T 
 
 1 
 
 nun inn i i ^iiii 
 
OF THE 
 UNIVERSITY 
 
 OF 
 
 
QUESTIONS AND ANSWERS 
 
 ABOUT 
 
 ELECTRICITY. 
 
 A FIRST BOOK FOR STUDENTS- 
 
 THEORY OF ELECTRICITY AND MAGNETISM. 
 
 EDITED BY E. T.BUBIER, 2ND. 
 
 AUTHORS: 
 
 T. O'CONNOR SLOANE, A. M., E. M., PH. I). 
 CARYL D. HASKINS, M. I., E. E. 
 A. E. WATSON. 
 EDWARD TREVERT. 
 
 ILLUSTRATED, 
 
 NEW YORK : 
 
 D. VAN NOSTRAND COMPANY, 
 
 1802. 
 
COPYRIGHTED BY 
 
 BUBIER PUBLISHING COMPANY, 
 1892. 
 
 Press of G. H. & W. A. Nichols, Lynn. 
 
PUBLISHER'S PREFACE. 
 
 This little work has been prepared especially for the 
 young student or amateur. It is designed for a first book 
 upon electricity and magnetism and the authors are all well- 
 known, being recognized authorities up'on the subject. 
 The arrangement and classification of the questions and 
 answers has been made by Edward T. Bubier, 2d., Editor of 
 Bubier's Popular Electrician. We trust that the reader 
 will find the work of sufficient merit to interest and instruct 
 him. 
 
 BUBIER PUBLISHING COMPANY. 
 LYNN, MASS., September J, 1892. 
 
 3 
 M331733 
 
CONTENTS. 
 
 CHAPTER I. 
 
 PAGE 
 
 THEORY OF ELECTRICITY, 9 
 
 CHAPTER II. 
 THEORY OF MAGNETISM, 25 
 
 CHAPTER III. 
 VOLTAIC BATTERIES, 31 
 
 CHAPTER IV. 
 DYNAMOS AND MOTORS, 43 
 
 CHAPTER V. 
 ELECTRIC LAMPS, 58 
 
 CHAPTER VI. 
 MISCELLANEOUS ELECTRICAL APPARATUS, 66 
 
 CHAPTER VII. 
 ELECTRICAL MEASUREMENT, 77 
 
 CHAPTER VIII. 
 GLOSSARY OF ELECTRICAL TERMS, 88 
 
QUESTIONS AND ANSWERS 
 
 ABOUT 
 
 ELECTRICITY. 
 
 CHAPTER I. 
 
 THEORY OF ELECTRICITY. 
 
 What is the Theory of Electricity f 
 
 There is no satisfactory theory of electricity. The 
 best attempts at theories refer it to the luminiferous 
 ether. Stress of the ether represents static charges ; 
 the discharge brings about relief of the stress. A 
 continuous discharge through a conductor, represents 
 a current. The passage of the current stresses or 
 strains the ether, and establishes a field of force. But 
 what electricity is no theory pretends to tell us. 
 Charges are brought about by contact of dissimilar 
 substances, as in rubbing a stick of sealing wax upon 
 the coat sleeve, or by induction as in electric machines. 
 The work of electricity, its attractions and repulsions 
 are assumed to be done by the intermediation of the 
 ether. If it throws the ether into waves they are 
 identical with light waves. Unfortunately we have not 
 
10 QUESTIONS AND ANSWEKS ABOUT ELECTRICITY. 
 
 been able to make them short enough to really give 
 light or to affect the eye. A current of electricity 
 goes through a conductor because the conductor opens 
 a path for it through the ether. A current cannot go 
 quietly through the ether, because it only produces 
 stress or waves in it. 
 From What is the Word "Electricity" Derived? 
 
 The word Electricity is derived from the Greek 
 word "Electron" or amber. It was noticed by the 
 Greeks (some 600 B. C.) that if amber was rubbed, it 
 possessed the property of attracting to itself small 
 bodies, such as dust or bits of paper, etc. About A. D. 
 1600, Dr. Gilbert made some experiments and found 
 that other substances, such as diamonds, glass, sulpher, 
 sealing-wax, etc., possessed the same property, which 
 he styled electrics, since which time the word electric- 
 ity has been employed to denote this energy. 
 W7iat is Electrical Attraction and Repulsion? 
 
 When bodies which are in like electrical condition 
 are brought near togetheiythey repel each other. If 
 in unlike electrical condition they attract each other. 
 A body charged with electricity is surrounded with a 
 field of force, to which a species of polarity or direc- 
 tion is attributed. The attractions and repulsions of 
 electrified bodies are attributed to the actions of the 
 fields of force upon each other. If two wires are 
 parallel, and currents are going through each, they 
 will attract each other if the currents are in the 
 same direction, and repel each other if the currents 
 are in opposite directions. Here again the fields of 
 force are treated as the agents. Each wire is sur- 
 
THEORY OF ELECTRICITY. 11 
 
 rounded by a field of force. If the currents are in 
 the same direction, the two fields will become smaller 
 if the wires approach. But a field of force always 
 tends to contract itself. Hence the wires attract 
 each other. On the other hand if the currents are in 
 opposite directions, any approach of the wires brings 
 near together two fields of opposite polarity, which 
 cannot coalesce and which resist the crowding. Hence 
 the wires repel each other. If a stick of sealing-wax 
 is rubbed with a bit of silk, the two attract each 
 other. This is because they virtually are the 
 opposite ends of a field of force, which tending to 
 contract, draws them together as an India rubber band 
 would do. 
 
 What is Meant by Induction? 
 
 A current is said to be induced in a conductor when 
 it is caused by the conductor cutting lines of magnetic 
 force. A fluctuating current in a conductor will tend 
 to induce a fluctuating current in another running 
 parallel to it. A static charge of electricity is induced 
 in neighboring bodies by the presence of an electrified 
 body. A magnet "induces" magnetism in neighbor- 
 ing magnetic bodies. 
 
 What is Static or Frictional Electricity f 
 
 All electricity is one, but differs in degree and dis- 
 tribution. Static electricity is electricity in repose, 
 but strongly tending to motion. The stick of sealing 
 wax and the silk with which it is rubbed are statically 
 charged with opposite electricities, which tend to 
 unite, and which establish a field of force throughout 
 the intervening space. Such electrical excitement is 
 
12 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 termed static electrification. When the excitement is 
 enough, as in a Leyden jar, charged to a high degree, 
 the opposite electricities unite with a spark and noise. 
 Such uniting is termed the static discharge. As a 
 general rule static electricity involves very high 
 potentials and very small quantities of electricity. 
 It is like a very little air confined at enormously high 
 pressures. 
 What is Thermo Electricity and How is it Produced? 
 
 Thermo electricity is electricity produced by 
 heating the junctions of dissimilar metals. If a bar of 
 antimony has one end touched to a bar of bismuth and 
 the junction is heated, a potential difference will be 
 established between their ends. If a wire is carried 
 from the unheated end of one bar, to the correspond- 
 ing end of the other, a current will pass as long as 
 difference of temperature is maintained. By using a 
 great number of couples of bars, connected in series, 
 a considerable current can be produced. 
 What is Atmospheric Electricity / 
 
 Atmospheric electricity is electricity stored up in 
 the air. or charged upon the surface of water vesicles, 
 the little spheres of water which make up clouds and 
 mists, upon floating dust, or upon minute ice particles 
 or in the air itself. The cause of its production, and 
 of the extraordinary potential it may rise to, is not 
 adequately explained. If we assume a given charge 
 to be contained upon the surface of the minute water 
 vesicles alluded to, and if these condense into rain 
 drops, their surface area will be greatly reduced and the 
 potential of the charge will rise proportionately. This 
 
THEORY OF ELECTRICITY. 13 
 
 gives some basis for a theory of the high potential 
 which produces the lightning stroke in thunder 
 showers. Peltier considered that the atmospheric 
 electricity was due to induction from the earth. 
 Another theory attributes it to the friction of the 
 water vesicles against minute ice particles in the upper 
 atmospheric regions. The ice particles become posi- 
 tively charged, and the water particles negatively. 
 As the latter fall in the form of rain they carry their 
 charge down to the earth leaving the ice particles 
 positively charged behind them. 
 
 No theory is satisfactory. As a matter of fact the 
 atmosphere is almost always positively charged, and 
 the earth negatively, within nine feet elevation from 
 the earth, the potential may rise over 400 volts. At- 
 mospheric electricity is subject to perpetual changes, 
 and occasionally is negative. 
 
 What is Pyro-electricity ? 
 
 Electricity manifested by certain substances when 
 being heated, or cooled. Tourmaline, a natural 
 mineral, which occurs in elongated crystals shows it 
 strongly. If heated, the distribution of electricity is 
 affected, one end becomes positively and the other 
 negatively charged. This depends on the change of 
 temperature. If allowed to cool, the polarity is 
 reversed during the cooling process. If kept at a 
 constant temperature no electrification is developed. 
 The end of the crystal which is positively electrified 
 with rising temperature is called the analogous pole. 
 The other is the antilogous pole. Several other min- 
 erals, and organic bodies are pyro-electric. Fluor 
 
14 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 spar is affected not only by heat but by light from the 
 sun or from a voltaic arc. This is termed photo- 
 electricity. 
 
 What is Dynamic Electricity ? 
 
 Electricity in motion, or in the form of currents. 
 An electric light wire conveys a current of dynamic 
 electricity. It is the opposite of static electricity, 
 which is electricity in repose. Telegraphy, electric 
 lighting and transmission of power, electro-dynamic 
 machines and in general the commercial electric oper- 
 ations are in the field of current or dynamic elec- 
 tricity. Strictly speaking, the static discharge, such 
 as that of the Ley den jar is a current, but it is not 
 generally treated as dynamic electricity, the latter be- 
 ing restricted to current phenomena of some duration, 
 or produced by currents which are adapted to be of 
 such duration. Nevertheless, the two divisions inevi- 
 tably run together, being only varieties of the same 
 thing and the divisions of static and dynamic electri- 
 city are preserved as matters of convenience, rather 
 than for any other reason. 
 
 What is Magneto Electricity ? 
 
 Magneto electricity is the electricity developed by 
 the induction in a magnetic field of force. If a con- 
 ductor is swept across such a field, one which always 
 exists about the poles of a magnet, a difference of 
 potential will be created in its ends, and if those ends 
 are connected a current will flow through it. In gen- 
 eral terms it is a form of dynamic electricity produced 
 in a special way. It is identical with every other 
 current form. 
 
THEORY OF ELECTRICITY. 1& 
 
 What is an Electroscope f 
 
 It is an instrument for detecting whether a body is 
 electrified and whether the electrification is positive 
 or negative. There are several varieties, the best and 
 most sensitive being the gold leaf electroscope. It 
 may be described as follows : 
 
 Two strips of gold leaf are suspended within a 
 glass jar or wide-mouthed bottle upon a stiff piece of 
 brass wire. The wire is enclosed within a glass tube 
 which is pushed through the cork. Both cork and 
 tube should be well shellaced or paraffined. Upon 
 the upper ends of the wire is a round flat piece of 
 copper. This is a very delicate instrument and if it 
 is kept perfectly dry and free from dust will indicate 
 very small quantities of electricity. This instrument 
 will show that all kinds of friction will produce elec- 
 tricity. If a glass rod be rubbed with dry silk and 
 placed near the top of the electroscope the gold 
 leaves will be seen to repel one another. If you wish 
 to see whether a body is electrified negatively or posi- 
 tively proceed as follows: First charge the electro- 
 scope by touching the metal plate on top with a glass 
 rod previously rubbed with silk. This will make the 
 leaves diverge. Now if you approach the electroscope 
 with a positive electrified body the leaves will tend to 
 diverge still further, or if with a negatively electrified 
 body they will tend to close. 
 
 What is a Conductor? 
 
 A substance which will allow the passage of electric- 
 ity over it. All substances will do this, but some to 
 so small an extent, that they are called insulators. 
 
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18 QUESTIONS AND ANSWEES ABOUT ELECTRICITY. 
 
 to six revolutions for each revolution of the driving 
 wheel, the plates of small machines requiring a more 
 rapid revolution than those of larger ones. In front 
 of the plate A, \ of an inch from the glass, are the 
 combs Kand H, attached to a brass core at the centre 
 of the ebonite disc M ; and the combs K and L, in- 
 sulated by their attachment to ebonite rods projecting 
 from the disc M^ and connected by brass rods with 
 the Leyden jars C and Z>, and with the sliding-rods 
 P and R. These sliding-rods have ebonite handles, 
 and terminate in brass balls at their inner extrem- 
 ities. 
 
 The plates of sheet glass, about 1 of an inch thick ; 
 of good insulating quality, and well coated with 
 shellac. The stationary plate B has two circular 
 openings called windows, directly opposite the combs 
 JTand L\ and on its rear surface, are cemented two 
 paper inductors 3Tand -3T; J5Textendingfrom.Zrto L, 
 and JTfrom F'to K\ and each armed with a row of 
 points projecting into each window. 
 
 The Topler machine shown on next page has the 
 same general construction as the Holtz ; but, on the 
 front surface of the revolving plate, are cemented a 
 number of small metal discs, called carriers ; usually 
 made of tin-foil with raised brass centres, which, as 
 the plate revolves, are brought into contact with four 
 brushes; two attached to a stationary plate, and two 
 to the uninsulated combs. In this way the machine 
 is made self-inciting, as already mentioned. 
 
 The windows, and the rows of points projecting in- 
 to them, used in the Holtz stationary plate are omit- 
 
THEORY OF ELECTRICITY. 
 
 19 
 
 ted from the stationary plate of the Topler, and the 
 paper inductors are made- longer, and have small tin- 
 foil inductors under them, connected by tin-foil strips 
 
 THE TOPLER MACHINE. 
 
 with each other and also with the two brushes at- 
 tached to this plate. 
 
 This machine was constructed by Phillip Atkinson, 
 and patented April 10, 1883, and December 8, 1885. 
 
20 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 The principal points covered by the patents are as 
 follows : 
 
 1. The outside coatings of the Leyden jars C and 
 D are of sheet brass, nickel plated ; and are screwed 
 firmly to the base, forming cups into which the jars 
 fit closely, and are thus held in a fixed position ; af- 
 fording a firm support to the parts connected with 
 them, and preventing liability to accident or injury to 
 the jars or plates. 
 
 2. The induced current from these outside coat- 
 ings is conveyed down by the brass screws -which at- 
 tach them, and along copper wires underneath, to the 
 terminals of the switch S\ through which, when 
 closed, it passes from one jar to the other ; but when 
 open, as in the cut, it passes by the brass sockets, 
 seen on the edge, which are also connected with the 
 terminals, out through the conducting cords, and a 
 person, or other object, connected with their outer 
 extremities. As this induced current flows simultane- 
 ously with the direct current from the inside coatings, 
 the switch and sliding-rods place it completely under 
 control of the operater. 
 
 3. The brush holders, E and F, are attached to 
 the plate .Z?, through holes near its edge ; thus giving 
 a direct passage to the electricity from the carriers 
 on the plate A, where it is generated, through the 
 glass, to the tin-foil inductors, represented by the 
 dark shade, and the paper inductors .T'and X, repre- 
 sented by the light shade. By passing the electric 
 charge through the glass^ inside its edge^ an insulat- 
 ing margin is interposed between the conductors and 
 
THEORY OF ELECTRICITY. 21 
 
 the edge, thus preventing loss from leakage, which is 
 unavoidable when the brush holders are attached by 
 clamps or ears on the edge. 
 
 4. The carriers on the plate A are of sheet brass, 
 with raised centres, and are nickel plated, making 
 them both durable and ornamental. The hard nickel 
 surface is affected by the action of the brushes, or the 
 electricity, while tin-foil soon becomes defaced ; and 
 the carrier, being practically one piece, and its entire 
 surface cemented to the glass, its raised centre can- 
 not become detached, as may happen when the centre 
 is put on separately over a tin-foil base. 
 
 5. The combs T^and J^ also JTand X, radiate at 
 an angle of 45 degrees to each other, from the central 
 disc 7!/, to which they are attached ; so that any pos- 
 sibility of error in regard to their position, or of dis- 
 placement, is practically impossible. 
 
 The following improvements may also be noticed : 
 
 The base is made of two-inch strips, glued together 
 lengthwise, and heavy cleats screwed on underneath; 
 giving all the advantages of iron as to freedom from 
 warping, with the insulation and elegant finish of the 
 wood. The driving-wheel is of ebonite and the iron 
 casting, on which it is mounted, slides in grooves on an 
 iron plate, and is moved by the adjusting screw 0, to 
 regulate the tension of the belt. 
 
 The ebonite insulators, which support the plate .Z?, 
 have soft rubber packing, to ease the pressure on the 
 glass. 
 
 The conducting rods of the Leyden jars pass 
 through ebonite caps with cork attached underneath, 
 
22 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 which gives them a fixed vertical position, and affords 
 firm support to the sliding-rods" and the combs con- 
 nected with them above. 
 What is a Condenser? 
 
 It is an apparatus for collecting and holding electric- 
 ity. It consists of alternate layers of conducting sheets 
 and insulating material, the conductors being very 
 close together, and the adjacent ones being charged 
 with the opposite kinds of electricity. Their proximi- 
 ty enables them to hold a larger amount of electricity 
 than they could if alone. Condensers are sometimes 
 called accumulators. A condenser is the modern and 
 practical form of a Leyden jar, altered in appearance 
 and used for different purposes. Its construction in- 
 volves tinfoil, but varnished silk or paper is used in- 
 stead of glass. Alternate sheets of tinfoil are con- 
 nected to one wire or binding post, the rest of the 
 sheets to another post. The effect is the same as if 
 but two large sheets were used, of an area equal to the 
 sum of the small ones. Condensers are used in the 
 bases of large induction coils. At the make and break 
 contacts on such coils, destructive sparks are con- 
 stantly burning. The condenser dissipates these 
 sparks and increases the intensity of the induction in 
 the coil. The amount of electricity a condenser will 
 hold in the static form is measurable. This leads to 
 valuable practical application. Sometimes an ocean 
 telegraph cable breaks ; it becomes necessary to locate 
 the fault by measuring the static capacity of the cable 
 and comparing the results with a condenser of known 
 capacity, the distance to the break can be calculated. 
 
THEORY OF ELECTRICITY. 23 
 
 Describe a Leyden Jar ? 
 
 Opposite conditions of electricity attract one an- 
 other, and although electricity cannot flow through 
 glass it can act across it by induction. For example : 
 Placing a plate of glass between two pith balls, one 
 being electrified positively, the other negatively, will 
 not interfere with their attracting or repelling one 
 another, although the electric charges cannot pass 
 through the glass. On this principle was invented 
 the Leyden jar, and other condensers. The Leyden 
 jar was accidentally discovered by Musschenbroek, 
 and his pupil Cuneus, in the town of Leyden, from 
 which it derives its name. It usually consists of a 
 glass jar on which is pasted two coatings of tin-foil, 
 one on the inside, and one on the outside, the coating 
 covering the jar, three-fourths of its length. Electric 
 connection is made by a chain, or a flexible wire 
 hanging into the jar from a brass rod, which may be 
 supported by a wooden cover to the jar, to which the 
 rod is fixed. A brass nob is attached to the top of the 
 rod. To charge the jar, it is necessary to hold or con- 
 nect this nob to the prime conductor of an electrical 
 machine ; the outer coating being either held in the 
 hand, or connected to the earth by a wire. The jar 
 can be easily charged in a few minutes in this way, 
 and if made of good glass, kept dry and free from dirt, 
 will retain its charge for many hours. The jar may 
 be discharged by holding it in one hand by the outer 
 coating and touching the brass nob with the other hand. 
 The person so doing will see a bright spark pass be- 
 tween the nob and the hand, making a sharp report, 
 
24 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 and at the same time giving him a convulsive 
 shock. 
 
 A very simple Ley den jar can be made in the fol- 
 lowing manner, and was the original experiment of 
 JVfusschenbroek and his pupil : Take a glass bottle, 
 fill it about two-thirds full of water, make a hole 
 through the cork and push through it a long nail, so 
 that it hangs -low into the water, when the cork is in 
 the bottle. This jar can be charged like the modern 
 Leyden jar, and in the same way, the water acting as 
 the inner coating and the hand as the outer. When 
 the jar is charged, it can be discharged by holding it 
 in one hand and touching the top of the nail with the 
 other. Thin glass has a greater capacity as an accu- 
 mulator, than thick glass, but if the glass should be too 
 thin, the jar will be liable to be destroyed by the 
 spark of a powerful charge actually piercing it. A 
 powerful battery may be made of Leyden jars by con- 
 necting a number or them together by thin inner coat- 
 ings, then also uniting their outer coatings. Care 
 should, however, be taken in discharging this battery 
 of Leyden jars, by using a pair of discharging tongs, 
 as a shock from such a battery might prove fatal. 
 The discharging tongs is an arrangement consisting 
 of a brass rod with two brass knobs, and insulated 
 from the hand by a glass handle. 
 
THEORY OF MAGNETISM. 25 
 
 CHAPTER II. 
 
 THEORY OP MAGNETISM. 
 
 What is the Theory of Magnetism ? 
 
 The most generally accepted theory is known as 
 Ampere's theory ; it holds that every particle of a 
 magnet has a minute current of electricity circulating 
 around it ; that the result of the aggregation of these 
 particles with their currents is the production of a 
 sheet, as it were, of current circulating around the 
 outside of the magnet. If we look at the North pole 
 of a magnet, the current is assumed to go around it in 
 a direction opposite to that of the hands of a watch, 
 and the reverse for the South pole naturally. No en- 
 ergy is expended in keeping up this current because 
 each one of the constituent currents is of such minute 
 dimensions that it maintains itself, once started. 
 
 What is Meant by Magnetic Attraction and Repul- 
 sion f 
 
 This is really a continuation of the preceding an- 
 swer. We have seen that currents in similar direc- 
 tions tend to approach each other. Bearing in mind 
 the direction of the Ampereian currents it will be 
 seen that if the North and South poles of a magnet face 
 each other, the currents of each will be in the same 
 direction ; hence the North and South pole attract 
 each other. If two poles of similar names face each 
 
26 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 other, the currents will be in opposite directions and 
 therefore will repel each other. Another way to look 
 at it is to consider the field of force which these Am- 
 pereian currents create. If the North and South 
 poles of two magnets are brought near each other the 
 field extends from one to the other and they are 
 drawn together by the natural tendency to contrac- 
 tion of a field of force as if rubber bands were stretched 
 between. If similar poles are brought together the 
 opposite fields of force cannot coalesce, and they push 
 each other away just as two inflated rubber balls would 
 if pressed together. 
 Will a Magnet Act Across Bodies? 
 
 The action of a magnet is to some extent shielded 
 or cut off by any piece of iron. This is done by the 
 lines of force which should "emanate from its poles 
 being diverted or turned aside owing to their high 
 affinity for metallic iron. No body other than iron 
 and a few other substances, acts thus, and they only 
 act by concentrating upon themselves the attractive 
 power of the magnet. It is not a genuine cutting off 
 of the attraction. 
 How may Magnetism be Derived from the Earth f 
 
 By subjecting a bar of steel to molecular disturb- 
 ance while held in the magnetic meridian or approx- 
 imately north and south. The disturbance may take 
 the form of jarring, hammering, twisting or the like. 
 It is as if the polarity of the earth was striving to 
 make a magnet of it and could only succeed effectu- 
 ally when it was helped on its way by the disturbance 
 of the molecules. 
 
THEORY OF MAGNETISM. 27 
 
 What is Meant by Magnetic and Diamagnetic Bodies f 
 A magnetic, paramagnetic, or ferromagnetic body 
 is one which is attracted by the magnet, which, if 
 suspended in the neighborhood of a magnet tends to 
 stretch from pole to pole thereof ; which has a high 
 affinity for magnetic lines of force, and through 
 which lines of force (the elements of a field of 
 force) pass more readily than they do through air. 
 A diamagnetic body is exactly the reverse of the 
 above. Suspended in the neighborhood of a magnet 
 it tends to place its longest axis across the line con- 
 necting the poles, it has less affinity for lines of force 
 than has air and tends to be repelled by a magnet. 
 
 What are the Laws of Magnetic Force ? 
 
 Theoretically the laws are very simple ; magnetic 
 force varies inversely with the square of the distance 
 or follows the law of inverse square. In practice 
 owing to the different shapes of magnets, and the size 
 of their poles which is large compared to the distance 
 through which they act, the law of inverse squares 
 really does not apply and no general law can be 
 stated as a special law will exist for each case. 
 
 What is a Natural Magnet ? 
 
 The natural magnet or "lodestone" is an iron ore, 
 and frequently occurs in crystals. This ore is mag- 
 netic, that is, it has the power of attracting iron and 
 steel to itself, it is known to minerologists as magnetite, 
 it also has the property of pointing north and south 
 when it is suspended by a thread. 
 
28 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 What is an Artificial Magnet f 
 
 If a piece of iron or steel be rubbed or brought in 
 contact with a loadstone, or any magnet, it will be 
 found to have acquired all the properties of the mag- 
 net, in fact it has become a magnet and if it be hard- 
 ened steel with proper care it will retain the magnet- 
 ism for an indefinite period. A piece of steel or iron 
 may also be magnetized by winding insulated copper 
 wire around it and sending a current of electricity 
 through the wire. 
 
 ELECTRO MAGNET. 
 
 What is a ^Permanent Magnet f 
 
 A magnet which holds its magnetism indefinitely. 
 A piece of steel made glass hard and then magnetized, 
 becomes a permanent magnet. 
 What is an Electro Magnet? 
 
 A magnet produced by passing a current through a 
 coil of wire around a soft iron core. The core is mag- 
 netized while the current flows, but loses its magnet- 
 ism when the current stops. This form of magnet 
 may be made much more powerful than a permanent 
 magnet, and is therefore used in place of the latter 
 in dynamos. 
 
XII J MAGNETISM. 29 
 
 \\'/t<tf /.< Jf <i</-/t(;( Satotrati 
 
 \Vhen a magnet has been magnetized to the high- 
 legree it can attain it is said to be " saturated" 
 
 \\'/i<if /.< Jt<. <;<! if M<I<JI. 
 
 * iron after being magnetised retains a small 
 amount of magnetism after its temporary magnetism 
 has red. This small remaining charge is called 
 
 foal HKKjntfism" 
 
 Does a Permanent J/"////e/ I, \hrengthi 
 
 You may partially or wholly destroy the magnet- 
 el magnet by rough usage, as hitting it, 
 or k \ It will also lose its magnetism 
 
 on 1 '-sg. 
 
 W/.fit i f/,< sin-Hf/tli of a J/"///"'/ 
 ft i- a common error for one to suppose that the 
 
 n'j-th of a magnet is its lifting power, but thi 
 not so. The strength of a magnet is the strength 
 of its poles ami the strength of a magnet pole must be 
 measure'! by the magnetic force which it exert 
 example : Supposing there are two magnets A and B, 
 whose strengths we will compare by making them each 
 act upon the North pole of a third magnet, C. If the 
 th pole of A repel- C with twice as much force as 
 that with which the North pole of B placed at the 
 same distance would repel C, it would prove that the 
 strength >e that of B. 
 
 Can M<i<ji,<i lt>-< o/,/// o,,< J'ole? 
 
 the two poles are inseparable. If we break a 
 magnet into any number of pieces each piece will b<-- 
 
30 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 come an independent magnet with a north and a 
 south seeking pole. 
 What is a Magnetic Field? 
 
 It is the space around a magnet or it may be the 
 space around a conductor carrying a current of elec- 
 tricity which is pervaded by magnetic forces. Every 
 magnet is supposed to have what are termed lines of 
 force running around it and through it, or to possess 
 what is termed a magnetic field. 
 Describe the Magnetic Needle or Compass. 
 
 The common form of compass consists of a small 
 steel needle fitted with a small cap of brass or glass 
 by means of which it can be pivoted upon the sharp 
 point of a metal pin so as to turn with as little fric- 
 tion as possible ; it is then magnetized when it will set 
 itself into the magnetic meridian, or in other words 
 it will seek a north and south position. It is placed 
 in a small brass box and protected from dust, etc., 
 by a glass top. Under the needle is a card marked 
 with the "points of the compass." 
 
VOLTAIC BATTERIES. 31 
 
 CHAPTER III. 
 
 VOLTAIC BATTERIES. 
 
 What is the Voltaic Pile f 
 
 The voltaic pile was named for Volta, its inventor. 
 It consisted of discs of copper and zinc laid together 
 in pairs, each pair separated from other pairs on each 
 side by cloth, or paper, moistened in salt water. 
 These discs were placed in a vertical " pile," a zinc 
 at one end and copper at the other acting as termi- 
 nals of the series. A wire taken from each of these 
 end discs served to lead the electric current away and 
 provide for the return. The chemical action of the 
 salt water on the zinc developed an electric current, 
 which passed to the copper in contact with it, then 
 through the next moistened cloth to the second zinc, 
 and so on. Each separate couple contributes its pro- 
 portionate part of the total energy. 
 
 What is a Voltaic Battery f 
 
 The Voltaic Battery was easily developed from the 
 Voltaic Pile. The substitution of a vessel of salt water 
 for the moistened cloth was the only difference. Alter- 
 nate copper and zincs had then to be connected with 
 wires. Because the first battery was arranged with 
 the glass cups in a circular form, the invention was 
 called the " crown of cups." One couple or pair of 
 
32 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 BUNSEN CELL. 
 
 GROVE CELL. 
 
VOLTAIC BATTERIES. 33 
 
 plates does not properly constitute a battery. The 
 name " cell " should be applied to the unit. A " bat- 
 tery" is a combination of two or more cells. 
 Describe some Different Kinds of Voltaic Batteries. 
 
 The early forms of batteries were made on the 
 " one solution " plan with copper for one element, 
 zinc for the other, immersed in dilute sulphuric acid. 
 Wollaston's is a good example. The necessity for a 
 continuous working battery gave rise to " double 
 solution" or two fluid cells. Bunsen invented one 
 in which carbon and zinc formed the elements. The 
 carbon block was put in a porous cup filled with 
 nitric acid. The zinc was outside this cup in a glass 
 jar filled with dilute sulphuric acid. Grove's device 
 was the same with the substitution of sheet platinum 
 for carbon. Daniel's cells had the zinc in the porous 
 cup with the acid, while a copper plate was outside 
 in a solution of sulphate of copper. The gravity cell 
 is a modification of Daniel's depending upon the dif- 
 ferent specific gravity of the two solutions to keep 
 them separated. The Grenet, or Bichromate of Pot- 
 ash, is a single solution cell. A plate of zinc is held 
 between two carbon plates and immersed in a solution 
 of dilute sulphuric acid and bichromate of potash. 
 Leclanche and Samson cells use a pencil or cylinder 
 of zinc, a block of carbon surrounded by some form 
 of manganese, and immersed in a solution of sal- 
 ammoniac. 
 What is an Accumulator or Storage Cell f 
 
 The different forms of cells just described make 
 what are called " primary " batteries because the cur- 
 
34 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 GRAVITY CELL. 
 
 GRENET CELL. 
 
VOLTAIC BATTERIES. 
 
 35 
 
 rent originates directly in them. There is another 
 class of more modern development, called " secon- 
 dary," storage batteries, or accumulators. These can 
 generate no electricity of themselves, but have the 
 power of holding and giving out a current, after 
 
 LECLANCHE CELL. 
 
 having been " charged." This charging can be done 
 with ordinary primary batteries, but it is cheaper 
 to use dynamos. 
 
 Storage batteries are far from perfect, returning 
 only about one-half of the energy put into them. They 
 
36 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 are heavy and disagreeable to handle and require a 
 skilled electrician to maintain them in proper work- 
 ing condition. The usual construction consists of two 
 series of plates, alternate ones being connected to- 
 gether. These plates are made of lead " sponge " or 
 perforated sheets and the interstices filled with lith- 
 age or some patented preparation. A solution of 
 
 SAMSON CELL. 
 
 dilute sulphuric acid is used, as if they were primary 
 batteries. After having an electric current sent 
 through them for a certain length of time, chemical 
 changes take place in the plates and they will gener- 
 ate a current of electricity when placed in circuit. 
 The current flows in the opposite direction from 
 which they were charged. 
 
VOLTAIC BATTERIES. 
 
 37 
 
 How are Batteries Connected for Different Purposes f 
 The different arrangements in which cells or bat- 
 teries may be connected together depend upon the 
 conditions of the work to be done: The old expres- 
 sions, which are very simple were that the connec- 
 tions were for " intensity " or " quantity." Each cell 
 
 STORAGE CELL. 
 
 possesses a certain energy, measurable in "volts" and 
 " amperes," or " intensity" and quantity. If the car- 
 bon of one cell is connected to the zinc of the next 
 and so on, the total available "intensity" will be the 
 sum of the whole series. If the carbons are all con- 
 
38 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 nected together, and the zincs together by them- 
 selves, the " quantity " will be the sum of the whole, 
 
 What is Connecting in Multiple f 
 
 The latter arrangement described above is called 
 connecting in " multiple." That is, they are a multi- 
 plicity of paths, a part of the current in each. The 
 effect is the same as if one large cell were made with 
 plates of an area equal to the sum of the individual 
 cells. The intensity or " voltage " of such an ar- 
 rangement is small, being that of one cell. Hence 
 the current can travel but short distances, only a few 
 feet, and except for use with large wires this arrange- 
 ment should not be adopted. The quantity or " am- 
 page" (number of amperes) being large, deflagrating 
 effects can be produced. It is seldom that batteries 
 are connected in this way for practical purposes. 
 
 What is Connecting in Series? 
 
 When the zinc of one cell is connected to the cop- 
 per or carbon of the next, all the current has to go 
 through the cells in " series" hence the designation, 
 coupled in " series." Such is the usual arrangement 
 in order to get as high " voltage " as possible. 
 Telegraph and fire alarm systems are illustrations of 
 this arrangement, often having several hundred cells 
 in one circuit. 
 
 What is Connecting in Multiple Series? 
 
 Combinations of these two methods make two other 
 arrangements technically designated as "multiple 
 series," and "series multiple." It is not often that 
 batteries are coupled in these ways, but -it is neces- 
 
VOLTAIC BATTERIES. 39 
 
 sary, sometimes to secure a certain strength of cur- 
 rent. Suppose for instance there are at hand eight 
 cells each capable of supplying two volts and three 
 amperes and it is desired to send through the wires 
 in circuit 12 amperes under a pressure of four volts. 
 By connecting the cells together in series, groups of 
 two, the right voltage can be secured. The groups 
 can then have all their copper terminals connected to 
 one wire, the zincs to the other, and twelve amperes 
 of current will result. The individual cells are in 
 series, the groups in multiple and arrangement called 
 multiple series. The method of connecting the five 
 incandescent lamps together in electric cars is an 
 illustration of this arrangement. In the early days 
 of incandescent lamps it was not uncommon to sup- 
 ply them from the arc light circuits. The current, 
 after lighting several arc lamps would arrive at a 
 group, usually eight, of incandescents. These lamps 
 were connected in multiple so that only one-eighth 
 of the current went through each. Thus the lamps 
 were in series with the rest of the circuit, but in mul- 
 tiple with each other, so the arrangement was called 
 series multiple. 
 
 What are Chemical Actions which Take place in a 
 Cell? 
 
 A current of electricity can be produced in battery 
 only under conditions that the two electrodes differ 
 in " electric state." That is, one shall be acted 
 upon, or decomposed and the other unaffected by the 
 surrounding liquid. The more rapid the disintegra- 
 tion of the active metal the greater the current. 
 
40 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 When a battery is in operation, the zinc is slowly dis- 
 solved ; the solution becomes charged with some solu- 
 tion (usually sulphate) of zinc. When all the acid 
 has been used up, the solution is entirely a "salt," 
 as long as the free acid exists the battery may be said 
 to be energetic, but having a diminishing strength. 
 When the " salt " alone is present the electro-motive 
 force is reduced but is constant. It is under these 
 conditions that the " gravity " cells derive reputa- 
 tion of constancy. 
 
 What is Local Action in a Cell? 
 
 If zinc was chemically pure and the acids pure 
 there would be no action on the zinc except that for 
 which the electric current could account. But there 
 are traces of iron, copper, lead and other metals in 
 the zinc which form independent circuits by them- 
 selves. This action serves only to diminish the 
 strength of the acid by setting up a counter electro- 
 motive force and dissolve the zinc uselessly. 
 
 Why is the Zinc Used in a Cell Amalgamated, and 
 
 How is it Done ? 
 
 A remedy for this " local action, is amalgamation of 
 the zinc. This is an expression for coating the sur- 
 face with mercury. With this application, ordinary 
 zinc acquires the properties of the pure metal and is 
 unattached detrimentally by the acid. A simple way 
 of amalgamating is as follows : Clean the zinc by 
 scouring, and washing in dilute sulphuric acid. 
 Rinse the zinc in clean water without touching it with 
 the fingers, and immerse it in a vessel of mercury. 
 
VOLTAIC BATTERIES. 41 
 
 Another method is to dissolve one-half pound of 
 mercury in two pounds of nitric acid. After cleaning 
 the zinc, as before, an immersion for a few minutes in 
 this mixture will coat the zinc with a uniform layer of 
 mercury. A little mercury kept in the bottom of bat- 
 tery cells will serve to keep the zincs constantly 
 amalgamated. 
 
 What is Polarization and What are JKemedies 
 Usually Employed to Prevent it ? 
 As acid attacks the zinc plate in a simple battery 
 cell, hydrogen bubbles are liberated, these bubbles 
 travel through the liquid, and upon arriving at the 
 copper, or carbon plate, they cover in a short time 
 its entire surface, and the strength of the cell is 
 diminished. The reason is that the hydrogen forms a 
 kind of insulating shield, and the electricity cannot 
 reach the plate itself. Further, a layer of zinc is de- 
 posited on the copper, still further reducing the cur- 
 rent. Snee invented a method of freeing the " nega- 
 tive " plate by covering it with finely divided plat- 
 inum. The hydrogen bubbles escaped from these 
 points with considerable success. In the Bichromate 
 cells the bichromate of potash chemically unites with 
 the hydrogen. The only successful method of get- 
 ting rid of this "polarization" produced by the hy- 
 drogen, is the interposition between the two electro- 
 des of a porous diaphram. Unglazed pottery is best. 
 To increase the output of the cell it is usual in addi- 
 tion to this device, to put a different solution inside 
 the porous cup from that outside. The hydrogen as 
 before is liberated at the surface of the zinc and 
 
42 <tUK0TIOVB AUD ANSWERS ABOl T ELI 
 
 reaches the porous cup. Some passes off upwards 
 into the air, the rest meets the acid or solution in the 
 porous cup and is taken into chemical union. The 
 L< ( lanche and Samson are illustrations of remark- 
 able successful one-fluid batteries. Their merit lies in 
 the large area of carbon or negative in com- 
 
 parison with the /inc. It requires some time for tl,i- 
 large surface to be coated with bubbles, and mean- 
 while the cakes of manganese, attached to the <-ar- 
 i, have chemically disposed of a good portion of 
 the gas. Still it is not possible to get a < -ontinuous 
 current from them for more than a juart-r of an 
 hour. They are particularly adapted to telephone 
 and hell work, which require only intermittent cur- 
 vity batt' - almost altogether u-ed 
 
 when- a con-tanf and continuous current U wanted, 
 as for lire Indeed t he 
 
 if they are not utili/ed after befog IV 
 working i<l<r. Tba] ai d< anl\ . cheap and ea-ily 
 : u hite voliitiofi ot' sulphate of /inc 
 ind the /inc in the top ot' the jar, and the blue 
 OOpptf in the lot t (.in. -eparated ly ^rax ity 
 i/iakes a |.ietl\ and happv illuMration of sim- 
 plicity a nd eHicac\ . |;un-en and QTOT6 lotteries are 
 .nit lo handle l'i-om the nature of the acids 
 j.loved, and their [}( i^ attended with noxious 
 In inc. \\hidi are dan^eroiiH to hreatli. 
 
DYNAMO^ AM) MOTORS. 43 
 
 CHAPTER IV. 
 
 DYNAMOS AND MOTORS. 
 
 What is a Dynamo t 
 
 A dynamo is a mechanical device for generating 
 electricity. In 1867 it was suggested by Siemens 
 and by Wheatstone that a coil of wire rotating be- 
 tween the poles of an electro-magnet might from the 
 residual magnetism induce a small current of electrici- 
 ty which when transmitted through the coils of the 
 electro-magnet might exalt its magnetism and so pre- 
 pare it to induce still stronger currents. It is certain 
 that electric currents derived from chemical action in 
 battery cells differ in nature from those produced by 
 mechanical motion in dynamos. In results however, 
 there is no perceptible difference. The current from 
 batteries is uniformly constant and regular in its 
 flow. From dynamos the current can be, at will, 
 uniformly continuous, pulsating, and even alternating. 
 Electric light and power were not practicable until 
 dynamos were invented. The electric currents at- 
 tainable from batteries, is extremely meagre and 
 costly, and except where very small amounts are 
 needed, as in telegraph and telephone apparatus, 
 have proved their utter incapacity. A dynamo 
 needs simply to be driven at a certain rate of speed 
 by a steam engine, or water-wheel, and while revolv- 
 
44 QUESTIONS AND ANSWEES ABOUT ELECTRICITY 
 
 DIRECT CURRENT DYNAMO. 
 
DYNAMOS AND MOTORS. 45 
 
 ing currents of electricity are developed, which can 
 be collected by suitable appliances and carried away 
 by wires to lamps, motors, etc. The currents are due 
 to magneto-electric induction. There are two types 
 of dynamos the continuous curretn and the alternat- 
 ing current. In the continuous current dynamo the 
 current generated always flows in the same direction, 
 there being a commutator from which the current is 
 
 ALTERNATING CURRENT DYNAMO. 
 
 collected by brushes. In the alternating current dy- 
 namo the current generated flows at rapid intervals, 
 first in one and then in the opposite direction. The 
 field magnets of this machine must have a continuous 
 current to excite them and this current is generated 
 by a small continuous current machine which is called 
 the exciter. There is no commutator but a col- 
 
46 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 lector consisting of two metal rings upon which the 
 brushes rest. Dynamos have been made in which no 
 iron at all was in the armature, but such machines 
 have a small output of electrical energy. Some ma- 
 chines have been made in which the armature is sta- 
 
 ELECTRIC MOTOR. 
 
 tionary, the field magnets of the dynamo revolving, but 
 they are as yet experimental. Usually the armature 
 forms the inside or the centre of the machine ; the 
 mechanical construction is then easiest and the more 
 delicate parts protected from injury. 
 
DYXAMOS AND MOTORS. 47 
 
 What is an Electric Motor? 
 
 An electric motor is, commonly speaking, the re- 
 verse of a dynamo. A dynamo, driven by mechani- 
 cal power develops electricity ; a motor absorbs the 
 electric current from a dynamo, and transforms elec- 
 trical power into mechanical power; restores, as it 
 were, the original power that actuated the dynamo. 
 It is erroneous to suppose that a motor will give back 
 more or even as much power as was expended in 
 driving the dynamo. Friction of bearings, resistance 
 of wires, and energy expended magnetising the iron 
 cause various losses which, from the principles of con- 
 servation of energy, are insurmountable. 
 What is an armature ? 
 
 In the usual forms of dynamos and motors the re- 
 volving part is called an " armature." This name is 
 borrowed from the phraseology adopted in days when 
 horse shoe permanent magnets were invented. The 
 piece of soft iron that is kept across the poles of a 
 magnet sometimes called the " keeper" is technically 
 defined as the armature. Its use is to provide a path 
 for lines of magnetic force as they travel from one 
 pole piece to the other. The armature of 'a dynamo 
 or motor consists of an iron core or cylinder mounted 
 upon a suitable shaft. Copper wires are wound over 
 the surface of this cylinder. As the magnetism 
 travels through the iron, currents of electricity are 
 generated in the wire, if the case at hand is a dynamo ; 
 or if it is a motor the wires serve to convey the cur- 
 rent from its source. There are several ways of ar- 
 ranging the coils of wire upon an armature, viz : 
 
48 QUESTIONS .AND AXSWEHS ABOUT ELECTRICITY. 
 
 w 
 
 o; 
 
 H 
 
 3 
 
 5 
 8 
 
DYNAMOS AND MOTORS. 49 
 
 Drum Armatures in which the coils are wound longi- 
 tudinally upon the surface of a cylinder or drum ; 
 Ring Armatures in which the coils of wire are wound 
 around a ring instead of going completely around 
 the outside of the armature core, each turn of wire 
 going through the opening in the middle and thence 
 back to the outer surface ; Pole Armatures in which 
 the coils are arranged radially with their poles point- 
 ing outwards, and Disc Armatures having coils 
 arranged in or on a disc. 
 
 What are Field Magnets upon Dynamos or Motors ? 
 Field magnets of dynamos are the "inductors." 
 "That is, they " induce " or persuade the current to be 
 generated. They are simply large and somewhat 
 peculiarly shaped electro-magnets. The first dyna- 
 mos were made with permanent steel magnets for the 
 inductors, and from that circumstance derive their 
 name, magneto-machines. Such machines are still in 
 use as in some medical apparatus and in telephone 
 call bells. For a given size electro-magnets are many 
 times stronger than permanent ones; besides iron is 
 cheaper than steel and more easily put in any desired 
 shape. Permanent magnets, so called, gradually lose 
 their strength, and the difficulty of " charging " them 
 is serious. Electro-magnets do not lose their strength 
 by use, but in most dynamos the regulating qualities 
 depend upon a variation of the magnetism in the 
 inductors. The ends of the field magnets are circu- 
 lar in form, and come very close to the armature, so 
 that the air gap, through which the magnetism must 
 
50 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 SECTION OF RIN(. A KM All KK 
 
 RING ARMATURE SHOWING METHOD OF WINDING. 
 
DYNAMOS AND MOTORS. 51 
 
 go to pass through the iron core in the least possible 
 distance. Cast-iron is usually employed for field 
 magnets, but it is common to see wrought iron form- 
 ing part of the magnetic circuit. The "pole pieces " 
 which embrace the armature are best made of cast- 
 iron, as they will hold some "residual" magnetism, 
 and serve to "start" the dynamo. Wrought iron 
 " cores " over which the wire is wound makes very 
 strong magnets. A cast or wrought iron block to 
 connect the ends of the magnets furtherest from the 
 armature is called the magnetic " yoke." Sometimes 
 the " fields" are used in a double capacity i. e., to fur- 
 nish magnetism, and to give mechanical strength to 
 the machine ; this principle is simply an economy of 
 material. Dynamos or motors are simplest made 
 with a single magnet, having the two poles N and S, 
 Multipolar machines are fast coming into the market 
 having several poles, alternately N and S arranged 
 symmetrically around the armature. Alternate cur- 
 rent machinery needs many poles in the magnetic in- 
 ductors. 
 What is a Commutator and WJiat is its Use ? 
 
 As a coil of wire that is wound upon an armature, 
 leaves one pole piece, a current is induced in the wire 
 in a certain direction, as the same coil continues its 
 revolution and approaches the next pole, a current is 
 induced in the opposite direction. A " commutator " 
 is a device to set all the alternate currents flowing in 
 one direction ; the commutator consists of separate 
 bars or segments of a circle, in number equal to the 
 number of armature coils. Each coil is successively 
 
52 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 connected to a different bar, and as these bars are all 
 carefully insulated from each other the current gener- 
 ated in one coil cannot interfere with that generated 
 in any other. The segments or bars are usually of 
 copper, as that metal is one of the best conductors of 
 electricity. The segments are held in place by means 
 of rings at the ends leaving the outer surface avail- 
 able to run. 
 
 What is the Use of ^Brushes upon a Dynamo or 
 
 Motor ? 
 
 The "brushes." The name of these necessary 
 adjuncts to dynamo and motor is due to* the brush- 
 like form in which the wires are grouped together. 
 By making the " brushes " of wires or thin leaves of 
 copper, a large number of points are in contact with 
 the commutator bars. The use of brushes is to col- 
 lect the current that is induced in the armature wind- 
 ing, and after the current has done its work, return it 
 to the armature. In other words the brushes provide 
 a path into the revolving armature and out again. In 
 dynamos for supplying arc lamps, the current is small 
 and the brushes consist of one layer of sheet copper, 
 about .3^ in thickness; dynamos for running incan- 
 descent lamps supply a large current, and the brushes 
 are made of many layers of fine copper wires or 
 copper foil. 
 
 What is the Difference Between a Ring and a Drum 
 
 Armature ? 
 
 The distinction between "ring" and "drum" arma- 
 tures is based, not upon the form of the core so much 
 as upon the ma nner of winding the conducting wires 
 
DYNAMOS AND MOTORS. 53 
 
 In the past, ordinary drum armatures had solid cores, 
 that is, the sheet iron discs of which the core consists 
 rested directly upon the shaft. All small machines 
 with drum armatures are constructed this way. The 
 wires are wound back and forth lengthwise of the core, 
 passing over the ends close to the shaft to get from one 
 side to the other. On the surface, the wires resemble 
 the arrangement of the tightening strings on a drum, 
 hence the name. In recent large dynamos, the mass 
 of iron would be entirely too large if extended to reach 
 the shaft, and the cores are hollow, or rather made in 
 the form of rings, with the wire still wound on the 
 outside surface only. Ring armatures derived their 
 name from the use of ring core such as has just been 
 described ; but the winding is threaded in and out, 
 first on the outer surface, then down the side, through 
 the ring, up the side again, and alongside the first 
 turn. Thus the entire outer and inner surfaces of the 
 ring are completely covered. Ring armatures first 
 received practical application in dynamos. Gramme 
 borrowed the idea from Pacinotti, and this class of 
 armatures is commonly known as the " Gramme ring." 
 Siemens developed the drum form and his name is 
 often used in connection with it. The recent prac- 
 tice of putting a drum winding or a ring core is 
 rather confusing to dynamo nomenclature. 
 What is a Collector Ming upon a Dynamo ? 
 
 Currents of electricity are developed in an arma- 
 ture in alternating impulses. Hence an alternating 
 current is in the more natural form. By use of a 
 commutator, all these currents may be set flowing in 
 
54 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 the same direction. Such a current may be said to 
 be " rectified." When it is desired to use an alter- 
 nating current, it must be taken from the armature 
 by means of collector rings, with brushes resting upon 
 them as in the case of a commutator. The wind- 
 ing on the armature is one continuous path, the dif- 
 ferent coils being connected together except at the 
 final ends. Each of these ends is brought to a sepa- 
 rate copper ring mounted upon the shaft. These rings 
 are insulated from each other, a brush upon each ring 
 serving to receive the current. The current passes ofT 
 one brush and returns by the other. An instant later 
 No. 2 brush receives the current, returning by No. 1, 
 and so on alternately, in some machines making 15,000 
 reversals per minute. 
 What is the Difference Between a Series, Shunt or 
 
 a Compound Wound Dynmo or Motor ? 
 
 In order to generate the magnetism in electro-field 
 magnets a current of electricity must be employed. 
 In the first, dynamos, batteries or small magneto- 
 machines were used. Present alternating current 
 dynamos usually receive current for their fields from 
 small direct current dynamos called " exciters," The 
 main dynamo is then said to be "separately excited." 
 It is usual to have each direct current dynamo excited 
 by current from its own armature. Sometimes 
 it is necessary to send the entire current developed in 
 the armature around the field magnets ; in this case 
 the wire should be somewhat larger than that on the 
 armature. Such a field winding is called "series." 
 Instead of sending all the current around the field, a 
 
DYNAMOS AND MOTORS. 
 
 55 
 
 small part, one or two per cent of the entire current, 
 can be set aside for this sole purpose. Then the wire 
 is fine and the small amount of current is compensated 
 for by making many turns around the iron of the 
 field. The current thus consumed does not go away 
 
 SERIES WOUND DYNAMO. 
 
 from the dynamo at all, but has a circuit of its own 
 apart from the lamps or motors supplied by the main 
 part of the current. Such a field winding is called 
 " shunt.'' Combinations of shunt and series make a 
 "compound" winding. 
 
56 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 Q O Q O 
 
 O O O O O O O OQcT 
 
 I 
 
 SHUNT WOUND DYNAMO. 
 
 oooooooooo rooooo 
 
 COMPOUND WOUND DYNAMO. 
 
DYNAMOS AND MOTORS. 57 
 
 For what Purpose are each of these Different Wind- 
 ings Used? 
 
 Dynamos for arc lighting are " series " wound. 
 As the number of arc lamps in a given circuit varies, 
 the potential (in volts) must vary accordingly. The 
 current (in amperes) must be kept constant in order 
 that the lamps may burn with a uniform brilliancy. 
 This " regulation " can be effected by making the field 
 magnetism depend upon the number of lamps burning. 
 The " series " winding accomplishes this result. For 
 incandescent lamps and plating, the potental (in 
 volts) should remain constant, while the current (in 
 amperes) should increase as the load increases. The 
 field magnetism should remain constant or nearly so. 
 The "shunt " winding furnishes a constant magnet- 
 ism, practically independent of the real load of the 
 dynamo. Shunt winding as just explained will make 
 a dynamo supply its current at a nearly constant poten- 
 tial. If a few c< series " turns are added the regula- 
 tion becomes exact and automatic. For losses due 
 to resistance of wires and slipping of belts as dyna- 
 mos increase their load or work there are a few extra 
 series turns put on. This enables the dynamo to raise 
 its potential slightly to cope with all demands. For 
 instance, ordinary incandescent dynamos run at 110 
 volts when few lamps are burning. As the full num- 
 ber is added, the potential should raise to about 125 
 volts at the dynamo, in order that the lamps some 
 distance away may receive 110 volts. Such winding 
 is called " compound " and is receiving extended ap- 
 plication on incandescent and railway dynamos. 
 
58 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 CHAPTER V. 
 
 ELECTRIC LAMP S . 
 
 What is an Electric Arc f 
 
 In 1810 Sir Humphrey Davy discovered the phe- 
 nomena of the electric arc. His description is as fol- 
 lows : " When pieces of charcoal about an inch long 
 and one-sixth of an inch in diameter were brought 
 near each other (within the thirtieth or fortieth part 
 of an inch) a bright spark was produced, and more 
 than half the volume of the charcoal became ignited 
 to whiteness; and by withdrawing the points from 
 each other, a constant discharge took place through 
 the heated air in a space equal at least to four 
 inches, producing a most brilliant ascendant arc of 
 light, broad and conical in form in the middle." Of 
 course the light did not last long, as the charcoal, 
 being soft, burned rapidly away. The necessary cur- 
 rent was supplied by a battery of 2000 cells, with zinc 
 and copper plates, the exciting fluid being dilute sul- 
 phuric and nitric acids. Davy touched the charcoal 
 points together horizontally after attaching the wires 
 to the battery, and then separated them. The stream 
 of hot flames which followed or joined the points 
 were deflected by air currents and took the form of 
 an arch or curve, which gave the name to the phe- 
 
ELECTRIC LAMPS. 
 
 59 
 
 THE ELECTRIC ARC. 
 
60 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 nomena. *" The arc proper is composed of a stream 
 of vapor arising from the actual boiling or vaporiza- 
 tion of the solid or fused ends of the separated con- 
 ductors. In so far as the surrounding air mixes or 
 combines with this vapor stream, it is modified by the 
 presence of oxygen and nitrogen, but the air or any 
 other gas is not essential to be present, and is merely 
 incidental to the formation of the true arc stream in 
 air." 
 Describe the Arc Lamp. 
 
 The Arc Lamp now in general use consists sim- 
 ply of two hard carbon rods, one above the other, 
 and a mechanical contrivance to feed them. It is 
 necessary that the mechanism should start the arc by 
 causing the pencils to touch and then separate them 
 to the requisite distance for the production of a 
 steady arc ; it should also cause the carbon to be fed 
 into the arc as fast as they consume, and to approach 
 or recede automatically, in case the arc becomes too 
 long or too short ; it should further bring the carbons 
 together for an instant, to start the arc again if it 
 should go out. There are a great many forms of arc 
 lamps, but the one in general use by a number of the 
 large companies is the clutch lamp. This is a simple 
 device, consisting of a clutch to pick up the upper 
 carbon holder, the lower carbon remaining fixed. The 
 clutch is worked by electro-magnets, through which 
 the current passes. If the lamp goes out the magnets 
 release the clutch, and the upper carbon falls by its 
 own weight and touches the lower carbon. Instantly 
 
 *Paper read by Prof. Elihu Thomson at Providence, R. I. 
 
ELECTRIC LAMPS. 
 
 61 
 
 ABC LAMP. 
 
62 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 the current starts round the electro-magnets, caus- 
 ing it to act on the clutch, which grips the carbon- 
 holder and raises it to the requisite distance. When 
 the arc grows too long the lessening attraction on the 
 clutch permits the carbon-holder to advance. In a 
 double-carbon lamp when one carbon has burned out 
 
 INCANDESCENT LAMP. 
 
 the current is shifted automatically to the other, thus 
 making the life of the lamp twice as long. 
 Describe the Incandescent Lamp. 
 
 The lamp consists of a glass globe or bulb, from 
 which the air has been exhausted, containing a car- 
 bonized fiber of bamboo. The carbonized fiber is at- 
 
ELECTRIC LAMPS. 
 
 63 
 
 tached to two platinum wires fused in the glass, the 
 free ends of the wires being connected to the copper 
 sockets of the lamp, which are insulated from each 
 other by Plaster of Paris. The wires are then con- 
 nected to the external circuit. Figure 1 is a sectional 
 view of a familiar type of the 16 candle-power lamp, 
 
 c being the carbon loop ; b the glass bulb ; f the col- 
 lar; and w w the platinum leading wires. In order 
 to produce light the carbon loop is brought to a white 
 heat or incandescence, by the heat energy of an elec- 
 tric current. No known substance will endure this 
 temperature of white heat without, in time, disinte- 
 grating, but carbon seems to stand this white heat 
 
64 QUESTIONS AND ANSWEItS ABOUT ELECTRICITY. 
 
 longer than any other substance especially when it is 
 enclosed in a high vacuum. But all incandescent 
 lamps " fail " after running a certain number of hours, 
 because their filaments disintegrate they do not 
 burn at the temperature of incandescence. The aver- 
 age life of an incandescent lamp is from six hundred 
 to one thousand hours, after that the filament be- 
 comes worthless and must be renewed. The carbon 
 loop is usually made from some vegetable fiber, such 
 as is obtained from bamboo or some plant possessing 
 a similar structure. Silk is used by some manufactur- 
 ers but as yet has not proved to give as good results 
 as bamboo. As the object is to obtain a compact car- 
 bon, a fiber rich in this element is the best. It must 
 have a straight grain and possess great tensile 
 strength in order to endure the process of reducing 
 its size to the required proportions. This process 
 consists of shaving or drawing them through a series 
 of dies, each die removing a small portion of the sur- 
 face until the proper diameter is obtained. This di- 
 ameter is varied according to the candle-power and 
 voltage of the lamp. Having brought the fibres to 
 the proper size, they are then baked or carbonized by 
 a method similar to gas making, except that the resi- 
 due is the article particularly desired, and not the 
 gases that are driven off. The fibre is now bent 
 around a graphite block so as to form a loop, a num- 
 ber of fibres being put on each block, which are then 
 packed in a pot containing carbon dust and subject to 
 the intense heat of a furnace for a number of hours. 
 During this process air must be excluded from the 
 
ELECTRIC LAMPS. 65 
 
 pot containing the fibres, otherwise a certain portion 
 of their structure will be burned. Having properly 
 carbonized the fiber it is attached to the wires (w w) 
 which have previously been fused into the glass (s) ; 
 this is now enclosed in the glass bulb and the lamp 
 is now ready to be connected to the vacuum pump 
 by means of which the bulb is exhausted of air. 
 
66 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 CHAPTER VI. 
 
 MISCELLANEOUS ELECTRICAL APPARATUS. 
 
 Describe an Electric Bell. 
 
 The electric bell in common use consists of an 
 electro-magnet having an armature to which is at- 
 tached a small hammer, so arranged that by sending 
 a current through the circuit the armature is made 
 to vibrate and the hammer beats against a gong. 
 The bell is usually operated by a battery, and the 
 circuit may be closed by simply pressing a small push 
 button, thus causing the current to flow along the 
 line and around the coils of the electro-magnet, which 
 draws the armature toward it. A contact breaking 
 consists of a spring, tipped with platinum, which rests 
 against a platinum tipped screw is attached to the 
 armature. This makes and breaks the circuit which 
 causes the hammer to beat against the gong and then 
 fall back against the screw which immediately closes 
 the circuit again, causing the armature again to be 
 attracted toward the magnet, and so on. In fact an 
 electric bell is a minature electric motor. 
 Describe the Electric Telegraph. 
 
 The principles of electro-magnetism early suggested 
 the possibilities of transmitting messages by means of 
 wires. That the electro-magnet could be at a long 
 distance from the battery, or that an operator by 
 
MISCELLANEOUS ELECTRICAL APPARATUS. 67 
 
 merely touching two wires together, could cause a 
 movement in an electro-magnet a long distance away 
 was a fact not long left undeveloped. Early it was 
 proposed to use 26 or more separate wires and send 
 impulses of electricity over these in the order desig- 
 nated by the letters of the words to be spelled. The 
 expense of this large number of wires happily com- 
 pelled the invention of some cheaper device. Prof. 
 Morse found that two wires would be sufficient, the 
 different letters to be distinguished from each other 
 by allowing short, long or interrupted impulses 
 of current to be sent over the lines. When the wires 
 were touched together by means of a "key" at the 
 sending station the current would go away to the 
 end of the wires and attract the armature of an 
 electro-magnet at the receiving station, on this arma- 
 ture is a needle point that punctures a paper strip 
 kept travelling beneath by means of cloth work. If 
 the current passes for an instant only, a prick is made 
 through the paper, called a Ci dot," if for a longer 
 time a slit or " dash." By an accepted code made 
 by combinations of dots and dashes, the whole alpha- 
 bet and symbols are arranged. Since this receiving in- 
 strument records the messages, it is called a "register." 
 Attempts at economy led to experiments with rail- 
 road rails used as one wire. The device was success- 
 ful, and it was even found that the earth was a suffi- 
 ciently good conductor. To an experienced operator 
 the clicks of the electro-magnet are as intelligible as 
 the record on a strip of paper ; it is usual now to dis- 
 
QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
MISCELLANEOUS ELECTRICAL APPARATUS. 69 
 
 pense with the recording device and depend upon 
 sound alone; the receiver is then called a "sounder." 
 
 1 
 
 b 
 
 c 
 
 d 
 
 e 
 
 t 
 
 g 
 
 
 h 
 
 j 
 
 k 
 
 
 1 
 
 m 
 
 
 n 
 
 
 
 pqrstuv w 
 
 x y z & . ? 
 
 i 2 3 A 
 
 10 
 
 MORSE TELEGRAPH ALPHABET. 
 
 What is a Relay? 
 
 For long distances the number of batteries required 
 to operate the sounder is large. Even thus equipped 
 with batteries the current in very small and can be 
 used to operate a "relay" only. The relay is pro- 
 vided with a delicately balanced armature, the motions 
 of which, under the influence of the current, open 
 and close a battery circuit, which is located at the re- 
 ceiving station. The sounder operated by these "local" 
 cells strikes the sounder loud enough to be heard. 
 The progress of telegraphy has even surpassed the 
 use of a special wire for each operator. Duplex and 
 quadruplex systems allow two or /bwr messages to be 
 sent over the same wire at the same time by different 
 operators without interference. A diagram of a 
 telegraph circuit is given in Fig. 2. 
 
70 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 f! 
 
 rr 
 
 a 
 
 B 
 
 - 
 
 2 @@ D 
 
MISCELLANEOUS ELECTRICAL APPARATUS. 71 
 
 Describe the Telephone. 
 
 It is strange to think that the telephone operates on 
 the same principle as the telegraph. The only differ- 
 ence consists in the delicacy of the telephonic appara- 
 tus, and the minuteness of the amount of the electric 
 current employed. A telegraphic message is sent by 
 the movements of a key in the operator's hand ; a 
 telephonic message by the vibrations of a diaphram 
 when affected by the undulations of the voice. 
 A simple telephone, as constructed by Bell, con- 
 sisted of a bar magnet, on one end of which was a 
 small coil of fine insulated wire. In front of this end 
 and very close but not touching was a thin iron dia- 
 phram, such as tintypes are made on. The ends of the 
 wires were led away to an exactly similar instrument. 
 When the vocal disturbances in front of one telephone 
 vibrated the diaphram, minute currents of electricity 
 were generated, which travelled over the wires and so 
 affected the magnet in the receiving telephone that 
 similar vibrations of that diaphram were produced 
 and restored, as it were, the original words. The 
 present telephonic installation is somewhat more 
 complicated, in fact, all that the original Bell tele- 
 phone is used for is as a receiver. A magneto- 
 machine is used to ring the bells, a Blake and Edison 
 transmitter receives the message and a battery to 
 supply a current. 
 
 What is a Microphone? 
 
 The real transmitting apparatus of a telephonic 
 system is the " microphone." This device takes the 
 meagre motions produced by the voice and magnifies 
 
72 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 their effect. A battery supplies a current which flows 
 as long as the telephone receiver is off its hook. The 
 current passes through two carbon buttons in suc- 
 cession, that lie touching each other loosely, then 
 through the primary of a small transformer, or induc- 
 tion coil and back to the battery. The primary of the 
 
 FIGURE 3. 
 
 coil is attached to the line wires, or to one wire, the 
 other to the ground. When, by the voice, the dia- 
 phram, against which the carbon buttons rest, vibrates, 
 these buttons are compressed slightly, or released, 
 which causes a better or poorer path for the battery 
 current. The transformer magnifies the intensity of 
 these variations and goes out over the line into the 
 receiver at the other end. An illustration of a micro- 
 phone is given in Fig. 3. 
 
MISCELLANEOUS ELECTRICAL APPARATUS. 73 
 
 What is an Induction Coil? 
 
 Any coil, consisting of two pieces of wire entirely 
 distinct and independent of one another, wound upon 
 a core generally, but not always of iron. The passage 
 of an alternating, vibratory, or intermittent current 
 through one of these wires, (termed the primary coil) 
 induces a current to flow in the other wire, provided its 
 two ends are joined through a conducting substance. 
 Ruhmkorff coils, converters, transformers and weld- 
 
 INDUCTION COIL. 
 
 ing machines are all induction coils. An induction 
 coil may be made by winding a short length of rather 
 large wire, say No. 16, and a great length of very fine 
 wire around a bundle of soft iron wire, carefully 
 insulating the coils from one another, and both from 
 the iron. By passing the current from a battery and 
 " interrupter " through the heavy coil, a comparatively 
 strong potential may be obtained from the fine wind- 
 ing, sufficient to give a shock or a bright spark when 
 the ends are brought together. 
 
74 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 What is a Ruhmkorff Coil ? 
 
 A kind of induction coil invented by Ruhmkorff. 
 Originally the Ruhmkorff coils were made in com- 
 paratively small sizes, as it was found impossible to 
 insulate the secondary wire sufficiently to resist the 
 high potential of the electricity. The different layers 
 of wire were laid the entire length of the coil, but 
 separated from each other by silk. Ritchie wound 
 -the secondary in sections, each on a spool of the 
 finished diameter of the cell, but very short, requiring 
 
 KUIIMKOKFF COIL. 
 
 eight or ten such spools in a row to give the requisite 
 total length. These spools were made of hard rub- 
 ber, and could stand very high potentials. Ruhm- 
 korff bought one of these coils, took it to pieces, and 
 copied the construction in the large sizes of his 
 manufacture. 
 
 What is a Transformer? 
 
 A "transformer" or "converter" is an induction coil, 
 designed as a rule to reduce high to low pressure in 
 connection with electric lighting. 
 
MISCELLANEOUS ELECTRICAL APPARATUS. 
 
 75 
 
 TRANSFORMER. 
 
76 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 What is the Principle of the Electric Welding 
 
 Machine f 
 
 An electric welding machine is a kind of induction 
 coil, having a very short, heavy secondary, generally 
 consisting of but one turn and capable of carrying an 
 enormously heavy current reduced by the primary. 
 Pieces of metal attached to movable ends of the 
 secondary are melted, or welded at their ends by the 
 heavy current. The welding machine Is used to weld 
 or unite pieces of metal, such as pipe, rod, wire, etc. 
 
ELECTRICAL MEASUREMENT. 77 
 
 CHAPTER VII. 
 
 ELECTRICAL MEASUREMENT. 
 
 Ifow are Currents of Electricity Measured? 
 
 By measuring the effect of a current upon a mass 
 of iron or upon a magnetic needle, or upon another 
 current. Thus, imagine a small coil of wire with its 
 axis vertical. Let a bar of soft iron be suspended 
 vertically by a spring with its end just entering the 
 coil. The bar should be of such size as nearly to fill 
 the interior aperture of the coil. If now a current is 
 passed through the coil the bar will be attracted and 
 will descend more or less deeply into the coil as the 
 current is stronger or weaker. Such are the essential 
 parts of an apparatus for measuring a current. The 
 movements of the core indicate strength of the cur- 
 rent. Again let a coil of wire be placed around a 
 compass. The wire must be carried across the top, 
 down one side, across the bottom and up the other 
 side. Then, if the coil is turned north and south, a 
 current passed through it will make the needle of the 
 compass turn aside, either to the east or west. The 
 amount of displacement will be greater as the current 
 is greater. This is another type of current measur- 
 ing apparatus. The first described apparatus is a 
 solenoid instrument, the second described one is a 
 galvanometer. In all cases, either by trial or calcula- 
 
78 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 tion, the movements of a galvanometer needle or of 
 the other moving piece in a current measurer must be 
 made to give the strength of current causing them. 
 What are the Names of the Different Electrical 
 Units and What do They Mean? 
 The ampere is the unit of current strength. It 
 means a strength of current that will decompose 
 .09326 milligrams of water in a second ; that will pre- 
 cipitate 1.11815 milligrams of silver per second from 
 a solution of metal. The above weights are given 
 differently by different authorities. The coulomb is 
 the unit of quantity. It is the quantity of electricity 
 passed by one ampere per second. Hence the values 
 just given for the ampere are really the values of the 
 coulomb. The volt is the unit of electromotive force. 
 It is what produces a current through a wire or other 
 conductor, just as pressure forces water throngh a 
 pipe. A gravity battery, such as seen in telegraph 
 offices gives an electromotive force of almost exactly 
 one volt. The ohm is the unit of resistance. Just as 
 a pipe by friction resists the passage of water, so a 
 wire or other conductor resists the passage of elec- 
 tricity. A large wire like a large pipe resists it less 
 than a small one. If twice as thick as a given wire, 
 it resists only one quarter as much. A pure copper 
 wire .325 inch thick and 10,000 feet long, or one .10 
 inch thick and 1,000 feet long has almost exactly one 
 ohm resistance. The farad is the unit of capacity. It 
 is the capacity of a surface which at one volt pres- 
 sure will retain one coulomb of electricity. Electricity 
 acts like air. Twice as much air as it normally holds 
 
ELECTRICAL MEASUREMENT. 79 
 
 can be pumped into a given bottle if the pressure is 
 doubled, and three times as much if the pressure is 
 tripled and so on. So a surface of one farad capacity 
 will hold two farads at two volts pressure, and three 
 farads at three volts pressure. The capacity of a sur- 
 face is the same, whether it is the surface of a solid 
 metallic object or is merely coated with the thinnest 
 gold leaf. There is no such thing as capacity of a 
 solid volume, it is purely superficial. These are the 
 five principal electric units used in practice. 
 What is the Law of Inverse Squares ? 
 
 The law of change of intensity of radiant energy 
 with distance. If light is given by a point or very 
 small object, the light given by it is stronger, the less 
 the distance. The law of inverse squares state that 
 the intensity of the light at a distance of 2 is one- 
 fourth as strong as at a distance of 1 ; at a distance of 
 8 it is one-ninth as strong ; at a distance of 4 it is 
 one-sixteenth as strong and so on, the denominator of 
 the fraction in each case being the square of the dis- 
 tance expressed in terms of any selected standard 
 distance. The same law applies to heat derived by 
 radiation from a point or small object, and to other 
 such cases. It is the law of gravitation. While 
 theoretically it is only true when applied to points, it 
 is practically accurate when the objects are very 
 small in proportion to their distances. This is why 
 it appilies to the sun, the planets and their satellites. 
 
 What is the Unit of Quantity of Electricity f 
 The coulomb is the practical unit. 
 
80 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 What is the Unit of Pressure ? 
 The volt is the practical unit. 
 
 What is the Unit of Energy ? 
 
 The unit of electric energy is a coulomb urged by a 
 pressure of one volt. It is called the volt coulomb. 
 But as a rule what is wanted is the rate of energy, not 
 the mere quantity of it. The unit of activity or rate 
 of energy is an ampere urged by a pressure of one 
 volt ; it is called the volt-ampere or the watt. Seven 
 hundred and forty-six (about) watts are equal to one 
 horse power. 
 
 What is Ohms Law? 
 
 The law stating the relations of current strength, 
 electric pressure and resistance. It states the simplest 
 possible relation, one which has by experiment been 
 found to be the true one. It states that the current 
 strength is equal to the electric pressure divided by 
 the resistance, when all are expressed in accordant 
 units, such as the ohm, volt and ampere. Thus, in a 
 circuit of one ohm resistance, with one volt electro- 
 motive force or electric pressure, a current of one 
 ampere will be produced. Again, if in the same 
 circuit there were ten volts pressure, there would be 
 ten amperes of current ; if the resistance of the circuit 
 were twice or three times as great, the current would 
 be one-half or one-third as strong. 
 
 What is a Resistance in a Circuit ? 
 
 A wire or other conductor acts for electricity as a 
 pipe does for water. It resists its passage. If large 
 it resists less than if small, just as a pipe does. If 
 
ELECTRICAL MEASUREMENT. 81 
 
 twice as long a wire resists twice as much as another, 
 otherwise the same. If half as thick as another wire 
 otherwise the same, it resists four time as much, or in 
 inverse proportion to its cross-sectional area .5. 
 
 What is Meant by Potential ? 
 
 Electricity is evenly distributed, except where 
 some disturbing cause crowds more into one place 
 than into another. This raises the potential of the 
 given place, and the rise of potential, which is really 
 the rise of electric pressure, tends to drive the elec- 
 tricity back again. It will force it in a current 
 through a conductor leading to a place of less poten- 
 tial. Potential is best thought of as electric pressure. 
 
 What is a Watt ? 
 
 The unit of rate of electric work or energy. It is a 
 current of one ampere urged by a pressure of one 
 volt. It is sometimes called a volt-ampere. (See 
 Answer 6). 
 
 What is the Unit of Current Strength ? 
 
 The ampere, already described. (See Answer 2). 
 Describe the Galvanometer, its Construction and 
 Use. 
 
 Wind a number of turns of wire around a wooden 
 ring and support it on its edge. Inside the ring place 
 a compass. Turn the ring so that it is in line with 
 the magnetic needle, and you have a galvanometer. 
 In the real instruments every kind of modification is 
 introduced. The coil may have a very large number 
 of turns, and be made of exceedingly fine wire, or it 
 may be a single turn of thick wire, or may be repre- 
 
82 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 sented by a bent bar of copper. The magnetic needle 
 may be long or short, and may be poised on a point, or 
 may be suspended by a very fine filament or thread, 
 sometimes so fine that it is barely visible. In the 
 latter case a little looking glass is attached to the 
 needle. This reflects a spot of light, exactly as boys 
 do with a hand mirror to annoy people in the street. 
 The movements of this spot of light are used to show 
 
 GALVANOMETER. 
 
 the minute movements of the needle. If a current is 
 passed through the coil of a galvanometer, the needle 
 will try to turn so as to point right across the coil. 
 The extent of its movement will depend upon the 
 strength of the current. The galvanometer is used 
 for three general purposes. One is to show if there 
 is any electromotive force or potential difference 
 between two points. For this use it must be very 
 delicate, but in this case it is not a measuring instru- 
 
ELECTRICAL MEASUREMENT. 83 
 
 ment, it is only used as an indicator. The next pur- 
 pose is to measure currents. The needle will be 
 deflected more or less in proportion to the current and 
 the relation of the deflections to the currents must be 
 ascertained for each galvanometer. The third pur- 
 pose is to measure the electromotive force or poten- 
 tial difference between two points. A galvanometer 
 with a coil of a great number of turns of very fine 
 wire is used for this. The deflections of the needle 
 are in proportion to the current going through the 
 coil, and this current is proportional to the electro- 
 motive force or potential difference between the ends 
 of the galvanometer coil. If, therefore, these ends 
 are connected to the points whose potential difference 
 is to be measured, the movements of the needle will 
 be greater or less as this potential difference is greater 
 or less. This gives the basis for the measurement. 
 There are a great number of ways of conducting 
 these measurements. A whole book might be devoted 
 to the different methods of measurements, in almost 
 all of which the galvanometer is used in some way. 
 Describe a Voltmeter. 
 
 A voltmeter is a current measuring instrument of 
 any type, which is wound with fine wire of very great 
 length. In the first answer and in the twelfth answer 
 current measures are described. Either one, with 
 proper graduation, becomes a voltmeter if its coils 
 are of fine enough wire and of high enough resist- 
 ance. Ayrton's voltmeter is of the solenoid type, as 
 described in the beginning of the first answer. The 
 attracted bar is suspended by a long spiral spring. 
 
84 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 SPRING VOLTMETER AND SPRING AMMETER. 
 
ELECTRICAL MEASUREMENT. 85 
 
 The effect of this is that as the bar is drawn down- 
 ward, it rotates or turns around its vertical axis. An 
 index like the hand of a clock is fastened to the top 
 of the bar, and as the current passing through the 
 coil attracts and draws the bar downwards, it twists 
 around and the hand moves like the hand of a clock 
 over a horizontal dial. A scale marked off by trial 
 for volts is provided so that the hand points to the 
 volts at once. The coil is of very fine wire with a 
 great number of turns or convolutions. A current 
 passing through a conductor heats it ; a strong current 
 heats it more than a weak one does. Cardew's volt- 
 meter is based on this principle. It includes a long 
 fine wire, through which a current due to the differ- 
 ence of potential between any two points of a circuit, 
 to which it may be connected, passes. This current 
 heats the wire more or less and expands it. The 
 expansion moves an index over a scale and the move- 
 ments of the index indicate the voltage to which the 
 current is due. 
 
 Describe an Ammeter. 
 
 An ammeter is identical with a voltmeter, except 
 that it is wound with thicker wire, and of fewer 
 turns. The difference between them is this. The 
 ammeter has to measure the entire current that is 
 flowing, and all of that current must go through its 
 coils. The voltmeter, on the other hand, must meas- 
 ure an exceedingly small fraction of the current, so 
 small that it can be taken out of the circuit, without 
 affecting it. Hence an ammeter must be of very low 
 
86 QUESTIONS AND ANSWERS ABOUT. ELECTRICITY. 
 
 WHEATSTONE'S BRIDGE. 
 
ELECTRICAL MEASUREMENT. 87 
 
 resistance, while the voltmeter should be of very 
 
 high resistance. 
 
 Describe a Wheats toners Uridge. 
 
 A Wheatstone bridge is a contrivance for measuring 
 the resistance of any conductor. Imagine two con- 
 ductors lying side by side in a straight line, with their 
 ends connected together in pairs, and a current sent 
 through them. If a wire is now connected across 
 them and is so placed that the proportionate resist- 
 ances of the two parts of one conductor shall be the 
 same as that of the two parts of the other conductor, 
 no current will go through the cross connecting wire. 
 A Wheatstone bridge consists of the above system of 
 connections, with a very sensitive galvanometer in 
 the cross circuit. The four divisions, determined by 
 the cross circuit connections are called the arms of 
 the bridge. The conductor whose resistance is to be 
 measured, forms one arm. The other arms are made 
 up of resistances, all of which are known, or one of 
 which is known, and the proportions of the other two 
 to each other are known. By varying these resist- 
 ances until the galvanometer shows no current the 
 proportion of all four arms to each other is known, 
 and hence the actual resistance of the unknown 
 wire. 
 
QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 CHAPTER VIII. 
 
 GLOSSARY OF ELECTRICAL TERMS. 
 
 ACCUMULATOR. See battery and condenser. 
 
 AMMETER. An instrument for measuring current 
 strength. 
 
 AMPERE. The unit of current strength. It is the 
 flow of electricity produced by the pressure of one 
 volt on a resistance of one ohm. 
 
 ARC. The stream of hot gasses and particles of 
 matter arising from the boiling or vaporization of 
 two conductors when a current is passing between 
 them. 
 
 ARMATURE. That part of a dynamo in which the 
 current is induced. It may be a stationery or mov- 
 ing part, but is generally the latter, and is composed 
 of coils of wire which "cut" the lines of magnetic 
 force produced by the fields. This "cutting 57 
 induces a current in the coils. 
 
 BATTERY. One or more cells in which electricity 
 is produced by chemical action. There are two 
 elements of different substances and a liquid in 
 every voltaic battery. A primary battery is one 
 in which the "elements" are placed and used until 
 they are worn out. In a secondary or storage bat- 
 tery or accumulator the " elements " are placed in 
 the cell and first " formed" by the passage of a 
 
GLOSSARY OF ELECTRICAL TERMS 89 
 
 current of electricity through them. The cell is 
 then said to be charged and may be used to supply 
 electricity. The term battery is also used to desig- 
 nate a collection of Leyden jars in which the static 
 electricity is stored. 
 
 BRUSH. A collection of metal sheets or wires which 
 press against the commutator of a dynamo to col- 
 lect the electricity, or of a motor to supply it. Car- 
 bon brushes are coming into use now, especially in 
 railway work. 
 
 B. & S. Brown & Sharp. The wire gauge used in 
 Amereica. 
 
 B. W. G. Birmingham wire gauge. The English 
 wire gauge. 
 
 CELL. The jar in which the elements and liquid of 
 a battery are placed. The term is used also for the 
 jar and its contents. 
 
 C. G. S. The abbreviation of centimeter, gramme, 
 second, and used to designate the so-called absolute 
 system of measurements. 
 
 CIRCUIT. A system of conductors over which elec- 
 tricity passes. 
 
 COIL CLOSED. The coils of an armature are said 
 to be closed when the end of one is connected to 
 the beginning of the next at the commutator bar. 
 An open coil armature is one in which each coil is 
 independent of the others and has its own commu- 
 tator bars. 
 
 COMMUTATOR. That part of a dynamo on which 
 the current from the armature is rectified before 
 passing to the external circuit. The current in a 
 
90 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 given section of an armature alternates and must be 
 made continuous on leaving it. This is done by 
 the commutator, which consists of a series of insu- 
 lated metal bars connected to the armature wires, 
 and so placed as to feed into different brushes as 
 the current changes. 
 
 CONDENSER. An apparatus for collecting and 
 holding electricity. It consists of alternate layers 
 of conducting sheets and insulating material, the 
 conductors being very close together, and the ad- 
 jacent ones being charged with the opposite kinds 
 of electricity. Their proximity enables them to 
 hold a larger amount of electricity than they could 
 if alone. Condensers are sbmetimes called accumu- 
 lators. 
 
 CONDUCTOR. A substance which will allow the 
 passage of electricity over it. All substances will 
 do this, but some to so small an extent that they 
 are called insulators. 
 
 COULOMB. The unit of electric quantity. It is the 
 amount of electricity which flows past a given point 
 in one second on a circuit conveying one ampere. 
 
 CURRENT. The flow of electricity in a conductor 
 analogous to the flow of water in a pipe. A contin- 
 uous current is one that does not change its direc- 
 tion, while an alternating current is one that 
 periodically reverses. 
 
 CUT OUT. An arrangement for interrupting a cur- 
 rent or for shunting it around some part of a 
 circuit. 
 
GLOSSARY OF ELECTRICAL TERMS. 91 
 
 DYNAMO. A machine driven by power which fur- 
 nishes electricity. 
 
 DYNAMOMETER. An apparatus for measuring 
 the power given out or consumed by a machine. 
 An electro-dynamometer is an instrument for 
 measuring a current by the mutual action of two 
 coils through which it passes. 
 
 E. M. F. An abbreviation for electro-motive force. 
 This is the pressure which forces the electric cur- 
 rent through a conductor. 
 
 ELECTRO-MAGNET. A magnet produced by pass- 
 ing a current through a coil of wire around a soft 
 iron core. The core is magnetized while the cur- 
 rent flows, but loses its magnetism when the current 
 stops. This form of magnet may be made much 
 more powerful than a permanent magnet, and is 
 therefore used in place of the latter in dynamos. 
 
 FARAD. The unit of capacity. A condenser that 
 will hold one coulomb at a pressure of one volt has 
 a capacity of one farad. 
 
 FILAMENT. In an incandescent lamp the thread of 
 carbon which becomes luminous when the current 
 is passed through it. 
 
 GALVANOMETER. An instrument for detecting 
 and measuring the electric current by the action of 
 a coil of wire upon a magnetic needle. 
 
 INDUCTION. A current is said to be induced in a 
 conductor when it is caused by the conductor cut- 
 ting lines of magnetic force. A fluctuating current 
 in a conductor will tend to induce a fluctuating cur- 
 rent in another running parallel to it. A static 
 
92 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 charge of electricity is induced in neighboring bodies 
 by the presence of an electrified body. A magnet 
 "induces" magnetism in neighboring magnetic 
 bodies. 
 
 INDUCTION COIL. An arrangement by which an 
 alternating or fluctuating current in a coil of wire 
 will induce an alternating current in a parallel coil. 
 
 INSULATOR. The opposite of a conductor. A 
 body which will not allow the passage of electricity 
 except in such small quantities as to be negligable. 
 
 LINES OF FORCE. Imaginary lines which radiate 
 from a magnet and " show by their direction the 
 path which a free magnetic pole would take if left 
 to itself. Conventionally, the strength of a mag- 
 netic field is indicated by the number of these lines. 
 Their form is shown by the well-known experiment 
 with the magnet and iron filings. 
 
 MAGNET. A body possessing the property of at- 
 tracting iron, steel and a few other metals. 
 
 MAGNETIC FIELD. The space around a magnet 
 in which its power of attraction is exhibited. 
 
 MULTIPLE or MULTIPLE ARC. A method of 
 connecting electric conductors by which a number 
 of sources of electricity feed directly into or a unm- 
 ber of receivers of electricity take it directly from 
 the same mains. 
 
 NEGATIVE. A conventional term to indicate the 
 direction of flow of a current, or the state of elec- 
 trification of a body. The negative or terminal of 
 a dynamo is the one at which electricity enters it 
 from the external circuit, while the negative ter- 
 
GLOSSARY OF ELECTRICAL TERMS. 93 
 
 minal of a lamp or instrument is that connected to- 
 wards the negative terminal of a dynamo. It is 
 designated by 
 
 OHM The unit of electrical resistance. 
 
 OHMS LAW. States that the current in any circuit 
 is equal to the E. M. F. acting on it divided by its 
 resistance. 
 
 PERMANENT MAGNET. A piece of hardened 
 steel which retains its magnetism after the magnet- 
 izing influence is removed. 
 
 PARALLEL. See Multiple. 
 
 POLE. Those parts of a magnet which show the 
 strongest magnetic force. In a bar magnet this is 
 generally a short distance from the ends. The pole 
 of a dynamo or battery is one of its terminals. 
 
 POSITIVE. A conventional term to show the direc- 
 tion of a current. In a dynamo or battery it is the 
 terminal at which the electricity leaves it. It is 
 designated by + . 
 
 RESISTANCE. The opposition offered by a body 
 to the passage of electricity through it. 
 
 RHEOSTAT. An apparatus for throwing a variable 
 resistance into a circuit at will. 
 
 SERIES. Two or more conductors are said to be in 
 series when they are so connected that the same 
 current that passes through one passes through the 
 other. 
 
 SHORT CIRCUIT. An indefinite term used gen- 
 erally in the case of dynamos and batteries for a 
 resistance between the terminals lower than the 
 machine or battery is calculated to stand or run on 
 
94 QUESTIONS AND ANSWERS ABOUT ELECTRICITY. 
 
 in practice. With lamps the term is used for a 
 low resistance between the terminals, which de- 
 prives it of most of the current. 
 
 SHUNT. A shunt is a conductor connected around 
 another in such a way that it deprives the first of a 
 part of the current. 
 
 SOLENOID. A hollow coil of wire. 
 
 VOLT. The unit of electro-motive force or pressure 
 analogous to the head of water in hydraulics. 
 
 VOLTMETER. An instrument for measuring the 
 voltage or pressure on a circuit. 
 
 WATT. The unit of work. The watts developed 
 in a circuit are equal to the current multiplied by 
 the E. M. F. Seven hundred and forty-six watts 
 equal one horse power. 
 
 WATTMETER. An instrument for measuring the 
 electrical energy in a circuit. 
 
I N DKX. 
 
 Accumulator 33, 37 
 
 Arc, electric 58. 60 
 
 lamp 60, 62 
 
 Armature, what is an 47 
 
 drum 48 
 
 difference between ring and drum 52, 53 
 
 disc 49 
 
 pole 49 
 
 Ammeter, description of 85 
 
 Ampere 78 
 
 Alphabet, Morse telegraph 69 
 
 Amalgamated zinc 40 
 
 Apparatus, miscellaneous 66, 76 
 
 B 
 
 Batteries, different kinds of 33 
 
 Battery, voltaic 31 
 
 accumulator 33, 36 
 
 Bunsen 32, 33 
 
 Grove 32, 33 
 
 Grenet 33, 34 
 
 gravity 33, 34 
 
 Leclanche 33, 35 
 
 storage 33, 37 
 
 Daniels 33 
 
 Samson 33, 36 
 
 connected for different purposes 37, 38 
 
 chemical action in a 39 
 
 local action in a 40 
 
 polarization of a 41, 42 
 
 Brushes, their use upon dynamos and motors 52 
 
 Bell, electric 66 
 
 Bodies, magnetic 27 
 
 diamagnetic 27 
 
96 INDEX. 
 
 Currents, electric 11, 14 
 
 how measured 77 
 
 Circuit, resistance in a 80 
 
 Conductor 15 
 
 non 16 
 
 list of 16 
 
 Coulomb 79, 80 
 
 Condenser 22 
 
 Connecting in series 38 
 
 in multiple 38 
 
 in multiple series 38 
 
 in series multiple 39 
 
 batteries for different purposes 37 
 
 Coil induction 73 
 
 Kuhmkorff 74 
 
 Cell, accumulator 33, 37 
 
 storage 33, 37 
 
 Bunsen 32, 33 
 
 Grove 32, 33 
 
 gravity 33, 34 
 
 Grenet 33, 34 
 
 Leclanche 33, 35 
 
 Daniels 33 
 
 Samson 33, 36 
 
 voltaic 31 
 
 connected for different purposes 37, 38 
 
 chemical action of a 39 
 
 local action of a 40 
 
 polarization of a , . . .. 41 
 
 Commutator 51 
 
 its use 51 
 
 Collector ring 53 
 
 D 
 
 Dynamo, alternating current 45 
 
 direct current 44, 45 
 
 description of a 43 
 
 collector ring upon 53 
 
 brushes upon 52 
 
 difference between series, shunt and com- 
 pound wound 54, 57 
 
 dynamic electricity 14 
 
 diamagnetic bodies 27 
 
97 
 
 Earth magnetism 26 
 
 Electricity, atmospheric 12 
 
 frictional 11 
 
 dynamic 14 
 
 magneto 14 
 
 pyro 13 
 
 static 11 
 
 thermo 12 
 
 word derived from 10 
 
 Electric arc 58 
 
 lamps 60, 65 
 
 miscellaneous apparatus 66, 76 
 
 bell 66 
 
 telegraph 66, 71 
 
 telephone 71 
 
 welding 76 
 
 Electrical attraction 10 
 
 measurement 77, 87 
 
 repulsion 10 
 
 units 78, 81 
 
 Electroscope 15 
 
 Energy, unit of : 80 
 
 F 
 
 Farad 78 
 
 Field, magnetic 30 
 
 magnets 49 
 
 Force, magnetic / 27 
 
 laws of magnetic 27 
 
 G 
 
 Gravity cell 33, 34 
 
 Grenet cell 33, 34 
 
 Grove cell 32, 33 
 
 Galvanometer, construction of 81, 82 
 
 H 
 
 Holtz machine 17 
 
 I 
 
 Induction 11 
 
 coil 73 
 
 Incandescent lamp 62, 65 
 
 Influence machines 16, 24 
 
98 INDEX. 
 
 J 
 
 Jar, Leydeu 23, 24 
 
 L 
 
 Lamp, arc 60, 62 
 
 incandescent 62, 65 
 
 Law of inverse squares 79 
 
 of magnetic force 27 
 
 Ohms 80 
 
 Leyden jar 23, 24 
 
 M 
 
 Machine, influence 16, 24 
 
 dynamo 43, 46 
 
 magneto . 49 
 
 welding 76 
 
 Holtz 17 
 
 Topler 19 
 
 Magnet, artificial 28 
 
 electro 28 
 
 permanent 28 
 
 strength of 29 
 
 the two poles inseperable 29 
 
 field 49 
 
 natural 27 
 
 act across bodies 26 
 
 loss of strength 29 
 
 Magneto machine 49 
 
 Magnetic attraction 25, 26 
 
 pole 29 
 
 saturation 29 
 
 repulsion 25, 26 
 
 bodies 27 
 
 force 27 
 
 field 30 
 
 needle 30 
 
 Magnetism derived from the earth 26 
 
 theory of 25 
 
 residual 29 
 
 Multiple, connecting in 38 
 
 series 38 
 
 Microphone 71, 72 
 
 Measurement, electrical 77, 87 
 
 Motors, electric 47 
 
INDEX. 99 
 
 N 
 
 Needle, magnetic 30 
 
 o 
 
 Ohms law 80 
 
 P 
 
 Pole, magnetic 29 
 
 Polarization, remedies, etc 41 
 
 Potential 81 
 
 Pressure, unit of 80 
 
 R 
 
 Resistance in a circuit 80 
 
 Ruhmkorff coil 74 
 
 Repulsion, electrical 10 
 
 Relay 69 
 
 S 
 
 Squares, law of inverse 79 
 
 Storage cell 33, 37 
 
 Strength of a magnet 29 
 
 loss of 29 
 
 unit of current 81 
 
 Saturation, magnetic 29 
 
 Series, connecting in 38 
 
 multiple. 1 38 
 
 Shunt-wound dynamo 56 
 
 Static electricity 11 
 
 T 
 
 Theory of electricity 9 
 
 of magnetism 25 
 
 Transformer 74, 75 
 
 Telephone 71 
 
 Telegraph 66, 69 
 
 alphabet 69 
 
 diagram of circuit 70 
 
 u 
 
 Units, names of electrical 78, 79 
 
 of quantity 79 
 
 of pressure 80 
 
 of current strength 81 
 
 of rate of electric work 81 
 
100 INDEX. 
 
 V 
 
 Volt 80 
 
 Voltmeter 85 
 
 W 
 
 Watt 81 
 
 Wheatstone's bridge 86, 87 
 
 Winding of dynamos 57 
 
 Welding, electric 76 
 
 Z 
 Zinc, amalgamation of 40 
 
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 General Library 
 
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