280 SCHOOL SCIENCE AND MATHEMATICS

depth and breadth of the science of Comparative VertebrateAnatomy. By making an intensive and somewhat exhaustivestudy of one phase of the course, he developed a greater degreeof respect for the science of Comparative Anatomy and therebyobtained a richer and more mature concept of science.

2. The students obtained a more comprehensive point ofview through coordinating and integrating their knowledge.This led to a more complete understanding of the ancestry ofman, of the orderly progress of the organic world; and of im-portant trends in Comparative Anatomy.

3. It provided the superior students an excellent opportunityfor self-expression.

4. The mechanics and technique involved in the preparationof the theses and the delivering of the lectures provides an in-tegration between the work of the departments of biology andEnglish.

5. The geology and paleontology involved in the studies of-fer an opportunity for the integration of work in the BiologicalSciences with that of the Physical Sciences.

6. Any study involving the progress of a science necessitatesa consideration of historical, sociological, and philosophicalfactors, and thus the Biological Sciences meet on a commonground with the Humanities and the Social Sciences.

MEASURING TO A MILLIONTH OF AN INCHWITH A POCKET HANDKERCHIEF

BY GEORGE WOOLSEYValencia High School, Placentia, California

Several years ago I attended a lecture given by Dr. Millikanin which he discussed relations between the wave and corpusculartheories of light. During the course of the lecture he demon-strated the formation of diffraction patterns by asking the mem-bers of the audience to look through their pocket handkerchiefsat two small lights on the speaker’s platform, one red and theother blue. He called attention to the fact that the red imagesare farther apart than the blue ones, thus giving a very simpledemonstration that the wave length of red light is greater thanthat of blue light.

It occurred to me that this experiment might easily be

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adapted to measure the wave length of light in a way whichwould be suitable for use in high school physics classes. Sincethen several classes have made use of the experiment for thispurpose. The method of using the experiment quantitativelyis this:

Bright lights are placed behind two small openings a fewcentimeters apart. These openings are covered with glass of thecolor of which the wave length is to be measured. When thestudent looks through his handkerchief at these lights at afairly close distance the pattern that he sees consists of twosets of nine images.

The student is instructed to back up until the two inner rowscoincide, thus making the distance between adjacent imagesequal to one half the distance between the apertures. The dis-tance between apertures and the distance from the openingsto the point of observation are measured. The number ofthreads per inch are next determined by means of a linen testermagnifier. With this data the student-is ready to compute thewave length of the light by means of the diffraction formula.The diffraction formula adapted for use in this experiment is

d~

2nl

where X=wave length in inches.d= distance between apertures.Z= distance from apertures to point of observation

(same units as d)n=number of threads per inch.

Representative data obtained by means of this experimentindicate the degree of accuracy which is likely to be attained.

X X %Light d I n (calcd) in.XlO-6 differ-

cm cm in.XlO"6 enceClear tungsten

filament 4.10 876 100 23.4 22.8 2.6Red 1.67 322 100 25.9 25.6 1.2Blue 1.67 346* 100 16.1 18.5 13.0

* Due to poor intensity of the blue light the two inner rows were not made to coincide but weremade as far apart as were the other rows. For this arrangement the formula becomes X =d/3nl.