubbedglass globe or tube, and therebythe sameness of the electric matterwith that of lightning completelydemonstrated.”49

In experimenting with lightning andFranklin’s pointed rods in Europe, several sci-entists received severe shocks, in one casewith a fatal result. Professor Richman, ofSt. Petersburg, while experimenting during athunder-storm, with an iron rod which he haderected on his house, received a shock thatkilled him instantly.

About 1733, as we have seen, Dufay haddemonstrated that there were two appar-ently different kinds of electricity; one calledvitreous because produced by rubbing glass,and the other resinous because produced byrubbed resinous bodies. Dufay supposedthat these two apparently different electric-ities could only be produced by their respec-tive substances; but twenty years later, John

49Franklin, op. cit., pp. 107, 108.


Canton (1715-1772), an Englishman, demon-strated that under certain conditions bothmight be produced by rubbing the same sub-stance. Canton’s experiment, made upon aglass tube with a roughened surface, provedthat if the surface of the tube were rubbedwith oiled silk, vitreous or positive electric-ity was produced, but if rubbed with flannel,resinous electricity was produced. He discov-ered still further that both kinds could be ex-cited on the same tube simultaneously with asingle rubber. To demonstrate this he used atube, one-half of which had a roughened theother a glazed surface. With a single strokeof the rubber he was able to excite both kindsof electricity on this tube. He found also thatcertain substances, such as glass and amber,were electrified positively when taken out ofmercury, and this led to his important dis-covery that an amalgam of mercury and tin,when used on the surface of the rubber, wasvery effective in exciting glass.

XV. NATURALHISTORY TO THETIME OFLINNÆUS

Modern systematic botany and zoology areusually held to have their beginnings withLinnæus. But there were certain pre-cursors of the famous Swedish natural-ist, some of them antedating him by morethan a century, whose work must notbe altogether ignored—such men as Kon-rad Gesner (1516-1565), Andreas Cæsalpi-nus (1579-1603), Francisco Redi (1618-1676),Giovanni Alfonso Borelli (1608-1679), JohnRay (1628-1705), Robert Hooke (1635-1703),John Swammerdam (1637-1680), MarcelloMalpighi (1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort (1656-1708), RudolfJacob Camerarius (1665-1721), and Stephen

423


Hales (1677-1761). The last named of thesewas, to be sure, a contemporary of Linnæushimself, but Gesner and Cæsalpinus belong,it will be observed, to so remote an epoch asthat of Copernicus.

Reference has been made in an earlierchapter to the microscopic investigations ofMarcello Malpighi, who, as there related, wasthe first observer who actually saw blood cor-puscles pass through the capillaries. Anotherfeat of this earliest of great microscopistswas to dissect muscular tissue, and thus be-come the father of microscopic anatomy. ButMalpighi did not confine his observations toanimal tissues. He dissected plants as well,and he is almost as fully entitled to be calledthe father of vegetable anatomy, though herehis honors are shared by the EnglishmanGrew. In 1681, while Malpighi’s work, Anato-mia Plantarum, was on its way to the RoyalSociety for publication, Grew’s Anatomy ofVegetables was in the hands of the publishers,making its appearance a few months earlierthan the work of the great Italian. Grew’sbook was epoch-marking in pointing out thesex-differences in plants.

Robert Hooke developed the microscope,and took the first steps towards studying veg-etable anatomy, publishing in 1667, amongother results, the discovery of the cellular

XV. NATURAL HISTORY 425

structure of cork. Hooke applied the name“cell” for the first time in this connection.These discoveries of Hooke, Malpighi, andGrew, and the discovery of the circulation ofthe blood by William Harvey shortly before,had called attention to the similarity of ani-mal and vegetable structures. Hales made aseries of investigations upon animals to de-termine the force of the blood pressure; andsimilarly he made numerous statical experi-ments to determine the pressure of the flow ofsap in vegetables. His Vegetable Statics, pub-lished in 1727, was the first important workon the subject of vegetable physiology, and forthis reason Hales has been called the father ofthis branch of science.

In botany, as well as in zoology, the clas-sifications of Linnæus of course supplantedall preceding classifications, for the obviousreason that they were much more satisfac-tory; but his work was a culmination ofmany similar and more or less satisfactory at-tempts of his predecessors. About the year1670 Dr. Robert Morison (1620-1683), of Ab-erdeen, published a classification of plants,his system taking into account the woody orherbaceous structure, as well as the flow-ers and fruit. This classification was sup-planted twelve years later by the classifica-tion of Ray, who arranged all known vegeta-


STEPHEN HALES’S EXPERIMENT TO DETERMINE

THE PRESSURE OF THE FLOW OF SAP

(A branch, b, has been cut off and an open glass tubefitted over the end, the pressure being indicated by therise of sap in the tube)


bles into thirty-three classes, the basis of thisclassification being the fruit. A few years laterRivinus, a professor of botany in the Univer-sity of Leipzig, made still another classifica-tion, determining the distinguishing charac-ter chiefly from the flower, and Camerariusand Tournefort also made elaborate classifica-tions. On the Continent Tournefort’s classifi-cation was the most popular until the time ofLinnæus, his systematic arrangement includ-ing about eight thousand species of plants,arranged chiefly according to the form of thecorolla.

Most of these early workers gave attentionto both vegetable and animal kingdoms. Theywere called naturalists, and the field of theirinvestigations was spoken of as “natural his-tory.” The specialization of knowledge had notreached that later stage in which botanist, zo-ologist, and physiologist felt their labors to besharply divided. Such a division was becom-ing more and more necessary as the field ofknowledge extended; but it did not become im-perative until long after the time of Linnæus.That naturalist himself, as we shall see, wasequally distinguished as botanist and as zo-ologist. His great task of organizing knowl-edge was applied to the entire range of livingthings.

Carolus Linnæus was born in the town of


Rashult, in Sweden, on May 13, 1707. Asa child he showed great aptitude in learn-ing botanical names, and remembering factsabout various plants as told him by his father.His eagerness for knowledge did not extend tothe ordinary primary studies, however, and,aside from the single exception of the studyof physiology, he proved himself an indiffer-ent pupil. His backwardness was a sore trialto his father, who was desirous that his sonshould enter the ministry; but as the youngLinnæus showed no liking for that calling,and as he had acquitted himself well in hisstudy of physiology, his father at last decidedto allow him to take up the study of medicine.Here at last was a field more to the liking ofthe boy, who soon vied with the best of hisfellow-students for first honors. Meanwhilehe kept steadily at work in his study of natu-ral history, acquiring considerable knowledgeof ornithology, entomology, and botany, andadding continually to his collection of botan-ical specimens. In 1729 his botanical knowl-edge was brought to the attention of Olaf Rud-beck, professor of botany in the University ofUpsala, by a short paper on the sexes of plantswhich Linnæus had prepared. Rudbeck wasso impressed by some of the ideas expressedin this paper that he appointed the author ashis assistant the following year.


This was the beginning of Linnæus’s ca-reer as a botanist. The academic gardens werethus thrown open to him, and he found timeat his disposal for pursuing his studies be-tween lecture hours and in the evenings. Itwas at this time that he began the prepa-ration of his work the Systema Naturae, thefirst of his great works, containing a compre-hensive sketch of the whole field of naturalhistory. When this work was published, theclearness of the views expressed and the sys-tematic arrangement of the various classifica-tions excited great astonishment and admira-tion, and placed Linnæus at once in the fore-most rank of naturalists. This work was fol-lowed shortly by other publications, mostlyon botanical subjects, in which, among otherthings, he worked out in detail his famous“system.”

This system is founded on the sexes ofplants, and is usually referred to as an “artifi-cial method” of classification because it takesinto account only a few marked characters ofplants, without uniting them by more gen-eral natural affinities. At the present time itis considered only as a stepping-stone to the“natural” system; but at the time of its pro-mulgation it was epoch-marking in its direct-ness and simplicity, and therefore superiority,over any existing systems.


One of the great reforms effected by Lin-næus was in the matter of scientific termi-nology. Technical terms are absolutely nec-essary to scientific progress, and particularlyso in botany, where obscurity, ambiguity, orprolixity in descriptions are fatally mislead-ing. Linnæus’s work contains something likea thousand terms, whose meanings and usesare carefully explained. Such an array seemsat first glance arbitrary and unnecessary, butthe fact that it has remained in use for some-thing like two centuries is indisputable evi-dence of its practicality. The descriptive lan-guage of botany, as employed by Linnæus, stillstands as a model for all other subjects.

Closely allied to botanical terminology isthe subject of botanical nomenclature. The oldmethod of using a number of Latin words todescribe each different plant is obviously toocumbersome, and several attempts had beenmade prior to the time of Linnæus to substi-tute simpler methods. Linnæus himself madeseveral unsatisfactory attempts before he fi-nally hit upon his system of “trivial names,”which was developed in his Species Plan-tarum, and which, with some, minor alter-ations, remains in use to this day. The essenceof the system is the introduction of binomialnomenclature—that is to say, the use of twonames and no more to designate any single


CAROLUS LINNÆUS


species of animal or plant. The principle isquite the same as that according to whichin modern society a man has two names, letus say, John Doe, the one designating hisfamily, the other being individual. Similarlyeach species of animal or plant, according tothe Linnæean system, received a specific or“trivial” name; while various species, associ-ated according to their seeming natural affini-ties into groups called genera, were given thesame generic name. Thus the generic namegiven all members of the cat tribe being Fe-lis, the name Felis leo designates the lion; Fe-lis pardus, the leopard; Felis domestica, thehouse cat, and so on. This seems perfectlysimple and natural now, but to understandhow great a reform the binomial nomencla-ture introduced we have but to consult thework of Linnæus’s predecessors. A single il-lustration will suffice. There is, for example, akind of grass, in referring to which the nat-uralist anterior to Linnæus, if he would beabsolutely unambiguous, was obliged to usethe following descriptive formula: GramenXerampelino, Miliacea, prætenuis ramosaquesparsa panicula, sive Xerampelino congener,arvense, æstivum; gramen minutissimo sem-ine. Linnæus gave to this plant the name Poabulbosa—a name that sufficed, according tothe new system, to distinguish this from ev-


ery other species of vegetable. It does not re-quire any special knowledge to appreciate theadvantage of such a simplification.

While visiting Paris in 1738 Linnæusmet and botanized with the two botanistswhose “natural method” of classification waslater to supplant his own “artificial system.”These were Bernard and Antoine Laurentde Jussieu. The efforts of these two scien-tists were directed towards obtaining a sys-tem which should aim at clearness, simplic-ity, and precision, and at the same time begoverned by the natural affinities of plants.The natural system, as finally propoundedby them, is based on the number of cotyle-dons, the structure of the seed, and the in-sertion of the stamens. Succeeding writerson botany have made various modifications ofthis system, but nevertheless it stands as thefoundation-stone of modern botanical classifi-cation.

a history of science, - sandroid.org€¦ · fifteenth-century medicine . . 52 new beginnings in...

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