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"TIIE

MODEL ENGINEER and ELECTRICIAN.

EDITED BY

PERCIVAL MARSHALL, A.I.Mech.E. Published every Thursday. Price Id. Post Free, 3d.

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r l•

a

The Model Engineer

Series No. 24

Small 6 Price D.

Net

flectrical Measuring Instruments

if Practical Handbook describing the making and using of Galvano-p meters, Voltmeters, Ampremeters, Wheatstone Bridges, and

other Instruments for detecting and measuring • Electric Currents

FULLY ILLUSTRATED

PERCIVAL MARSHALL & CO., LONDON, E.C.

Cro wn Svo. Cloth. Price T WO SHILLINGS NET.

Post Free, 2g. 3d.

Containing 166 pages, stlth 193 original Illtutrattens.

Practical Lessons ,7 IN

Metal Turning. A Handbook for Young Engineers and Amateur

Mechanics. SECOND EDITION

By PERCIVAL MARSHALL 4 (Associate of tha Instantloo of Mothermal Fag:news; First Homers I.

Mechanical Engineering, Medallist in Metal Working Tools, and Mitchell Scholar, City and Gmlds of London lentitow

Editor of The Model Bwrstrer)

CONTENTS. CHATTER L—TOOIS AND TOOL HOLDERS.

CHAPTER IL —MEASURING APPLIANCES.

CHAPTER IIL —CHUCKS AND M ANDRELS.

CHAPTER IV.—HO W TO CENTRE W ORK FOR THE

LATHE.

CHAPTER V. —DRIVING W ORK BET WEEN CENTRES. CHAPTER VL —TURNING W ORK BET WEEN CENTRES.

CHAPTER VIL —CHUCK AND FACE PLATE W OR K

CHAPTER WIL —DRILLING AND BORING IN THE LATHE. CHAPTER IX. —SCRE W CUTTING.

Every Amateur Mechanic and Engineering Apprentice should have this book.

PERCIVAL MARSHALL tt CO., 26.29 Poppin's Court, Fleet Street,

LONDON, E.C.

The " Model Engineer terms, No no

Model Steamer Building. A P.CIOA Handhr:t on the design and c instructEn of Modal

Stesincr Hulls, Deck FOlilltZ, sod -the, ALIN 64 Imes,

39 SA A irels cf Cc NI LA1S .—Cencrst thita on

Dungnink. coil. L1.1:11n, 11,1e1 StrimeiA--lhe CA A/Venetic/A of

Model Steno lunch 11111 fret t 3 bo 11 A kt-dcl Sicaindip

with Wooden full- rho C5'nstrucit3a if I M, I:1 M I-ea:

Destroyer— lel SIV3n Itissent,er Ftddle St. niner—rottino

for Model Tzri I: 1,1-

PERCIVAL MARSHALL et CO. 26 29 Poppin', Court,

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- I/ 1 1 5 • \15•11./ g E lee ,

\Iv .1. IA I cul, Ii t" I I/ 1r Ier MiLel I A Ind,

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Fleet Street, Lon Ion F C.

CONTENTS TA61

IMITRIIIIINTS TOR 1.A.S1144 Mr ItSENCT OF As LLLCIRIO CLIRRPNI, DLICAORS, G..icessourrrns, 7

INSTRUIII6VHD cOR MLA,UI)NO 1.-RISiUk% on QbANTIII .11 AN I-.11A.11,1,: el;PRCITI, A.MPIHEMbIBP4,

IN5TR0URVI,3 IOR Ifrasociso ResNrrscr, IN 1114.1.1STOXt Pripet, 26

ion Mist Inc SULU: 35

59 PRACIrAL Dri urs or CON,IIIICTIOI;

Tnr PRINUPLISS UTON suucii learenincer. NIetsuniso Issniumesrs Wore,

11,4 10 UAL VI rearm:cr. ‘Irsserri ...-

Issrpe.wercrs, .

42

(:1

How in elm**. 11.11:11.1CAL Unerrorusn I ssruunts . S4

PREFACE

Ina importance of a knowledge of the construction and us( of 1uc.1s.1run instruments to the worker in

the ever widening field of electrical enoncering

cannot I* 0501 -stin ILO 1k cnd monis to cm.

trot and bend to his will a class of appriatus or

or chinc which to all appearance ma) Le of 1,ertect

construction and yet refuses to work and fulfil the

function lot which it was designed A leakage of electivity does notlecomc, luke st;ram visible to the

eye, or hiss like compressed iii, the fault must, be

discovered by the aid of a suitable insti ument which

will indicate the presence or absence of an electric

current recoiding to the particuku ciretunstince ot

the case. The information in this book is intendyl

for those who will require to make simple tests and metsurements u hen buildnic; and using small.pouer

dynamos (-lulu) motets, or sirnilor inulnuen, and

fittin; up rust ill thous of clectir bells, teleplimus

and indicators or constructing and working with

inducticn coils and batteries

The designs and descriptions haNe been selected

from a number which lii e. appe from time to

1':

10 SMALL ELECTIdf ILL Manne r nesruertmers.

The wire used for the cods may le- either No 28 or 30 S W G covewd. About 0 iris. w the wire is passed through one ot the holes hi the ends of the reel, and this piece clamped with the thumb while the reel ni wound continuously in the slum direction until almost filled with tho wire Now pass the finishing end of the coil. through the other hole in the reel and temperanlv w lap the tiv, owls together The reel should now be steeped for ten iiiinetes in melted paraffin Nif Ix, after which it shiaild be Imeg up to allow the wax to drip and sot. The ends of the wires should now be untwistal and straight: ned out and then bared ot then covering fir a length of 1 in, at the ends This bared portico el the wne must be made clean and bright by sand-papering or soaping with an old penknife Ilw case is a piece of brass tubing, 3 ins. diameter

and 2 ins long, it is placed upon the base with its edge reshot; in the groove cut to weeive it, The reel is placed inside the Cibt, and secured to

the base, coils uppermost, by the aid of the little sprire; brass k-nces (fig 4) These are screwed to the base 1 in apart with thew longest part sertical, and the reel then forced between them. If the knees do not grasp the reel firmly, then upright pieces must he pressed slightly inn arils until they. de so }lg. 3 is a sectional view showing how the reel is held by the smuig knees. The ends of the coils are passed through the holes

in the base and then earned along the inside; of the grooves in the under side of base and finally well

TO DEILCI PRIISINCE OT A ClInIttla 11

twisted round the shanks of the binding-screws The binding-screws should base lock-nuts for clamping the Ri1C8, and these nuts must be removed to allow the wiles to be twisted around the shanks of the binding screws, and then replaced and screwed uo very tight Neither these lock ands nor any part of the shanks of the binehn,, screws should reach to the level of the under sulfate of the lase, and the groos cs for the wiles and lo:kin1LS should be deep enoui;h to allow these to sink about no or mere beneath the surface. The next part demanding our di-flit-ion is the

IA.:. krtus knee

Tie n—nacci.k of Lecl.

graduated circle This is a coadbeard circle 3 ins diameter and dixidect into degrees in the order 0 9% 0, 00, en either side of the tete line. This card is glued down upon a thin boxwood disc of the same, diameter as the e,ud in thick A needle pont is fixed in the centre of the disc

and earl, point upwards And should protrude about 1. in. frie small holes should le bored in the cud and disc to take a couple of very small round head brass screws foi fixing the disc and its card to the reel These screws should enter the sides of the re-il at the middle of their length and thickness and great care must be taken to mend the screws

•

4 12 SMALL TITIAIICAL ',MASHI NG IM MINENT%

coming into contact with the coils or their instils': mg cowling It should be observed dist tlat Aye line of thc graduated ciicle should he parallel to the length of the coils he magnetic needle is 2 in long, mid should be

pioxided at its cantle with an a,z•nc no 1 ip with

tic lilt::: sir G

which to pivot it on the needle point The iuistru-Ir,ent should be coward with glass to pieserve it from dusk te if possible, the realer shatild obtain a 3.m lens-mounting off a disused magic lantein or telescope, and fh a puce of 21 oz glass in the place originally occupied ty the lens The mounting will ho found to have suers threads cut upm it ; amidst threads shoull be cat on the inside of the

TO DFTFCT THE PRFSENCE or A CURRFNT 13 m

brass oase so that the glass top and its mounting can be screwed on. The instalment will now be complete and ready

for use 11 hen using the instrument, sin ays turn it round mitt' the needle points to /pro, the coils and the needle will then be in the in ignetic meridian, and will not be affected by the earth a maL,netism. A Sian ix 'Winn( 11 DYf FL 10F —The case is made

of well-seasoned cedar. in thick, and incasines outside 31„ ins by 3 ins bv 2 ins in clerdi The sides may te dxtailed te;Alier or fixed by brass curter plates let in flush with vbo solfuo of the weed (sae fig 6) A Mice ei sheet brass, in thick. is now cut to it inside the CASC. 11114

is fez the di it plate, and shoat. 1 be quite flit, as one side is to he •palaslicd to fix this plate in the Cls6 WO shill re-,aire a hole in each coiner to take screws screwed into the four corner pieces shown in fig. 6. rhe face of the dial should he in below the level of the case. The coils are wound on two formers made of

thin sheet. brass (see fig 7) which with all the other figuies (except fig 10, which is full sin is half sire The sue of the hole through the formers is 1i ins by one I in wide One flange is in wide all round and the other is in deepra on cno side, Ind also tuined up to form 4 foot. i in wide, by which the coils are seemed to the dial plate These formers no built up with the soldering iron, and - mat be neatly male and all ien;Miess in the , nit , 01_,, in I ctrucss c iietiilt mcatlie.1 elf

14 SMALL ELECTRICAL MEASIILING INSTRUMENTS

The formets should now be carefully insulated with thin silk, paying attention to the corners. A layer of thin brown paper, well shellac varnished, will do, if put on carefully The "gatintay'. %%tie should hut be pet OW It

consists of two layeis of No. 22 5 W silk-coveted, and leasing 6 ins out at each end lot connections Wind both formers exactly alike A 'Ayer of silk ribbon or thin brown parer is put over the,c r its,

and on top of them are wound the fine wire made up of seven or eight layers of No, er 10 silk-coveted coppei woe As this wiro is vciy fine and eisily broken, it is best to solder altt:zt 10 ins of thicket woe, wry, 22 to it, and nnatly wcap the jent with silk Leave Ault 6 ins oat fur comet-wits as before, and winding in the 891In) direction, and starting in the same place as Wong pat on the seven or eight I iyeis When finishing off, schler a piec-e of thicket vine on, so that the last three or four turns ale taken up by the thicker wile, leaving a length over for connections A layer of silk ribton round the coils will give a better finish to the job, and also mown the woe from being damaged. [he needle is made he'll a piracy of high quality

steel ins I trig, in wide: and 11G in. thick, filed to the shape shown in fig. 8 After being drilled with a k m hole in the centre, it is made a bright (hut), led in the fire or blowpipe flame, and immediately quenched in cold water Ibis harden-ing is neeessiay, or the needle would not retain its magnetism for any length of time The nefille is

1.•

•

TO DIIT4CT 11Tr TR MENCE or A CLERENT. 15 „

now to be magnetised (see Chap V) or should the maker know anyone who has charge of a motor or dynamo he will be able to get it done for 'Thank you,' and' bile you wait" Ihe pointer is now made to the shape slt, in in the view of the dial front (fig 9) It can be made of brass, ivory, bone, or aluminium; the lowei portion must be heavier than the top, 60 that the pointer always hangs vertically

/4. 7 —1 'IT an kriA C-.Iv.

Ii- S —Needle. 9 —Dot

The spindle is made. of -1-16-in. diameter silver steel .

Ion; enough to fit between the brackets, next to be described One end of the spindle is fitted with a pm of nuts , both ends ire panted and hardened. We now req,nre two brackets of in sheet lu ASS,

or they may be cast, one Trade to the sizes and shape shown in fig 10, which us full 7,116. and another 6 \SCIly similar, except that it is only ie in. high. A

16 SMALL ELECTRICAL MFASITRPTS INSTRUMENTt.

deametex steel screw is fitted in the rendre of each bracket, the ends of the screws being counter-sunk by dull, the cutting cd.ips of which am o at in ancje of 60 dcgs to each othen. fr. screws shoul I also lime a lock-nut, and be carefully Ind,limed The coils can now he fitted to the back ef tin! dill

plate. I in apart and the bracket s atterwaids the smaller one on the fame ml the 1€ i III Vi ii Coils on the l!L A (see fiL!! 11) Li ii II, I !!!! I and spindle ati out put int I pl I !it' 114_1 I

CD

ii 13 —lia t,.1 11 ,

needlua is adjusted to sw tipt in the it!! In. it the mil, and the painter just ele i of the di id ft 1, \ PI Ills of Mita U111(11 tie placed one Tit vi It I I III pointer. The spindle is ti ulatc 1 IiiII I •1 in the brackf ts to swing faci IN lint wit I 1 I. ,I1 I Ind fixed I -3 Ile li!Lk-nuk II 1,1 I ILL Oily t 0.11,r be eugr al, oi a a ik nit} Ii liv. 11) it by sicws We now take the r ase y WI and fix Once ter-

minals in the top and then Its tlic did plate with thc coils etc in position. The stutm; ends of enc fine wire coil and one thick wire coal of the same Loblin ate to tie connected to the outside terminals, one to

10 DRITC1 IRE PRESENCE or A CULAEST. 17 r

each, and their finishing ends ate to be paned respectaely to the starting ends of the coils on the other' bobbin, the remaining ends ate to be both connected to the middle terminal If you have, any difficulty with these connections or may lilac wound a coil in the wrong direction, they may be winked out experimentally with the aid of a b awry, laying one coil at a time (see Chap NI ft4 3g) A glass front and plain back are fixci to the case by countersunk views let in flush Nvith the iaa af the mood. and the ease ainclind at polished t3 suit the maker's taste or alalitia.. F',r a. small outlay we have now a gal-%linemen-1 which would cost up to a ;umea in the shops to use the instrument the quantity coils arc used when la-. 11- Caned. ),butiten inecsuring y I M -

inas as bittea cells: and the fine cods arc ItSPd for detecting leilizas on hue eyries etc. 'the instal-ment must net be luel on lain dy names or lattenes ot accumulatcis or the coils will be burnt out.

Sr:45111UL GAll.ANOVILIEE or smut r, CORSE UG-.10 \ — MIS is a useful galvinonnter far use with a Wheatstone ot metre brulae, or is a leak domain or tester, it is senhitave enoiqh to how a large deflection

'/

(0th ad

•

18 SMALL ELECTRICAL MEASURING INSTRISHICHTS

if a carbon .pd zinc plate are held in either hand—the hands being damp, end the plates, of course, joined to the terminals a the instrument by two wires, or a considerable movement will be observed if a silver coin is laid on the table, 4 drop of moisture Is placed on it, and the head of a steel screw made to touch the moisture It will show any qf the usual experiments, such as induced currents, thermic effects, etc,

FIG. 12 —The Complete Inatmment

The finished inslaument is shown (fig 12), it essentially consists of a wooden frame with aluminium sides carry in;:, 1000 turns of fine copper wire; in the centre of this frame is pnoted an agate centred ma,metao needle, this needle carries a light plater at neat an;les to it, which in turn main, a white paper aim at one end. This arm appears through one end of the central aperture, and shows the slightest movement of the magnetic needle upon a

TP PhTEC; THE rREShliCE 01, A CURRENT 19 "

ac4le The Seale Si ff be green or red paper, end then the pointer's movement can be distrnctly seen at a considerable distance off. In construct, take a piece of irr in sheet aluminium

(brass will do if lacquered after), cut two plates from it 4 by 1i and square the edges and round pff the comma, from the centre cut two slots 1! by (A, fig

OF

4' • ••( -- •

A

0

0

F°

ii l --11•11wcod Frame

13); these nraY b.9 cut ont with 3p ordinary het law 4m1 finished up vv-ith # smooth ale A hardwood frame is nqw made; the end pieces being 11 by 11 by ti n must be dc ad true rad square This hest done with file and square as if metel wa being worickcl, thus ivoidurg tho use of inictuiste planes and chisele The side peps I) may bc cut from thin

22 SMALL ELFXTRIDAL MEASIAING INSTRUMRNTS

evenly' Clit h light White paper pointer 1 in long by f in wide and stick it tri ,he bent Mid of the aluminium pointer

mece of cork is now c .; f in by 1 in by 1in, and a hue needle point broken off f in long is pushed into the centre of the cork, see that it stands (fl., 16) central and upright, glue the calk in the centre of the wood frame. taking (AM to keep

• all glue and dirt off the needle point. Cut a piece of 4reen or red paper lf ins hi f in wide rule a. cultist hue, and mark off similar hues every in apart as N fig 15 This is the scale. and is Muck on the plate which carries the terminals (as fig. 12) The needle may now be carefully mounted on its

centre, and should move very freely. To use the instrument, it is advisable to keep it permanently on a shelf or br acket made for it -and under .1 dust tight glass shads Run two light wires from the terminals along the walls to our work bench or experimental bench The pointer cal be brought to tem (the centre line) by pl wing a weak horseshoe or bar Magnet on the shelf it is advisable to set the galvanometer up about two y aids irom the table, and then there is no fear of any dam t action of electro. magnets, etc upon the needle if we ale experiment mg with these-

1!I

Olt

ClEIAPTFR II

INSTRUAIENIS TO Air VSCSA TNT PRTSSURT on QUANTTIV or AN Etscrkic Co mm' Vora-afEILRS AND AMInftTAIETTIS

TIM instrument here described may be made either as a voltmeter or as an amperemeter, the only differ-ence being in the winding of the coil The voltmeter is intended to read to 20 volts and

the amperemeter to 4 amperes The first part to be made is the base, which may

be cut from a piece of mahogany board 1 in. thick, and turned in the lathe to the shape shown in the drawings This could, however, be v ery easily made by using two thin ,pieces of wood, and cutting out, one of them with a fret-saw, then screwing it to the other and finishing off nicely with a file and glass paper The containing ease C C (shown in figs 17 Mid

18) is a piece of large brass tube, 4 ins in diameter and 2 ins long. Holes should be drilled around the circumference of this for the purpose of ventilation; and small countersunk holes for wood serewi at one end to fasten the tube to the Mined part of baseboard.

24

".\

•

I ii

24 SMALL RIF,CTRICAL MeASURING risninsizarrs

Ihe coaer ox outside urn R R (fig 17), which keeps the glass in position, is made from a length of 1 in brass tube, bent in s curie by hal& the two ends being soldeiod together. A ship of sheet biass is not procured in wide, and soldeied mound the edge of this tube, so as to be a snug fit on the outside of containing case (sec S S. hg 17). The glaso front can be taken from an old thrum clock.

Bliss -NSF

Fir U — S imiii mai, 1, ram tPI (501 owl Plan )

The botbm ccnstructel in the followinz manner 'Iwo pieces of fretwood being cbtamed 21. ins square. with the corners cut oft as in fig 18, tor thc hole is nest cut out of the middle of each and a piper tube 114 in thick, line ins dismc lei, 1 me lona made snd given' in these holes sa al. to tom s bobbin and when dry this is wound for use is i voltmetni with No 36 <o wn ceserul ccpper Mlle till neatly full. Pieces of wood are then cut to

TO MEASURE THE TRESSINT or A CURRENT 25 •

fit, and g,lund in each cornet of the bobbin as sup-ports (see nfotted lines in fig 18), the bobbin screwetl

--44 .0, on the base, and an ordinary wire nail (minus tho held) driven into the base at right hand side of paper tube (inside) as shown at W, fik., 18 '1 lie action is made from a piece of brass wile

*cif

"OA

(1,

/BOBBIN ;

TERMINALS

Tic 1R- --S,ctx,..n nk, rt Simpk :hind

about 4 in. thick and 1.4 ins len in cull end of which is dulled A small hole with a needle drill About it in, deep .,1n culinary fine pm (without tho head) is. soldered in inh end to u.t straight pivots (fig. 17) It is say neces,ary to have 4 gooa working fit in the bearings, and yet no binding. as, should the holes in bearings be a shade toa ei ton 511111,

CRAPTER III

DISH-1'ACR rb FOR MEASOF1XG FLCCFRIOAL RT.SISIANCE Fog WIIEtT.,10141? BRIDOR

iange ot the bridge to be descubed is from .1 to 999 ohms, but it may be used merely as a variable xesistance, the Simple Sensitive Galvanometer in ChIptFt 1, would he suitable for use% ith it The wile used for the resistances which constitute

the am mus arms of toe bride is No 26 s.n G. mangaiun wire The use of maugamn reduces to a minimum any eirors which may wise from changes of tempeiature, but the lengths of mange = given here mu.st not be strictly adhered to, owing to slight variations in the composition of inangamn. It will he nocessmy to rpt the specific iesistance of tho par-ticular alloy used, a hen the length of wire neces-

sary may be found from the foirmila !.4.

whew 11 18 the resistance, A the cross.sectional area of the wire used, and p the specific resistance, the result being divided by 30 48 to bung to feet Thus the specific resistance of the manganin used hero is 4 2000 The, efine the length of No 26 wire necessary

28

*I'

O MFASURE ELFCTII1CAL RF9ISTANCI. 29

to give 10 ohms iesistance is I= 10 x '00164 x 109 .T2.7c1617:-.i046

=128 ft. And the N al10118 resistances used in the box are

1 iesistance of 20 ohms = 256 ft. 9 millstone% „ 10 , each = 115 2 9 „ „ 1 „ „ = 11 32 9' , '1 „ 1 1E2 „ 2 2 , „ = 512 „

Therefore the total len„sth of wire i 15s r 92 The box is made hem i-in teak, and is 12 111S ly 9

Mb, by 3 ins, the top is 13 ins ty 10 ins, by g in., thus ON el lapping and giv-ing a better finish to tho box. The ot her material requiled is follows —Thu ty -

two brass studs of the kind shown in fig. 19, boen briss-

terminals (in this ,•"°••••..,,.,./zr.... (ASO of two diffeient Mac% which. IS mi)-be seen, adds to the rt. 19 —Bra. Stuls fa Rest.t,

appearance of thc box, although for all practical purposes they could equally well have all been of the same size) a piece of sheet brass, a length of brass wire, on which

Bildgc

30 saran. rtikeTrucar, MEASURING NSTRUMEITIL

to wind the resistances, a piece of ebonite from which to make the knobs for the keys and lovers, and brass nuts for the terminals and studs Ihe keys are made horn kin sheet braes, and

ale of the dimensions SfiCO714 in fig. 20. 4 hole is drilled and tapped through the terminal disc and key, into which a piece of brass wire is screwed, leaving about 1 in protruding from the under side This protruding piece is then sunk into the wood, thus

Etc 20 —Detael ci key foi Wheatstone

effectusily preventing the key from turning when the te-mmal head is screwed down All the other terminals are pinned down in the same manner. .Vt the end of each key is fixed an ebonite knob" by means of a small wind he,, led screw nail. the head of the screw nail ilso serving as a contact The othsr contacts foi the keys are. made by turning down a briss stud, until there is only about if, in left to project abose the top. The pins for the levers (fig 23) ate made from

pieces of 1-in dram brass wire 11 ins lung, bcFpy‘ed,.

TO MEASURE IOACTEICAL RESISTANCE

to take a ni.t at each end On the end of the uni which projects above the top, and just below the

thread, a piece of braes tubing is sweated, thus providing a shouldet to bear on a brass washer, otherwise a tluckel piece of wire would be necessary,

in

32 SMALL LLECTIU M MEASURING INSITUMLATS

and then it would iequile to be turned down The pus passes thiough the above-mentiontd washes, which has time holes dulled in it, to enable it to be screwed It the top and then tluough two hi ass w ushers on the inside of the box —one a fiat washes, and the other a sluing wahser , the burner to present the spun washes from eating into the wood and the latter to pit Ss against the Out to present it born tsumnii, when the level is moved oars the studs

The kver itself is made horn 5J in sheet lnass, bioad enough to span two studs mil haring On

hole dulled at one end. tint u.,11 as huh the pin passes The studs are bellow and are sexersed bath inside and out, the inside thread to take s pier( ef blass wits obollif, in diametes on which

the icsistamess ar wound Ha nn ... blind the necessaiy lent!th ts give tle-requnediesistance , it must be wound nonAnductis els —re it issuer Ix, mound en the donbl is SIICIVEL II; 19 one end beinc soldered to the wire on which it is wound and the other end connected to the nes( pie.:e of brass wire. Shellac smash or paraffin wax should be used unspariugb lot the resistance code rot shot t-cucuiting either the 20 ohm oi the

WhEotstano

Ji.

IL

no 23 —Detail of Lovers is Budge

73 MEASURE FLECITICAL RLSISfANCE 33 s

2-ohm resistance so as to make the mho aims equal, or as 10 1, two pieces of sheet topper are made as shown in the drawing, and sweated to the ends of a short length of flexible cord To use the budge, connect the battery, galvano-

meter, and the resistance to be measured, as shown in the diagram Make a rough estimate

&nes 1,6..3 II brt cb.

Warlar SprIns w..4e.

of the unknown ressstance and place the levers accordingl) aftenvuds moving them about until no deflection of the galvanometer is observed when both keys ire tipped Then if the 20-ohm resistance be short-circuited, so that the ratio arms no equal the. unknown resistance will be equal to the sum of the resistances in the sarious rheostats If the un known resistance be estimated at lases 100 ohms, short moult the 2 ohm se.sistance, making* the ratio

3

i ]

34 SEAL! TLECTRICAL MEASURING INSTRUMENTS

as 10 . 1 then the unknown les stance will be equal to ten times the sum 1 the osistaaces in the vat ions rheostats It will thus be seen that fca resistances over 100 ohms the degree of accmacy which can be attained is to 1 ohm, while for resist-ances less than 100 ohms a degree of accuracy can be attained to 1 ohm Hie reason why. by making the ratio as 10 . 1, the range of the bridge may be incioased sill be bettoi understood by comparing the wiring deigram (fig 21) with the diagram (fig 22) When there is no potential dal-1616nm b tween the pts. C audit then there will be no tendency for a current to flow along the woe connecting the gab a-nomotei with these points, and therelcie there will be no deflection of the galvanometer needle This happens when a=b and .e=fler when a is in the same ratio to 6 23 X is to ft The connections we shown in the genetsl anangernent, alio the manner in which the resistances we cannected although the resistances am only shown in one ot the rheostats still tho other resistances are connected in the rune way. While making s teat, the gala;nometer should if

possible b placed on a sepi_ate table so as to be as free horn vibra,ioo as possible, bit before cr.ti fleet ing it ks, bar, the". batten kcy should 1 e tipped, and if any deflection is ob,cived on the gal% anomotci it should be tiktn into .account, or the wiles lemling to the gdvinometer should be twisted together Also, the battery key should be tapped before the galvanometer key.

CHAPTER IV

INSTRIJMENTS Ion Musuu m STAIR, ELECTRICITY

GOLD Lriar ELECTROSCOPE —This instrument consists of the base (fig 24), into which fits the glass bell yar shown in fig 25 The top plate or table (fig 26) is struck from sheet brass in thick This can be cut to shape as near as possible with a back-saw, and having been • fitted with the kia brass wire

I To of kl,t1,4.011t.

seen in hg 26, turned up in the lathe Or it may be trued up with a filo and then fitted to the brass wire by soldering. Soldering is an easy matter when done in the right viav- Well clean the surfaces to be soldeied together by filing Mint quite bright, heat over the spirit lamp or Bunsen burner and use rosin as a flux, touch the centre of the brass plate with a stack of solder, and when the termer is

do

•

38 SMALL zurarmeal, MEASURING INSTALMENTS

of gum on the fiat sides of the rod and hold your breath for a moment, whilst the strips are taken up on a needle point and set in place on the rod. The strips may be cut by placing the gold leaf between a sheet of clean notepapet and cutting the notepaper into strips- This, of course, will cut the leaf at the same tune Place the yar in the groove in the base, and all is complete If propel ly made this elctroscote will le very sensitive, and should possess an excellent appearance

CHAPTER V

PRACTICAI DEI MS or CONSIST ,ION —MAGNUM-1NG 5bLIJ.ES, Snsknsiox I rariansc; DEVIt AND

10 'UM'S NL1GNCII0 ISEEDLVI — These are usually of lozem,-e ships and flat, not circular lic a iminz; needle though such a needle can be med. it is advisable to keep to the iecognised form Ihe needle must be made of steel which can It hardened iron or tin will not do Such matenal as steel watch and clock springs will do very well If you take a piece of old spring anneal it first by making at red bat and allowing it to cool slowly , if it is buried in lime or ashes it will cool more slowly than if exposed to the •an When filed to shape make the needle red mi and plunge it 1010 as itet to harden it, this hardening will make the steel very Mittle so that care roast be used in h,mdfing, but it is advisable to make the needle aeiy hard, lee ause the baldet it is the better will the ma,,metnni be re t lined, you can, however, re-magnetisc the needle any number of tunes should it become weak by loss of magnetism during use

89

V

•

42 SMALL ELECTRICAL MEASURING INSTRUMENTS

needle upon one of the poles of a dynamo, in this instance the magnet would be, of course, fixed and the needle moved, but the method of stroking always in one direction must be adhered to Supporting the needle — When supported on a

point, the centre of gravity of the needle must be below the points tip or it will not remain in positron, this is managed by fitting a little brass cup into a hole in the centre of the needle as shown in fig 31, taking care that the point comes well through the needle, the cup it, made with a slight shoulder, which is burred down over the needle after it has been slipped on. Note --it is of no use to attempt to magnetise

a needle whilst it is red-hot, or to harden it after it has been magnetised, heating it destroys the magnetism lieu LING SCDEWS.—For the purpose of setting a

galvanometer truly level, so that lho needle ITITS swing freely, attachments known as levelling screws are of ten fitted These consist of brass strips screwed to the base, each strip being drilled and tappe to receive a vet tical milled head screw (fig 32 shows such a levelling screw ), three are alw ays used. becaaso a body will rest firmly upon an uneven surface if supported upon three points, the Mass snips should be faxed at three equ Ili% -spaced intervals. as shown in the sketch (fig 33), s Inch represents a galvanometer base fitted with three levelling screws, the screws are placed with then points downwaids, by screwing any one up or down the instrument will be tilted

PRACTICAL DETAILS OR CONSTRUCTION 43. • at that place and very accurate levelling can be quickly attained, the dunensions are approximate, and may be altered tq slut any particular requtrements WINDINGS or lusTatrittsrs —These are not cal-

culated with the accuracy required for windings of dynamos and motors, except in some very special case the exact gauge of wire or quantity does not matter, the gauge is selected so is to be appropriate for the current which the mstrumt nt has to carry but any thing within several game, numbETs will do, if the instrument is to measure small currents -a fine gauge of wire is selected if it will be used to measure heavy in lents 'a coarse wire is selected it the instimnent es required for measuring both iv eak and heav 3 curientv two or three vandin„,s are sometimes put on the same instrument as in the case of the vertical detector described in Chapter I Far very heavy currents insulated fiat copper strip may take the place of wire, being 101141 up into a roil this is especially useful for amperemeters A coil of fine wire having, a great number of turns and carrying a very weak current has practically the sante power as a coil of similar sue consisting of few turns of thick sue but carrying i strong current If the coil does not have suffiment effect, wind on some more sue and try again, Silk covering is best for fine wires, but cotton covering will do

46 SMALL ELECTRICAL MEASURING INSTRUMENTS

instrument might be quite accurate enough for many purposes, especially as you would know the value of the readings Suppose you had graduated a voltmeter up to 10 volts by means of ten Daniell cells, you would know that each volt on your scale represented more than an actual volt; in fact, your 10. volt division would represent nearly eleven volts, and you would make allowance accordingly when reaeli Le. the scale-You will probably find that the needle moves a

much greater distance for an addition of one soh when in the middle of the scale than when near either end; this is a pocuhanty of certain types of instruments, the spaces from volt to volt can be divided up into divisions to show quarter and half ,olts by dividers, but the emu t positions should bear some relation to the general character of the stale; in the middr... of the scale the half volt will -be about cential between the volt divisions, but at the ends the hall volt will be rather more to the right or left, according to the amount the scale generally is opening out or shutting up AurrautitgrEas —The method of connection is

shown in fig. 35. and the instructions given for voltmeters apply to amperemeters also, but whereas to calibrate a voltmeter you need a very small current and a large number of cells, to calibrate an amperemetei you need only one en two cells, but thc y must be capable of gisang a lar4e current, as you must base the amperes required by the highest reading you are going to mark on the scale. The

PRACTICAL DRTAIIS or CONSTRUCTION 47

resistance must be of wire thick enough to carry the current Having conneeted the instruments m circuit

StawelonikrAzmad

8attely Ilegulateng Restseance

. Ix:: 35.

ohrp?reae}, don g teded

Z Oh 71e,, z..4..vee

Afloat toe lie JO

Indrumeat net v eas&01

kirrialu51.7lcsAllome

_Balky =-

adjust the resistance until the standard instrument reads, say. 1 ampere. then mark oft your division on the scale under test readjust the resistance until

•

48 ISMAIL ELECTRICAL MEASURING INSTRUMLSTS

the standard reads 2 amperes, and murk off the second di r ision, and 20 on, intermediate divisions can be marked if you can get a sufficiently fine adjustment of the resistance There is a method by which the standard ampere.

meter can be dispensed with provided you have your voltmeter ready, and this is as follows • obtain a length of wire of known resistance, say 2 ohms, and of thick enough gauge to carry the largest current your amperemeter is to take, connect it to a battery or dynamo so that it is in series wrth your amperemeter (see fig 36), and join your voltmeter to its ends; a regulating resistance is required to Nary the current By Ohm's Law the current flowing through the resistance will be equal to the volts applied to its ends divided by its iesistance in ohms as you know whit that iesistance is, and can see what the volts are at any given instant by means of the voltmeter you can calculate the amperes flowing through the amperemeter. Tor instance, if the voltmeter reads 10 volts the current would be 10 volts divided by 2 ohms (if the previously mentioned wire was used)=5 Amperes; you would therefore mark the ampere scale at the place where the pointer was standing as 5 amperes You do not need to know the \ohs of the battery exactly, but it is obvious that you must select your resistance to suit the curient to be measured and the volts of your battery

CHAPTER V1

Jur RUM MIES MON MERIT ELACIFIC AI MLASURING RUMTVIN \VOSS

Gar aLsowirrans —These instruments usually work by the attraction or repulsion of a magnetised needle placed near a wire carrying the °learn current, sometunes a second, wile, through which the current also passes, is used instead of the needle the wire is wound into a coil to incteaso the effect If you support a magnetised needle upon a pivot at its centre or suspend it by means of a fine thread so that it can freely turn round like a compass needle, and present one of the poles of a naamet to °abet end; that and will be atti acted to or reptile l from the magnet - like poles repel one another, unlike poles attract one another. When an electric current passes through a Nine, that wire becomes a ratort but its poks are at light angles to its lensth insteul of in the dim ec mon of its length, as in the case of the nivnetned needle or steel bar magnet, and these poles remain thus no matter whether the wire is kept in a straight length or wound up into a circular or flattened coil Unlike the steel bat ritinet !wat-

t,/ 4

50 SMAIL ELECTRICAL MEASURING METRO/4E4TV

ever. the N. and S poles are not permanently fixed, but may be respectively on one side or the other of the ware. accoiding to which way the current is sent along it If such a coil of wire is fixed in position and a

magnetased needle pivoted or suspended close to it so that one side of the coil can affect the needle when current is passed through the wire, such an arrangement will produce the same effect as the bar magnet refer id to did upon the suspended magnet-ised needle, according to winch end of the wire the current enters, so will the needle be attracted or iepellecl. If a light pointer is attached to the needle, the lattet with the coil can be enclosed in C ease, or the needle even placed inside the coil, as its ass emept weld be shown by the projecting end of the. Kamm It glair be considered that any coil of wire catrying a current is a guagnet as long as the [lucent flows. We shall now be able to understand the working of the galvanometers described on lrapter Taking fit stly the simple Gal% anoscope or Detector

In this instrument the magnet..ed needle is sup ported on a pivot directly over the coil of wire which (lanes the euirent, as soon as the current flows an ins isible magnet is mated by the lines of force set up by thc current, as indicated in fig 17 by the dotted hnetr, the i polo of the needle is attracted l)y the S pok of the magnet, and the & pole of the needle is attracted hi the N pole of the rorgnet, and the needle turns in t,he direction of the

4s,

THE RIIIHmELFR tryog willow INSTRUMENTS WOVE 51

arrows, the movement being assisted by the repelling action between the hlte poles of needle and nia;net respectively I! the current is sent through the coil of wire in a icverse direction, that ia. allowed to entei at the other end of the wile, the inveable magnet will also be created with rea eras poles. the Isf pole being where the a pole was tri the fast instance, consequently the needle will then move in the opposite duection, the gleatet the strength of the eta/lent the gmitar wll be the MON ement, of the needle Ilona thie ?me point In ;ft, instrument the deflection of the nee,* is not ,toily propothonal to the strength of the can iei,t . Li (=lent of h ill an ampere moves the needle throu,-,h ten decrees a movement of twenty clegiees will opt necessarily show that the current strength has increased to one empire, it will only mean that a larger cuirent is flowing through the coil, but will not indicate the amount (see Ch inter VIII.) In older that this instrument may work in this

m inner it is neeessaly that the needle rests in the position shown on fig 37, ES it is a magnetic needle, it will like s compass needle always ender; our to point north and south, so that you must twin the case of the instrument iound until the needle is in the collect position before bending cturent through the coil, if the needle lies across the coif you can readily see that the invisible magnet waft merely hold it in that position, and no indication of the cunent will take place VrarricAL DETEcros.—A galvanometei which is

THL I FINCH I ES LI ON NE HICH i\SikUtiIiiS NI CH It 53

52 strict P LLCTRICAI MFASUIsING INS1RLINIEE, Ts.

independent of the before-mentioneil necessity of satin; (ho ncedle in the it to pointy-1i can be made by pivoting the medic, sertioally insteul of horizon-tally, and tins is attained in the Veitical Detectoi des( tibed in Chapter I The principle on winch it vicaks is just tho same as that applying to (ho Hotizontil Gale inometet , instead, however, of 'dying open the magnetism of the earth ta retain the needle at the Ate position, it is kept. them by means of a weight ananged that, so long as the instrument i. placed on a keel suppott the needle will point, to zero when no cantent is flowing through the coils without the nee mity of placing it in a position facing north or south or any paiticular direction. The neeile is placed inside the mils of who fen convenience and as before must lie in the same directam is the sine, ashen an electric cuirent pissed through the coils an invisible Lu magnet

is piodtu cal as be h re—see dotted lines in fig OS, in win': Ii the coils are shown farthet apart than detnall used, to more clearly slow the needle The needle will be attaacted by the poles of the magnet in the direction indicated by the allows, when the current is sent through the coils of wire in '1 inverse dace ti.n the poles of the magnet, will be ics Erse(' and the net 1k will be defh (-led in the revetse thiection One cod only could he used and the action would

be the same but a bettei effect is pioduced by using a put of cells one on each side of the needle It will be been from this that IE is necessaty to so wind

the call4 that they assist each other, And do not

oppose, if they opposed each allot they would each ti) to create a magnet but having,. pols at opposite sides the iesult being that the two magnets would be hying the one to pull the needle one w ay and the sec and to pull it :in opposite direction, so that no deflection would be obtained This Frau * of opposing cods is used in an institunent teemed the Diffetential Gals anometet, t sepnate tumult being sent throu;h each coil the object be iii,., ti Ascettnn if the two currents are equal in stren,,;th, if they

I 1, 3'. s

ale so. the needle does not move but i one is stronger than the other, then it will ()rope vet the weaker coil m pi ipoitim to the difference 1,etwe en them, and the needle will give a deflection in one direction •ot the other Such an instrument is geneially only used in ads ant ,,t1 work and fot telegriph signalling ant except is in interesting example tried not be must& ted by the clementiry woikeo To return to out Ncitical Deteetae the dree:tion

of winding is shown in fig 35, if you should happen

54 SMALL Arsenate". MhAbURING MATIMMEMTS

to have wound one coil in the reverse direction there is no need to rewind it, but simply connect end B Instead of end A to end 0 of the first coil It is not usual to attach a separate balante.Weight- for the purpose of bringing the needle to the zero positron two methods are employed; either the needle is fixed 60 that, the aide on which it turns doesi not iS0 exactly through its centre, in winch case eine end will be heavier than the other Ad olisoys hang at the bottam, or the pointer is made with a weighted end (this is the better method), as shown in the illustration in Chapter I., which produces the same result It no essential that both coils and needle are vertical; if the needle is horizontal and the coils vertical, no deflection will be obtained When two sets of cods are weund as described in

Chapter I.. each set is quite independent of the other, and can be rep:Wed as if the other set did not exist, current no only sent through one set of coils at the same time Lhe Simple Sensitive Gals anometei works in the

same manner as the Detector shown in fig 1; the needle is inside the coil instead of being on the top, it is again essential for the needle to he in the same direction as the rods arid be preferably Set N.. and B, like a compass However. as explained in the directions for malung. as this is 4 very sensitive instrument, the needle can be brought to zero by the action of a weak magnet. Vorisirna-s tun Avirtsrmermis lhti principle

of the attraction and reptilsion between poles of

THE HtIRMIPLMI UPON WHICti Ifrendriticiete \Malt 65

rinignete (a niagnetilied needle is simply 0 bar magnet On a &Mill scale) is largely used for ainperemeters rind voltmeteris, these instruments being in leahty galvarioineters ceinstructed lot some definite kind of Measiireiiient; when Made on this principle they are known as electroinagriene instruments. In the voltmeter and amperemirter desenbed in Chapter II. the toil of ware attempts as in the galvanometers previonsly referred to to produce an invisible magnet passing through its centre• but as the two pieces of soft non AV and F have been placed inside it. the force of the coil is concentrated in them and - they become two small bar magnets whenever a current passes through the coil, the N. pole of W being at the same end as the N pole of F, and the S polo of W bean; at the &IMO end as the S pole of F. As neither magnet can turn round, these poles repel one another, consequently the movable magnet r thrust away from the fixed magnet W, the stronger the current flowing in the coil the more powerful will be these magnets and the greater the repelling effect It is to be noticed that the prnitiple of Attraction between magnetic poles is not used in these instruments, and that the es ales inagnetisni does not affect the moving magna, so that to bung it back to zero it me necessary H. add Some means of trintrol; this Is 'usually dotr., ...I means Of a spring of a weight In the in. ......eents described, a Small Weight is attacb•el to the spindle on which the moving magnet IlltAeS. So that the repelling frirce is compelled to lift the weight. It Will be seen front

.1

•

I;

l!'

56 SMALL TIZOPRIOAL MEASURING INSTRUMENTS

this that it is necessary to fix the instrument vettical and in one cettrin position only (see Chaptet \ II) Such an instrument is termed a gravity voltmeter oi ampciemetet because the force of gravity is used to control the movement of the needle When a spring is used instead of a weight, it takes the form of a watch hairspring threaded mei the spindle, to which the inner end of the spring is fixed; the other end being attiched to the bearing support (see t, 39); the rotation of tile siundlc

sp,ra Azurior•r]

coil

te ids to wind up the vring Such an instrument Lan to uset in aay position and is termed a spring-controlled voltmeter or ampmemeter the spring should tc. mule of a material which is not affected by magnetism, such as palladium or phosphor brows. There are other systems of movement in use fat voltmeters and ampetemeters , one is known as the Hot Wire system, in which a thin wire rs tightly stretched between 4 S)ste m of levers and tire curient pissing thritegh the wire heats it and Causes It to expand in length, per maim, one of the levers to move this movement is transferred to the

•MV•IR

As45

IRE PRINCIPINS UPON WHICH INSIEUMLNTS WORK 57

pointer by a link or gearing, the stiongei the current the mole the heat which is developed, 'emit hug in gteatel expansion of the wire, and therefote a laiget movement of the pointer. Another method is termed the Moving Coil system instruments of this class have a rectangular coil of very fine wire attached to the spindle, and ItlItIllged 60 that the edges of the coil par allel to the spindle move close to the poles of a pOWC i ful horseshoe steel magnet, the spnulle is controlled by a hairspring at eich end The current to be measuted is sent through one spring into the coil, and leaves through the spring at the other end the movement forms practically a magneto electric mote with a one cod armature. which turns through smaller or huge. angle according to the. strength of the current flowing through the cod Both Hot Wire and Moving instruments demand the Inghest class of workman; ship, they may be considered as too drincult for an amateur to construct, but being laigeo used, ate referred to as 4 matte' of ruttiest There is yet another (lass of voltmeters called

Electrostatic instruments; the,e depend for their action uuon the attraction effect between plates of metal which are st Wean) charged with electricity The moving plates are in the form ot vanes which move tear to the fixed plates and have the indicating pointer fixed to them the positive at i negative pales of the source of current 410 attached to the fixed and moving plates, one pole to c oh, no current flows a static charge only being created, ana in this

tr-•

62 SMALL ELECTRICAL MEASURLIO INSTRUMENTS

the insulated wise or metal, and one wire from the galvanometei to the metal which is in contact with the earth, by which is meant also us contact with any suppoit to which the metal is fixed m on which it rests 'earth' does not necessarily mean the ground If the galvanometer needle does not move, these is no leak, if it moves very slightly oi gives only a fault indication of moving, the leak is only

;1'4114 7 Galva/um:air rm. 40

partial, and is ptobably caused by moisture, so that, before unwinding the coil cis removing any wires, an attempt should be made to cliv up any moisture by was ruing the coil, sad then the test should be made again in order to ascertain if there is any impiove-ment If the needle moves quickly to one side and gives s large deflection. the leak is caused by metallic contact and is called a 'dead ear th ', no amount of (hying will remedy it, bqt the place must be sought foi and repail made,

HOW TO HSE ;14CCTEICAL stmaorino wsruntalttrys f/

To PirrEcT A PRE4K iiiA WIP:— Fig 41 sh9vm the eminectiona telt be coade when testing to find if a wire or coil of wire is without a hienk throughout Its length In the illustratmo a field magnet cod is being tested, one wire from the battery is piped to one end of the coil of wire, and one wire from the galvanometer is 401 4 to thp other encl,, if the needle moves quickly and gives a large deflection it

Fit 41

is a sign that there is no break in the wire but if there is on movement of the needle at all it shows that the wire is broken sonic:Theis or if thote, is a veil slight mmeinent it shows that the break is partial, such as might be caused by ti crack thiough the wise this test is termed a. continuity test, and Toy be 4enerally used to meet t,ain it circuits through switchboards, instruments, airangoolents of wires for lighting. etc are complete. IpENTITyINO IRE Pros or COILS, The

64 SMALL riven/0AL MEASURING 1,181RUMENTS,

principle of this test, which is really a continuity test, is illustrated in fig 42, which shows its appli-cation in sorting out the correct ends of a set of armature coils Imagine an armature which has been fitted with a new commutator, and that the disconnected ends have become mixed up so that you cannot tell by looking at them to which cod

they belong Apply the continual test by joining one wire hem the battery to the end of one coil, then, taking the free who from the detector t:alt nornotei in your band, touch the bared ends of all the other ca-Jo, one at a time, as soon as the needle moves you know you have found the °diet end of the coil to which the battery vine is joined To Drum/Ilse cur POLARIIY of A 13tarritv err

Dr./Me —In the fotejoing testa the ditection in

HMV '10 USE 111.11CIRIGAI DIRASURING INSTRUNIIINTS 65 "

which the needle meted did not affect the test, it was sufficient to note the absence or presence ot the deflection, MO did not iegune to note whether it moved to the right or the left hand, but in the test which we are now dealing with, it is thc direction in wind* the needle moves which is going to tell us what we want to know According to which way a cutient is sent through the coils of a gab, anomaei, so will the needle move to the iiht or left hand ThetNh there is no scientific reason to say that the (Intent leaves any particular terminal a a primary battery it is agreed, as a mattet of convenience, to always consider that the current leaves the battery hem the terminal which is connected to the carbon or copper plate and to call that the positive tumoral the zinc connected terminal lianig called thc negative terminal The first thud, to do, therefore, is to con inex t, one of the terminals of the galvanometer, it dote not matte' which to the cAlbon oi copper connected ektminal of a battery (en accumulator wall do if you brow which is the positive terminal, it is goneially marked with a or a red mark), and mark it with some dist-inguishm sc,,ii then touching the other terminal with the wire which is connected to the negative terminal of the battery, note in which thiection the needle mores, baying done this, you bay e an insti ument which will enable you to asceitaur tho pol ore) of any source of electric current, because when you connect the ;alimionietei to any terminals from which electric current CAR flow, if the needle moves in the direction in which it did when you

5

70 %NATI TIECTRICAI MFAqURING INSTRINUNTS

a faulty lamp or to want of volts; in this case the voltmeter becomes a shunt across the mains It may be, however, that this last lamp is connected to the mains by very long wires in a branch circuit., and that though there is correct pressure in the mains the lamp burns dull, you therefore connect the voltmetei as shown in fig 47 to find out if you haw dropped too many volts in the branch eiretut, the instrument is now connected as a shunt to the terminals of the lamp, and indicates the voltage at that It may be that the current is supplied by a

dynamo lighting, say, 5 lamps in series, each requiring 50 volts, the Nonage at, thr dynamo terminals mill therefore be 250 volts; the, last lamp is buinin„: dull, and you desire to blow if it is mo wing proper pres.sure, the voltmeter is to be connected as shown to the terminals of the lamp, and it will indicate the volts at that particuhr point horn one terminal of the lamp to the otbei Fig 48 shows a diagram of a 4-cell accumulator, and method of applying a voltmeter to test the voltage of one of the cells, the; wires from the voltmeter are pressed against the lead connecting straps at the ends of the positive and negative plates, scratching into the surface of the lead so as to get a good contact How TO USN AN ANOTRIOTETER — This instrument

is usually called an ammetei, the word being shortei and convenient to use Its use is to measure the current flowing through a circuit and it 19 always connected directly in the circuit through which the

•

72 artALI IttreTRICAI MFAMMPIG Disreumons

cuaient is flowing When used to measure the current taken by a motor, limp, or any piece of apparatus, the ammetei is always to he connected in scares with it. As the instrument should interfere as little as possible with the existini; conditions of the circuit, and should pound the current to pass heely without hindrance, its coils must have a wry- low resistance, on this account an ammeter should never be connected to the terminals of a

pannary battery glimekr or accumulator

to ascent = how much current such a bitter) will gne, unless yen desire to find out what the battery will do when short, crr

ofeewmado• CUltEd as the he 18

ammeter, having in exceedangly low resistance, will foim a short circuit. A large rummy latter) of low resistance, such as a bichromate or Bunsen cell, would discharge a very heavy eurient on %holt circuit. and the coils of the ammeter woad,' be probably burnt out if you ms-ha such a test and kft the instrument in ciicuit lox mo m thin a second im two Some ex maples of the use of an ammeter -are, to

measure Clio amperes flowing through (1) A main „aur a , c2) a Manch circuit ; (3) the normal working

s:4Wel

now ro use ro renu m mresinaNG INSTRUMENTS 73

current given by a dynamo oi battery , (4) the total current taken by a motor, (6) the volts at the ends of a known resistance, (6) the resistance of a wire or coil of wue rig 49 shows an ammeter connected in the main circuit of a dy namo lighting a number of lamps, the whole of the current passing to the lamps flows throuish the ammeter, which thus indicates, not the current taken by one limp or ty any particular lamp, but total the current taken by them altogether In fig. 50 the ammeter is shown as alianged to

ME1S1116 the current in e branch circuit which may consist of one or more lamps, or a motor ete, the instrument does not now take any notice of the current consumed by the lamps in the main circuit but only indicates how many amperes are passing through the branch circuit, another ex ample of the measurement of a branch circuit as ,axa n in fig 51 which shows the ammeter connected so as to measaue the mutat which is flowing through the shunt field coils of a dy namo: as in the previous case, the in-strument does net take any notice of the main current which is flowing to the lamps, but only Indic ates bow many amperes are passing into the field coils of the dynamo. Example .1"N o 3 is a case in which the condituris of the circuit must be adjusted to suit the nature- of the test You do not, as a rule repute to know what a batter) 01 dynamo will do if shoat-circuited, frit you do retinue very often to know whit current can be continually obtained as a winking rate To ascertain this, the first thing ta do is to apply a working load to the

74 sMAIJ 11114•TRICAI sirssmrso INSIRUURNTS

bittery OT dyn Imo to he tested either in the form of

limps or s woe reqstince, thou,11 Inv convenient method of prodding s lord (in te mlopted this

Nrc.

TIOW TO U4R PIVCIIUCAL. NYAKTRING INSTR OCCNTS 75

means that you must get some idea as to what the generator will stand in the way of (intent output unless you care to run the risk of damaging it through an overload Fig 62 shows the method of connecting the ammeter, the resistance represent-lug the load you adjust the load until the amphes indicated by the instrument represent the amount

Anzinder

flaut Orme/ Fru .."1

of =rent which the generrtoi ought to gire, and then continue the test as long es desired NC hen wire resistance is used you will find that of tel s short time the Lunent will fall this wry be owing to loss in the generatur but it ins', also be caused by increase of resistant e due to the passage of the current through the wire doYclopm; heat, so tliat before condemning the ;enexstor you should II) and bring the current up to its full value spin by

76 slIALL ELECTRICAL MEASURING INSTFUMINTS

cutting out some of the wire, this deciinse of the excess resistance pet nitting more cunent to flow

rl 52

.ilfaryrz Fir is

Example No 4 to measme the total cut lent. taken bya niotor Connect the anunetei in series with the motor, 35 shown in fig 53. it does not matte' whether

HOW 10 USE FL1.CTRICAL MNASURING INSTRUMENTS 77

you comma the ammeter to the positive oi nebatave main Example No 5 to measure the volts at the ends

of a known resistance ibis method depends upon the principle hid down by Ohm's law, that if you know the cunent in =pews which is flowing through a resistance whose v duo in ohms is known, then you can find out what me the volts at the ends of that resistmice by the formula L =CR ; that is the

Reststante Ohms

unknown voltace is equal to tho amperes multiplied by the resistance Fer instance suppose a battery whose wits are unknown is capable of dischaiging a current of, say, 4 or 5 :imptres; conue:t the terminals in scnes with a resistance of which you know the value in ohms (let its suppose it is 2 ohms), and with the =uncle' the ammeter indicates, say 3 amp( re* then 2 x 3=6; therefore the batter' is giving 6 Nolte ' As 3 rule, you know the s oltage which a battery will give by knowing the type and

78 SMALL ELECTRICAL MEASURING INSISUAIINIS

monk' of its cells, but this method may be very useful to find out the voltage which is at the ends of a coil of wire in a circuit which may also contain a number of other cods of wile, so that though you may know the volts at the ends of the circuit, you do not know the volts at any particular part The value of the resistance of the cod of wire is obtained either by reference to a wire-maker's table ot by means of a Wheatstone bridge, such as described it Lb apter III. It is importont to have the connecting wires AV of large section and as short as possible, so that thy carry the content very easily , if they ate small you will not get .a tine rosult, is some of the voltrgc will be absorbed befote tho current reaches the resistance In any case there will be al loss of volts in the wires VT W. but of they are thick and short it will be so small that you can neglect it - Example 6 to measure the resistance of a coil of vote .1 he principle of Ohm's law is again applied hue If you send a current of which you know the value in ampeies through an unknown resistance, you can find the value of this resistance in ohms provided you know tho volts at tho ends of that resistance, be-

cause R —E that is, the volts divided by the amperes (

wall tell you the ohms of the resistance The con-nections are mado as in fi„., 55 Suppose the voltage lb 100 volts and you find that a current of 2 amperes • is flowing through the lesistonce, then 100 volts divided by 2 ampetes gives 30 ohms as the iesistance of the coil of wire is in the previous example, it

now to tut sucTrucAL mustnum INS1SUMENTS. 79

it, important that the wires Joining up the resistance and ammeter are of ample sue. Fig 56 shows a switchboard for use with a dy namo

chaigong accumulators, the method of connecting the voltmeter and ammeter is shown, it will be seen that the voltmeter is connected as a shunt to the dynamo teams, and indicates the voltage where the current enters the switchboard, and that the ammeter is in series with the accumulators, so that it will

Ilea.dance =known-

JJauts 2Volblts

amotekr

measure the amperes passing into the cells It a regulating resistance us used on the switchboard then you will probably pude" to know the voltage it the terminals of the cells, as it does not matter what voltage the dynamo us giving so long as the right voltage it, at the accumulate' terminals, on tlois ease the Noltmeter wires would be Joined to terminals C instead of to the terminals D D It is sometunes desired to cut ammeters and

voltmeters out of circuits without disturbing the

60 SMALL /EXEC 1} DivitrUU5).75

cuiient flowing through the mains, this is acconi.

phshed in the following way — with in ammeter, by

means of a shoit circuiting plug , and with a volt-

meter ; by means of in open-enotutuig plug There

is a distinct difteioneo between the two methods

with M a rauder the plug arts as a by -piss thzough

which the (intuit flows instead of pine, into the

rig,. ,f1

instruments, with a oltmeten the plug opens the

voltaic tri a mine and cuts dr all (anent horn th

instrument Fi,i. 07 and 5S show the connections,

fl; 59 shows an enlarged view of the plug and bbs.k

which consists of a pan of hi iss blocks drilled with

taper bole into which fits a brass when tho

plug is pushed into the hole the two blocks ate

connected to,--ethet when it is taken out they ire

disconnected from one mothec

. 7,21.17.8

82 SMALL ELRCTIUCAL M ISCUING INSTRUMENTS

Ammeters and voltmeters must always be set so that their needles are pointing to /OM before any current is passing through them A gravity-con-trolled mati nment must be set upright—it will not iudicate in any other but a vet tical position, a spring-controlled instrument, on the contra)), can be used in any position (6eo Chapter VI ) Many instruments

ra

are very susceptible to outside influence of magnets or wares carrying currents so that it is well as a getter al rule to keep your msti uments away is fat as possible from a dynamo or cable. If 3 ou have any doubt is to whether the instrument is giving a true reading, cut off all current from it, and see if the needle moves when the dynamo is at work it is by no means unusual for an ammeter to nidicate several amperes

HOW 10 1AC rt.felincet MEASURING, II.STRUMENTS 88

without being connected to anythini; merely because it was neat the field magnet of a dynamo which was at work Some instruments only indicate when the positive

pole of the mains is connected to a particular one of then terminals, which means that the current must always pass tluon6h the instrument in ODO direction; in such a case the terminal is generally marked + , lint if. on trying an instrument, you find that it does not :give a movement of the needle, or the needle moves the wrong way, try changing over the com m. turns of your wires so th•A, the positive wire will be connected to the other terminal

HOW TO CHOOSS in icuulastu, 85

CHAPTER VIII

How 10 CHOOSE hIlk ITICA1 MEASURIN4 INS1h1 815515

IN order that -an mitt =cut should be of maximum usefulness it should he selected with reteience to the particular range or class ot IIIE-35incnitnt in which you desire greatest. accuracy All insti =outs have their limitations; semi are much better adapted for certain work than others, and the following hints will assist the leadca to make his choice GAL V Vs01ILTEJ.S tough work, such as detect •

ing Laments when making apparatus in the woikshop, a simple holizontal pattern with pivoted needle and scale (landed into degrees will suffice; but if the tune taken up in testing is important, a veitical pattern deter tot galvanometer with weighted needle is bettei, is the needle of the horizontal pattern swings about great deal, so that 3 cur may have to w ait some little time before it conies to rest at the zero position, the vertical detector pattern is also more useful for out door work or testing wiring in a house, as it does not termite setting to tem and is mote poi table When very minute currents ieguire to be detected, and for

84

delicate testing genoially, the astatic pattern of galvanometer is regrired, in which the needle is suspended by means of a single thread of cocoon silk. There me various patterns of this instrument, that known as the Thompson Reflecting Galvano-meter being a recognised type In this instrument there is a very small mirror fastened to the needle, winch itflects a beam of light from a lamp upon a horizontal scale fixed about three feet or so in front of the instrument; when the needle Mustfi the mu m moves also and the beam of light becomes mall) a long pointer, having no weight and moving over the scale, the 1111ild3 of a wire in the beam form. mg the indicating point. 1 hem is also another type of i;ilv anometer suitable

for very delicate work_ In this class of instrument a needle fitted with a h;lit pointer is pivoted inside a single coil of wire The sensitive 6advanometei described in Chapter I is of this type and may be considered as a sufficiently delicate institiment for all oidinaly purposes. One objection to the delicate galvanometem just described IS, that their needles swing veiy much before coming to rest at the zero maik—they are not what is called dead beat Where rapid delicate testing is desired. it is very

desuable that the instrument should be dead beat There lb a type of instrument in which the coil cculy-ing the etuient is suspended by stretched delicate wares so that its sides move near the poles of a powerful steel horseshoe ma;net Ibis kind of galvanometer is called a D'Arsonval pattern, after

88 swam. ELECTRICAL IITEASURPIG m um mers HOW 10 MOOSE INSTROMENIS 89

methods employed little vane moving in oil or an air cylinder may be attached to the spindle But there 16 one class of instruments termed Moving Cod ammeters and voltmeters which are automatically dead beat by vertu° of the principle on which they are constructed In these instruments a small coil of wire attached to the pointer moaes near the poles of a powerful steel magnet; they are very sensitive, not much affected by outside magnetic influence, and are suitable for very accurate measurements, but they can only be used for continuous ...anient work Vol 711F1 FRS FOR TESTING BA I I rams — High

iesistance batteries such as small chy cells are not c•apst le of vying a large cur rent , if you desire to test such cells by measuring their volts it 18 necessary to use a a el tineter which has a compliativEly high resist • IliCh, or else the instrument will draw more cunint out of the cell than it gives in rearlar work con-sequently its voltage will fall, and you do not get a fan. test. You should therefore be careful to see that your voltmeter is adapted for this particular class of work if you wish to get accurate results; do not accept a casual test with any soltmeter as ea rdence of the condition of such a cell, Batteries such as the &chromate pattern or an accumulatoi may be safely toted with any ordinary voltmeter as they will give a fair amount of current AiseeNATivo Cum.VisT INsTRU611 Iv TS —Testing of

insulation, the conductivity of wires and MC19111e. ments of a similar character, are generally done with continuous eminent, in the case of alternating

eminent you require to measure amperes and volts,

ae watts or electric powei which in alternatingcunent week is not always found by multiplying

together the volts and ampules as in the ease of continuous cuircnt, whenever the current is flowing through any apparatus having coils of wire or electro-magnets in the enema such as a motor or transformei, you would not i4et the watts by merely multiplying the amperes and volts together, though your result would be fairly correct in the case of alternating current 14-;htang incandescent lamps. Whilst some types of ammeters awl voltmeters are specially suit-able for use wit-h alternating current, instruments of similar principle to those described in Chapter II can be used with either alternatini; or continuous cur rent. When intended fel use with alternating current they are tested with that- kind of current and marked accorrlin,Ty but it a continucms-cuirent mstrument is used with alternating current it will probably, in the ease of types as described in Chapter IT, in-dicate about 10 per cent. less than the true reading, espe, tally it it n aoltmeter, Unless the instrument has been made with a view to mete the alternating current it will get hot ,miter a short time, so should only be used for a few moments at a stretch. In instruments desined for alternating current. if the ecul is wound on a metal bobbin, the metal must be drawled at one place by means of a saw, cut so that the centre and flanges do not form a complete ring WATTAlt:11:RS are instruments for measuring

electric power, and they automatically multiply the 7

To 6 MODEL ENGINELR" SERIES No 3 EDITED Mt PERCIVAL MARSHALL, A I Maui, F

Electric Bells and Alarms. Srsrniu Entitov

Br F E. POWELL

Mush Wed Ivan numerous Engrantngs and ()puma! Drawings.

CONTENTS —Preface Chaptcr I —Electra° Bells ; Pianciples of their Construction ' Venous T)pcs ; Single Stroke , Continuous Ring ing , Bracket , MagnctoBells II —Batteries Leclanche, Sealed; Carporoes , Agglomerate, Dry, How to Connect up the Cells, Wire III —Pushes, Switchea, Burglar Alarms, Door Tnggers, Indicators , Relays. IV — How to Install Electric Bells V —Examples of Special Bell Circuits; Connections to ' Earth" VI —Electnc Clock 41arms VII —Faults and Repairs; Hints on Testing , Battery and Bell ; Current Detectors, How to keep the Battery in Ord&

"Tto Mont Etter/11,ER" Sums No 4

TELEPHONES AND mllet-JePlitoives • • HO W TO MAKE AND FIX THEM.

EDITED BY

PERCIVAL MARSHALL, AT Mech.E. —

Fishy Illustrated with Onfonal Diagrams and Drawings - --- —

FIFTH HOIT1014.

CONTENTS —Preface Chapter I.—The Pnnmples of Tele phone Construction II —Microphones and How to Make Them III —How to Make a Simple Telephone IV —How to Make and Fix a Wall Telephone V —How to Make a Desk Telephone. VI —Telephone Circuits ; 'Test ng, Faults and Repairs, Battenes Wires Insulators , Earth Connections VII —Modern Types of Domestic Telephones.

From all Agents for viii tiOr L I.NGINEFIl,pove ed. nett on. pera free d from

PERCIVAL MARSHALL & CO., 26-ae Peppin'. Court, Rant street, LONDON, B.C.

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iles I littler. By W Graftrn 143 Illustr I ne hen Foetal, 44 50 00

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Mechanical Engineering Meterlais By Edward C R. Marks A M I C B M I 11.P Past .. 04 Is fid

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Locomotives of the L B & S C R A complete history of all the l000mo lives of the LB d SC R h om 1.7 to the present day 144 altostrati ... from Drawings and Photogra ys es cry engine ill.tratad and de..cribsid Poetage 9d 5. ad

LocoMotive Engine Driving By Michael Reynolds A Practical Manuel for Ensin .rs in charge of Locomotive Engin . Eleventn edition in eluding a Key In IS, Locomotive Fngine Crown live Cloth Pon age 44 . td

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Lockwood • Diet; o aaa of 1 1.-1,1.40 Eng, ,,s . in s- Tri m. By Horner, A %I (ALL. Cry, e .00 -1 63013 1,f, 30,0 Third El fon rts...ee sidi Irtres -r the Den.Ing Ofneo Patti. n Sh ry. I r., n1 rot. L I' a. a. Snieht 001 Bo, er chop., etc etc Cr .....n c, C 43. 7. Id

s Marine Engineer s Pocket book Ds A C Wenner, C H. C -.Mount • latcht Baird T ale Roles and Daa •-• 12 ,1neers Third Edit or, re,leed enkreed 00,0 oirtodate Susan. .ith 'thumb Ind.,. Leather. Postage , ge Od

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Steam Engineering The Stearn Turbine By Robert M. Nei.son WO B. A 51 I M B With

141 Ilitstrat.Ers Soo Pest,ge ad IS. Ed Steam Engine Theory and Practice By W Ripper Kith 438 Innen.

tons Posts,. 41 00 04

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Stationary Engine Driving By Mohoel Re m,Ids A P- -encal hianual tor Engineer. in CI,..,.. of Stat ona.y hex on. W Jrd Woodcuts Roth Edit.,, Mt, C.1.411 Postota Ed 3.

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Blementary Manus! no Ste ., and the Steam Enema By Prof, lammeoe For First year St.dants Ninth Eddie,. ho med With Nur [nations Ind Esamanat on Papers Postage 9d la Id

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Prattl ul Dynamo and Motor Coast, [action. By A W Marshall, AFAI H E A Handbook of Coostructvc DEW]. sod Workshop Methods umd oc building small machines Postage 04 e le Od

The A.B.0 of Dynamo Design. By Alfred H Ave ry AX E D With 51 Illustrations and 103 pages becond Edition Pease. id Is Od

How to Manag o a Dynamo By S R Botto m A Handbook for engineers. Eleetne Light Engineers, and Islectro Pleters Illustrated 'Third Ed.., revised and enlarged Post Son Cloth Pocket 142.1 Postage 24 Is Od

Care and Management of Electrical Machin•ry A handbook for the use of power umrs and attendant, Illustrated Postage Id Is Od

Small Dynamos and Motors How to Make Test and Revak. Them By P 13 Powell C0313111111 Inst mctions and Drawing. for Making Small Dyininoe and Motors of various M., 'ram 10 to 500 watts including tables of euitable windings Polly Illustrefeel Third Edmon Postage Id 64.

Small Electric Motor.. Ho w to Make and Um Them By P H Powell, Fully Illustrated with Ongioal Diagram. and Drawings Postage Id 64

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131ecti lc lighting aid POP,G3 lolatr,blttt ,n Ey W. P.. or 51nycock M 1 E L An Elam. for Sf F .ftb ri,•sed

Vyl I. M. tl 111 ,,trat, .e 11 . 6, 04 Vol. II Wth 401) t I: ... Ts 64

Practical Llectric Light I itting By r C Ails p A Teem's° ar06. Wiring and Fitting-6y of Bf.11in p & min a- t t, to Cential 50.01,0 Mains, and the Laying dcwn cf Pin .te InM tol.t. .m th 24 Illustranc m. Fourth Edition revised. Ponige ad 5. Od

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Amateur Electn6aWs. Woo asliop fly S R. 8:11,1e. A Handbook of Practical Instretian a the Waking of eleare4 Motels not Sorb inces In To 3 I/cli mes Postai, 2 I ch . Rich Is 64

Private HMI.. Electric Lighting By F H. laylor A NI I P E Describes Modern Si,th:ds Wl n, nd F tting, including a lot, on Small Getters ting Plants Postage sad • • In Od

A Guide to Electric Lighttig By S. It. 13,tt.:ne. To. Ha.,,nrlders and An desire rn I 00.5 14 Is Od

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Electrical Apparatus. Th• Conetruction of La, gill/W .118n Coils It A T Hare A Workahop

Handbooh With 13 Illustrations 152 rages Postage 44 . I. Od

electrIcel Influence Machines Thelr Des elcpment nod Modern Forms. Instructions for Making Them By J Gray B So Secood

Edition Reswed with Ina Illustration, P.,oavo Jd no Id.

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sf

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28-29, POnPIN S COURT k LEFT STREET LONDON 11. C

eleCtrie illiltruttlent- MakIng Ulf Am aaaaa s By 9 13 Bottone A Prao heel Handbook With 96- Illustrations Seventh Edition Revised end Enla,ged Postage 9d • 3. 6d

Induction Coils lay 0 E Bonney A Practical Manual for Amateur Cod makers rime edition Revised With 101 Illastratio m Footage 3d 3s Od

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Induction Coil. for Amateurs How to Make and Use The m Edited by Percivel Marshall A 1 Mecti 13 COMMA. Inn, fictions for omitting a powerful Shosking Cool, etc I ully III istrated Poatage Id 64

SimigIste,Eiliffycl acracL M ,l Mc,nholl Ale4:0, filowAtje Zellec.a, FLondd Us: Thom.

how to make Simple Modell With 44 Illiortrationa Postage Id 61 Small Accumulators How Mode and Used Edited by Percival Marshall,

AI M E Ones full Instructions for Making Charging and Using Small Accum.letris VSOh 41 011 stiati.ns Smedh £4,10 Postage Id 6d.

electric Balton . How to. Make and Use The m Felted by Percival Maitnall A I Wech P A Practical Hinlb k tbc Lenstructi m and Gras ol Pt .," Batier. m Tully r.ted S ml Ltition Postage Id 64

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m .... Hun and Electricity for Beginners By 14 C Hadley 13. % (Coed) Adapted to the Ekareata y Stage of the S. Kenci.gton Syllabus Globe Ion Pastagc 04 .. gs 64

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electrical Englneenng 13a.,s It Ectt.rie Coes Fill construct • nil Details of all the Ar,Ifumes deo- bud Ind ewer My selected !west a., en:blies the student to test Imawled u how 1.00 la ton.. laultr..tc Pcntati ad

2. Od Th• Study of FlactricIty tor Beginners By N.f.rman H Scnneidu Com-

oro:rig El m env °.1 Eleg.trc tr lad Itlag,et ;in as apfl cd to Dynamos. Mot ,. Ind Wiens, erarches f M ,la loop Cloth P: stage lid

Electrical Circuits nrd Dili/ MI6. By Norman H xh miler. Clivteos 2a1d1 Drismos of Coo metf lam, Chib Podsge I ti Is 64

Miscellaneous Electrical Subjects. Electric Traction By I. H Ruler El I II B„ /4 I C. El Wfth eturomou,

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The EIrmteliePlaters Handbook By 0 E Roo my A Practical Manual for Amateurs end Students t, Blear° Metallurgy A. ith full Index end JAI Illustrstion, Third Edition Revised and Enliirged with on Appendix oa Nickel Plating for Cycles Postege 54 s. Od.

Electrical Experiments By 4 B Bonney A Manual of Instructive Amuse meet With 144 Illusteetions Second Edition Postage 14 Its 6d

11 ' V:te a t:s r ggr.1:.,21g AArns = of l006r000,00 end toated

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X Ray. Simply Explained A Handbook on the Theory and Practice of Radio-graphy Folly Illustrated Postage Id 6.1

Eleetric Power What it is and what it can do ByA W Marshall, A MI C E . Poetise id

34

Reference and Pocket Books.

A Packet Book el Plectrical Rule. and Tabl m By J Munro C II, and Prof Joins. . With le mma . Diagrams Sixteenth Edition thcroughly revised snd eiderci.d ter the me of Electrum. and Engineers Leather Pocket sire Postage 24 On ad

A Childs to the F too thed! ',eli mination. By r H Toylor A Handbook of Refcrencs ire Students Ind Leachers w th an sppendix of specimen Qo mtons and Memel" Clotho Prst age &I • . is Sal

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Whittaker.. Electrical Engineer • Pocket Book Edited by Renelni Edgcumbe A M 1 lo P %Sable, Illustrations L“ther. Postage3d Be 6d

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Practical Electrician • Pocket-book end Diary By H T Crowe. SI 101 B Cloth Poetace Ad Is Od

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The Electricel Engineer s Pocket Book By H R Kam m MI E R All I Lb Cannata], of Modern Rile. Pormids Tables. and Data Second Ldition thoroughly reousid with additions. A ith num.°. Munn.. no m Royal d3tio thlong Leether Praise Ad On od

The Handy ElechIcel Dicttonary By W L Weber At L 0,00, never.' thousand definitions 214 pages. Pocket sire Postage Id Cloth en Od Leather Pc stace Id . Ie. 9d

Telephones, Telegraphy, and Bells.

T.I. sf g gYli LE Sr SN II A 216'7111cillr Stvoy PPO's'iageld 6". 268 1.):1

11"vv7tr ZuziaiM:::" E ;jolt' So 44

Ogd Practical Electric Bell Fitting Fly F C: Allot0 tenth Ldition 186 illus

entice. Crown Ito Posto,e Sd . 30 64.

TeleiE nils -i,T.li gr.raC ztrucct,lao:a Fitt too ing Ia By P C Allsop 3a Slitah

Plectiic Bells and All About The m By 5 11 Bottone A Practical Book for Piactical Men Si th mole thin 100 Illustrati.ns Sixth Edition, revised iced enlarcad Prato,' 94 3s Od

topelaimeaa Tree p nted W,tb 87 illeLtreation,a, Wapv• ,a 1ly, S. R Bot t on e co3. on,,I,

Preciical Telephony, By Joe Bell A I . cad S. Wilson. A Simple end Preens-II Handbook for the tee of Students and Employees Copeoudy Ill m tooted Postage 44 3.1 64.

IT

28-29, POPP/NS Couni, FLEET Sraarr, LONDON, EC 13

Telv mple gs:naugl; ca gy Jposo., 13gee112,, A 1 13 Ind S Wilson A M LEgla

How to betel Electric Bells Annunciators aril Alarms By Ho man H Schneider Oive. Kim., 39 Disgramo Limp Cloth Postage lid Is Ild

Teloat oaniciaTag gabileg A U itiara,htla Piled Tha:In pa ly,:ta H Hyde A coil

fliscbic Bells and Alarms By P E Powell Owes instructions for Boong name to any part of any ordinal, building St Illustrations Seventh edition Pontage Id Gd

Tel. irat naaef AnardahMa,licrzcil mr ri ciAwptoaa /Le isia Tal book aTalutra . 1.3,r,lasted by od

Using of Simple Forms of Telephone.. and Microphones Fifth Edition Vith se Illustrations Postage Id . ea.

WOODWORKING. Modern Practical Joinery. By 0 Ellis I POO Illast-ations Imperiel

too Postsge id I2s Ed, Practice! Stair Building end if landfall., By W H Wood %%oh PS

Plates Crown Ito Postage od . I Os 6d

" ntlinT g,,:eleij ;k 01 Tool, 61-11:1,411.' cod st2f7;Zuf.TrIal...1 Working Draw I n,-0 768 pages. Ityyll gra- Llerh MAU, Od

The Art and Craft of Cabinet Slaking. By D Donn,-, A Practical Handbook to tie Construct on of Cabinet Furn.taro the Use !Tools. Fume bon of 'ousts Hint, on Designing and .5ettes 011 %tooth terneenng etc. With )19 Iliustintines Poetsge 4d Ss Od

Historic Oint ment B3 R Wile SOO Illustrations Postage Id Ss Ott Woodcarving C. CI Lel and 'With nernerous Illustrations. 1-north Edthoe

Pop Ito PreMge 4d. • .. . . Ss Od cabinet Making for Ameteurs Dein, (Jew Directions Haw to Construct

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The Cabinet- Maker'• Guide to th• Entire Construction of Cabinet ' Work By_lbeherd flameout Illustrated sit1 Plans Se am. and Work Log OritAtif,a ineloding Venceiing Marcuebse, liable ALL Sto ma Inlayieg eta Crown gm Cloth Pc. ege Sd. 2. gd

Carpentry and Joinery Workshop Practice By C. F and A 0 Mitchell A Practical IlltMrated Man ,. oi I', the ,-se of Student* Cloth gilt. Pos pita 3d • gs 64

Circular Work at Carpentry and Joinery By Gearge Collings A Pratt, • cal Treatise on Circular Wolk of Sin,lc and DoebleC...nature With Diagra m Third Edition 12.mo Cloth' Poste & Sd Zs gd.

A Practical Treatise an Itandrail,ng. Ey Genes. Cann,. Shev, ng Neon sad Simple Methods foi (Molina the Pitch ,f ths Pl‘ak. Drawing the Mould, Bevelling- Jointing op and S-tu the Wreeth Second Edition, revised end C(11.1e&Ad with an addition of A Tree... on Stair Building With Plate. and Dia:rams Ihno Cloth Postage CI Be ad

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Instruction Including Niumenum Remota for Valais, Polishes, Vivaielme, Ol me-Lacquers etc, -Poo na 2d la. ed

Cabinet Workers Handy book By Paul N 11,sluck. A Practical Mused on Dm Toole Materiels Applia,.cre. nod Proe m.. Employed lis rabliee Work With upwards of 109 Illustnitions 144 nag. Inc Clotf, Poetess 3d le Od..

4777-7 •

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Wood•CarvIng for Am aaaaa • By ri Denning Full Instructio m for Pro diming all the Different Varieties of Ca melia Second Edition. In Paper Postase 2d . I. Od

Hint, on Chip Carving By F3 Roue Poeta,. 24 IN Rd Hints on Wood Carving By B Rowe Postage 24 Is ad, A ankle to Poker Work By W D Thompson A Practical Manual fot

Amateurs contoining o full deectiption of the necessary Tools and Instrit tions for their Use Ill mtrated In Paper Footage 24 le Rd

maniunaklc?0„1:tatt: Z.,,,f,o4Ag°,tr.dillzATrVPrOl Putt Witted. In Paperni Postn, 24 I. Rd

Mounting and I ranting Pictures Pi comsat under the direction of Paul N Haiduck A Practical Manual with 2.10111ustraho m Cloth Post:1 02d In Oel

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Wood worker • Hsndybook By Paul N Hasluck Ernbiacing Inforrnati m on the Tools Matenal Appliances and Processes hinplo,ed in Woodworking With 104 Illustrate° . 141 payee Boo Cloth Portaye 1.1 is Oa

Wood•Turner s fond hook Pa-it N Has!. oh A Practical /Manual for Workers It the Lathe uith over 103 III s rat,ns 111 pace. Caoun Cloth Postaye 34 .. . I. Rd

The Beginner • (Hilda to Carpentry By Id 1,rris A Pract.c d Hand ho. k for .11 Pcsirners in Co I'. tr0 Ill tr ited 0111, °maim, end Photo. thou's, how To:'. sh.el. no eud Cr:wn fur Postai, 3.1 le Rd

Polish... and Stains lot 7. onds. Ott Dud Donning A Cmmlete Guide to Polishing Wrodurrk uith disetions 1.r tit: ntny ond fill Informoticn for makiny the Stains Polla n Ott In Pape Postoye 21 Is 04

Ho me Decoration Comprising M hittwashing Paperhanging, Paint-ing etc By Paul N Hssluck A Pt zones allnual with 74 Illustrotions Cloth Postnye ad I. Od.

Soft Woods and Colonial limbers 4 practical hendb,ok no the ulection and uses of Soft Moods sod C.:1:nia. Ti nbers Fully Moser tted Pastos.

Mt. Hardwoods English and Fen elan Descrbes Hart and Fancy Woods used

by cirpent.... and 0th net on tnt, llltont ntn I Postage Id , Rd W oodwork Joints • He w to Make and Whet. to Use Them, By a

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The Beginner • (mole to Prttm ork Centain ng 1,11 Instnudiaas on Tools Mater ills and Moth els .000 .rkinc Stt f sire on,sinal Entoot k Design. are ',nen with this work P.,-,..0 led dd

PHOTOGRAPHIC BOOKS. "Photography" Bookshelf Series No. 1 Photographs to- Ail 13, W Jorome Harrison F 0.6 174 pages

Illustrated. Sloth Editun Cloth Postai.: 2d net Is Rd No a. PIMIC11C•1 SlIde Maktn• By G 1. Ha-ris P It P S. 134 page.

Illustrated Cloth Pests', 21 . not la Od No 3 The Nand Camera and How to Use it Illustrited Fifth Edition

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24 net In od No.3Seco Photogrephv in Colours 13, R Child Bayley F R P S Illustrated

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Cloth Postage 24 net la 04 No. es Practical Orthochromatic Photography By A Payne, F C 9

178 pages 63 Illustration. Cloth Postoye 24 net Is Rd No. Es intenelf motion and Reduction By H W Bennett P R PS

128 pages Cloth Postoge 24 net Is Rd No. 16 reining Bromide Prints By R B Blake Smith 108 pages Cloth

Postage 24. net Is Rd No a 4 r4icti AllyPiri'io,lets.s.Z sl cp,44,1to/r,..z.h; . By C H Hevoi t V.ol I.

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No. lb Practical Frame Making By Colonel W L h merre Cloth Postaye 21 (In the Prom ) not to Rd

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"The Amateur Photographer" Library.

No I. Platinu m Toning 13, I yontl Clark fifth lidition i.or rI I. Croon lig i Cloth Posta., 2,1 n

No 2 P O P By A Hanle,. Hinton This is a v. rk on winds' 111H2 to ' Plat notspe Printiny li, the .ame author Pmtage 31 , , net le Rd

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No Der41 =e2r and Developors By George i Ilnun Croun Ono dio,,, . .

No 6 The Art of Retouching By ..1 Hubert, Eleventh 1141itiln: ile .‘. °.1 04

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No 8 Carbon lonhntinPg / V .1B I Wall Sixth •Pil ticn . Cr,tru. to, 8...d. Cook P mtage NI

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No 18 Arehltectural Photography By 0 A T Middleton A RI B A Practical Lemions and Suggeetions for Amateurs Contlining over 40 Illus-trations Crown awl Cloth. Postage 24 . net le ad

No T6 MOunts and Frames, and Ho w to Make Thent By Rev P C Lambert M A Second Edition With many Illustranons Crown Ilvo Cloth Poetege 2d net Is Od

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Parte I and II in one volume handsomely bound in cloth Crows Postage Sd net ge. 111.1

No ile,„,,,,, ThectrlevtleLot Negfaihre Pool. C Lambert M A024 not r og,u1

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age 2d net Is Cid No. 28 Portraiture for Amateurs Piot II By Res 0 C I sinbert Poet

age 2d net le ad No. Elementary Chemistry of Photographic Chemicels fly C %ord..

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METAL WORKING TOOLS AND THEIR USES.

No. 7 of "THE MODEL ENGINBER" SERIES.

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