DEE 
 
 
 ELECmO-TECiiHICAL 
 SERIES 
 
BY THE SAME AUTHORS 
 
 Elementary Electro - Technical Series 
 
 COMPRISING 
 
 Alternating Electric Currents. 
 Electric Heating. 
 
 Electro-magnetism. 
 
 Electricity in Electro-Therapeutics. 
 
 Electric Arc Lighting. 
 Electric Incandescent Lighting. 
 Electric Motors. 
 
 Electric Street Railways. 
 Electric Telephony. 
 
 Electric Telegraphy. 
 
 Cloth, Price per Volume, $1.00. 
 
 Electro-Dynamic Machinery. 
 Cloth, $2.50. 
 
 THE W. J. JOHNSTON COMPANY 
 
 253 BROADWAY, NEW YORK 
 
ELEMENTARY ELECTRO-TECHNICAL SERIES 
 
 THE ELECTRIC MOTOR 
 
 AND THE 
 
 TRANSMISSION OF POER 
 
 BY 
 
 EDWIN J. HOUSTON, PH. D. 
 
 AND 
 
 A. E. KENNELLY, Sc. D. 
 
 NEW YORK 
 
 THE W. J. JOHNSTON COMPANY 
 
 253 BROADWAY 
 
 1896 
 

 
 COPYRIGHT, 1896, BY 
 THE W. J. JOHNSTON COMPANY. 
 

 PREFACE. 
 
 THERE is probably no subject, con- 
 nected with the application of electricity, 
 that has come into greater prominence 
 during the last decade, than the electric 
 transmission of power. The electric 
 motor is now to be found everywhere 
 driving machinery of all sizes. It permits 
 a single, large, economical* engine to oper- 
 ate a number of small motors over a large 
 area. 
 
 This little volume of the Electro- Tech- 
 nical Series has been prepared with the 
 object of rendering the principles of elec- 
 tric motors clear to those who are not 
 specially trained in electro-technics. For 
 
 M289307 
 
IV PREFACE. 
 
 this reason, in this, as in all other books of 
 the series, vexed questions as regards the 
 priority of invention have been carefully 
 avoided, and facts, rather than names, have 
 been presented to the reader. Only such 
 portions of the history of the subject as are 
 necessary^to a logical comprehension of its 
 development are given, and no mathe- 
 matical treatment other than simple arith- 
 metic has been employed. 
 
 The authors are indebted to the editors 
 of Cassie^s Magazine for cuts in the book 
 relating to the Niagara power transmission. 
 
 Notwithstanding the apparent complex- 
 ity of the electric motor, the authors 
 believe that the student will be in pos- 
 session of all its essential elementary 
 principles after reading this book. 
 
 AUGUST, 1896. 
 
CONTENTS. 
 
 I. INTRODUCTORY, . . . . 1 
 II. SOURCES OF ENERGY, . . .19 
 
 III. ELEMENTARY ELECTRICAL PRINCIPLES, 29 
 
 IV. EARLY HISTORY OF THE ELECTROMAG- 
 
 NETIC MOTOR, .... 73 
 
 V. ELEMENTARY THEORY OF THE MOTOR, 119 
 VI. STRUCTURE AND CLASSIFICATION OF 
 
 MOTORS, 162 
 
 VII. INSTALLATION AND OPERATION OF 
 
 MOTORS, 200 
 
 VIII. ELECTRIC TRANSMISSION OF POWER, . 217 
 
 IX. ALTERNATING-CURRENT MOTORS, . 241 
 
VI CONTENTS. 
 
 CHAPTER PAGE 
 
 X. ROTATING MAGNETIC FIELDS, . .;; 284 
 XL ALTERNATING-CURRENT TRANSMIS- 
 SIONS, .. :j ,;*,.. '.. .., ' ,. , . 302 
 XII. MISCELLANEOUS APPLICATIONS OF 
 
 ELECTRIC MOTORS, . . . . 335 
 
 INDEX, . . . . . -? 359 
 
THE ELECTRIC MOTOR AND 
 
 THE TRANSMISSION OF 
 
 POWER. 
 
 CHAPTER I. 
 
 INTKODUCTOKY. 
 
 THE nineteenth century owes its promi- 
 nence in physical science, largely to the 
 discovery that energy is indestructible, and 
 that the universe possesses a certain stock 
 or store of energy which it is impossible 
 either to increase or to decrease. 
 
 All natural phenomena are attended 
 by transformations of energy. When 
 
2 THE ELECTRIC MOTOR AND 
 
 energy disappears in one form, the nine- 
 teen tli century doctrine of the conservation 
 of energy, bids us look for some other 
 form in which we know it must reappear. 
 The fact that phenomena occur at one 
 point of space where the energy necessary 
 for this causation did not previously exist, 
 proves that energy must have been taken 
 from some store or stock and transmitted 
 to that point. Consequently, the doctrine 
 of the conservation of energy necessitates 
 the doctrine of the transference or trans- 
 mission of energy, in contradistinction to 
 its creation. In other words, the discov- 
 ery of the indestructibility of energy was 
 also the discovery of the possibility of its 
 transmission. 
 
 The discovery of the doctrine of the in- 
 destructibility and increatability of energy 
 followed upon the discovery of the in- 
 
THE TRANSMISSION OF POWER. 
 
 destructibility and increatability of matter. 
 Our belief in these doctrines is the result 
 of our universal experience, and any ex- 
 planation of natural phenomena, that neces- 
 sitates the creation, either of energy or of 
 matter, may be unhesitatingly rejected. 
 
 Energy is the capability of doing work. 
 In other words, when work is done energy 
 is expended. But it must not be supposed 
 because the energy is expended, that it is 
 thereby destroyed. The energy has only 
 changed its form or its position. For 
 example, when a charge of gunpowder is 
 placed in a gun and fired, the energy 
 which previously existed in the gun- 
 powder is liberated, by the act of firing, 
 and is principally expended in moving 
 the ball from the gun, some being acci- 
 dentally expended in heating the gun. 
 Although the energy is thus properly 
 
4 THE ELECTRIC MOTOR AND 
 
 spoken of as being expended by the gun- 
 powder in doing this work, yet it must be 
 remembered that the energy is not there- 
 by annihilated, but is merely transformed. 
 The moving ball expends some of its 
 energy of motion in moving aside the air ; 
 a part is expended in producing sound, and 
 the remainder, usually the greater part, is 
 given up in the concussion against the 
 body it strikes. All this energy finally 
 takes the form of heat in the gun, in the 
 air, and in the body struck, in which form 
 it usually permanently remains. Conse- 
 quently, after- the gun has been fired, there 
 is less chemical, but more heat energy in 
 that part of the universe. 
 
 As another example take the case of a 
 reservoir filled by a pump with water. The 
 filled reservoir represents a stock or store 
 of energy derived from the work expended 
 
THE TRANSMISSION OF POWER. 5 
 
 in pumping. So long as no water is 
 allowed to leave the reservoir, no work is 
 done, and the store of energy remains un- 
 changed. If, however, the water be per- 
 mitted to escape through a water-wheel, 
 the energy in the reservoir is expended in 
 turning the wheel ; that is to say, the 
 energy of the moving water is transferred 
 to the moving wheel, which in its turn, 
 may transfer it to machinery connected 
 therewith. Here each moving part ex- 
 pends its energy ; but such energy is not 
 annihilated; it is merely transferred. If 
 the water-wheel were employed to drive 
 another pump which filled a similar reser- 
 voir to the same level, and no loss of 
 energy occurred in its transference, the 
 escape of water from the first reservoir 
 would result in the filling of the second 
 reservoir with the same quantity of water 
 and to the same depth. In practice, this 
 
6 THE ELECTEIG MOTOR AND 
 
 never occurs; losses always take place in 
 the machinery. Such losses, however, are 
 not annihilations of energy. The energy 
 which disappears, takes some other form, 
 generally as heat produced by frictions. 
 
 The water of a river flowing through its 
 channel, represents a stock of energy that 
 is being expended at a certain rate. The 
 amount of energy present in the moving 
 stream depends both upon the quantity 
 of water, and on the speed with which 
 it moves. A certain proportion of this 
 energy is capable of being transferred 
 from the stream to a moving water-wheel, 
 or water motor, and the water, which has 
 passed through the wheel or motor, loses 
 some of its motion in consequence. 
 
 The source of energy in the moving 
 water of a river is to be found in the sun's 
 
heat, wlvd* conv 
 
 1L\ /O 
 
 into vapor^^^arried this 
 land, where i^>^^ecj[j^ii3^ -boadeil sed and 
 fell as rain. The energy in the moving 
 water, however, is only a portion of that 
 which it acquired in falling from the 
 higher to the lower level. 
 
 In each of the preceding cases the mov- 
 ing machinery ceased its motion, when 
 energy ceased to be transferred to it ; and, 
 in each case, we have been able readily 
 to trace the source of the driving energy. 
 The case of a man, who expends muscular 
 or nervous energy, in doing work, forms no 
 exception to this rule. In order to permit 
 the man to continue expending energy in 
 such work, it is necessary that his stock of 
 energy be replenished from time to time ; 
 in other words, that energy be transferred 
 to him from some other source. This is 
 
8 THE ELECTRIC MOTOR AND 
 
 accomplished by his assimilating food, 
 which contains chemical energy imparted 
 to it from the sun. 
 
 Strange as it may seem, the transference 
 of energy from assimilated food to the 
 organism of the man, is similar to the 
 transference of energy from a lump of 
 coal to a steam engine. The chemical 
 potential energy of the coal, liberated 
 by burning under a boiler, is transferred 
 to the steam ; and the energy of the steam, 
 is transferred to the working parts of the 
 steam engine. In man, it is the chemical 
 potential energy of the food assimilated, 
 which enables him to perform his varied 
 functions. In the steam engine it is the 
 chemical potential energy of the coal which 
 enables it to work. 
 
 Before leaving the subject of energy it 
 
THE TRANSMISSION OF POWER. 9 
 
 will be advisable to obtain definite ideas 
 concerning its measurement. The amount 
 of energy required to be expended in order 
 to raise one pound against the earth's 
 gravitational force, through a vertical dis- 
 tance of one foot, is called a foot-pound. 
 Thus, to raise a steel fire-proof safe, 
 weighing 5,000 pounds, from the street 
 to a room, 100 feet above the street level, 
 requires the expenditure of energy equal 
 to 100 x 5,000 = 500,000 foot-pounds. 
 Energy is measurable in units of work, 
 and the foot-pound is the unit frequently 
 employed in English-speaking countries 
 for this purpose. 
 
 The international unit of work is called 
 the joule. A joule is approximately 0.738 
 foot-pound, and is, therefore, roughly, 
 equal to the amount of energy required to 
 be expended in order to raise a pound 
 
10 THE ELECTRIC MOTOR AND 
 
 through a distance of 9", against gravita- 
 tional force. A foot-pound, is, therefore, 
 greater than a joule, being, approximately, 
 equal to 1.355 joules. 
 
 If we could compute the total energy of 
 the universe, it would, of course, be capable 
 of being expressed either in foot-pounds or 
 in joules. As we have already stated this 
 total is believed to be constant, all so- 
 called expenditures of energy merely 
 altering the character of the stock, and not 
 its amount. 
 
 It is necessary carefully to distinguish 
 between the expenditure of energy and 
 the rate at which it is expended. Thus if 
 a man weighing 150 pounds ascends a 
 flight of stairs 100 feet high, he must 
 necessarily expend energy amounting to 
 150X100 = 15,000 foot-pounds. So far 
 
THE TRANSMISSION OF POWER. 11 
 
 as the result is concerned, namely his 
 reaching the top of the stairs, the same 
 amount of work must be done whether he 
 does this in five minutes, or in one 
 minute ; but the rate at which he requires 
 to expend energy in the two cases in order 
 to mount the stairs, would be very differ- 
 ent ; for, in the first case he would expend 
 15,000 foot-pounds of work in five 
 minutes, or at an average rate of 3,000 
 foot-pounds per minute, while in the 
 second case he would expend 15,000 foot- 
 pounds of work in one minute, or at an 
 average rate of 15,000 foot-pounds per 
 minute ; that is to say, his activity, or rate- 
 of-expending-energy, would be five times 
 greater in the latter case than in the 
 former. 
 
 A unit of activity or rate-of-expending- 
 energy, frequently adopted in English- 
 
12 THE ELECTEIC MOTOR .AND 
 
 speaking countries, is the foot-pound-per- 
 second. A similar unit employed in deal- 
 ing with machinery is called the Jiorse- 
 power and is equal to 550 foot-pounds-per- 
 second. 
 
 The international unit of activity is the 
 joule-per -second / or, as it is more fre- 
 quently called, the watt. Expressed in 
 foot-pounds-per-second, the watt is 0.738 
 foot-pound-per-second, so that 746 watts 
 are equal to one horse-power. As the 
 watt is usually too small a unit for con- 
 veniently dealing with machinery, the 
 kilowatt or 1,000 watts, is generally em- 
 ployed. One kilowatt (KW), is, approxi- 
 mately, 1 1/3 horse-power (1.34 HP), i. e. 
 746 watts = 1 HP. 
 
 As we have seen, natural phenomena 
 require an expenditure of energy to pro- 
 
THE TRANSMISSION OF POWER. 13 
 
 duce them. It is convenient to regard 
 such phenomena either from the stand- 
 point of the energy they consume, or of 
 the activity they require to have sus- 
 tained. 
 
 We can regard these phenomena as 
 capable of being reproduced by the expen- 
 diture of the proper amount of energy. 
 Since the chemical potential energy in a 
 pound of coal is a definite quantity, we 
 know that by the liberation of this energy 
 we can produce a certain phenomenon, 
 such, for example, as raising a weight to 
 a given height, or in overcoming certain 
 resistances, as in sawing a log of wood. 
 If the same phenomenon is to be produced 
 at some point where this energy does not 
 exist, it is evident that this amount of 
 energy must be transmitted from some 
 other point. 
 
14 THE ELECTRIC MOTOR AND 
 
 In mills and manufactories, where dif- 
 ferent machines are to be driven, it is pos- 
 sible to determine the exact amount of 
 energy required to drive them. We can, 
 therefore, calculate the amount of steam 
 power or water-power required to be sup- 
 plied to such establishments. In actual 
 practice, the problem presented is the 
 determination of the most effectual and 
 economical means whereby this amount of 
 power may be transmitted from the point 
 of supply to the point of delivery, where 
 the machine has to be driven. 
 
 Various means have been adopted for 
 the transmission of power to considerable 
 distances. The principal of these are : 
 
 (1) Rope transmission. 
 
 (2) Pneumatic transmission. 
 
 (3) Hydraulic transmission. 
 
 (4) Electric transmission. 
 
THE TRANSMISSION OF POWER. 15 
 
 Rope transmission finds its most exten- 
 sive use in the operation of cable cars, 
 where it is sometimes employed for dis- 
 tances of several miles in a single section. 
 
 Pneumatic transmission is employed ex- 
 tensively in Paris, where there are about 
 35 miles of pneumatic mains. It is also 
 used extensively in mining operations, 
 and to some extent, in systems of railway 
 signalling. When used in mining, it 
 possesses the advantage of aiding the 
 ventilation. 
 
 Hydraulic transmission is in fairly 
 extensive use for distributing power in 
 European cities where the distribution 
 distances are not excessive. 
 
 There can be no doubt that any of the 
 preceding systems is capable, when prop- 
 
16 THE ELECTRIC MOTOR AND 
 
 erly installed, of transmitting power with 
 fair economy over considerable distances. 
 A transmission system consists of gener- 
 ators at the transmitting end, which trans- 
 form the energy supplied into a form in 
 which it can be transmitted ; motors, or 
 devices at the receiving end, for transform- 
 ing the energy so transmitted into the 
 form available for use; and connecting 
 systems joining the generators and motors. 
 In considering the relative advantages of 
 any transmission system, it is evident that 
 account must be taken of the cost of instal-" 
 lation of the entire system, and of the rela- 
 tive efficiencies of the generators and 
 motors ; or, combining these things, of the 
 cost of delivering power. In addition 
 to this we must consider the readiness 
 with which the transmitted power can be 
 transformed, and the safety with which it 
 can be both transmitted and employed. 
 
THE TRANSMISSION OF POWER. 17 
 
 111 contrasting the relative advantages of 
 rope, pneumatic, and hydraulic transmis- 
 sion, rope transmission is often advanta- 
 geous where the power has to be 
 transmitted in the open country in bulk, 
 but, where power has to be transmitted to 
 a number of consumers in a city, pneu- 
 matic or hydraulic transmission possess 
 advantages over rope transmission, espe- 
 cially in cases where the exigencies of 
 the work require the direction of the 
 motion to be frequently and abruptly 
 changed. 
 
 While pneumatic and hydraulic trans- 
 mission systems possess marked advantages 
 in certain directions, yet electric transmis- 
 sion is so convenient, the efficiency of the 
 generators and motors so high, the cost of 
 transmission over considerable distances so 
 comparatively low, and the flexibility with 
 
18 ME ELECTRIC MOTOK. 
 
 which electricity lends itself to the purposes 
 of general distribution so marked, that 
 electricity is already in extensive use in 
 the United States for the transmission of 
 power. 
 
PROPERTY CF' 
 
 
 SOURCES OF ENERGY. 
 
 THE known sources of energy may be 
 classified as follows : viz., 
 
 (1) Chemical energy, as of coal and 
 other combustibles. 
 
 (2) Water power. 
 
 (3) The earth's internal heat. 
 
 (4) The earth's motion. 
 
 (5) Solar heat. 
 
 Tracing these various sources of energy 
 to their origin, it soon becomes evident 
 that they are all derived from the sun as 
 the prime source. A lump of coal, when 
 burned, gives out, in its radiant light 
 
 19 
 
20 THE ELECTRIC MOTOK AND 
 
 and heat, the solar activity of a past geo- 
 logical age. So also the energy of food, 
 which when assimilated, is the source of 
 energy in the muscles of animals, has 
 been derived from the sun in more recent 
 times. Wind power and water power also 
 manifestly derive their energy from the 
 sun. 
 
 * 
 
 The earth's heat is properly to be re- 
 garded as a source of power. Since the 
 entire interior of the earth is believed to 
 be highly heated, we evidently .have in it a 
 great storehouse of natural power, which 
 although never yet practically employed, 
 yet is capable of doing an enormous amount 
 of work. Since it is generally believed, in 
 accordance with Laplace's nebular hypo- 
 thesis, that the earth and all members of 
 the solar system once formed a part of the 
 sun, and were disengaged from the sun's 
 
THE TRANSMISSION OF POWER. 21 
 
 mass while in an incandescent condition, 
 this source of heat also owes its origin 
 to the sun. 
 
 The rotary motion of the earth may 
 be regarded as a source of power. With- 
 out stopping to discuss the various methods 
 which have been proposed to obtain motion 
 from the rotation of the earth, we would 
 point out that the only practical means 
 for doing this is by the employment of 
 machines driven by the tides. 
 
 It is evident, from a consideration of 
 the above, that all the natural sources 
 of power available to man on the earth 
 either have been, or are being, derived 
 from the sun, and are divisible into three 
 great classes ; namely, 
 
 (1) Solar energy imparted to the earth 
 at the beginning of its career. 
 
22 THE ELECTRIC MOTOR AND 
 
 (2) Solar energy imparted to coal dur- 
 ing past geological epochs ; and, 
 
 (3) Solar energy imparted to the earth 
 at the present time by direct radiation. 
 
 Although, as we have already seen, the 
 total amount of energy existing in the uni- 
 verse is believed to be constant, yet the 
 amount residing in the sun and in the 
 earth, is believed to be steadily diminish- 
 ing, being lost by radiation into interstellar 
 space at a comparatively rapid rate. 
 
 A motor which receives power and 
 transmits it to the machinery it drives 
 is a device for transforming or trans- 
 ferring energy. A certain amount of 
 energy must be expended in driving it ; that 
 is a certain amount of activity must be 
 delivered to the machine. This activity 
 is generally known as the intake of the 
 
THE TRANSMISSION OF POWER. 23 
 
 machine. The machine, in operating, de- 
 livers to the machinery it drives a certain 
 amount of activity which is called its out- 
 put. The output can never exceed the in- 
 take. In point of fact, since certain losses 
 occur in the operation of the best designed 
 machines, the output can never even equal 
 the intake, and, in many machines, is con- 
 siderably less than the intake. The ratio 
 of the output to the intake is called the 
 efficiency of the machine. 
 
 In order to illustrate the preceding 
 principles we may consider the following 
 example. A line of shafting in a machine 
 shop, is a machine for transferring energy 
 from a source, say a steam engine, to one 
 or more driven machines, such as lathes, 
 saws, etc. The amount of activity de- 
 livered to the shafting by the engine may 
 be, say 10 horse-power, or 746 x 10 = 7,460 
 
24 THE ELECTRIC MOTOR AND 
 
 watts = 7,460 joules-per-second, or 5,500 
 foot-pounds per second. A certain amount 
 of this activity is expended in overcoming 
 the friction of the shafting; i. e., in heat- 
 ing the journals, in churning the neigh- 
 boring air, in shaking the building, and in 
 stretching the belts. The remainder of 
 the activity is delivered to the lathes. If 
 this total delivery or output, be 8 HP = 
 746 X 8 = 5,968 watts, the efficiency 
 
 of the shafting will be = 80 per cent. 
 
 Again if an electric motor receives an 
 intake of 50 horse-power, and has an out- 
 put of 45 horse-power; i. e., delivers 45 
 horse-power at its pulley, then its efficiency 
 
 will be = 0.9 = 90 per cent. 
 
 In considering the amount of power 
 
THE TRANSMISSION OF POWER. 25 
 
 required to be drawn from any natural 
 source in order to perform a given amount 
 of work, allowance must, therefore, be made 
 for the loss in transformation. For ex- 
 ample, it can be shown that a pound of 
 good coal, if thoroughly burned in air, is 
 capable of yielding a total amount of 
 energy equal to 15,500,000 joules, or, 
 11,440,000 foot-pounds. Consequently, if 
 the energy so liberated were applied to 
 drive a steam engine, this steam engine, if 
 burning one pound of coal per hour, would 
 be able to raise a weight .of one pound 
 11,440,000 feet in that time, and would, 
 therefore, be exerting an activity of 5.778 
 horse-power, or 4,310 watts. In point of 
 fact, however, the best steam engines and 
 boilers are only capable of delivering 
 
 about y^ths of one horse-power-hour, with 
 one pound of coal, so that the efficiency of 
 
26 THE ELECTRIC MOTOR AND 
 
 such an engine and boiler would only be 
 
 8 
 ' = 0.1385, or 13.85 per cent., and, in 
 
 o.77o 
 
 fact, with the types of engine ordinarily 
 employed, the efficiency is commonly only 
 about 8 per cent. 
 
 This comparatively low efficiency of a 
 steam engine and boiler is due to the com- 
 bination of two very different causes. 
 One of these lies in the working tempera- 
 ture, or the difference in temperature 
 between the steam admitted to the engine 
 and the steam leaving the engine. It is a 
 law of nature that the amount of heat 
 which can be mechanically realized from 
 the liberation, during combustion, of a 
 given quantity of chemical energy, 
 depends upon the working temperatures. 
 With the working temperatures which are 
 imposed by practical considerations in the 
 
THE TRANSMISSION OF POWER. 27 
 
 best steam engines, the efficiency due to 
 this cause is restricted to about 25 per 
 cent., so that if the steam engine and 
 boiler were perfect machines, losing none 
 of the power which was capable of being 
 delivered to them, they could not under 
 these circumstances have an efficiency, 
 taken in conjunction, of more than 25 
 per cent. The balance of the work is 
 uselessly expended in heating the air and 
 water. 
 
 The second source of loss lies in the 
 necessary imperfections of engine and 
 boiler as machines. The above losses are 
 due to frictions and loss of heat by con- 
 duction, convection, radiation and conden- 
 sation. Retaining the same working 
 temperature, these losses are reduced by 
 all improvements in the engine and boiler, 
 considered as machines for effecting trans- 
 
 o 
 
28 THE ELECTRIC MOTOR. 
 
 formation of energy. The efficiency of an 
 engine and boiler, considered as receiving 
 only the energy which is rendered available 
 by the range of working temperature, is 
 at the best about 56 per cent., so that the 
 nett efficiency, reckoned from the total 
 chemical energy of coal, in the best engines 
 and boilers is only about 0.25 X 0.56= 0.14, 
 or 14 per cent. 
 
CHAPTER III. 
 
 ELEMENTARY ELECTRICAL PRINCIPLES. 
 
 THE grave mistake is not infrequently 
 made that because we are still ignorant of 
 the real nature of electricity, we are neces- 
 sarily equally ignorant of the principles 
 controlling its action. In point of fact 
 the engineer has to-day a more intimate 
 knowledge of the laws of electricity, than 
 of the laws which govern the application 
 of steam. Since, in the study of the 
 electric motor, a knowledge of the more 
 important laws of electricity is neces- 
 sary, it will be advisable to discuss them 
 briefly, before proceeding further with the 
 subject. 
 
30 
 
 THE ELECTRIC MOTOR AND 
 
 All electric current, or electric flow, re- 
 quires for its existence a complete conduct- 
 ing path as represented in Fig. 1. Here 
 
 6 VOLTS 
 3 OHMS 
 
 L 
 
 3ROP1 VOLT 
 
 2 AMPERES 
 
 2 AMPERES 
 
 2 AMPERES 
 
 2 AMPERES 
 
 DROPS VOLTS 
 2 AMPERES 
 1 OHM 
 
 s 
 
 DROP1 VOLT 
 
 E.M.F. 10 VOLTS 
 
 FIG. 1. ELECTRIC CIRCUIT, INCLUDING SOURCE, LAMP 
 AND CONDUCTING LEADS. 
 
 a voltaic battery, or other electric source, 
 supplies an electric current through the 
 completed circuit, A B C D. Unless a 
 completed path be provided for the passage 
 
THE TRANSMISSION OF POWER. 31 
 
 of the electricity, both through the source 
 and the external circuit, an electric current 
 cannot be sustained. All practical elec- 
 tric circuits of this character consist of 
 three separate parts ; namely, 
 
 (1) The electric source. 
 
 (2) Conducting wires or leads. 
 
 (3) An electro-receptive device tra- 
 versed by the current. 
 
 In all electric circuits of this type, it is 
 convenient, for purposes of description, to 
 regard the electricity as leaving the source 
 at a point called its positive pole, and 
 returning to the source, after it has passed 
 through the circuit of the receptive de- 
 vices placed therein, to a point called its 
 negative pole. The current, after entering 
 the source, flows through it and again 
 emerges at its positive pole. It will be 
 seen that the path thus traversed by the 
 
32 THE ELECTRIC MOTOR AND 
 
 current is circuital, in so far as it again 
 reaches the point from which it started. 
 The conducting path forms what is called 
 an electric circuit. It must not be sup- 
 posed, however, that circuits are neces- 
 sarily circular in outline, since a circuit 
 will be established no matter what the 
 shape of the conducting path, provided 
 only that the electric flow reaches the 
 point from which it is assumed to have 
 started. 
 
 An electric circuit is said to be made, 
 completed, or closed, when a complete con- 
 ducting path is provided for it. It is said 
 to be broken, or opened, when this conduct- 
 ing path is interrupted at any point. 
 
 When an electric source, such as shown 
 in Fig. 1, is open or broken, the current 
 ceases to flow, and, consequently, the 
 
THE TRANSMISSION OF POWER. 33 
 
 source ceases to furnish electricity. It 
 does not, however, cease to furnish a 
 variety of force called electromotive force. 
 As long as the circuit remains open the 
 electromotive force produced by the bat- 
 tery does no work; i. e., expends no 
 energy. It is only when a conducting cir- 
 cuit is provided for it, that it can produce 
 a motion of electricity and thus do work. 
 In point of fact all electric sources are 
 to be regarded as sources of electromotive 
 force, usually abbreviated E. M. F., rather 
 than sources of current, since they produce 
 E. M. F. whether their circuit is opened 
 or closed. Morever, the conditions of 
 their working remaining the same, the 
 value of their E. M. F. remains un- 
 changed ; whereas, as we shall see, the 
 value of the current they produce, de- 
 pends entirely upon certain conditions of 
 the circuit with which they are connected. 
 
"34 THE ELECTRIC MOTOR AND 
 
 Regarding Fig. 1, as a typical instance 
 of a working electric circuit, provided, as 
 already mentioned, with a voltaic battery, 
 conducting leads, and an electro-receptive 
 device or devices, let us inquire liow we 
 can ascertain the amount of electricity that 
 will flow through the circuit in a given 
 time. In this, as in any similar electric 
 circuit, the strength of current which flows, 
 that is, the quantity of electricity which 
 passes through the circuit per second, is 
 dependent on two quantities ; namely, on 
 the value of the E. M. F., which may, for 
 convenience, be regarded as an electric, 
 pressure causing, or tending to cause, the 
 electric flow, and on a quantity called the 
 resistance of the circuit, which acts so as 
 to limit the quantity of electricity passing 
 through the circuit in a given time. The 
 current strength passing is related to these 
 quantities in a manner discovered by Dr. 
 
THE TRANSMISSION OF POWER. 35 
 
 Ohm, and expressed by him in a law, 
 generally known as Ohm's law, as fol- 
 lows: The current strength in any circuit 
 is equal to the E. M. F., acting on that 
 circuit, divided by the resistance of the 
 circuit. 
 
 In order to assign definite values to the 
 above quantities, certain units are em- 
 ployed. The units in international use 
 are as follows: the unit of E. M. F., 
 called the volt; the unit of resistance, 
 called the ohm, and the unit of current 
 strength or flow, called the ampere. Ohm's 
 law, expressed in terms of these units, 
 is as follows ; namely, 
 
 volts 
 
 amperes = , 
 
 ohms 
 
 Suppose, for example, in the case of the 
 simple electric circuit shown in Fig. 1, 
 
36. THE ELECTRIC MOTOR AND 
 
 that the E. M. F. of the voltaic battery is 
 10 volts, and the resistance of the entire 
 circuit, including the resistance of the 
 source, the conducting wires and the 
 lamp, is 5 ohms ; then, in accordance 
 with Ohm's law, the current strength 
 
 , , , 10 volts 
 
 would be ; = 2 amperes. 
 
 D ohms 
 
 The volt is, roughly, equal to the 
 E. M. F. of a blue-stone voltaic cell, such 
 as is commonly used in telegraphy. The 
 ohm is the resistance of about two miles 
 of ordinary trolley wire, and the ampere 
 is about twice as strong a current as is 
 ordinarily used in a 16 candle-power, 110- 
 volt, incandescent lamp. 
 
 The dynamo-electric machine is the 
 practical source of the powerful electric 
 currents that are in common use. 
 
^* pw ^f% 
 
 fl^ PPr^r-^. fy 
 
 ' vtjFiiRTv & 
 
 THE TliANSl^I^ION OF POWER: I 37 
 
 .^ ^ 
 
 /r-> 
 
 Dynamos can be extracted to give an 
 E. M. F., varying fronT^fe^Mi^ t<> 
 10,000 volts. The E. M. F. employed for 
 street railroad systems is about 500 volts. 
 The E. M. F. employed for continuous-cur- 
 rent incandescent electric lighting is about 
 115 volts. 
 
 There are a great variety of voltaic 
 cells. The value of the E. M. F. varies in 
 each, but in general, is comprised be- 
 tween 2/3rds volt and 2 1/2 volts. As 
 this pressure, or, as it is frequently called, 
 voltage, is insufficient to operate most 
 receptive devices, it is necessary to in- 
 crease it by connecting a number of sepa- 
 rate cells together so as to permit them to 
 act as a single cell or battery. Such con- 
 nection may be effected in various ways, 
 but the readiest is connection in series, 
 which consists essentially in connecting the 
 
38 THE ELECTRIC MOTOR AND 
 
 positive pole of one cell to the negative 
 of the next, and the positive of this, 
 to the negative of the next, and so on 
 through the entire number of cells, as 
 
 FIG. 2. VOLTAIC BATTERY OF THREE CELLS IN SERIES. 
 
 shown in Fig. 2, where three separate, 
 Daniell gravity cells are connected in 
 series. If the E. M. F. of each cell is, say 
 1.1 volts, the E. M. F. of the battery will 
 be 3.3 volts. Dynamos may also be con- 
 nected in series, but since it is easy to 
 construct a dynamo for the full E. M. F. 
 required, the expedient is rarely resorted to. 
 
THE TRANSMISSION OF POWER. 39 
 
 The resistance offered by a pipe to the 
 flow of water through it increases with 
 the length of the pipe and also with the 
 narrowness of its bore. A long, narrow 
 pipe has a higher resistance, and permits 
 less water to flow through it in a given 
 time, and under a given pressure, than a 
 short pipe of large diameter. In the same 
 way, the resistance of an electric wire 
 increases with its length and with its 
 narrowness. A long, fine wire has a high 
 resistance, as compared with a short, thick 
 wire. Thus, one foot of very fine copper 
 wire, No. 40 A. W. G. (American Wire 
 Gauge), having a diameter of 0.003145 
 inch, has a resistance of, approximately, 
 one ohm. If, therefore, the length of a 
 wire be fixed, we can make its resistance 
 almost anything we please by altering its 
 area of cross-section. If we double the 
 cross-section, we halve the resistance, 
 
40 THE ELECTUIC MOTOR AND 
 
 the resistance increasing directly with 
 the length, and inversely with the cross- 
 sectional area of the wire. 
 
 There is another way of varying the re- 
 sistance of wires of the same dimensions ; 
 i. e.j by employing different materials. In 
 other words, the resistance of a wire 
 depends not only upon its length and 
 cross-section, but also upon the nature of 
 its su bstance. The specific resistance of iron 
 is about 61/2 times as great as that of 
 copper, so that a wire of iron would have 
 6 1/2 times as much resistance as a wire 
 of copper having the same length and 
 cross-section. 
 
 In order to compare readily the specific 
 resistances of different materials, reference 
 is had to a quantity called the resistivity. 
 The resistivity of a material is the resist- 
 
THE TRANSMISSION OF POWER. 41 
 
 ance offered by a wire having unit length 
 and unit cross-sectional area. These unit 
 values are generally taken as one centi- 
 metre for the length, and one square centi- 
 metre for the area of cross-section, so that, 
 when we speak of the resistivity of copper 
 as being 1.6 microhms, we mean that a 
 wire 1 centimetre in length and having a 
 cross-section of 1 square centimetre, has a 
 resistance of 1.6 microhms; i. e., 1.6 mil- 
 
 Months of an ohm -J. The resist- 
 
 ance of one metre of this wire would be 
 
 1.6 x 100 
 
 =160 microhms, and the resist- 
 
 ance of one metre of a wire having a cross- 
 sectional area of 2 square centimetres 
 
 in , 1.6 x 100 
 would be - - = 80 microhms. Con- 
 
 2i 
 
 sequeritly, if the resistivity of a material is 
 known, it is easy to determine what the 
 
42 THE ELECTRIC MOTOR AND 
 
 resistance of any uniform wire will be of 
 given length and cross-sectional area. 
 
 In English-speaking countries, where 
 lengths are generally measured in feet, and 
 the diameters of wires in inches, it is con- 
 venient to employ as an area of cross-sec- 
 tion the circular mil. A mil is a unit of 
 length of the value of one thousandth of 
 an inch, and a wire, one inch in diame- 
 ter, is said to have a diameter of 1,000 
 mils. If we square the diameter of a wire 
 in mils, we obtain its area in circular mils, 
 so that a circular wire, one inch in diame- 
 ter, has an area of one million circular mils, 
 A circular mil-foot is a unit of cross-sec- 
 tion and length possessed by a wire one 
 foot long and having a diameter of one 
 mil, and, consequently, an area of one cir- 
 cular mil. A circular mil-foot of copper 
 has a resistance of 10.35 ohms, at 20 C. ; 
 
THE TRANSMISSION OK lo\VI-:iI. 43 
 
 so that if a wire be one mile long, and 
 have a diameter of 0.2 i noli, its, : cross-sec* 
 tion will be 200 X 200 = 40,000 circular 
 mils, and its length will be 5,280 feet, so 
 
 5,280 X 10.35 
 that its resistance will be - 
 
 1.366 ohms at 20 C. 
 
 The resistivity of all metals is increased 
 by an increase in temperature. In most 
 metals this increase is about 0.4 per cent, 
 per degree Centigrade, reckoned from the 
 resistivity at zero Centigrade, so that, at 
 the temperature of boiling water, the 
 resistivity of copper is about 40 per cent, 
 greater than its resistivity at the freezing 
 point of water. In computing the resist- 
 ance of a wire, therefore, its temperature 
 must be taken into account. 
 
 AVhen a current of water flows through 
 a pipe, the quantity of water which passes 
 
44 THE ELECTRIC MOTOR AND 
 
 depends both on the flow, and on the time 
 during which the flow takes place. In 
 the same way the quantity of electricity 
 which passes through a wire depends both 
 on the rate of flow, or the number of 
 amperes, and on the time during which 
 the flow takes place. In determining the 
 quantity of water which passes through a 
 pipe, the gallon is frequently employed 
 as a unit of quantity. Similarly, in 
 determining the quantity of electricity 
 which passes through a wire, a unit of 
 electric quantity called the coulomb is 
 employed. As in water currents, the 
 gallon-per-second might be employed as 
 the unit of current, so in the electric cur- 
 rent, the unit-rate-of-flow is taken as a 
 coulomb-per-second, a rate of flow the same 
 as the ampere already referred to. The 
 coulomb is, therefore, the quantity of 
 electricity which passes through a circuit 
 
THE TRANSMISSION OF POWER. 45 
 
 during one second, when the current 
 strength is one ampere. Thus, again 
 referring to the simple electric circuit 
 shown in Fig. 1, the value of the current 
 flowing through which was calculated 
 as two amperes, the quantity of electricity 
 would be two coulombs in each second, or 
 120 coulombs per minute. 
 
 A reservoir filled with water may be 
 regarded as a store of energy and can be 
 caused to expend that energy in doing 
 work, by permitting the water to escape 
 so as to drive a water motor. The 
 amount of energy, which can be trans- 
 ferred from the reservoir to the motor, 
 will depend both on the quantity of water 
 in the reservoir, and on the vertical height 
 through which the water is permitted to 
 fall. Thus, if the reservoir contain 1,000,- 
 000 pounds of water, and this drives a 
 
48 ME ELECTKIC MOTOR AND 
 
 E. M. F. of 10 volts is active. This pres- 
 sure corresponds to the total difference of 
 level between the water in the reservoir 
 and the motor which it drives. Every 
 coulomb of electricity which flows through 
 this circuit requires an expenditure of 
 work equal to 10 volts X 1 coulomb = 10 
 volt-coulombs = 10 joules = 7.38 foot- 
 pounds. Since, as we have seen, the 
 current strength iu this circuit is 2 
 amperes ; i. e., 2 coulombs-per-second, the 
 work done will be 2 X 10 = 20 joules 
 in each second. A joule-per-second is 
 called a watt ; consequently, the activity 
 in this circuit will be 20 watts. In any 
 electric circuit the rate at which work is 
 being expended ; i. e., the activity of the 
 circuit, expressed in watts, is equal to the 
 product of the total pressure in volts 
 multiplied by the current strength in 
 amperes. 
 
THE TRANSMISSION OF POWER. 49 
 
 This activity has to be supplied to the 
 circuit by the electric source. In the case 
 of a dynamo, the activity is supplied by 
 the engine or turbine driving the dynamo. 
 In the case of a battery, the activity is 
 supplied by the chemical energy of the 
 cell, in other words, by the burning of the 
 zinc in the battery solution. 
 
 The activity so expended in an electric 
 circuit appears in one of three ways : 
 
 (1) Heat. 
 
 (2) Mechanical work. 
 
 (3) Electro-chemical work. 
 
 The relative expenditure of activity in 
 these three different ways is determined 
 by the distribution of what is called the 
 counter E. M. F. y abbreviated C. E. M. F. 
 For example, in Fig. 1, an E. M. F. of 10 
 volts acting in the circuit is opposed by 
 
48 THE ELECTRIC MOTOK ANT) 
 
 E. M. F. of 10 volts is active. This pres- 
 sure corresponds to the total difference of 
 level between the water in the reservoir 
 and the motor which it drives. Every 
 coulomb of electricity which flows through 
 this circuit requires an expenditure of 
 work equal to 10 volts X 1 coulomb = 10 
 volt-coulombs = 10 joules = 7.38 foot- 
 pounds. Since, as we have seen, the 
 current strength in this circuit is 2 
 amperes ; i. e., 2 coulombs-per-second, the 
 work clone will be 2 x 10 = 20 joules 
 in each second. A joule-per-second is 
 called a watt; consequently, the activity 
 in this circuit will be 20 watts. In any 
 electric circuit the rate at which work is 
 being expended ; i. e., the activity of the 
 circuit, expressed in watts, is equal to the 
 product of the total pressure in volts 
 multiplied by the current strength in 
 amperes. 
 
>THE TRANSMISSION OF POWER. 49 
 
 This activity has to be supplied to the 
 circuit by the electric source. lu the case 
 of a dynamo, the activity is supplied by 
 the engine or turbine driving the dynamo. 
 In the case of a battery, the activity is 
 supplied by the chemical energy of the 
 cell, in other words, by the burning of the 
 zinc in the battery solution. 
 
 The activity so expended in an electric 
 circuit appears in one of three ways : 
 
 (1) Heat. 
 
 (2) Mechanical work. 
 
 (3) Electro-chemical work. 
 
 The relative expenditure of activity in 
 these three different ways is determined 
 by the distribution of what is called the 
 counter E. M. F., abbreviated C. E. M. F. 
 For example, in Fig. 1, an E. M. F. of 10 
 volts acting in the circuit is opposed by 
 
50 THE ELECTRIC MOTOR AND 
 
 a C. E. M. F. ; i. e., a back pressure, or 
 oppositely directed E. M. F. opposing the 
 flow of the current. 
 
 The passage of water through a pipe is 
 always attended by a back pressure. For 
 example, if a powerful stream of water be 
 forced through a long hose, there will be 
 a difference of pressure between the two 
 ends of the hose, owing to the resistance 
 encountered by the water during the pas- 
 sage. If the water escapes freely from the 
 distant end into the air, the pressure in the 
 hose, at a distance of say two hundred feet 
 from the end, may be, perhaps, five pounds 
 per square inch above the pressure of the 
 air. This is the back pressure due to 
 the flow of water. It increases with the 
 rapidity of the discharge. 
 
 In an electric conductor or circuit, the 
 
THE TRANSMISSION OF POWER. 51 
 
 product of the current strength in amperes 
 and the resistance in ohms, gives the back 
 pressure, or C. E. M. F. in volts. Thus in 
 the circuit of Fig. 1, where the resistance 
 of the entire circuit is 5 ohms, and the 
 current 2 amperes, the C. E. M. F. is 
 2x5= 10 volts, which is equal to the 
 driving E. M. F . This, in fact, follows 
 from a consideration of Ohm's law; 
 namely, that the E. M. F. divided by the 
 resistance gives the current strength, so 
 that the current strength multiplied by 
 the resistance, is equal to the E. M. F. 
 
 Since the resistance of the circuit, shown 
 in Fig. 1, is made up of the resistance of 
 the voltaic battery, the conducting wires 
 and the lamp, the C. E. M. F. or fall of 
 pressure of 10 volts, is distributed in these 
 portions according to their respective re- 
 sistances. If the resistance of the battery 
 
52 THE ELECTRIC MOTOR AND 
 
 be 1 ohm, that is, if the battery con- 
 sidered as an electric conductor composed 
 of liquids and metals, offered a resistance 
 of 1 ohm to the passage of the current 
 it generates, the C. E. M. F. set up in the 
 battery by the current strength of 2 
 amperes will be 2 amperes X 1 ohm = 
 2 volts. Or, regarded from the standpoint 
 of Ohm's law, 2 volts will be the E. M. 
 F. necessary to force 2 amperes through 
 the resistance of the battery. As it is 
 usually expressed, the " drop" or fall of 
 pressure in the resistance of the battery 
 will be 2 volts. Again, if the resistance 
 of the conducting wires leading to the 
 lamp ; i. e., the leads, be 1 ohm, or 1/2 
 an ohm in each conductor, the drop in each 
 will be 2 amperes X 1/2 ohm = 1 volt. 
 Since the resistance of the lamp is 3 
 ohms, the C. E. M. F., or drop in its resis- 
 tance, will also be 2 amperes x 3 ohms = 
 
THE TRANSMISSION OF POWER. 53 
 
 6 volts. The total drop, or C. E. M. F. 
 due to resistance, will, therefore, be 6 volts 
 in the lamp, 2 volts in the conducting 
 wires, and 2 volts in the battery, making 
 the total C. E. M. F. equal and opposite 
 to the driving E. M. F. ; namely 10 volts. 
 
 As we have seen, the activity expended 
 by a source is the product of the driving 
 pressure or E. M. F. in that source, and the 
 current strength in the circuit expressed 
 in coulombs-per-secoud, or amperes. Simi- 
 larly, the activity in watts, expended on 
 a source of C. E. M. F., is the product of 
 that C. E. M. F. in volts, and the cur- 
 rent strength passing through the circuit. 
 Thus, the activity expended in the lamp 
 of Fig. 1, will be 6 volts x 2 amperes = 
 12 watts, or 8.856 foot-pounds-per-second, 
 expended in the lamp as heat. Again, the 
 activity expended in the two conductors is 
 
54 THE ELECTRIC MOTOR AND 
 
 2 volts x 2 amperes = 4 watts, or 2.952 
 foot-poimds-per-second. The activity ex- 
 pended in the internal resistance of the 
 battery will be also 2 volts x 2 amperes = 
 4 watts 2.952 foot-pounds-per-second, 
 while the activity expended in the entire 
 circuit of the battery will be 10 volts x 
 2 amperes = 20 watts = 15.76 foot-pounds- 
 per-second. 
 
 Summing up the various activities in 
 the circuit, we have, as follows; viz., 
 
 The activity expended on the circuit by 
 the source is 10 volts X 2 amperes = 20 
 watts = 20 joules-per-second. Of this the 
 activity expended in the circuit by the 
 lamp is 6 volts X 2 amperes =12 watts; 
 the activity expended in the two leads, is 2 
 volts x 2 amperes = 4 watts; the activity 
 expended in the battery, is 2 volts X 2 am- 
 peres = 4 watts ; total activity = 20 watts. 
 
THE 
 
 DIESEL fl 
 
 OF POWER. 
 
 In the 
 
 pended by the c^ji^cal energy in the bat- 
 tery, and is liberale^efitii'ely in the form 
 of heat ; that is to say, the battery is 
 warmed, the wires are warmed, and the 
 lamp is warmed. The lamp becomes 
 much hotter than either the battery or 
 the wires, because the heat is liberated in 
 a very small volume of material, and can 
 escape only from a very contracted sur- 
 face. All activity expended against the 
 C. E. M. F. of drop is thermal activity and 
 is usually to be considered as wasted 
 activity, except in the case of electric 
 heaters or electric lamps, where this 
 C. E. M. F. and activity are designedly 
 employed for warming the surrounding air 
 or other bodies. 
 
 When an electric motor is so placed in 
 any circuit, that a current passes through it, 
 
56 
 
 THE ELECTRIC MOTOR AND 
 
 there will be produced in it a drop or C. 
 E. M. F. due to resistance only ; provided 
 that the motor be prevented from moving. 
 If, however, the motor be driven by the 
 
 FIG. 3. ELECTRIC CIRCUIT CONTAINING SOURCE, LEADS 
 AND MOTOR. 
 
 current, then there is produced an addi- 
 tional C. E. M. F. which is generated by 
 the rotation of the motor. Thus, if the 
 motor M, in Fig. 3, has a resistance of 1 
 
THE TRANSMISSION OF POWER. 57 
 
 ohm,- and the leads to the motor have each 
 a resistance of 1 ohm, while the internal 
 resistance of the battery or electric source 
 is also 1 ohm, then the total resistance 
 of the circuit will be 4 ohms, and, as long 
 as the motor is prevented from running, 
 the current strength in the circuit will be 
 10 volts divided by 4 ohms = 2.5 amperes. 
 The activity expended by the source will, 
 therefore, be 10 volts x 2.5 amperes = 25 
 watts, and this activity will be entirely 
 expended in heating the circuit. 6 1/4 
 watts will be expended in warming the 
 battery, 6 1/4 watts in warming each 
 wire, and 61/4 watts in warming the wire 
 wound upon the motor. 
 
 If, however, the motor be permitted to 
 run, and, therefore, to do work, it must 
 expend energy ; and this expenditure must 
 be supplied from the circuit as the pro- 
 
58 THE ELECTRIC MOTOR AND 
 
 duct of a C. E. M. F. and the current 
 strength which it opposes. Thus, if the 
 motor by its rotation generates a C. E. 
 M. F. of 2 volts, in addition to its 
 C. E. M. F. of drop, the E. M. F. acting 
 on the circuit will be 10 volts in the bat- 
 tery, less 2 volts C. E. M. F. of rotation 
 produced by the motor, or 8 volts, as the 
 resultant driving E. M. F., capable of be- 
 ing expended in forcing current through 
 the circuit against resistance. The current 
 strength will, therefore, be 8 volts -r- 4 
 ohms = 2 amperes, and the activity of the 
 source will be 10 volts x 2 amperes = 20 
 watts = 14.76 foot-pounds. The drop in 
 the battery will be 2 amperes X 1 ohm = 
 2 volts ; that in each of the leads 2 volts ; 
 and that in the winding of the motor 2 
 volts. The total pressure at motor termi- 
 nals is, therefore, 4 volts. The activity 
 expended as heat will, therefore, be 2 volts 
 
THE TRANSMISSION OF POWER. 59 
 
 X 2 amperes = 4 watts in the battery, 4 in 
 each of the wires, and 4 in the motor 
 winding = 16 watts in all. The activity 
 in the motor available for mechanical 
 work, is, however, the C. E. M. F. of rota- 
 tion, or 2 volts x 2 amperes = 4 watts, so 
 that the total amount of work which the 
 motor can perform mechanically is 4 watts, 
 or 2.952 foot-pounds-per-second. It is to 
 be observed, therefore, that while 20 watts 
 are expended by the source, only 4 
 watts can in this instance be utilized for 
 mechanical purposes, the balance being 
 expended in heating the circuit. 
 
 Analyzing the activity in the circuit we 
 have : Total activity of battery 10 volts 
 x 2 amperes = 20 watts = 14.76 foot- 
 pounds-per-second. This must be ex- 
 pended in the circuit as a whole. The 
 drop, or C. E. M. F. due to resistance in 
 
60 THE ELECTRIC MOTOR AND 
 
 the two leads, is 4 volts, so that the 
 activity in wanning the leads is 4 volts x 
 2 amperes 8 watts. The drop in the 
 battery is 2 volts, so that the activity in 
 warming the battery is 2 volts x 2 amperes 
 4 watts. The drop in the motor is 2 
 volts; the C. E. M. F. of rotation is 2 
 volts; the total C. E. M. F. is 4 volts. 
 The activity in the motor is, therefore, 4 
 volts X 2 amperes = 8 watts ; total, 20 
 watts. Of the 8 watts total activity in 
 motor, 4 watts will be expended in heating 
 its wire, and 4 watts in producing rota- 
 tion. 
 
 We have already referred to the fact 
 that when water escapes from a reservoir 
 through a pipe a back pressure, or a coun- 
 ter watermotive force is produced in the 
 pipe, tending to check the flow. Fig. 4, 
 represents a reservoir 7?, maintained at a 
 
THE TRANSMISSION OF POWER. 
 
 61 
 
 practically constant level. Suppose a 
 horizontal pipe B O, be provided with 
 an outlet at O. If the outlet at O, be 
 temporarily closed, then the pressure from 
 the water in j5, will cause the water to 
 
 01 23456 789 10 
 
 t 
 
 
 ^ . 
 
 rt* 
 
 ^ 
 
 f* 
 
 
 
 
 
 
 
 ~~~ 
 
 *-- 
 
 
 g 
 
 f 
 
 
 
 
 
 
 R 
 
 
 
 
 
 "" -~ 
 
 
 jj 
 
 
 
 
 
 
 
 
 
 
 
 . . 
 
 L 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 
 3 C 
 
 1 
 
 ) i 
 
 : 
 
 1 <j 
 
 Ir k 
 
 L I 
 
 i 
 
 C 1 
 
 j G 
 
 FIG. 4. RESERVOIR DISCHARGING WATER THROUGH AN 
 OUTLET PIPE. 
 
 stand at the same level A A', in all the 
 vertical pipes, 1, 2, 3, 4, etc. If, however, 
 the outlet pipe be opened, the pressure 
 at the outlet will fall to zero ; i. e., become 
 that of the pressure in the air, and the 
 liquid will escape owing to the difference 
 of pressure between this point and that 
 
62 THE ELECTRIC MOTOIl AND 
 
 in the reservoir. There will, therefore, 
 be established a gradient of pressure b C\ 
 which will be practically uniform if the 
 pipe be uniform, and the pressure in the 
 pipe will be represented by tbe respective 
 columns of water at Z>, <?, d, e, /, etc. The 
 back pressure at the reservoir, due to the 
 flow of water through the pipe, is l> B, or 
 the fall of pressure in the reservoir. At 
 1, the back pressure is represented by 
 the column c C, and the drop of pressure 
 in the length B C, is represented by the 
 column of water c c. Similarly, the back 
 pressure at 2, is represented by the 
 column d I), and the drop in the length 
 CD, bjr the column dd'. Similarly, the 
 drop in the whole length B O, is b B, 
 or A' O. In other words, the pressure 
 b B, is that which is required to produce, 
 through the resistance of the pipe, the 
 actual flow which takes place through it. 
 
THE TRANSMISSION OF POWER. 63 
 
 If we consider a pound of water in the 
 pipe after leaving the reservoir, then when 
 this pound of water has reached the 
 point 1, it has virtually fallen through the 
 height c c', and, therefore, the amount of 
 work expended by the reservoir in forc- 
 ing the water through the pipe against 
 this back pressure c c', will be this pound 
 multiplied by the number of feet in 
 c c'. Again, if the flow from the reservoir 
 be say 50 pounds-per-second, then the ex- 
 penditure of activity in foot-pounds-per- 
 second, will be 50 pounds x height O A'. 
 If this be 10 feet, the activity of the reser- 
 voir will be 50 X 10 = 500 foot- pounds-per- 
 second = 678 watts. 
 
 The preceding principles are those, 
 which as we have seen, apply to the elec- 
 tric circuit. If we represent the number 
 of pounds of water by the coulombs, the 
 
64 THE ELECTRIC MOTOR AND 
 
 difference of level in feet, by the volts, 
 and the pounds-per-second, by the amperes, 
 the analogy is complete : for, if we multiply 
 the current flow in amperes, by the drop 
 of pressure caused by the resistance in 
 volts, we have the joules-per-second, or the 
 watts of activity, expended by the electric 
 source in order to drive the electricity 
 through the circuit against its resistance, 
 or against the C. E. M. F. which this resist- 
 ance produces. It must be remembered, 
 however, that electricity is not a gross 
 liquid like water and that these are merely 
 analogies. 
 
 Fig. 5 represents a reservoir with an out- 
 let pipe as before, but coupled to a small 
 water motor M, inserted in the pipe. This 
 water motor absorbs activity by reason of 
 the back pressure it is capable of develop- 
 ing when in rotation. It will be observed 
 
THE TRANSMISSION OF POWER. 
 
 65 
 
 that the driving pressure in the reservoir is 
 now equal to the sum of the drops of pres- 
 sure in the pipe, and the back pressure of 
 the motor M. Thus d ly is the drop of pres- 
 sure in the first section of the pipe, d^ the 
 
 B 
 
 FIG. 5. DISTRIBUTION OF PRESSURES IN MOTOR AND 
 PIPE. 
 
 drop of pressure in the second section of 
 the pipe, and I>, is the back pressure due 
 to the action of the motor, so that d ly B, 
 and dfy are together equal to P. 
 
 The activity expended by the reservoir in 
 forcing the water through the pipe and 
 motor together, is equal to the flow, say 
 50 pound s-per-second, multiplied by the 
 
66 THE ELECTRIC MOTOR AND 
 
 total driving head JP, say 10 feet = 50 x 
 10 = 500 foot-pounds-per-second. Of this 
 activity that which is expended in forcing 
 the water through the pipe, against the drop 
 of pressure due to its resistance, is ex- 
 pended in warming both the pipe and the 
 water, while the activity expended against 
 the back pressure J3J of the motor, may be 
 entirely employed in producing mechanical 
 work, and would be so expended if the 
 motor J/, were a perfect machine. Thus 
 if c/ l7 be 2 feet and d%, 2 feet, while B, is 
 6 feet, the activity expended in heating 
 the pipe and its contents is 4 feet X 50 
 pounds-per-second = 200 foot-pounds-per- 
 second ; while the activity expended in the 
 motor is 6 feet x 50 pounds-per-second = 
 300 foot-pounds-per-second. Moreover, the 
 larger the pipe, and the shorter its length, 
 the less will be the drop for a given flow, 
 and the greater the proportion of activity 
 
THE TRANSMISSION OF POWER. 67 
 
 which may be expended in driving the 
 motor. 
 
 The electric analogue is shown in Fig. 
 6, where the source is represented as a 
 
 ;d> 
 
 [3 
 
 FIG. 6. ELECTRIC ANALOGUE SHOWING DISTRIBUTION 
 OF PRESSURE IN MOTOR AND WIRES. 
 
 battery or dynamo producing the E. M. F. 
 or difference of electric level E. The cir- 
 cuit A. I), extends from one pole of the 
 battery to the other, although not so shown 
 in the drawing. The motor M, produces a 
 back pressure B, which we may assume to 
 be entirely due to its rotation, the resist- 
 ance of the motor being negligible ; the re- 
 
68 THE ELECTRIC MOTOR AND 
 
 sistance of the conducting wires is 2 ohms 
 each, the drop in the conducting wires is 
 represented by d^ and d%, as before, but 
 expressed in volts instead of in feet. If 
 the E. M. F. at generator terminals be 10 
 volts, d and d 2 , each 2 volts, and the back 
 pressure of the motor 6 volts, then the 
 current through the circuit will be 10 - 
 6 = 4 volts divided by 4 ohms = 1 ampere. 
 The activity expended by the source will be 
 10 volts x 1 ampere =10 watts = 7.38 foot- 
 pounds-per-second. The activity expended 
 in each of the leads will be 2 volts X 1 
 ampere = 2 watts, or 4 watts in all, and 
 the balance, or 6 watts, must be equal to 
 the activity expended in the motor ; namely, 
 6 volts x 1 ampere. If the motor could be 
 made perfect, it would supply 6 watts 
 mechanically at its shaft, or 4.428 foot- 
 pounds-per-second, available for driving 
 purposes, and the proportion of the avail- 
 
THE TRANSMISSION OF POWER. t>9 
 
 able activity in the circuit to the total activ- 
 
 r* 
 
 ity expended would be = 60 per cent. 
 
 In practice, owing to the existence of vari- 
 ous f rictional forces in the motor, its output 
 would be less than 6 watts, say 4, making 
 
 E( 
 
 m 
 
 FIG. 7. DISTKIBUTION OP ELECTRIC PKESSUKE IN A 
 CIRCUIT. 
 
 its efficiency = 66 2/3 per cent., and the 
 
 4 
 efficiency of the circuit = 40 per cent. 
 
 Fig. 7 represents a more nearly com- 
 plete analysis of the distribution of drop 
 and expenditure of energy in a circuit 
 
70 THE ELECTRIC MOTOR AND 
 
 consisting of a source, a motor and conduct- 
 ing wires. 
 
 The E. M. F. of the battery or source 
 is represented by JK. The resistance of 
 the battery by the length O A, the resist- 
 ance of conducting wires by the lengths 
 A B and CD, arid the resistance of the 
 motor by the length B C. Then, if e /, 
 represents the back pressure of the motor 
 due to its rotation, the pressure in the cir- 
 cuit will follow the line o a b f e c D. If 
 o, represents 10 volts, A, 1 ohm, A B 
 and C D 2 ohms each, B C, I ohm, then 
 the total resistance of the circuit will be 
 6 ohms. Also, if the back pressure e /, 
 be 4 volts, the total E. M. F. in the circuit 
 available for producing current through 
 resistance will be 10 4 = 6 volts, so that 
 by Ohm's law the current strength will be 
 6 volts divided by 6 ohms = 1 ampere. 
 
THE TRANSMISSION OF POWER. 71 
 
 The activity expended in the source will 
 be 1 watt; that in the conducting wires 
 4 watts ; and that in the resistance of the 
 motor 1 watt, making a total thermal ac- 
 tivity of 6 watts, and leaving an activity 
 of 4 watts to be expended in the motor 
 available for purpose of producing rota- 
 tion. As a matter of fact, however, the 
 back pressure in the motor is not devel- 
 oped at any one spot, say halfway 
 through its resistance, but will probably 
 be developed uniformly through all parts 
 of the resistance, and the combined effect 
 of C. E. M. F. due to rotation and drop in 
 resistance will be indicated by the dotted 
 line b c, having a different gradient to the 
 line o b, or c D. 
 
 It will be observed that the drop in the 
 battery is the difference in pressure be- 
 tween E, and A a, or o. The drop in 
 
72 THE ELECTRIC MOTOR. 
 
 the leads will be the difference in pressure 
 between A a and JB , and between Co 
 and i>, respectively. The total drop in 
 the motor will be b g, or the difference 
 between B b and C c. This drop is com- 
 posed of two parts ; namely, e f, due to 
 rotation which would disappear when the 
 motor came to rest, and which represents 
 the C. E. M. F. available for useful work, 
 and the difference between e f and b g, 
 which is the drop in the resistance of the 
 motor with a current of one ampere. 
 
CHAPTER IV. 
 
 EARLY HISTORY OF THE ELECTROMAGNETIC 
 MOTOE. 
 
 PROBABLY one of the most valuable gifts 
 of electromagnetic science to the industrial 
 world is that of the electromagnetic 
 motor. The history of this subject is not 
 only interesting on its own account, but 
 also affords, perhaps, the best line that can 
 be followed in the discussion of its theory. 
 
 The electric motor, as it exists to-day, is 
 a marvel of ingenuity. As a means for 
 converting electrical into mechanical en- 
 ergy it cannot but be regarded as an ex- 
 ceptionally efficient piece of apparatus. 
 
 73' 
 
74 THE ELECTRIC MOTOR AND 
 
 Like other great achievements, the electric 
 motor has not been the product of any 
 single man or nation, but is rather the 
 embodiment of the life work of many able 
 workers, from many countries, through 
 many years. As Emerson has aptly ex- 
 pressed it : " Not in a week, or a month, 
 or a year, but by the lives of many souls, 
 a beautiful thing must be done." 
 
 Since the electromagnetic motor con- 
 sists essentially of means whereby a con- 
 tinuous rotary motion is produced, by the 
 combined agency of an electric current 
 and a magnet, we must regard the first 
 electric motor as being due to Faraday, 
 who, in 1821, produced the apparatus 
 shown in Fig. 8. Here a permanent steel 
 bar magnet S N, is fixed in a cork, which 
 wholly closes the lower end of a glass 
 tube. Enough mercury is poured in to 
 
THE TRANSMISSION OF POWER. 
 
 75 
 
 partly cover the magnet. An electric cur- 
 rent is caused to flow in the neighborhood 
 of the magnet, through a movable wire 
 a b y so suspended as to be capable of rotat- 
 
 FIG. 8. THE FIRST ELECTROMAGNETIC MOTOR. 
 
 ing its lower extremity about the axis of 
 the tube. Under the combined action of 
 the current and the magnet, a continu- 
 ous rotary motion is produced. The 
 
76 THE ELECTRIC MOTOE AND 
 
 direction of this motion depends upon the 
 direction of the current, as well as on 
 the polarity of the magnet ; that is to say, 
 if the motion be right-handed, or clock- 
 wise, when the current is in one direction 
 through the wire, it will be left-handed, 
 or counter -clockwise, if the direction 
 of current be reversed. Similarly, a re- 
 versal of the polarity of the magnet, will 
 reverse the direction of the motion. The 
 current passes through the conductor in the 
 upper cork to the hook a, thence through 
 the movable wire a b, and out, by means 
 of the mercury and the lower conductor. 
 
 Let us inquire into the cause which pro- 
 duces the electromagnetic rotation in the 
 case of the simple apparatus shown in Fig. 
 8. To do this, a brief examination into 
 the elementary principles of magnetism 
 will be necessary. 
 
THE TRANSMISSION OF POWER. 77 
 
 We have experimental knowledge of the 
 fact that magnets possess the power of 
 mutual attraction and repulsion, at sensible 
 distances from one another. It would 
 seem at first sight, that magnets possess 
 the power of producing action at a dis- 
 tance, without the presence of any inter- 
 vening mechanism, or connecting medium, 
 but this doctrine is now totally discredited. 
 Indeed, it can be shown that a certain 
 influence emanates from the magnet, so 
 that a magnet is a piece of visible matter 
 accompanied and surrounded by an in- 
 visible influence, which must be regarded 
 as a part of the magnet itself. More- 
 over, the invisible part is much larger 
 than the visible part. This invisible 
 part, or magnetic field, may be described 
 as a region traversed by an emanation 
 called magnetic flux. The existence of 
 this flux is shown either by the action 
 
78 TI1K ELECTRIC MOTOR AND 
 
 exerted upon a movable compass needle, 
 when brought into or out of the field, 
 or by the power it possesses to cause 
 iron filings to align themselves in definite 
 directions. In Fig. 9, the direction of the 
 flux paths is shown by means of the group- 
 ings of iron filings which have been 
 sprinkled on a glass plate placed over a 
 bar magnet. 
 
 Regarding the grouping of filings as 
 indicating the paths of magnetic flux, in 
 the plane of the glass plate, it will be 
 seen that curved chains of filings connect 
 the two ends JV, and $, of the magnet, 
 although in the outlying portions of the 
 figure the interconnection of these lines 
 is not shown. We know, however, that if 
 the figure were large enough, all the lines 
 would be found to form complete closed 
 paths. Moreover, it can be shown that 
 
80 THE ELECTRIC MOTOR AND 
 
 this flux not only occupies the space out- 
 side the magnet, but also penetrates its 
 substance, and that, in fact, each flux path 
 forms an endless chain, passing through 
 both the substance of the magnet and the 
 region outside the magnet. The question 
 naturally arises whether the magnetic flux, 
 or at least that part of it which lies out- 
 side the magnet, is not due to the presence 
 of the air or other gross medium occupying 
 this space. This, however, is not the case, 
 since the same phenomena occur if a 
 vacuum exists outside the magnet, that is 
 to say, if the magnet be enclosed in a 
 chamber exhausted by an air-pump. 
 
 There is, however, a medium called the 
 universal ether, which, as can be shown, 
 does fill this, as well as all other space. 
 The air-pump is unable to remove this me- 
 dium, since it can readily pass through the 
 
THE TRANSMISSION OF POWER. 81 
 
 substance of glass or of any other known 
 material. Although the exact nature of 
 magnetic flux is unknown, yet it is con- 
 venient, for purposes of explanation, to 
 assume that it consists of a streaming motion 
 of the ether ; the curved lines, occupied 
 by the iron filings, corresponding to the 
 stream-lines or lines in which the ether is 
 flowing. 
 
 Since a flow necessitates a motion in a 
 definite direction, it is conventionally as- 
 sumed that the ether streams; i. e., the 
 magnetic flux, issue from the magnet at its 
 north pole ; namely, the pole which would 
 point northwards, if the magnets were 
 freely suspended, and after having passed 
 through the region outside, returns into the 
 substance of the magnet at its south pole, 
 then passing through the substance of the 
 magnet and reissuing at its north pole. 
 
82 THE ELECTRIC MOTOR AND 
 
 In other words, a magnet may be regarded 
 as a means for producing a streaming mo- 
 tion of the ether. That is to say, an ether 
 streaming, called magnetic flux, moves in 
 closed paths or circuits around the mag- 
 net. According to this view, a bar magnet 
 acts relatively to the ether whicli per- 
 meates and surrounds it, in the same way 
 as a tube placed in water and furnished 
 with a pump in its interior, which causes 
 a steady stream of water to emerge from 
 the tube at one end, and to re-enter at the 
 other end, after passing through the sur- 
 rounding liquid. 
 
 What we call the magnetic properties 
 of a magnet only continue to exist while 
 the magnet is producing these streaming 
 ^ther motions ; that is, while it is producing 
 magnetic flux. Anything which causes 
 this motion to cease, causes the magnet to 
 
THK TRANSMISSION OF POWEK. 83 
 
 lose its magnetic properties, and anything 
 which enables the magnet to again pro- 
 duce this flux, will enable it to regain its 
 magnetic properties. Since a magnetized 
 bar of hardened steel retains its magnet- 
 ism for an indefinite time, we assume that 
 it possesses the power of indefinitely pro- 
 ducing the ether motion. This could ex- 
 ist without loss of energy if we assume, as 
 we believe to be true, that ether is a fric- 
 tionless fluid. 
 
 But there are other ways of setting up 
 streaming ether motion ; i. <?., producing 
 magnetic flux around gross matter. If an 
 electric conductor, say a copper wire, has 
 an electric current passed through it, the 
 streaming ether motion will be set up in 
 concentric circles around it. The presence 
 of this circular magnetic flux may be 
 shown by groupings of iron filings ob- 
 
84 THE ELECTRIC MOTOR AND 
 
 tained in a similar manner to that de- 
 scribed in the case of the bar magnet and 
 
 FIG. 10. CIRCULAR DISTRIBUTION OF FLUX AROUND 
 ACTIVE CONDUCTOR. 
 
 shown in Fig. 9. Such groupings in the 
 case of an active wire are shown in Fig. 
 10. Here a horizontal sheet of paper has 
 
THE TRANSMISSION OF POWER. 85 
 
 been placed perpendicularly to a vertical 
 wire while an electric current is passing 
 through it. 
 
 The circular magnetic flux, produced 
 around an active conductor by an electric 
 current, like the flux produced by a per- 
 manent bar magnet, has a definite direction 
 dependent on the direction of current in 
 the wire. If the current be considered to 
 pass through the wire away from the 
 observer, the magnetic streamings around 
 the conductor will have the same direction 
 as that of the hands of a watch, as seen by 
 an observer facing them. Reversing the 
 direction of the current will reverse the 
 direction of the streamings. The stream- 
 ings cease as soon as the current ceases. 
 In other words, the magnetic flux around 
 a wire is dependent upon the existence of 
 the electric current. 
 
86 
 
 THE ELECTRIC MOTOtt AND 
 
 Fig. 11, represents diagrammatically the 
 magnetic flux passing through the north 
 pole of a magnet into the region occupied 
 
 FIG. 11. DIAGRAMMATIC KEPRESENTATION OF FLUX 
 FROM MAGNET, SHOWN IN FIG. 8. 
 
 by the wire a b, of Fig. 8. If no current 
 passes through the wire, this magnetic flux 
 does not tend to produce any motion in 
 the wire. If, however, a current passes 
 through the wire, so that magnetic flux 
 
THE TRANSMcr 
 
 Y/ 8 ?^ P <rV 
 
 streams around it, W^% the interactions of 
 the two magnetic nS^re^pi^duce a t^- c 
 dency to move the conductor across the 
 magnetic flux from the magnet, and, con- 
 sequently, cause the wire to move in a 
 circular path around the magnetic pole. 
 The combination, therefore, of an active 
 conductor and an independent magnetic flux, 
 constitutes a simple electromagnetic motor. 
 
 As is well known, action and reaction 
 are always equal and opposite, so that 
 if the magnet pulls the wire around 
 it through the medium of the inter- 
 acting magnetic fluxes, the wire is also 
 producing a pull on the magnet. Conse- 
 quently, if the wire be fixed and the mag- 
 net be free to move about its vertical axis, 
 it may be made to rotate. This was 
 actually done by Faraday, and others after 
 him, in a variety of apparatus. 
 
88 THE ELECTRIC MOTOR AND 
 
 Feeble as was the early motor of Fara- 
 day represented in Fig. 8, yet it essentially 
 embodied the principles of the most com- 
 plex, powerful and efficient electromag- 
 netic motors of to-day, and a comprehen- 
 sion of the principles involved in this 
 simple motor gives the clue to the action 
 of all modern motors. 
 
 Fig. 12, represents a modified form of 
 the early motor shown in Fig. 8. Here the 
 electric current passes from the base of the 
 instrument through the vertical bar mag- 
 net A J3. The metallic support D, has 
 pivoted at its upper extremity a delicately 
 suspended rectangular conductor E F, 
 which has its two free ends dipping into 
 a circular trough of mercury. The current 
 divides through this rectangular loop, pass- 
 ing down through E and F. Under these 
 circumstances, a continuous rotary motion 
 
THE TRANSMISSION OF POWER. 
 
 89 
 
 of the rectangular circuit is produced. 
 This apparatus only differs from the pre- 
 
 FIG. 12. MODIFIED FORM OF FARADAY MOTOR. 
 
 ceding in the fact that two wires carry the 
 current past the magnet, instead of one. 
 
90 THE ELECTRIC MOTOR AND 
 
 The fact that magnets exhibit mutual 
 attractions and repulsions for one another, 
 was known from the dawn of magnetic 
 science, before the Christian era, and the 
 idea of obtaining mechanical motion from 
 magnets naturally originated at, perhaps, 
 an equally early date. Continuous motion 
 was, and still is, impossible with perma- 
 nent magnets, for the reason that when a 
 magnet has attracted either a piece of iron, 
 or another magnet, it cannot again repel 
 the same unless its magnetism is reversed, 
 and no means for reversing magnetism 
 were known, until the magnetic properties 
 of the electric current were discovered. 
 
 Although Faraday was the first to pro- 
 duce a continuous electromagnetic rotation, 
 and is justly entitled to the honor of pri- 
 ority, yet the principle which he adopted 
 was that discovered by Oersted in 1819. 
 
THE TRANSMISSION OF POWER. 91 
 
 Oersted's discovery not only showed how a 
 magnet could be produced by an electric 
 current, but also, for the first time in the 
 history of science, afforded the means of 
 
 reversing at will the direction of mag- 
 es o 
 
 netism, and thus obtaining a continuous 
 rotary motion. 
 
 Oersted showed that when an electric 
 circuit was completed, the circuit thereby 
 acquired magnetic properties, and pos- 
 sessed the power of attracting or repelling 
 magnets brought into its vicinity, the ten- 
 dency of such attraction or repulsion being 
 to cause a magnet to set itself at right 
 angles to the electric current. The ap- 
 paratus for demonstrating this important 
 principle consists essentially of a wire A B, 
 carrying a current, and brought into the 
 vicinity of a freely suspended horizontal 
 compass needle, as shown in Fig. 13. As- 
 
92 THE ELECTRIC MOTOR AND 
 
 FIG. 13. OERSTED'S EXPERIMENT. 
 
 suniing the magnet to be placed parallel 
 to the conductor, then as soon as the cur- 
 
TJIE TRANSMISSION OF POWER. 93 
 
 rent flows through the wire, the needle 
 will be deflected and will tend to occupy a 
 position at right angles to the wire. On 
 the cessation of the current in the wire, 
 the needle returns to its original position 
 under the influence of the earth's magnet- 
 ism. The direction in which the needle 
 is deflected will depend upon the direction 
 of the electric current. If we reverse the 
 direction of the current in the wire, we re- 
 verse the direction of deflection in the 
 needle, because we reverse the direction 
 of the magnetic flux passing around the 
 wire. Also, if Ave obtained one direction 
 of deflection when the wire is held above 
 the needle, the opposite direction of deflec- 
 tion will be obtained when the wire is held 
 beneath the needle. The cause of these 
 phenomena is due to the mutual action of 
 the flux produced by the needle and that 
 produced by the current in the wire, which 
 
94 THE ELECTRIC MOTOR AND 
 
 latter disappears on the cessation of the 
 current. 
 
 It would be possible, by suitably chang- 
 ing the direction of the current, to set up a 
 continuous rotation of the needle, and, in 
 point of fact, the electric motor of to-day 
 consists of means whereby the direction of 
 the current is changed at such times as 
 will eft'ect the continuous rotation of the 
 magnet. 
 
 Various devices were suggested by Fara- 
 day and others for producing continuous 
 rotary motion by electromagnetic action. 
 For example, in 1823, Barlow produced 
 the apparatus shown in Fig. 14. Here 
 an electric current passes between the 
 centre of a star-shaped wheel and emerges 
 at its lowest point, which dips in a 
 trough of mercury included in the circuit. 
 

 THE TBANSM 
 
 <b 
 
 PROPERTY CF ' 
 
 OF POWER. 9(T ' 
 
 A horse-shoe 
 
 magnetic flux, which acting 
 
 the flux produced by the current 
 
 FIG. 14. BARLOW WHEEL MOTOR. 
 
 through the star wheel, produces a con- 
 tinuous rotation of the latter. Here that 
 part of the wheel lying between its axis 
 
96 THE ELECTRIC MOTOR AND 
 
 and the point dipping into the mercury 
 cup corresponds to the movable wire 
 shown in Figs. 8 and 13. Instead, however, 
 of the same wire, or wires, being continu- 
 ously acted on, different portions or teeth 
 of the star wheel are continuously acted on. 
 As before, the direction of motion is at 
 right angles to the magnetic flux produced 
 between the poles of the horse-shoe. 
 
 A modification of Barlow's wheel was 
 shortly afterward made by . Sturgeon. 
 Here a continuous disc, instead of a star 
 wheel, was employed for the moving part. 
 
 None of the early motors, so far de- 
 scribed, were capable of exerting much 
 activity, but such activity as they did 
 exert, was derived, as in the case of all 
 electric motors, from the source supplying 
 their driving current. 
 
THE TRANSMISSION OF POWER. 97 
 
 The mechanical activity developed in a 
 motor, neglecting frictioual losses, is equal 
 to the product of the current strength in 
 amperes, passing through the motor, and 
 the C. E. M. F. in volts developed by the 
 motor through its rotation. The star wheel 
 represented in Fig. 14, produces a C. E. M. 
 F. when it commences to turn, and to this 
 extent the rotating motor tends to act as a 
 dynamo-electric machine, or source of E. 
 M. F. It is a general law, discovered 
 by Faraday, that when an electric con- 
 ductor is moved across a magnetic flux, 
 an E. M. F. is developed in the con- 
 ductor, whether a current be flowing 
 through the conductor or not. Conse- 
 quently, when the spurs of the star wheel 
 rotate under the influence of the force pro- 
 duced by the mutual interaction of the 
 fluxes of the magnet and the current, 
 generally called the electro-dynamic force, 
 
98 THE ELECTRIC MOTOR AND 
 
 the motion of the spurs through the flux 
 produced by the magnet, establishes in the 
 spurs an E. M. F. which is counter, or op- 
 
 ^rrgpHE^^: ' 
 
 FIG. 15. FARADAY'S Disc DYNAMO. 
 
 posed, to the direction of the current in 
 them. The product of this C. E. M. F. 
 and the. current strength, is equal to the 
 activity developed by the wheel. 
 
 Any electric motor is, therefore, capable 
 of acting as a dynamo, if, instead of being 
 
THE TRANSMISSION OF POWER. 99 
 
 driven by the current, it is moved by 
 mechanical force. In fact no electromag- 
 netic motor can operate unless it be cap- 
 able, under the circumstances, of acting 
 as a dynamo, since, otherwise, the motor 
 w^ould be unable to absorb or take activity 
 from the circuit. This fact, however, was 
 not discovered until 1831, when Faraday 
 produced what was, in reality, the first 
 dynamo-electric generator designed for 
 purposes of producing electromotive forces 
 in this manner. 
 
 Faraday's early apparatus is represented 
 in Fig. 15. Here a disc of copper is so 
 mounted as to be capable of rotation be- 
 tween the poles of a horse-shoe magnet. 
 Under these circumstances, E. M. F's. will 
 be set up in the disc, between its centre 
 and edge, and these E. M. F's. may be 
 caused to produce a current in an external 
 
100 THE ELECTRIC MOTOR AND 
 
 circuit by means of collectors, one con- 
 nected with the axis of the disc, and the 
 other with its periphery. The direction 
 of these E. M. F's. will depend both on 
 the direction of rotation of the disc and on 
 the position of the poles of the magnet. 
 Reversing either the polarity of the mag- 
 net, or reversing the direction of rotation, 
 will reverse the direction of the E. M. F. ; 
 and, consequently, the direction of the cur- 
 rent supplied to the external circuit, but it 
 always happens that the direction of the 
 E. M. F. which is developed in such a 
 machine, or indeed, in any motor, when 
 rotated by electromagnetic forces supplied 
 by a current, is opposed or counter to the 
 direction of the driving current. 
 
 If, therefore, instead of rotating the 
 wheel shown in Fig. 16, it be left at 
 rest, and an electric current from an 
 
THE TRANSMISSION OF POWER. 
 
 101 
 
 external source be sent through it in the 
 direction of the arrows, then, under the 
 influence of the electro-dynamic force a 
 
 a 
 
 FIG. 16. JACOBI'S ELECTRIC MOTOR. V 
 
 rotation of the wheel will be produced in 
 the opposite direction to that represented 
 by the arrow. 
 
102 THE ELECTRIC MOTOR AND 
 
 Without attempting to trace fully the 
 gradual developments of the electric 
 motor, it suffices to say that one of the 
 earliest practical motors was produced by 
 Jacobi in 1834, and perfected in 1838. 
 This motor is interesting from a historical 
 standpoint, from the fact that in its im- 
 proved form it was employed for the pro- 
 pulsion of a boat on the river Neva, in 
 1838. In this case the motor was driven 
 by a voltaic battery. 
 
 Jacobi's electric motor is represented 
 in Fig. 16. Here two vertical, parallel 
 frames of wood, support a number of 
 horse-shoe electromagnets / i. e. y horse-shoe- 
 shaped iron cores, wound with insulated 
 copper wire. Such a magnet acquires its 
 magnetism almost instantly on the passage 
 of an electric current, and almost instantly 
 loses it when the current ceases. It is 
 
THE TRANSMISSION OF POWER. 103 
 
 thus capable of becoming magnetized and 
 demagnetized with great rapidity. The 
 magnets in the outer frame were kept per- 
 manently excited by a steady electric cur- 
 rent from the battery. Between these 
 frames a wooden star wheel was supported 
 on the axis a a. In the spurs of this 
 star wheel were mounted the six sets 
 of electromagnets s, s, s, s, s, s. The in- 
 sulated wires leading to these bar mag- 
 nets were connected with the commutating 
 apparatus c, in such a manner that the 
 brushes A, 7i, resting on the commutator 
 disc, supplied an electric current to the 
 rotating magnets from the battery. As 
 soon as the current was supplied to the 
 star wheel magnets, they attracted the 
 fixed electromagnets in their vicinity and 
 pulled around the star wheel to meet 
 them, but just as they came opposite to 
 one another, the rings 6 Y , reversed the cur- 
 
104 THE ELECTRIC MOTOR AND 
 
 rent passing into the moving magnets, 
 thus permitting the magnets in the frame 
 to repel them, and the magnets next in 
 succession to attract them. In this way 
 a continuous rotary motion was produced. 
 
 The first electric motor produced in the 
 United States was that of Davenport, who 
 in 1837, designed an electromagnetic motor 
 in which permanent magnets, placed on a 
 fixed frame, attracted and were attracted by 
 electromagnets placed on a moving frame. 
 Davenport perfected his motor to an ex- 
 tent which enabled him to apply it to the 
 driving of a printing press, and to the 
 operation of a small model of a circular 
 railway, which he exhibited at Springfield, 
 Mass. 
 
 The principal of the operation of the 
 Jacobi motor may, perhaps, be better un- 
 
THE TRANSMISSION OF POWER. 
 
 105 
 
 derstood by an examination of a motor de- 
 signed by Ritchie, which operates on the 
 
 FIG. 17. RITCHIE'S MOTOR. 
 
 preceding principles. Ritchie's motor is 
 shown in Fig. 17. Here a movable elec- 
 
106 THE ELECTKIC MOTOR AND 
 
 tromagnet A J3, is caused to continuously 
 rotate under the mutual interaction of its 
 flux and the flux produced by a perma- 
 nent magnet N 8. Suppose the electro- 
 magnet to occupy at any instant the posi- 
 tion shown in the figure, and suppose, 
 moreover, that the current be flowing 
 through the coils of the electromagnet in 
 such a direction as to produce a south pole 
 at A, and a north pole at , and that the 
 permanent magnet has its north pole at JVJ 
 and its south pole at /X Then an attrac- 
 tion will take place between the poles of 
 the permanent and the electromagnet, 
 which will cause the latter to be moved 
 around its axis in the direction of the 
 arrow. 
 
 If the current continued to flow steadily 
 through the coils of the electromagnet, the 
 movement of the magnet would cease as 
 
OflWWlH. t'i UOl/ Cl 
 
 THE TKANSMIS 
 
 soon as its poles came 
 poles of the permanent 
 moment, by means of the commutator (7, 
 the current is reversed in the electromagnet 
 by reversing its polarity. Under these 
 conditions, aided by the momentum of the 
 moving electromagnet, repulsion is pro- 
 duced between the poles N~ and A, and 
 the rotation is continued in the same 
 direction until the pole A, of the electro- 
 magnet comes over the pole /S y , of the per- 
 manent magnet, when the commutator 
 again reverses the direction of the current. 
 On this account the pull will not be uni- 
 form in such a machine at all positions of 
 the electromagnet. Moreover, if the ma- 
 chine were to stop with its electromagnetic 
 poles vertically over the permanent mag- 
 netic poles, it would require a mechanical 
 motion before the current could again pro- 
 duce continued rotation. 
 
108 
 
 THE ELECTRIC MOTOR AND 
 
 The next important development, his- 
 torically, was that made by Elias, who 
 
 FIG. 18. ELIAS' MOTOR. 
 
 in 1842 designed the motor shown in 
 Fig. 18. Here, two coaxial iron rings are 
 supported in the same vertical plane. The 
 
THE TRANSMISSION OF POWER. 109 
 
 outer ring is fixed and the inner ring is 
 movable about its axis. In this form of 
 motor it will be noticed that, instead of 
 employing a permanent magnet for the 
 fixed magnet, an electromagnet is em- 
 ployed. This marks a considerable ad- 
 vance in the art ; for, while it is now 
 obvious that a fixed electromagnet is equiv- 
 alent to a fixed permanent magnet, yet 
 at the early date of which we are speaking, 
 this was by no means an obvious matter. 
 In fact, the earlier motors were constructed, 
 as we have seen, with permanent magnets, 
 while the modern motor, when of any con- 
 siderable size, is invariably provided with 
 electromagnets. 
 
 Broadly, then, an electromagnetic motor 
 consists of two parts, in one of which the 
 magnetic flux is fixed, and in the other the 
 magnetic flux is movable, being changed 
 
110 THE ELECTRIC MOTOR AND 
 
 at suitable intervals by the action of a 
 commutator. The fixed part is called the 
 field magnet, and the magnetically moving 
 part the armature. In nearly all cases it 
 is the magnetically moving part which 
 rotates, the field magnets being usually 
 fixed and the armature moving; but, as 
 we have seen, this is not essential, since 
 action and reaction are always equal and 
 opposite, and we may have the magnetically 
 fixed part rotary, and the magnetically 
 moving part at rest. In order conven- 
 iently to distinguish between the mechan- 
 ically moving and the magnetically moving 
 parts, the name stator is sometimes applied 
 to the part which is mechanically fixed, 
 and the name rotor to the part which 
 rotates, no matter what their magnetic 
 condition may be. 
 
 Referring again to Fig. 18, the outer 
 
THE TRANSMISSION OF POWER. Ill 
 
 fixed ring constitutes the field, and the 
 inner movable ring the armature. Both 
 field and armature are so wound with coils 
 of insulated wire as to. produce six poles 
 at equal angular distances around their 
 circumference, adjacent poles being of 
 opposite polarity, as indicated by the 
 letters N, S, 'N, S, N, S, in the field, and 
 ?i, s, Uj s, n, s, in the armature. 
 
 In this early form of motor, instead of 
 employing the same current to excite both 
 the field and armature, a separate current 
 was employed to excite the field magnets, 
 or, as it is now expressed, this was a 
 separately -excited motor. The current pass- 
 ing through the armature was supplied 
 through the terminals 7?, .B'. The com- 
 mutator G, which was so arranged that the 
 brushes 7?, 72, resting on the commutator 
 segments, supplied current through the 
 
THE ELECTRIC MOTOR AND 
 
 armature by the wires f,f, in a direction 
 which produced the poles n, s, n, s, n, s, 
 when the armature occupied the position 
 indicated in the figure. Here the north 
 poles in the armature attract the south 
 poles of the field, and the south poles of 
 the armature attract the north poles of the 
 field, in such a manner as to cause the 
 armature to be pulled around clockwise, 
 or in the direction of the arrow. As soon 
 as the poles in the armature come beneath 
 the field poles, the armature poles are 
 reversed by the brushes changing the seg- 
 ments upon which they rest at the commu- 
 tator, and thus reversing the direction of 
 current and the polarity of the armature y 
 so that, aided by momentum, the arma- 
 ture poles repel the field poles nearest 
 to them, and attract those ahead of 
 them, thus maintaining a continuous rota- 
 tion. 
 
THE TRANSMISSION OF POWER. 
 
 This early type of machine must be 
 regarded as exhibiting a considerable ad- 
 vance over its predecessors, and would, 
 indeed, with comparatively small modifica- 
 tion, make a motor approximating to the 
 type of motors in modern use. It belongs 
 to the type of machine now well estab- 
 lished, called a multipolar machine, since 
 it has more than two poles. It is, in fact, 
 a sextipolar, or six-pole machine. 
 
 The type of machine shown in Fig. 10, 
 was constructed by Froment in 1845. 
 Here, as will be seen from an examination 
 in the figure, a continuous rotatory motion 
 is obtained by means of the action of 
 electromagnets upon pieces of soft iron, 
 called armatures, attached to the periph- 
 ery of a movable wheel. The current 
 is supplied from the battery B, to the 
 motor through the terminals T, T, and 
 
114 THE ELECTRIC MOTOR AND 
 
 through the commutator C\ to the magnets 
 M M in such a manner that when the 
 
 FIG. 19. FROMENT'S MOTOR. 
 
 circuit is completed, the magnets M, M, 
 attract the soft iron bars A, A, A, and 
 pull the armature around, say in a clock- 
 wise direction. As soon as the bars 
 A, Ay Ay are opposite to the magnet 
 
THE TRANSMISSION OF POWER. 115 
 
 poles, the current is cut oft' at the commu- 
 tator, the armature continuing iu rotation 
 
 o 
 
 by its momentum until the bars are ready 
 to be attracted by the next succeeding 
 magnets, when the circuit is closed at the 
 
 commutator. Successive magnetic im- 
 
 ~ 
 
 pulses are thereby created, which result 
 in a continuous rotatory motion of the 
 armature. A number of motors, of dif- 
 ferent designs, but based on this general 
 principle, were constructed by Froment. 
 
 Between 1845 and the present date, 
 very many electromagnetic motors have 
 been designed. With the limited space 
 at our disposal we will not attempt any 
 farther to trace the early history of the 
 electric motor, except to give a description 
 of a very excellent form of early motor 
 designed by Pacinotti in 1861, and repre- 
 sented in Fig. 20. Here the armature A, 
 
116 THE ELECTRIC MOTOR AND 
 
 is mounted on a vertical axis between the 
 poles of the electromagnets J/i, and M& 
 which constitute the field magnets. The 
 current is supplied through the terminals 
 2J, and T%, say from T to the magnets J/i, 
 and M& thence through the commutator 
 apparatus 6 Y , to the armature, leaving by 
 the terminal jT 2 . The field magnets M^ 
 and J/2 are, therefore, excited in series 
 with the armature, so that the machine 
 is said to be series-wound. 
 
 The armature consists of an iron ring, 
 wound at intervals with coils of insulated 
 wire connected with the commutator, in 
 such a manner as to produce poles in the 
 armature between the polar projections N 
 and 8, of the field magnets. The armature 
 turns so as to bring its poles directly 
 opposite to the field poles. As it moves, 
 however, the poles in the armature are 
 
118 THE ELECTRIC MOTOR. 
 
 shifted by the action of the commutator, 
 so that a continuous rotation takes place. 
 Like all electromagnetic motors this 
 machine, when independently driven as 
 a dynamo, is capable of producing an 
 E. M. F. provided the field magnets are 
 suitably excited. The handle and disc 
 shown behind the motor, were intended for 
 the purpose of demonstrating this fact. 
 
CHAPTER V. 
 
 ELEMENTARY THEORY OF THE MOTOR. 
 
 HAVING thus briefly traced some of the 
 early history of electric motors, we will 
 proceed to the theory of their operation.- 
 Although this theory could readily be 
 deduced from any of the motors we 
 have considered, yet it will, perhaps, be 
 preferable to base it upon a more modern 
 type of motor, such as the machine shown 
 in Fig. 21. This machine is of the bipolar 
 type. It has two field poles -N and S, 
 produced by the magnetizing coils Jt/, M. 
 Between these poles the armature A, is 
 free to revolve. The commutator C, and 
 pulley P, are carried by the armature shaft. 
 
 119 
 
120 THE ELECTRIC MOTOR AND 
 
 The brushes , J9, rest upon the com- 
 mutator, and supply the current to the 
 armature from the main terminals T, T, 
 
 FIG. 21. BIPOLAR ELECTRIC MOTOR. 
 
 in such a manner as to produce in it two 
 poles, n and s, midway between the poles 
 N and S, of the field magnet. The arma- 
 ture is, therefore, pulled around in the 
 
THE TRANSMISSION 
 
 direction of the arrow, 
 
 the current entering the 
 
 muted in such a manner as to maintain the 
 
 armature poles at their positions in the 
 
 vertical plane. 
 
 The power of an electric motor depends 
 upon two things; viz., 
 
 (1) Upon the pull it exerts at the cir- 
 cumference of its pulley, and, 
 
 (2) Upon the speed at which it runs. 
 The greater the pull, and the greater the 
 
 speed at which that pull is delivered, the 
 greater the activity of the motor. 
 
 Since it is the electro-dynamic force 
 \vhich causes the rotation of a motor, it is 
 clear that the pull, which will be exerted 
 at the circumference of the pulley, will 
 vary with the diameter of the pulley. It 
 is customary to speak of the effect of this 
 
122 
 
 THE ELECTRIC MOTOR AND 
 
 electro-dynamic force as the torque, a word 
 derived from the Latin verb to twist. Sup- 
 pose the electro-dynamic force of the motor 
 
 w 
 
 FIG. 22. TORQUE EXERTED UPON SHAFTS BY WEIGHTS 
 SUSPENDED OVER A PULLEY. 
 
 were capable of exerting a twist or torque 
 about the axis of the armature, represented 
 by the pull of 100 pounds' weight, sus- 
 pended over a pulley P, Fig. 22, 1 foot in 
 radius ; then it will be evident that if the 
 
THE TRANSMISSION OF POWER, 123 
 
 pulley were exchanged for one 4 feet in 
 radius, as shown at P', in the same 
 figure, the motor would only be capable 
 of lifting a weight of 25 pounds sus- 
 
 FIG. 23. EQUILIBRIUM OP Two EQUAL AND OPPOSITE 
 TORQUES. 
 
 pended over this pulley; or, a torque 
 of 100 pounds at a radius of one foot 
 is the same as that exerted by 25 pounds 
 at a radius of four feet. In fact it is 
 clear that if the two pulleys P and P', 
 
124 
 
 THE ELECTRIC MOTOR AND 
 
 were mounted side by side 011 the same 
 shaft, and the weights W and W\ sus- 
 pended from their peripheries on opposite 
 sides, the torques exerted would be equal 
 
 FIG. 24. DIAGRAMS OF TORQUE. 
 
 and opposite, or the shaft would remain in 
 equilibrium, as in Fig. 23. 
 
 Fig. 24, represents a torque of 20 pounds- 
 feet, acting about the axis of each of the 
 three pulleys P _P 2 , and P 3 ; for, at P^ we 
 have a force of 40 pounds' weight acting 
 
THE TRANSMISSION OF POWER. 125 
 
 at a radius of 1/2 a foot 20 pounds-feet ; 
 at P%, we have a force of 20 pounds' weight 
 acting at a radius of 1 foot = 20 pounds-feet ; 
 and, at P 3 , we have a force of 10 pounds' 
 weight acting at a radius of 2 feet = 20 
 pounds-feet. It is evident, that the torque 
 of a motor does not imply any particular 
 size of the pulley on the motor ; for, if a 
 pulley of large diameter be employed, the 
 force at its periphery will be comparatively 
 small, while if a pulley of small diameter 
 be employed, the force at its periphery 
 will be comparatively great. 
 
 In the same way, the amount of work 
 which a motor exerting a given torque will 
 perform, during one complete revolution 
 of its armature or pulley, does not imply 
 any particular diameter of the pulley ; 
 but, if the pull to be exerted is given, 
 then the limiting diameter, at which 
 
126 THE ELECTRIC MOTOR AND 
 
 that pull can be exerted is known. Thus 
 if a motor exerts a torque of 20 pounds- 
 feet independently of the speed at which 
 it runs, and the pulley P lf of Fig. 24 be em- 
 ployed on its shaft, with a radius of half a 
 foot, the motor will just be capable of lifting 
 40 pounds' weight on the periphery of the 
 pulley ; and, in one complete revolution, 
 the pulley will raise this weight through a 
 distance equal to its own circumference; 
 namely, to 1/2 X 6.2832 = 3.1416 feet, and 
 will, therefore, do an amount of work equal 
 to 3.1416 x 40 = 125.66 foot-pounds = 
 170.4 joules. If, however, the pulley jP 2 , be 
 employed, with a radius of one foot, the 
 motor will just lift a weight of 20 pounds 
 over its periphery; and, in one complete 
 revolution, will do an amount of work equal 
 to 6.2832 feet x 20 pounds = 125.66 foot- 
 pounds = 170.4 joules. Finally, if the 
 pully P 3j be employed, the weight, which 
 
THE TRANSMISSION OF POWER. 127 
 
 the motor \vill lift over its periphery, will be 
 just 10 pounds, and its circumference being 
 2 X 6.2832 = 12.5664 feet, the amount of 
 work done by the motor in one revolution 
 will be 12.5664 x 10 = 125.66 foot-pounds 
 = 170.4 joules; or, as we have already 
 stated, the work done by a given torque in a 
 given number of revolutions is independent 
 of the radius of the pulley. If the pulley 
 be large, the weight raised will be small, 
 but the lift per revolution great, while, if the 
 pulley be small, the weight raised will 
 be great, but the lift per revolution small. 
 On the other hand, if the weight to be 
 lifted be known, the size of the pulley 
 will be limited by the torque of the motor. 
 Thus, a motor of 40 pounds-feet torque 
 could not lift a weight of 5 pounds over 
 a pulley more than 8 feet in radius. 
 
 The activity of a motor, being the work 
 
128 
 
 THE ELECTRIC MOTOR AIS T D 
 
 done per second, will be equal to the prod- 
 uct of the torque and 6.2832 times the 
 number of revolutions per second. Thus, if 
 
 FIG. 25. MAGNETIC CIRCUIT OF MOTOR REPRESENTED 
 IN FIG. 21. 
 
 a motor, exerting a steady torque of 50 
 pounds-feet, runs at 1,200 revolutions a 
 minute, or 20 revolutions per second, the 
 activity may be reckoned directly as 50 X 
 6.2832 X 20 = 6283.2 foot-pounds per 
 
THE TRANSMISSION OF POWER. 129 
 
 second. A similar calculation will show 
 that the activity of the motor would be 
 the same with pulleys P 2 and P 3 . For, 
 although with the larger pulleys the per- 
 ipheral speed in feet per second would be 
 greater, yet the weights they would raise 
 would be correspondingly smaller. 
 
 The torque exerted by a motor is the 
 most convenient quantity for considering 
 and discussing its mechanical power, anjd 
 we will now proceed to consider how this 
 torque varies with the electrical conditions 
 in the motor. 
 
 To do this it will be necessary to con- 
 sider the magnetic flux passing through 
 the magnetic circuit of the motor. Fig. 25 
 represents diagrammatically the magnetic 
 circuit of the motor shown in Fig. 21. 
 Here the armature A, is situated between 
 
130 THE ELECTRIC MOTOR AND 
 
 pole pieces JV and &, and is separated from 
 them by two annular air-gaps, one between 
 the armature and JV, and the other between 
 the armature and 8. The magnetic flux, 
 which passes through this magnetic cir- 
 cuit, is produced by the magnetizing coils 
 which are wound upon the iron cores, 
 <7, C'. 
 
 We have seen that the current strength 
 produced by an electric source depends 
 upon the E. M. F. of the source, and the 
 resistance of its circuit. In the same way, 
 in the magnetic circuit, the magnetic cur- 
 rent, or magnetic flux, depends upon the 
 magneto-motive force of the source, and 
 upon the magnetic resistance of the circuit ; 
 or, just as we had, 
 
 T7S ~\jT TT1 
 
 Electric current or flux = 
 
 Electric Resistance 
 
 so here, 
 
 M. M. F. 
 
 Magnetic current or flux = =r= -. r 
 
 Magnetic Resistance. 
 
THE TRANSMISSION OF POWER. 131 
 
 Magnetic flux is estimated in units of 
 magnetic flux, commonly called webers. A 
 large motor may Lave a total magnetic flux 
 of millions of webers, while a small motor, 
 suitable for driving a table fan, may Lave 
 a total flux in its circuit of only a few 
 thousand webers. 
 
 The unit of magneto-motive force, usually 
 written M. M. F., is commonly called the 
 gilbert, and is the M. M. F. which would be 
 produced by a current of 0.7958 amperes, 
 flowing through one turn of wire. In other 
 words, a current of one ampere, passing 
 through one turn of wire ; i. e., one ampere- 
 turn, produces an M. M. F. of 1.257 gilberts. 
 The M. M. F. of a coil of wire is, therefore, 
 proportional to the number of ampere- 
 turns in it. If each of the coils on the 
 magnets of Figs. 21 and 25, have 2,000 
 turns, and carries a steady current of 5 
 
132 THE ELECTRIC MOTOR AND 
 
 amperes, then the M. M. F. of the coils 
 will be 5 X 2,000 = 10,000 ampere-turns 
 = 12,570 gilberts in each coil, or 20,000 
 ampere-turns, and 25,140 gilberts in the 
 complete circuit. 
 
 The amount of flux which will be pro- 
 duced by this M. M. F. will depend upon 
 the magnetic resistance of the circuit ; that 
 is, on the magnetic resistance in the iron 
 of the cores C O', the yoke Y, the pole- 
 pieces JVand S, the iron armature core A, 
 and the air-gaps, on each side of the arma- 
 ture, through which the flux passes. 
 
 The magnetic resistance of a circuit, 
 usually called its reluctance, is measured 
 in units of magnetic resistance commonly 
 called oersteds. The oersted is the resist- 
 ance offered by a centimetre cube of air, 
 that is to say, it is equal to the magnetic 
 
THE TRANSMISSION OF POWEK. 133 
 
 resistance wliicli a colunm of air offers 
 when it has a length of one centimetre and 
 a cross-sectional area of one square centi- 
 metre. As in the case of an electric cir- 
 cuit, the electric resistance increases with 
 the length of the circuit and decreases with 
 the area of cross-section, so in the mag- 
 netic circuit, the magnetic resistance or 
 reluctance increases with the length, and 
 decreases with the area of cross-section. 
 Thus, if each of the air-gaps in Fig. 25 is 
 one centimetre long in the direction of the 
 magnetic flux, and has an effective cross- 
 sectional area, called polar area, of 1,000 
 square centimetres, then the reluctance 
 
 of each air-gap will be = 0.001 
 
 oersted, and the total reluctance in the 
 air 0.002 oersted. 
 
 The reluctance of most substances is 
 
134 THE ELECTRIC MOTOR AND 
 
 practically the same as that of air, and is 
 not affected by the quantity of flux which 
 passes through it. In the case of iron, 
 however, the magnetic reluctance is very 
 small as compared with air, provided the 
 magnetic flux through it is not very dense. 
 When, however, the magnetic flux is very 
 powerful, so that a great number of webers 
 pass through each square inch of cross- 
 sectional area, the iron is said to become 
 magnetically saturated, and then offers a 
 greatly increased reluctance. Thus, at a 
 density of 5,000 webers-per-square-centi- 
 metre, which is commonly called a density of 
 5,000 gausses, the gauss being the unit of 
 magnetic density, the reluctance of a cubic 
 
 centimetre of iron is only about th 
 
 2,000 
 
 that of the reluctance of a cubic centimetre 
 of air ; but at a density of 1 6,000 webers- 
 per-square-centirnetre, or at 16,000 gausses; 
 
THE TRANSMISSION OF POWER. 135 
 
 i. e. y 16 Iciloyavsses, the reluctance of a 
 cubic centimetre of soft iron may be 
 
 that of air. The specific reluctance of iron 
 in terms of air; i. e., its reluctivity, varies 
 with the density of the flux passing through 
 it, and also with the quality of the iron. 
 The density of flux usually employed in 
 motors containing cast iron in their magnetic 
 circuit, is not more than 8,000 or 9,000 
 gausses; while in motors, employing soft 
 wrought iron or soft steel, the density 
 which may be employed is 12,000 to 15,000 
 gausses. There is, therefore, a considerable 
 magnetic advantage in employing soft iron, 
 or cast steel, in place of ordinary gray cast 
 iron, in the magnetic circuits of dynamos 
 and motors, since the former have a much 
 lower magnetic resistance. 
 
 If, in Fig. 25, we assume that the total 
 
136 THE ELECTUIC MOTOR AND 
 
 reluctance of the iron of the magnetic 
 circuit be 0.003 oersted, then the total 
 reluctance in the circuit composed of iron 
 and air, will be 0.003 + 0.002 = 0.005 
 oersted, and the magnetic flux passing 
 through the circuit will be 
 
 25,140 gilberts 
 
 ^ - --= 0,028,000 webers. 
 
 O.OOo oersteds 
 
 Fig. 25, shows that some of the mag- 
 netic flux does not pass through the 
 armature, but through the air on each side 
 
 o 
 
 of the field magnets. All such stray flux 
 not passing through the armature is use- 
 less for the purpose of rotating the arma- 
 ture, and is, therefore, called leakage flux. 
 Magnetic leakage necessarily occurs because 
 there is no known magnetic insulator. An 
 electric current can be restricted by the use 
 of insulators to the conductors conveying it, 
 such as air, dry wood, rubber, etc., but 
 
PROPERTY CF 
 
 THE TRANSMISSION >fo0WKR. 137 
 
 dry wood, rubber, glass 
 materials except the magnetic nietals7cor 
 duct magnetic flux with equal facility ; i. e., 
 have practically the same reluctivity. Con- 
 sequently, some of the magnetic flux pro- 
 duced in the circuit by the M. M. F. of the 
 field coils, will pass uselessly through the 
 surrounding air. The useful magnetic 
 flux is that which passes through the 
 armature. The leakage can be reduced by 
 diminishing the reluctance in the armature 
 circuit relatively to the reluctance of the 
 leakage paths surrounding the cores. 
 
 If the cross-section of the armature A., 
 be known in square inches, the total useful 
 flux passing through it may be readily 
 estimated ; for, it is usual to employ in the 
 armature core a flux density of, approxi- 
 mately, ten kilogausses. This is a density 
 well below saturation, and, since there are, 
 
138 THE ELECTRIC MOTOR AND 
 
 6.4516 square centimetres in a square inch, 
 there will be, approximately, 64,500 webers 
 of useful flux passing through each square 
 inch of armature section, at right angles to 
 the course of the magnetic flux through it. 
 If, for example, the armature core be 39" 
 long, and 20" in effective width, the cross- 
 sectional area will be 780 square inches, 
 and the probable amount of useful flux 
 carried by the armature will be 780 X 
 64,500 = 5,030,000 webers. 
 
 The torque exerted by a motor armature 
 depends upon three things ; viz., 
 
 (1) The useful flux passing through the 
 armature in webers. 
 
 (2) The current strength passing 
 through the armature in amperes. 
 
 (3) The number of turns of wire ; i. e. 
 the number of wires counted once around 
 the surface of the armature. 
 
THE TRANSMISSION OF POWEK. 139 
 
 If we multiply these three quantities 
 together and divide by 85,155,000, we 
 obtain the torque of the motor in pounds- 
 feet. 
 
 If the motor shown in Fig. 21 has a cur- 
 rent strength passing through its armature 
 by the brushes B, B, of 20 amperes, a total 
 number of wires counted once completely 
 around the surface of the armature, 
 amounting to 160, and a total flux passing 
 through the field magnets amounting to 
 5,000,000 webers, then the torque exerted 
 by the armature will be 
 
 20X160X5,000,000 
 
 85^^00^- - 187 ' 9 Pounds-feet. 
 
 If the pulley of this motor has a radius 
 of one foot, then, neglecting frictions, the 
 motor should be just able to start when a 
 weight of 187.9 pounds is suspended from 
 the periphery of its pulley. 
 
140 THE ELECTRIC MOTOR AND 
 
 It will be seen, from the foregoing, that 
 the torque exerted by a motor depends 
 upon the current strength passing through 
 its armature. If we cut off the current 
 from the armature, there will be no torque 
 exerted by the motor, even though the 
 field magnets be fully excited and their 
 maximum magnetic flux produced. This 
 must evidently be the case, since the cause 
 of the electro-dynamic force is the mutual 
 interaction of the field flux with the flux 
 produced by the current through its arma- 
 ture wires, and the latter ceases on the 
 cessation of the current. 
 
 We may now inquire into the causes 
 which determine the speed of a motor. 
 Let us suppose, for example, that the 
 motor shown in Fig. 21, has its field mag- 
 nets excited from some independent source, 
 so that the amount of flux which passes 
 
THE TRANSMISSION OF POWER. 141 
 
 through the armature may be regarded as 
 constant, and equal to, say, 5,000,000 
 webers. If the armature be connected 
 through its brushes, B, B, with a constant 
 electric pressure, say, for example, with a 
 pair of mains having a constant pressure of 
 10 volts, then the current strength, which 
 will tend to pass through the armature, will 
 be controlled by Ohm's law. Thus, if the 
 
 resistance of the armature were -r^th of 
 
 an ohm, the current strength, which would 
 tend to pass through the armature at rest, 
 
 would be 10 volts divided by th ohm 
 
 = 100 amperes. If the number of wires 
 upon the surface of the armature be 100, 
 counted once around, we have seen that the 
 torque exerted by the armature, with this 
 current strength, will be 
 
 100 amperes X 5,000,000 webers X 100 wires _ ,. ____,,- fppt 
 
 "- 8 ' >3 P unds - feet - 
 
142 THE ELECTRIC MOTOR AND 
 
 Supposing the belt to have been thrown 
 oft* the pulley of the motor; then under 
 this powerful torque the motor will be 
 started in rapid rotation. As soon as the 
 armature commences to revolve through 
 
 o 
 
 the flux produced by the field magnets, it 
 generates in the armature winding an E. 
 M. F. which is counter or opposite to the 
 current supplied to the armature. In other 
 words, the revolving motor armature com- 
 mences to act as a dynamo armature, oppos- 
 ing the current strength received from the 
 mains. The effect of this C. E. M. F. is 
 to reduce the amount of current received 
 by the motor. If, for example, the arma- 
 ture revolves at such a rate as to generate 
 a C. E. M. F. of 5 volts, the effective E. M. 
 F. acting in its circuit will be 10 5 = 5 
 volts, and the current will be reduced to 5 
 
 volts divided by TTth of an ohm, or to 50 
 
THE TRANSMISSION OF POWEK. 143 
 
 amperes. Similarly, if the speed at which 
 the armature runs is sufficiently increased 
 to develop a C. E. M. F. of 9 volts, the effect- 
 ive E. M. F. in this circuit will be 10 9 = 
 1 volt, and the current will be reduced 
 
 to 1 volt divided by -y-th ohm = 10 
 
 amperes. The armature, therefore, accel- 
 erates until such a speed is reached as 
 will limit the current passing through it to 
 just the value which is necessary in order 
 to overcome the torque imposed on the 
 motor ; i. e., the resisting torque. 
 
 The resisting torque will be very small 
 if the motor be disconnected from its belt, 
 being made up only of the frictions of 
 bearings, brushes, etc.; while, if the belt 
 be thrown on the motor, and it be con- 
 nected with a heavy load, the resisting 
 torque may be very considerable. The 
 
144 THE ELECTRIC MOTOR AND 
 
 current strength required to overcome this 
 torque is determined, as we have seen, by 
 the flux through the motor, and by the 
 number of turns of wire lying upon its arm- 
 ature. Consequently, the speed of an arm- 
 ature will automatically assume that value 
 at which the effective E. M. F.; namely, the 
 difference between the driving and C. E. M. 
 Fs., just enables this current strength to be 
 supplied through the armature resistance. 
 
 A ten HP motor, separately excited, 
 may be capable of developing an E. M. F. 
 in its armature of 13 volts, for every revolu- 
 tion that it makes per second ; that is to 
 say, if the armature be set in rotation, in 
 any manner, at the speed of one revolution 
 per second, or 60 revolutions per minute, 
 it \vill generate as a dynamo an E. M. F. 
 of 13 volts. If its speed be altered to 
 3 revolutions per second, its E. M. F. 
 
THE TRANSMISSION OF POWER. 145 
 
 will be 39 volts. If now this motor, dis- 
 connected from its load, be connected with 
 a pair of mains having a constant pressure 
 between them of 208 volts, the armature 
 will run at a speed of, approximately, 16 
 revolutions per second, or 960 revolutions 
 per minute, and thereby generate an E. M. 
 F. counter or opposed to the E. M. F. of 
 the mains, equal to 16 X 13 = 208 volts; 
 for, the resisting torque, made up of fric- 
 tion in the armature, will be very small, 
 and if the speed of the motor falls below 
 16 revolutions per second, or 960 revolu- 
 tions per minute, the current strength, 
 which will pass through the armature, will 
 be so rapidly increased that a powerful 
 electro-dynamic torque will be exerted 
 upon the armature causing it to accelerate, 
 and so regain its full speed. 
 
 If there were no friction whatever in the 
 
146 THE ELECTRIC MOTOR AND 
 
 armature, which of course is impossible, 
 there would, of course, be no current and no 
 energy required to drive the armature, and 
 if the pressure at its terminals from the 
 mains were 208 volts, the motor would 
 have to generate a C. E. M. F. of ex- 
 actly 208 volts, so that by Ohm's law no 
 current would pass through it and its 
 speed would be steady at exactly 16 revo- 
 lutions per second. If, however, a heavy 
 Joad be thrown on the motor producing 
 a powerful resisting torque of, say 100 
 pounds-feet, then the current strength, 
 which will be necessary to pass through 
 the armature in order to produce this 
 torque, may be, say 20 amperes, and if the 
 resistance of the armature be 1 ohm, the 
 C. E. M. F. must drop to 188 volts in 
 order that the driving E. M. F. shall per- 
 mit 20 amperes to pass through this resist- 
 ance ; namely, 208 -- 188 = 20 -*- 1 = 20 
 
PROPERTY OF 
 
 THE TRANSMISSION^ POWER. 147 
 
 amperes. The speed on 
 
 loaded will, therefore, drop to - = 14.46 
 
 1 o 
 
 revolutions per second, or 867.6 revolu- 
 tions per minute. 
 
 Summing up, therefore, if a motor be 
 separately excited, and be connected with 
 a pair of constant-potential mains ; i. e., a 
 pair of mains maintained at an electrically 
 constant difference of pressure or voltage, 
 the speed at which it will run, will de- 
 pend upon the number of wires lying 
 upon its armature. If the armature have 
 a large number of fine wires, its speed will 
 be comparatively slow, since its dynamo 
 action and C. E. M. F. for a given speed, 
 will be great ; or, in other words, the 
 speed required to produce a given C. E. 
 M. F. will be small. But if the number 
 of wires on the armature be small, the 
 
148 THE ELECTRIC MOTOR AND 
 
 speed at which it will have to run to 
 develop a given C. E. M. F. will be great. 
 As the torque imposed on the motor, or its 
 load is increased, its speed will diminish 
 in order to allow the necessary increase of 
 current to pass through the motor to over- 
 come this torque, and the amount of drop 
 in speed will depend upon the resistance 
 of the armature. If the resistance of the 
 armature be comparatively great, the drop 
 of pressure in the armature will be great, 
 and the speed must fall off considerably ; 
 while, if the resistance of the armature be 
 small, a comparatively small diminution in 
 speed will, by Ohm's law, permit a com- 
 paratively large increase of current 
 strength and torque. 
 
 Again, if the pressure on the mains with 
 which an armature is connected be in- 
 creased, the motor speed must increase in 
 
THE TRANSMISSION OF POWER. 149 
 
 order to develop a correspondingly greater 
 C. E. M. F. Thus, if a motor runs, light- 
 loaded, at a speed of 500 revolutions per 
 minute, when connected with a pair of 
 110- volt mains, it will run with the same 
 excitation at, approximately, 1,000 revolu- 
 tions per minute, when connected with a 
 pair of 220-Volt mains. This is evident, 
 since, approximately, the same small cur- 
 rent strength will have passed through it 
 in each case, and the C. E. M. F. devel- 
 oped by the motor armature, must be 
 'nearly 110 volts in the first case, and 
 nearly 220 volts in the second. 
 
 We have hitherto assumed that the 
 amount of flux passing through the ar- 
 mature was constant, owing to separate 
 excitation of the field magnets. It is evi- 
 dent, however, that if the flux passing 
 through the armature be varied, the speed 
 
150 THE ELECTRIC MOTOR AND 
 
 will also vary. Thus, if the machine 
 already considered, which had a flux of 
 5,000,000 webers, and 100 wires on its 
 armature, when connected with a pressure 
 of 10 volts, made a speed of 10 revolu- 
 tions per second, or 600 revolutions per 
 minute ; then, if we reduce the flux passing 
 through the armature by one half, or to 
 2,500,000 webers, the speed will be practi- 
 cally doubled, or increased to 20 revolu- 
 tions per second, or 1,200 revolutions per 
 minute. This is for the reason that the 
 armature must run faster through the 
 weaker flux in order to generate a given 
 C. E. M. F. If one revolution per 
 second produced one volt in a stronger 
 flux, two revolutions per second would be 
 required, per volt, in the weaker flux. 
 Consequently, we may always increase the 
 speed of a motor by weakening its field 
 flux ; i. e.j by diminishing the current 
 
THE TRANSMISSION OF POWER. 151 
 
 strength circulating in the field coils, and 
 their M. M. F. There will, of course, be 
 a limit to the degree at which this acceler- 
 ation can be produced, since, if the flux is 
 very much weakened, the flux produced 
 by the current in the armature winding 
 will overpower that of the field, and may 
 actually reverse it, thus tending to destroy 
 the C. E. M. F. of the armature, diminish- 
 ing its torque indefinitely, and requiring an 
 indefinitely high speed to check the cur- 
 rent strength, and the machine will there- 
 fore stop. On the other hand, if we 
 increase the current strength passing 
 through the field magnet coils, and so 
 increase their M. M. F., they will develop 
 a greater magnetic current or flux in the 
 magnetic circuit of the machine, including 
 the armature, and this increased flux will 
 produce the C. E. M. F. required from the 
 motor at a correspondingly reduced speed. 
 
152 
 
 THE ELECTRIC MOTOR AND 
 
 In practice, motors are not usually sepa- 
 rately excited, but are excited by a cur- 
 rent obtained from the mains supplying 
 the armature. The field winding may be 
 connected either in series with the arma- 
 ture, producing what is called a series- 
 
 FIG. 26. DIAGRAM OF SHUNT WINDING. 
 
 wound motor, or in shunt with the 
 armature, producing what is called a 
 shunt-wound motor. Fig. 26, represents dia- 
 grammatically the connections of a shunt- 
 wound motor. Here the ends b and c, of 
 the magnetic coils M, are connected in 
 shunt with the ends d and of the ar- 
 
THE TRANSMISSION OF POWER. 153 
 
 mature A. a and f, are the constant- 
 potential mains. If the resistance of the 
 magnet M, be assumed constant, by Ohm's 
 law the current strength through it 
 must be constant, and the effect is the 
 same as though the motor were separately 
 excited. The strength of current, which 
 the armature can carry continuously, de- 
 pends upon its size, winding and construc- 
 tion. The drop of pressure, which its 
 full-load current will produce, usually 
 varies between 2 per cent, and 10 per 
 cent, of the terminal pressure ; that is to 
 say, if the pressure between the mains a 
 and/, be 500 volts, then the full-load drop 
 in the armature will usually vary between 
 50 volts in a small motor, and 10 volts in 
 a large motor, the C. E. M. F. at full 
 load being respectively 450 and 490 volts. 
 The drop in speed of such a motor will, 
 therefore, usually vary between 10 per 
 
154 
 
 THE ELECTRIC MOTOR AND 
 
 cent, and 2 per cent., according to the size 
 of the machine, and, within these limits, the 
 machine automatically regulates its speed 
 according to the load. 
 
 The connections of a series-wound motor 
 are shown in Fig. 27. Here the magnet 
 
 FIG. 27. DIAGRAM OF SERIES WINDING. 
 
 coil M, is in series with the armature A, 
 between the mains a and/; that is to say 
 the current from the mains passes succes- 
 sively through the magnet M, and arma- 
 ture A. When such a machine is on light 
 load, with a small torque, the current 
 
&J!Bc'WRTY CF 
 
 THE TRANSMISSION 
 
 strength passing through tB 
 be comparatively small, and 
 of this current in the field coils will T)e 
 small, producing thereby a small magnetic 
 flux through the armature. The speed of 
 the armature will, therefore, be compara- 
 tively great. If, however, the torque on 
 the motor ; i. 'e., its load, be increased, the 
 current passing through the motor will 
 automatically increase, increasing thereby 
 the M. M. F. and flux through the 
 armature, thus reducing the speed. On 
 this account, as well as owing to the drop 
 of pressure in the resistance of the arma- 
 ture, a series-wound motor is much more 
 variable in its speed than is a shunt- wound 
 motor, but a series-wound motor, espe- 
 cially in small sizes, is simpler to construct ; 
 for, its field- winding consists of but com- 
 paratively few turns of coarse wire, while 
 a shunt motor field-winding consists of 
 
156 
 
 THE ELECTRIC MOTOR AND 
 
 many turns of fine wire, in order to reduce 
 as far as possible the current strength 
 employed in magnetizing them. 
 
 A compound-wound motor is a motor 
 whose field magnets are partly series- 
 
 FIG. 28. DIAGRAM OF COMPOUND WINDING. 
 
 wound and partly shunt- wound. Such a 
 winding is diagrammatically represented in 
 Fig. 28. Here the armature A, is in series 
 with the coarse wire coils m, and these two 
 are connected in shunt with the fine wire 
 coil .Af. When no current passes through 
 the armature, the field magnet M, is excited, 
 
THE TRANSMISSION OF POWER. 157 
 
 while the series coil m, is un magnetized. 
 When the full-load current passes through 
 the armature, the excitation of the series coil 
 m, reaches its maximum. The M. M. F. 
 of ra, is counter or opposed to the M. M. F. 
 of J/J so that the magnetic flux is slightly 
 weakened at full load, thereby necessitat- 
 ing a slight acceleration of the armature in 
 order to develop its C. E. M. F. This ac- 
 celeration may be adjusted so as to almost 
 completely counterbalance the drop in 
 speed, which would otherwise take place 
 by virtue of the drop of pressure in the re- 
 sistance of the armature, considered as a 
 separately-excited machine. A compound - 
 wound motor may, therefore, be adjusted 
 so as to have a practically constant speed 
 under all loads. 
 
 Tlie activity absorbed by a motor is usu- 
 ally measured as the product of the termi- 
 
158 THE ELECTRIC MOTOR AND 
 
 nal pressure in volts and the current 
 strength in amperes. Thus, if the motor 
 be connected with a pair of 220-volt mains, 
 and be observed to take a total current of 
 10 amperes, then the activity absorbed by 
 the motor will be 220 volts X 10 amperes = 
 2,200 watts = 1,622 foot-pounds-per-second 
 = 2.2 kilowatts = 2.949 horse-power. If 
 the motor were a perfect machine, expend- 
 ing no internal activity, under these condi- 
 tions, it would do mechanical work at a 
 rate of 2,200 watts, or 1,622 foot-pounds- 
 per-second, but its actual efficiency would, 
 probably, be about 82 per cent, in this size. 
 
 of machine, and the mechanical activity it 
 
 09 
 would exert, would be 2,200 X = 1,804 
 
 watts = 1,330 foot-pounds-per-second. The 
 motor could, therefore, lift 1 pound 1,330 
 feet per second, or 133 pounds 10 feet per 
 second, at this load. 
 
THE TRANSMISSION OF POWER. 159 
 
 The efficiency of motors varies with 
 their size. A very small motor, such as 
 that employed for driving a desk fan, has 
 an efficiency of, probably, only 30 per cent., 
 while a 1 horse-power motor will, prob- 
 ably, have an efficiency of 60 per cent., and 
 a 100 horse-power motor an efficiency of, 
 probably, 90 per cent. The efficiency may 
 be even still greater in larger sizes, al- 
 though, of course, it can never reach 100 
 per cent., since some activity is sure to be 
 lost within the motor. 
 
 It should be clearly borne in mind that 
 all improvements, which have yet to be 
 made in electro-dynamic motors, must be 
 almost entirely confined to the directions of 
 reduced speed or reduced cost, because the 
 efficiency is already so comparatively high. 
 If a 100 horse-power motor only wastes 
 about 10 horse-power at full load, in its 
 
160 THE ELECTRIC MOTOR AND 
 
 mechanical and electrical frictions, the 
 best possible motor of this size could only 
 save 10 horse-power under the same condi- 
 tions. The direction, in which we may 
 look forward to improvements in motors, 
 lies, therefore, almost wholly in reducing 
 their cost of construction and the speed at 
 which they run. 
 
 The work absorbed by an electric 
 motor from the circuit supplying it is 
 conveniently measured in units called 
 Idlowatt-liours, a kilowatt-hour being an 
 amount of work equal to that performed 
 by an activity of one kilowatt maintained 
 steadily for one hour. A kilowatt-hour is 
 equal to 1.34 (roughly 1 1/3) horse -power- 
 hours, or to 3,600,000 joules, or 2,663,000 
 foot-pounds. In Great Britain the kilo- 
 watt-hour is called the " Board of Trade 
 Unit." 
 
THE TRANSMISSION OF POWER. 161 
 
 The work consumed by an electric 
 motor is usually measured by a meter placed 
 in its circuit. The meter may be a watt- 
 meter, in which case its dial will show the 
 total amount of work received by the 
 motor in kilowatt-hours; or it may be 
 an ampere-hour meter, whose indications, 
 multiplied by the pressure of the circuit, 
 assumed as uniform, will give the total 
 amount of work consumed. Thus, if a 
 motor connected with a 220-volt, constant- 
 potential circuit, is shown to have received 
 5,000 ampere-hours in a month, by the 
 record of an amperediour meter, the total 
 work it has received will be 5,000 X 220 
 = 1,100,000 watt-hours = 1,100 kilowatt- 
 hours. 
 
CHAPTER VI. 
 
 STRUCTURE AND CLASSIFICATION OF MOTORS. 
 
 TURNING uow to the practical construc- 
 tion of motors, let us look at the motor 
 shown in Fig. 29, and in order to under- 
 stand its construction, let us take it apart 
 and study it in detail as shown in Fig. 30. 
 In these figures, corresponding numerals 
 represent corresponding parts. 1, is the 
 completed armature, mounted on its shaft, 
 with a commutator at one end, and with 
 the insulated winding wrapped round and 
 round the iron core or body, and suitably 
 connected with the commutator. The 
 shaft rests in journals 15 and 18, sup- 
 ported on pedestals 13 and 16. These 
 
 162 
 
THE TRANSMISSION OF POWER. 
 
 163 
 
 bearings are self -oiling ; that is to say, they 
 contain oil which is continually poured 
 upon the surface of the revolving shaft by 
 
 17 
 
 FIG. 29. FORM OP ELECTRIC MOTOR. 
 
 the action of the rings 19, as will be later 
 explained. 
 
 On the end of the shaft opposite to the 
 commutator is secured the pulley 5. The 
 
164 THE ELECTRIC MOTOR. 
 
 pedestals themselves rest upon the cast- 
 iron base plate 8, to which they are firmly 
 secured by bolts. This base plate forms 
 part of the magnetic circuit of the machine. 
 Upon its smooth surface are bolted the 
 field cores, 3, 3, on the heads of which 
 stand the pole pieces 2, 2. The pole 
 pieces are set in place after the magnets 
 coils 4, 4, are set in position. The 
 rocker arm 21, carries the two brush 
 holders 22, 22, in insulated sockets at each 
 extremity, and the brush holders, in their 
 turn, clamp the metallic brushes 23, 23, 
 which rest upon the surface of the com- 
 mutator at diametrically opposite points. 
 By moving the handle of the rocker arm, 
 the diameter upon which the brushes bear 
 on the commutator, called the diameter of 
 commutation, can be varied within suitable 
 limits; 24, are the cables connecting the 
 brushes with the terminals 6 and 7, mounted 
 
I PROPERTY Cf 
 
166 
 
 THE ELECTRIC MOTOR. 
 
 on a board above the pole-pieces, and to 
 which the main leading wires are attached. 
 The rods 12, 12, securely bolt the cores 
 
 FIG. 31. FORM OP CONTINUOUS-CURRENT MOTOR. 
 
 and pole-pieces to the base plate, and also 
 leave eye-bolts by which the machine can 
 be readily slung. 
 
168 THE ELECTRIC MOTOR AND 
 
 The motor shown in Fig. 31, differs 
 from that in Fig. 29, in the fact that the 
 armature and pole-pieces are supported 
 close to the base, so that the field magnets 
 are inverted. In other respects, however, 
 the parts are similar in each motor. This 
 motor is shown dissected in Fig. 32, where, 
 as before, corresponding parts are marked 
 with corresponding numerals. It is im- 
 portant to notice that in order to prevent 
 the magnetic flux produced by the 
 M. M. F. of the coils 12, from passing 
 entirely through the cast iron base, the 
 pole-pieces are supported on slabs of 
 zinc 5, which introduces a greater reluc- 
 tance into this path and enables almost all 
 of the magnetic flux to pass through 'the 
 armature core. 
 
 In order to obtain a better conception 
 of the construction, we may now consider 
 
THE TRANSMISSION OF POWER. 
 
 169 
 
 FIG. 33. MOTOR WITH RING ARMATURE. 
 
 the separate parts of the motor in fur- 
 ther detail, beginning with the armature. 
 Broadly speaking, armatures may be 
 divided into three classes; namely, 
 
 (1) Drum armatures. 
 
 (2) Ring armatures. 
 
 (3) Disc armatures. 
 
170 THE ELECTRIC MOTOR AND 
 
 Figs. 22, 29, 30, 31, and 32 represent 
 drum armatures; that is to say, armatures 
 which are simply drum-shaped or cylin- 
 drical in their appearance. 
 
 FIG. 34. MOTOR WITH GRAMME RING ARMATURE. 
 
 Fig. 33, represents a motor furnished 
 with a ring armature A A A. Here the 
 field magnets are placed inside the arma- 
 ture, as is sometimes the case, though 
 more frequently the armature is placed 
 inside the field, as is shown in Fig. 34, 
 
THE TRANSMISSION OF POWER. 171 
 
 FIG. 35. Disc ARMATURE. 
 
172 THE EL EOT HIC MOTOR AND 
 
 where the armature A, is placed between 
 the poles N and 8, of the magnet M. 
 
 An example of a disc armature is shown 
 in Fig:. 35. Here a number of insulated 
 
 O 
 
 radial conductors C, C, are held like spokes 
 in a wheel, and are connected together 
 by conducting strips #, $, s, at the centre 
 and edge of the wheel. In this arma- 
 ture the conducting bars &, &, &, on the 
 periphery of the wheel, form the commu- 
 tator upon which the collecting brushes 
 are intended to rest. Fig. 36 represents 
 the complete machine employing this 
 armature. The magnets are here enclosed^ 
 in a field frame, and present their polar 
 surfaces to each other across the disc 
 armature. Disc armatures are very seldom 
 used in the United States. 
 
 A drum or ring armature consists esseri- 
 tially-of three parts ; namely, 
 
THE TRANSMISSION 
 
 FIG. 36. Disc ARMATURE MOTOR. 
 
 (1) The 00r0 or body, which is always of 
 soft iron. 
 
 (2) The exciting coils, of insulated cop- 
 per wire, which are wound upon the core, 
 and in which the E. M. F. is generated by 
 revolution through the flux. 
 
 (3) The commutator, by means of 
 
174 THE ELECTRIC MOTOR AND 
 
 which the E. M. F.'s induced in the coils 
 are united and co-directed so as to pro- 
 duce a continuous E..M. F. in the circuit ; 
 or, regarded from a different standpoint, 
 the commutator distributes the cur- 
 rent received from the external circuit 
 through the armature winding, in such a 
 manner as to produce a continuously act- 
 ing torque; 
 
 Armature cores may be divided, from 
 another standpoint into two classes ; viz., 
 the smooth-core and the toothed-core. 
 Smooth-core armatures present a continu- 
 ously smooth, cylindrical surface before the 
 wire is wound upon them. Such a core is 
 shown in Fig. 37. Here /?, 8, is a steel 
 shaft, which carries two phosphor-bronze 
 spiders, one of which only is seen at B. 
 These spiders are clamped to the shaft and 
 support between them the hollow core 
 
THE TRANSMISSION OF POWER. 
 
 175 
 
 (7, <7, which consists of a number of thin, 
 soft iron plates, or annular discs, which 
 after being assembled, are pressed together 
 
 FIG. 37. SMOOTH-CORE ARMATURE BODY. 
 
 and then clamped by a spider between the 
 end plates P. 
 
 In the early history of the art, armature 
 cores were constructed of solid masses of 
 soft iron ; but it was soon found that such 
 cores became intensely heated when re- 
 
176 THE ELECTRIC MOTOR AND 
 
 volved through the field flux, even though 
 no insulated wire was wound upon their 
 surfaces. This heating was owing to the 
 fact that E. M. F.'s were induced in the 
 conducting iron mass, which set up pow- 
 erful electric currents, called eddy currents, 
 through its substance. These eddy cur- 
 rents did no useful work, and expended 
 power prejudicially in heating the core. 
 By using laminated cores j i. e., by divid- 
 ing the core into a number of separate 
 discs, with their planes at right angles to its 
 axis, while the passage of the magnetic flux 
 is not impeded, since it passes directly 
 through each disc, in its own plane, the eddy 
 currents, which tend to develop in a direc- 
 tion at right angles to the plane of the 
 discs, are very greatly checked and impeded 
 on account of the resistance offered to their 
 passage through the pile of discs. Conse- 
 quently, the loss of power from eddy cur- 
 
THE TRANSMISSION OF POWER. 
 
 177 
 
 rents is very greatly reduced by this 
 expedient of laminating the core, or build- 
 ing it of separate discs, and the process is 
 invariably adopted except in the very 
 smallest motors. 
 
 FIG. 38. TOOTHED-CORE ARMATURE IN VARIOUS STAGES 
 OP CONSTRUCTION. 
 
 Toothed-core armatures are those which 
 possess corrugated surfaces, like a cog 
 wheel. Such a toothed-core armature is 
 shown in Fig. 38 at A. It will be 
 observed that the surface of this core is 
 indented with grooves, running parallel to 
 
178 THE ELECTRIC MOTOR AND 
 
 the axis of the shaft. In these grooves 
 the conducting wires, protected by suit- 
 able insulating material, are subsequently 
 laid. At J3, the armature is shown with 
 
 FIG. 39. ASSEMBLAGE OP LAMINATED ARMATUKE CORE 
 Discs. 
 
 its winding in place, following the grooves. 
 At 6 Y the complete and covered armature 
 is shown. Fig. 39, shows a method of 
 assembling toothed-core armatures upon a 
 shaft, so as to form, when completed, a 
 
THE TRANSMISSION OF POWER. 179 
 
 drum armature. Here A y , >SJ is the shaft, 
 6', the assembled discs, and r, <, the discs 
 ready to be assembled. 
 
 It will be observed that when com- 
 pleted, and wound with wire, both the 
 toothed-core and the smooth-core arma- 
 tures are alike, in that they both present 
 
 FIG. 40. COMPLETED SMOOTH-CORE ARMATURE. 
 
 a continuous cylindrical surface, but in the 
 smooth-core armature this surface is 
 formed entirely of insulated wire w r hich 
 completely covers and hides the iron core. 
 In the toothed-core armature, however, the 
 iron teeth or projections extend to the sur- 
 face, and remain uncovered by wire, which 
 only fills the grooves between adjacent 
 
180 THE ELECTRIC MOTOR AND 
 
 teeth. Tli us Fig. 40, shows a completed 
 smooth-core, drum-armature, with the in- 
 sulated conducting wire lying over its sur- 
 face, parallel to the axis. In this arma- 
 ture it is necessary to hold the wire 
 securely in place by binding the brass 
 
 FIG. 41. COMPLETED TOOTHED-CORE ARMATURE. 
 
 wire b, />, />, tightly over mica strips and 
 soldering it in position. The ends of the 
 armature are covered - by canvas supported 
 on circular heads A, k. 
 
 Fig. 41, shows a completed toothed- 
 core drum armature. Here, as will be 
 
THE TRANSMISSION OF POWER. 181 
 
 seen, the external surface of the armature 
 consists of iron, between the bands b, 1). 
 
 Fig. 42 represents a portion of one of 
 the discs of a toothed-core armature. The 
 
 FIG. 42. PORTION OP Disc OF LAMINATED TOOTHED- 
 CORE ARMATURE. 
 
 circular holes are for the clamping bolts, 
 while the grooves are intended for the 
 reception of the insulated wires. 
 
 It will thus be seen that a toothed-core 
 armature is much more solid and secure, 
 when completed, than the smooth-core 
 
182 THE ELECTRIC MOTOR. 
 
 armature, arid, partly for this reason, the 
 toothed-core .aiunatures have come into 
 general, use. It is evident that the 
 toothed-core armature does not require 
 bauds on its surface to keep the wires in 
 place. Moreover, the length of the air- 
 gap or entrefer ; that is to say, the dis 
 tance between the iron in the armature 
 and the polar faces of the field magnets, is 
 greatly reduced, thereby reducing the 
 reluctance of the magnetic circuit, and re- 
 quiring much less M. M. F. in the field 
 magnet coils to produce a given amount of 
 flux through the armature. 
 
 Fig. 43 represents the winding of a 
 toothed-core armature B. Here, as will 
 be seen, the cotton covered wires are 
 passed through the grooves. A, shows a 
 complete armature with the wire con- 
 nected to the commutator (7. 
 
PROFE FYCF 
 
184 THE ELECTRIC MOTOR AND 
 
 A simple form of commutator, called a 
 two-part commutator is shown in Fig. 44. 
 Such a commutator would be suitable for 
 commuting the current produced in a single 
 loop of wire on an armature rotated in a 
 
 FIG. 44. DIAGRAM OP TWO-PART COMMUTATOR. 
 
 bipolar field. In this commutator the wire 
 
 W 2 , is connected to the segment 6' 2 , and 
 
 the wire W 1 , to the segment 6 Y1 . Under 
 
 these conditions, if the E. M. F. generated 
 
 in the loop whose terminals are W 1 and 
 
 W 2 , be in such a direction that W 1 , is 
 
THE TRANSMISSION OF POWER. 185 
 
 positive and W 2 , negative, the current will 
 flow from W 1 , to (7 1 , and out from the 
 brush JS\ through the external circuit 
 connecting the brushes, and return through 
 the brush 7? 2 , the segment <7 2 , and the 
 wire W 2 . After a quarter of a revolution 
 has bsen effected from the position shown, 
 and in the direction indicated by the 
 arrows, the brush .Z? 1 , will rest on the seg- 
 ment C 2 y and the brush B 2 , on the seg- 
 ment (7 1 . At the same moment, however, 
 if the commutator is properly placed, the 
 E. M. F. which is being generated in the 
 loop will be reversed by its passage before 
 the magnet poles. TP 2 , will therefore be 
 the positive pole under the new conditions. 
 The current will consequently flow from 
 W 2 , to C 2 , and brush J3\ and return after 
 traversing the external circuit through 
 jE> 2 , segment 6 n , and wire W l . Conse- 
 quently, although the E. M. F. in the 
 
186 THE ELECTRIC MOTOR AND 
 
 armature has been reversed, the brush 
 J3 l j is still positive, and the current in 
 the external circuit preserves its direction. 
 No matter how many bars a commutator 
 may possess, and no matter how many 
 wires or loops are undergoing cornmuta- 
 
 v v 
 
 b 1 
 
 FIG. 45 ARRANGEMENT OP BRUSHES ON A COMMUTATOR. 
 
 tion, the effect will be essentially the same 
 as that here described. 
 
 The arrangement of brushes resting in 
 contact with a commutator, for such a motor 
 as is shown in Fig. 31, is represented in 
 Fig. 45. Here b, b, I 1 , b l , are two pairs of 
 brushes, each pair being connected electric- 
 
THE TRANSMISSION OF POWER. 187 
 
 ally together and resting upon the commu- 
 tator bars. The brushes consist of metallic 
 strips or bundles of wire, usually of copper, 
 but sometimes consisting of carbon blocks. 
 They are held in place by devices called 
 brush-holders, a form of which is shown in 
 Fig. 46. Springs placed in these brush- 
 
 FIG. 46. BnusH-HoLDERS. 
 
 holders maintain a uniform electric pressure 
 between the brush and the commutator. 
 After the brushes have been so set as to 
 press upon opposite segments of the com- 
 mutator, they can be rotated together into 
 any suitable position by the rocker arm, 
 
188 THE ELECTRIC MOTOR AND 
 
 which is represented at 21, in Fig. 30, and 
 at 44, in Fig. 32. 
 
 We have seen that in all motors a certain 
 amount of energy is uselessly expended in 
 the friction between the revolving shaft 
 and its supports. In order to lessen this 
 as much as possible the bearings are kept 
 well lubricated. In practice this is almost 
 invariably secured by means of automatic 
 oilers, that is, by bearings which automa- 
 tically keep the rubbing surfaces lubri- 
 cated. Such an automatic, self -oiling 
 bearing is shown in Fig. 47. Here the 
 shaft is supported in the sleeve 8, of a 
 special alloy, called Babbitt metal, having 
 grooves cut in its interior, so as to dis- 
 tribute the oil freely over the revolving 
 surface of the shaft by the action of rota- 
 tion. This action is facilitated by the 
 action of two rings H, R, which rest 
 
THE TRANSMISSION OF POWER. 
 
 189 
 
 upon the shaft in grooves cut into the 
 Babbitt metal sleeve. These rings dip 
 beneath the surface of the oil in the 
 
 FIG. 47. AUTOMATIC SELF-OILING BEARING. 
 
 reservoir O. As the shaft revolves it sets 
 the ring into rotation, although the rota- 
 tion may be many times less rapid than 
 
190 
 
 THE ELECTRIC MOTOR AND 
 
 that of the shaft. The rings cany oil on 
 their surfaces up into the grooves and dis- 
 tribute this over the shaft. The oil, after 
 passing through the bearing, drips again 
 into the reservoir O. The level of the oil 
 in the reservoir can be observed by means 
 of the gauge glass G. The sleeve /SJ and 
 
 FIG. 48. DETAILS OF SELF-OILING BEARING. 
 
 its brass rings, are shown in greater detail 
 in Fig. 48. 
 
 The field magnets, the function of which 
 is to produce the flux passing through the 
 armature, consist essentially of coils of in- 
 sulated wire, provided with cores and pole 
 
THE TRANSMISSION OF POWER. 
 
 191 
 
 pieces, shaped so as to produce an annular 
 or cylindrical space for the rotation of the 
 armature. In Fig. 30, the field magnet 
 cores, with their pole pieces, are shown 
 
 FIG. 49. SKELETON OF MOTOR PARTS. 
 
 at 3 and 2, respectively. The coils of 
 insulated wire which surround them are in 
 practice wound on spools so that the entire 
 coil can be readily removed from the core. 
 Such a coil is shown at 4, in Fig. 30. The 
 
192 
 
 THE ELECTRIC MOTOR AND 
 
 cast-iron base of the machine forms part of 
 the magnetic circuit, as already mentioned. 
 
 FIG. 50. COMPLETE MOTOR OF TYPE SHOWN IN FIG. 49. 
 
 In Fig. 49, a skeleton representation of 
 the different parts of a particular form of 
 motor, is shown in place. Here the arma- 
 ture, with its commutator and pulley, is 
 mounted between the pole pieces of the 
 electromagnet as shown. In this machine, 
 
THE TRANSMISSION OF POWER. 193 
 
 > 
 
 the field cores (7, C, are clamped by bolts 
 in recesses prepared for their reception in 
 the cast-iron bed plate. A complete ma- 
 chine of the same type is shown in per- 
 spective in Fig. 50. 
 
 Since the torque of a motor depends 
 upon the amount of flux passing through 
 the armature, upon the current strength it 
 carries, and upon the number of wires 
 lying on the surface of the armature, it is 
 evident that a powerful torque necessitates 
 a powerful flux, a powerful current, and a 
 great number of wires. As we increase 
 these, we must increase the size of the 
 machine. Consequently, powerful motors, 
 are necessarily large, heavy motors. 
 
 It may be interesting to note the weight 
 and dimensions generally given to motors of 
 various sizes. A half-horse-power motor 
 of good type, weighs about 100 pounds, 
 
194 THE ELECTRIC MOTOR AND 
 
 or about 200 pounds per horse-power, and 
 occupies a floor space of 18" x 10." A 
 5-borse-power motor, of good type, weighs 
 about 600 pounds, or 120 pounds per 
 horse-power, and occupies a floor space of 
 28" x 20". A 15-horse-power motor of 
 good type, weighs about 1,500 pounds, or 
 100 pounds per horse-power, and occupies 
 a floor space of 4' 6" x 3'. A 60-horse- 
 power motor weighs about 6,000 pounds, 
 or about 100 pounds per horse-power, and 
 occupies a floor space of about 7' x 5', 
 while a 250-horse-power motor would have 
 a weight of about 25,000 pounds, or 100 
 pounds per horse-power, and a floor space 
 of 11' x 6'. It will be seen, therefore, 
 that small motors weigh about 200 
 pounds per horse-power or 746 watts 
 (roughly 750 watts) of full-load me- 
 chanical output, and large motors about 
 100 pounds per horse-power. The slower 
 
THE TRANSMISSION OF POWER. 195 
 
 the speed at which a motor is designed to 
 run, the greater will be its weight, other 
 things being equal. 
 
 It is convenient to remember that for 
 motors up to 10-horse-power, the number 
 of horse-power delivered is roughly equal 
 to the number of kilowatts absorbed at 
 the motor terminals. For example, a 6- 
 horse-power motor, delivering, therefore, 
 4,476 watts mechanically, absorbs roughly 
 6 kilowatts, or 6,000 watts, at its terminals, 
 whether the machine be built for circuits 
 of 100 volts, 200 volts or 500 volts. This 
 rule presupposes a commercial efficiency of 
 74.6 per cent. In large sizes the efficiency 
 increases and the rule cannot, therefore, 
 be relied upon. Thus a machine which 
 has a full-load output of 120 horse-power, 
 or about 90 KW, has an intake of, approxi- 
 mately, 100 KW. 
 
196 THE ELECTRIC MOTOR AND 
 
 The speed of motors depends upon their 
 size and construction. If two motors have 
 the same weight, floor space, efficiency, and 
 cost, the one which has the slower speed 
 of revolution is the better machine of the 
 two, because, by rewinding it for the 
 higher speed it could be made to have a 
 greater output, that is to be the equiva- 
 lent of a heavier machine. The speed of 
 a 1/2-horse-power motor of good type is 
 about 1,300 revolutions per minute at full- 
 load ; that of a 1-horse-power motor, about 
 1,000 revolutions per minute ; of a 5- 
 horse-power motor, 900 revolutions per 
 minute; a 15-horse-power motor, 750 revo- 
 lutions ; a 120-horse-power motor, about 
 550 revolutions and a 250-horse-power 
 motor, about 425 revolutions per minute. 
 
 Small motors are usually constructed 
 with two field magnet poles, or belong to 
 
^ 
 
 ' 
 
 THE TRANSMISSION! 
 
 PO* 
 
 :'> 
 
 C 
 
 the bipolar type. Beyono^a^fepr^ain size, 
 however, say 20-horse-power, n>is u&tialljr 
 more convenient and economical to con- 
 
 FlG. 51. QUADRIPOLAR MOTOR. 
 
 struct motors with four or more poles, 
 <|iiadripolar motors being common be- 
 tween 20-HP and 500-HR 
 
198 
 
 THE ELECTRIC MOTOR AND 
 
 A form of quadripolar motor is shown 
 in Fig. 51. Here there are four magnets, 
 M, M, M, M, and, consequently, four rnag- 
 
 FIG. 52. QuADiuroLAii MOTOK. 
 
 netic circuits through the armature. 
 There are also four sets of brushes, instead 
 of two, as in bipolar machines, but oppo- 
 
THE TRANSMISSION OF POWER. 199 
 
 site sets of brushes are connected together 
 electrically, thus making a single pair of 
 main terminals. 
 
 Another type of quadripolar motor is 
 shown in Fig. 52. Here only two sets of 
 brushes are employed, the winding and 
 connection of the armature coils being 
 such as to permit the use of two, instead 
 of four brushes. 
 
CHAPTER VII. 
 
 INSTALLATION AND OPERATION OF MOTORS. 
 
 THE installation of a small motor does 
 not require any particular preparation. 
 It is only necessary to bolt the base frame 
 of the motor to the floor, and set the 
 machine upon it. With heavy motors, 
 however, suitable foundations are neces- 
 sary in order to support them securely. 
 In most cases a belt tightener is employed, 
 whereby the tension of the belt can be 
 adjusted by sliding the motor along its 
 bed plate. This is represented in Figs. 51 
 and 52, where the handle H, enables this 
 adjustment to be made readily. Belts 
 should not be tightened so far as to add 
 
 200 
 
THE TRANSMISSION OF POWER. 201 
 
 considerably to the friction of the shaft 
 in its bearings, nor be left so loose as to 
 slip or flap. 
 
 Where steady driving under all varia- 
 tions of load is a matter of importance, 
 the shunt- wound motor ; or, in some cases, 
 the compound-wound motor, is employed, 
 and, in fact, series- wound stationary motors 
 are usually only employed in small sizes 
 such as in fan motors. 
 
 By reference to the connections of the 
 shunt-wound motor shown in Fig. 26, it 
 will be seen that the armature is connected 
 directly across the mains. If we assume 
 that this connection is made with the 
 armature at rest, and after the field circuit 
 has been closed, so as to excite the field 
 and produce the magnetic flux through 
 the armature ; then, since the resistance 
 
202 
 
 THE ELECTRIC MOTOR AND 
 
 of the armature is necessarily small, a 
 very powerful current will tend to flow 
 through the armature, owing to the 
 absence of any C. E. M. F. due to rota- 
 
 
 
 
 FIG. 53. STARTING RHEOSTAT. 
 
 tion. This first inrush of current and 
 violent resulting torque, are apt to be 
 injurious to the motor. When, therefore, 
 a shunt- wound motor is started from rest, 
 it is necessary to insert a resistance in the 
 
THE TRANSMISSION OF POWER. 
 
 203 
 
 armature circuit, so as to limit the amount 
 of current which shall pass through the 
 armature until it has been brought up to 
 speed and enabled to produce a suffi- 
 
 FIG. 54. STARTING RHEOSTAT. 
 
 ciently powerful C. E. M. F. Such adjust- 
 able resistances are called starting rheo- 
 stats. They consist essentially of coils of 
 wire, usually of iron, mounted in a suit- 
 
204 
 
 THE ELECTRIC MOTOR AND 
 
 able frame, and connected with contact 
 strips in such a manner as to permit their 
 ready insertion or removal from the circuit 
 by the movement of a handle. 
 
 FIG. 55. STARTING RHEOSTAT. 
 
 A form of starting rheostat is shown 
 in Fig. 53. Here coils of iron wire are 
 mounted on a suitable frame and con- 
 nected in series. By turning the switch 
 S, over the contact points, a greater or 
 smaller number of these coils may be 
 
THE TRANSMISSION OF POWER. 205 
 
 FIG. 56. INSTALLATION OF SHUNT-WOUND MOTOR. 
 
&06 THE ELECTRIC MOTOR ANJD 
 
 included in the circuit. When the switch 
 is on the extreme left contact point, no 
 coils are in circuit, and when on the 
 extreme right, all are in circuit. Fig. 54 
 shows a different type of starting rheostat 
 intended for use with small motors. Here 
 the resistance wire is imbedded in a suit- 
 able enamel on the lower surface of the 
 cast-iron plate shown, and the switch 
 serves, as before, to include more or less 
 of this wire between the terminals. Fig. 
 55, shows a similar apparatus of larger 
 sizes intended for use with more power- 
 ful motors. 
 
 Fig. 56 shows, in perspective, the ordi- 
 nary method of installing a shunt-wound 
 motor, and Fig. 57, the diagrammatic con- 
 nections of the same. Similar letters refer 
 to similar parts in both figures. It will 
 be observed that a pair of mains MM, and 
 
THE TRANSMISSION OF POWER. 
 
 207 
 
 M' M ', being connected with a constant 
 pressure of, say 110, 220, or 500 volts, ac- 
 cording to the circuit, and the winding 
 
 M* P.P. CUTOUT BOX 
 
 d 
 
 FIG. 57. CONNECTIONS OF SHUNT- WOUND MOTOB. 
 
 of the motor, are connected with the motor 
 tli rough the switch S, and the cut-out box 
 T. The switch S, consists of a handle at- 
 
208 THE ELECTRIC MOTOR AND 
 
 tached to a pair of copper knife Wades, 
 in such a manner, that on depressing the 
 handle, electrical connection is secured be- 
 tween the branch mains m, m, and the wires 
 a and &, leading to the motor, while if the 
 handle be raised, connection is instantly 
 broken. The switch is called a double- 
 pole switch, because it breaks contact 
 both on the positive and negative sides of 
 the circuit ; i. <?., on one side, at each knife 
 edge. The cut-out box T, contains a pair 
 of safety fuses of lead wires, having such 
 an area of cross section and resistance, 
 that they will melt if the motor should 
 receive an abnormal amount of current. 
 
 In order to start the motor from rest, it 
 is usual to throw oft' the load in the driv- 
 ing machinery, as far as possible, so as to 
 reduce the resisting torque on the motor as 
 far as may be convenient. The handle H, 
 
THE TRANSMISSION OF POWER. 209 
 
 of the rheostat _/?, is then so turned as to 
 cut off the current or disconnect its circuit 
 entirely. Under these circumstances, when 
 the switch /SJ is thrown, so as to complete 
 connection between the wires a and m, on 
 one side, say the positive side, and b and 
 m', on the negative side, then a compara- 
 tively feeble current will pass through the 
 field-magnet coils 6r, 6r, and steadily excite 
 them, this current being determined by 
 the resistance of the coils and the pressure 
 of the circuit. If now the handle H, be 
 turned slowly so as to close the armature 
 circuit through all the resistance in the 
 rheostat, a current will pass through the 
 wires b, c, the rheostat c/, and armature a, 
 and this current will start the motor from 
 rest, provided the resisting torque is not 
 too great. 
 
 As the armature accelerates, the resist- 
 
210 THE ELECTRIC MOTOR AND 
 
 ance in the rheostat is cut out, and, when 
 the motor reaches full speed, the handle is 
 turned so as to cut out all the resistance. 
 In order to stop the motor, the reverse 
 operations are effected ; namely, the rheo- 
 stat handle is turned, without, however, 
 pausing for the slacking of the armature 
 speed until the current is entirely cut off 
 the armature. The switch S, is then 
 opened so as to cut off the motor fields, 
 and the motor is thus entirely disconnected 
 from the circuit. In some cases, when the 
 speed of the motor has to be adjusted, a 
 separate rheostat, called a field rheostat, is 
 inserted in the circuit of the field coils C\ C, 
 and out of the path of the armature cur- 
 rent. By altering the resistance in the 
 field-magnet circuit, within proper limits, 
 the current strength passing through these, 
 being controlled by Ohm's law, will vary 
 the amount of flux passing through the 
 
THE TRANSMISSION OF POWER. 211 
 
 magnetic circuit including the armature, 
 and force the latter to vary its speed in 
 order to maintain a constant C. E. M. F. 
 
 FIG. 58. ADJUSTMENT OF BRUSHES ON A COMMUTATOR. 
 
 The correct position of a pair of brushes 
 resting on a bipolar commutator is shown 
 in Fig. 58 at A. If we suppose that this 
 
212 THE ELECTRIC MOTOR AND 
 
 is the position of sparJdess commutation; 
 i. e., the position at which the brushes will 
 pass current into the armature with the 
 least sparking, then, as the load is gradu- 
 ally applied to the motor, and it performs 
 more and more work, it is usually found 
 that the brushes have to be shifted back- 
 ward, or in the opposite direction to that 
 in which the motor is moving, in order to 
 preserve sparkless commutation. When 
 the machine is acting as a generator, a 
 forward lead of the brushes becomes neces- 
 sary, with increase of load, as at B, 
 whereas, when employed as a motor taking 
 current from the mains, instead of supply- 
 ing current to the mains, the lead of the 
 brushes is backward as at C. In the most 
 recent types of well designed motors, how- 
 ever, the sparking at the commutator is so 
 slight at full load that no shifting of the 
 brushes is necessary. 
 
PROPERTY C 
 
 THE TRANSMISSION OfhfrR. 213 
 
 We have already referred to 
 ciency of the motor ; namely, to the ratio 
 existing between the mechanical activ- 
 ity it develops at its pulley, and the electric 
 activity it absorbs at its terminals. The 
 losses which occur in the motor are all of 
 a frictional nature, but may be divided 
 into: 
 
 (1) Mechanical frictions. 
 
 (2) Magnetic frictions. 
 
 (3) Electric frictions. 
 
 Mechanical frictions are those which are 
 produced at the bearings, brushes and in 
 air churning. The magnetic frictions are 
 those which occur during the rotation of 
 the armature in the flux, and the conse- 
 quent rapid reversal of the magnetism in 
 its core. It is found that when iron has 
 its magnetism reversed, there is a certain 
 amount of energy expended in the iron at 
 
214 THE ELECTRIC MOTOR AND 
 
 each reversal. The more powerful the mag- 
 netism the greater will be the expenditure 
 of energy in every cubic centimetre or cubic 
 inch of iron per reversal. The energy 
 takes the form of heat, so that when we 
 rapidly reverse the magnetic flux in a piece 
 of iron or steel we heat it even though no 
 friction in the mechanical sense occurs. 
 This loss of energy by magnetic friction 
 is called loss of energy by hysteresis, or 
 hysteretic loss of energy. The more power- 
 ful the magnetic flux through the arma- 
 ture ; the more rapid the rotation, and the 
 greater the number of poles, the greater 
 will be the hysteretic loss of energy, In a 
 bipolar field, all the iron in the armature 
 core reverses the direction of its magnetic 
 flux twice in each revolution. In a quadri- 
 polar field it reverses four times in a revo- 
 lution, and so on. 
 
 Thus, referring to Fig. 25, it will be 
 
THE TRANSMISSION OF POWER. 215 
 
 observed that the armature A, is magnet- 
 ized by the flux passing through it in the 
 direction of the flux, having north polarity 
 over the surface opposing the field pole S, 
 where the flux emerges, and south polarity 
 where the flux enters, over the surface 
 opposite the field pole N. After the 
 armature has made half a revolution, the 
 direction of magnetism in its mass will be 
 reversed, the part marked n, in the figure 
 then becoming the part marked s, and 
 vice versa. It is this reversal of mag- 
 netism which gives rise to hysteresis, and 
 the more powerful the magnetic intensity 
 in the armature which has to be reversed, 
 the greater the hysteretic loss. 
 
 Electrical friction is due either to eddy 
 currents, or stray currents set up by dy- 
 namo action in the mass of the conductor, 
 armature core, or field poles ; or, to the 
 
216 THE ELECTRIC MOTOR. 
 
 ordinary thermal expenditure of energy by 
 the passage of the armature currents and 
 field currents through their respective 
 windings. If, for example, the field coils 
 of a motor take a current of 3 amperes 
 steadily, to excite them 'from mains at a 
 pressure of 110 volts, then they will expend, 
 in heating the field coils, an activity of 330 
 watts continuously. 
 
CHAPTER VIII. 
 
 ELECTRIC TRANSMISSION OF POWER. 
 
 THE high efficiency, low cost, and com- 
 parative ease with which the electric 
 motor can be controlled as to speed and 
 power ; the fact that it can be made to 
 automatically regulate the current it re- 
 quires ; and its cleanliness, noiselessness, 
 safety, compactness and portability, cause 
 it to stand to-day in these respects un- 
 rivalled as a prime mover. Not only, how- 
 ever, does the electric motor possess these 
 points of excellence far in excess of other 
 prime movers, but it also possesses special 
 advantages in the field of long distance 
 transmission of power. 
 
 217 
 
218 THE ELECTRIC MOTOR AND 
 
 It will be interesting to discuss the 
 electric motor in this respect aod to ex- 
 amine the conditions under which power 
 can be transmitted over considerable dis- 
 tances. Suppose, for example, that it is 
 desired to furnish, at a distant point, a 
 steady activity of 50 horse-power, for 10 
 hours a day. This power may be em- 
 ployed, for example, to drive the machin- 
 ery in a factory. We can either put a 
 steam engine in the factory, or install there 
 an electric motor, drive a generator at 
 some distant point, from a water-power or 
 steam engine, and connect the generator 
 with the motor by insulated electric con- 
 ductors. 
 
 A system for the distribution of electric 
 energy is represented in Fig. 59, where 6?, 
 is the generator, situated at the source of 
 power. M, is the motor at the factory, 
 
THE TRANSMISSION OF POWER. 219 
 
 or point where the power is to be de- 
 livered, and ab, cd, are the wires connect- 
 ing the two places. It is theoretically 
 possible to employ only one wire, using the 
 earth as a return conductor, as in teleg- 
 raphy, but in practice, this arrangement 
 has never been found satisfactory for the 
 
 FIG. 59. TYPICAL ELECTRIC TRANSMISSION SYSTEM. 
 
 transmission of power, and two conductors 
 are always employed. 
 
 The distance between 6r and M, the 
 generator and motor, that is between the 
 points of supply and delivery, may vary 
 from a few feet to many miles, In 
 
220 THE ELECTRIC MOTOR AND 
 
 factories, power is distributed from one 
 building to another, or from different 
 parts of the same building by means of 
 belts and counter-shafting. The friction 
 of such belts and shafts when long, may 
 represent a considerable waste of power, 
 so that it is often much more economical 
 to restrict the counter-shafts to short 
 lengths, each operated by a separate 
 motor, and distribute the power from a 
 single central source, or poiver "house, to all 
 these motors, as secondary centres of dis- 
 tribution. In such cases the transmission 
 lines may be only a few hundred feet in 
 length. 
 
 In cities, where electric central stations 
 have been constructed, the demand for 
 power, either for industrial or domestic 
 uses, may be supplied by motors operated 
 on electric circuits consisting of the street 
 
THE TRANSMISSION OF POWER. 221 
 
 mains. In such cases, the distributing cir- 
 cuits may be one or two miles in length. 
 Finally, cases may occur where power can 
 be developed under specially economical 
 advantages, at particular localities ; as, for 
 example, at a waterfall, where turbines 
 are installed, and thus cheap power may 
 be transmitted to a distant city at a cost 
 which may be less than that of producing 
 the power in that city by the steam 
 engine. In some cases, the distance to 
 which the pow r er may be transmitted may 
 be many miles. 
 
 Systems of electric transmission of 
 power are, to-day, in fairly extended use. 
 Moreover, this use is found in practice to be 
 so satisfactory that it is rapidly increasing. 
 
 The greatest distance to which power 
 has been electrically carried in any large 
 
THE ELECTRIC MOTOR AND 
 
 quantity is 109 miles, which is the dis- 
 tance between the river Neckar at Lauffen, 
 Germany, and the city of Frankfort. 
 During the Frankfort Electric Exhibition 
 of 1891, about 200 horse-power was 
 steadily transmitted from turbines driven 
 at Lauffen to the Exhibition Building at 
 Frankfort. 
 
 The longest electric power transmission 
 circuit operating commercially at the 
 present day is at the San Joaquin valley to 
 Fresno, Cal., over a distance of 35 miles, at 
 an alternating-current pressure (triphase) of 
 11,200 volts between cond uc tors. The next 
 longest circuit in the United States is from 
 Folsom to Sacramento, Cal., a distance of 24 
 miles, transmitting 3,000 HP. at 11,500 volts 
 alternating triphase pressure. The longest 
 circuit in Europe is from Tivoli to Rome, 
 a distance of 18 miles at an alternating- 
 
THE TRANSMISSION OF POWER. 223 
 
 current Uniphase pressure of 5,000 volts. 
 This system has been installed three years. 
 
 We propose to examine the conditions 
 which affect the problem commercially. 
 Assuming that the 50-horse-power con- 
 tinuous-current motor installed in the fac- 
 tory above referred to, may be wound for 
 any desired pressure, and will possess, 
 when so wound, an efficiency of 90 per 
 cent., then the electric horse-power which 
 must be supplied to its terminals, in order 
 to maintain a steady mechanical activity, 
 
 50 
 will be, T; = 55.55 horse-power = 55.55 
 
 \).J 
 
 X 746 = 41,440 watts = 41.44 KW. 
 This electric activity could be supplied as 
 41,440 amperes at a pressure of 1 volt, in 
 which case the motor would have to be 
 wound for 1 volt ; or, as 20,000 amperes 
 at a pressure of 2.072 volts ; or, as 1,000 
 
224 THE ELECTRIC MOTOR AND 
 
 amperes at a pressure of 41.44 volts ; or, 
 100 amperes at a pressure of 414.4 volts; 
 or, 10 amperes at a pressure of 4,144 volts. 
 In each case, the motor would have to he 
 wound for the required pressure. 
 
 Let us suppose that the cost of winding 
 the motor is the same whatever pressure 
 might be employed. This would not be 
 strictly true, since the winding for either a 
 very low pressure, or a very high pressure 
 motor would be comparatively expensive ; 
 but, within a certain range, say from 50 
 volts to 1,000 volts, the cost would, prob- 
 ably, be nearly the same. Similarly, the 
 cost of winding the generator for any pres- 
 sure may be considered at present as con- 
 stant. Let us also suppose that a certain 
 loss of power is allowed in the transmission 
 lines or conductors, say 10 per cent, of the 
 full-load power developed at generator ter- 
 
THE TRANSMISSION OF POWER. 225 
 
 minals. The efficiency of the line being, 
 therefore, ~, the power to be supplied at 
 
 the generator terminals would be 4 ^' 44 
 
 0.9 
 46.04 KW. 
 
 We then have an unwound generator at 
 the transmitting end of the line, whose 
 output, at full load, must be 46.04 KW, 
 an unwound motor at the factory, or 
 receiving end of the line, whose intake 
 must be 41.44 KW, and whose output 
 will be 50 horse-power, or 37.3 KW. 
 The size of the conductors between these 
 two points remains to be determined. 
 
 Let us suppose that the distance 
 between these two stations is 5 miles; 
 then the total length of circuit will be 10 
 miles, including the outgoing and return- 
 ing conductors. In order that the loss of 
 
226 THE ELECTRIC MOTOR AND 
 
 activity iri the resistance of these 10 miles 
 of conducting wire, shall as above 
 assumed, be 10 per cent, of the activity 
 supplied at the generator terminals, it is 
 necessary that the drop of pressure pro- 
 duced by the working current in these 10 
 miles, shall be 10 per cent, of the pressure 
 at the generator terminals. Thus, if the 
 pressure at generator terminals be 500 
 volts, and the pressure at the motor termi- 
 nals 450 volts, then the drop of pressure 
 in the line will be 50 volts, or 10 per cent, 
 of that at generator terminals, and the 
 activity expended in heating the resistance 
 of the line wires will be, in watts, 
 50 volts x working current in amperes, 
 
 while the activity expended in the 
 
 motor will be 
 450 volts x working current in amperes, 
 
 the total activity of the generator, being, 
 500 volts x working current in amperes. 
 
THE TRANSMISSION OF POWER. 227 
 
 If then, we wind the generator for 10 
 volts, and the motor for 9 volts, we lose 10 
 per cent, of our electric activity in the 
 
 line, but the current must be ^- - = 4,604 
 
 amperes, and the drop in the two lines 
 together, one volt, or half a volt in each. 
 The resistance of the two lines together 
 
 must, therefore, be - ohm, and the re- 
 4,604 
 
 sistance per mile must be T/rth of this, or 
 
 4fi 040 ohm. Ordinary trolley wire, No. 
 
 A. W. G., has a resistance of, approx- 
 imately, half an ohm per mile. Conse- 
 quently, the size of conductor, which 
 would have to be employed in order to have 
 
 only ohm per mile, w r ould have to 
 
 be - - = 23,020 times as heavy, or as 
 
228 THE ELECTRIC MOTOR AND 
 
 large in cross-section. Such an enormous 
 conductor would be prohibitively costly 
 and, therefore, such a system of transmis- 
 sion could not be carried out in practice. 
 
 If now, the generator were wound for 
 100 volts, and the motor for 90 volts, 
 representing a drop in the transmission 
 line of 10 volts, or 5 volts in each wire, 
 the current strength in the circuit would 
 
 be - _ 460.4 amperes. The resist- 
 
 ance of conductor, which would produce a 
 drop of 10 volts with this current would 
 
 10 I 
 
 be TTVTTT ohm =- r^7 " m > and this being 
 
 the resistance of 10 miles of conductor, 
 
 the resistance per mile should be .. - 
 
 460.4 
 
 ohm. If we assume the resistance of a 
 trolley wire, as before, to be exactly half 
 
THE TRANSMISSION OF POWER. 229 
 
 an ohm, the size of the conductor rieces- 
 
 460 4 
 
 sary would be equal to - = 230.2 
 
 2 
 
 trolley wires iu cross-sectiou or weight. 
 
 By increasing the pressure of trans- 
 mission ten times ; namely, from 10 volts to 
 100 volts, we have reduced by 100 times 
 the size of wire, which is necessary in 
 order to transmit a given activity of 50 
 horse-power with a fixed percentage of 
 loss, because we have reduced the current 
 strength ten times, and we have increased 
 the permissible drop in the circuit from 1 
 volt to 10 volts, so that the resistance has 
 been increased 100 times. 
 
 In the same way, if the generator be 
 wound for 1,000 volts, and the motor for 
 900 volts, allowing 10 per cent, drop in 
 transmission lines, as before, the current 
 
230 THE ELECTRIC MOTOR AND 
 
 strength necessary to deliver 46,040 watts 
 at the generator terminals will be 
 
 -y-^ - = 46.04 amperes, and the resistance 
 
 which will have to exist in the two trans- 
 mission lines, in order to produce with this 
 
 current a drop of 100 volts, will be 
 
 
 9 i >TO 
 
 2.173 ohms; or, t T7T~ ~ 0.217 ohm per 
 
 mile. If we assume that the trolley wire 
 has just 0.5 ohm per mile, then the size of 
 the wire necessary to employ between the 
 
 generator and motor will be -- 
 
 0.2173 
 
 2.302 times that of trolley wire. Roughly 
 speaking, therefore, the size of the wire 
 would only be twice that of the trolley 
 wire. That is, for a loss of 10 per cent, or 
 4.604 KW. in transmission the size of 
 wire for 
 
THE TRANSMISSION OF POWER. 231 
 
 10 volts at generator terminals, and 9 at 
 
 motor terminals, would have to be 
 
 23,020 times trolley wire. 
 100 volts at generator terminals and 90 
 
 at motor terminals, 230.2 times trolley 
 
 wire. 
 1,000 volts at generator terminals and 900 
 
 at motor terminals, 2.302 times trolley 
 
 wire. 
 10,000 volts at generator terminals and 
 
 9,000 at motor terminals, 0.02303 times 
 
 trolley wire. 
 
 In other words, the cost of copper 
 required for a given distance and given 
 loss in transmission varies inversely as the 
 square of the electric pressure. 
 
 We have hitherto assumed that the dis- 
 tance between the generator and the motor 
 was 5 miles. Let us now suppose that 
 
232 THE ELECTRIC MOTOR AND 
 
 this distance is doubled, or changed to 10 
 miles, and that the length of the circuit is, 
 consequently, changed to 20 miles. If, 
 as before, 10 per cent, of the electric ac- 
 tivity has to be expended in the resistance 
 of the circuit, then the same number of 
 volts drop will have to be developed in 20 
 miles, which previously were developed in 
 10, so that the resistance per mile of the 
 conductor must be halved for any given 
 pressure at generator and motor. 
 
 Thus, if the generator be wound for 
 1,000 volts and the motor for 900 volts, 
 the drop in the transmission lines will be 
 100 volts, as before. The current will be 
 46.04 amperes, and the resistance of the 
 
 circuit as before = 2.302 ohms, and 
 
 the resistance per mile, th of this, or 
 
THE TRANSMISSION OF POWER. 238 
 
 0.1151 ohm. requiring a wire _1^_1 
 
 0.1151 
 
 4.604 times that of trolley wire, or twice 
 as big a wire as when the circuit was only 
 10 miles in length. Moreover, since we 
 have to provide 20 miles of this double 
 wire, instead of 10 miles, it is evident that 
 the total weight of copper conductor will 
 have increased four times. 
 
 Similarly, it will readily be found that 
 if we trebled the distance between gener- 
 ator and motor we should have to use a 
 wire three times as large for 30 miles 
 as for 10 miles, and would, therefore, 
 require 9 times the total weight of the 
 copper needed in the first instance. In 
 other words, the total weight of con- 
 ductor required in a transmission system 
 varies with the square of the distance be- 
 tween generator and motor for a given 
 
234 THE ELECTRIC MOTOK AND 
 
 pressure of transmission, and for a given 
 percentage of loss of activity. In order, 
 therefore, to transmit power economically 
 over considerable distance, it is essential 
 to employ high electric pressures, since 
 otherwise the cost of copper becomes pro- 
 hibitive. 
 
 In building and winding continuous- 
 current dynamo machines, whether for 
 motors or generators, the limit of pressure 
 which can be safely employed, depends 
 upon the character of the insulation em- 
 ployed in the winding, and upon the 
 nature of the commutator. The commuta- 
 tor is obviously a weak point in such 
 machines, since the full electric pressure 
 has to be maintained between the brushes 
 which are only a few inches apart, and are 
 separated by only a few strips of mica on 
 a revolving cylinder. The highest electric 
 
THE TRANSMISSION OF POWER. 235 
 
 pressures which are employed in dynamo 
 machines are 10,000 volts. These pres- 
 sures, however, are only employed in a few 
 generators for series arc-light circuits and 
 are not employed in motors. The highest 
 pressures for which motors have been 
 built, are practically 2,000 volts, while 
 ordinarily 1,000 volts is the limit of pres- 
 sure in motor construction. Consequently, 
 under the conditions imposed by the art 
 of motor building, as it exists to-day, the 
 limitations of distance to which power can 
 be transmitted by the continuous current 
 are those which are prescribed either by 
 the cost of conductor, or by the cost of 
 power wasted in conductors at this limit- 
 ing pressure of 1,000 volts. Moreover, at 
 pressures exceeding this amount, the motors 
 become dangerous to handle without pre- 
 cautions, since the shock from a thousand 
 volt circuit is a serious one. 
 
236 THE ELECTRIC MOTOR AND 
 
 Assuming that the amount of money 
 which must be expended in conductors 
 to transmit' a given number of horse- 
 power over any actual distance, at, say 
 1,000 volts pressure, is not excessive ; or, 
 in other words, that it will pay to employ 
 continuous-current electric transmission 
 under these conditions, the question next 
 arises, What should be the percentage of 
 drop allowed in the line ? If we employ 
 a large percentage of drop we reduce 
 the size and cost of the copper con- 
 ductors, but at the same time we waste 
 more activity in the conductors, which 
 wasted activity has a money value. At 
 what point then should the drop be fixed 
 so as to secure the maximum economy ? 
 
 In practice the solution to this problem 
 can only be determined by making actual 
 estimates with different percentages of 
 
THE TRANSMISSION OF POWER. 237 
 
 drop. For example, if the distance be- 
 tween generator and motor be 1 mile, 
 and the pressure at the generator terminals 
 1,000 volts, then the problem is to deter- 
 mine what shall be the most economical 
 drop to employ in the line conductors. It 
 is evident that the amount of power to be 
 transmitted does not enter directly into 
 this question, because, if we double the 
 power transmitted, we marely double the 
 whole transmission system, including gener- 
 ator, wires and motors, so that we may, for 
 convenience, simply consider the transmis- 
 sion of one horse-power. Let us suppose 
 that 1 KW capacity in motors costs say 
 $40 when installed, so that 1,000 KW maxi- 
 mum mechanical delivery at the motor 
 shaft costs $40,000 in motor machinery. 
 Then, if the efficiency of the motor be 
 taken, at say 90 per cent., which would 
 be a fair value for moderately large sizes 
 
238 THE ELECTRIC MOTOR AND 
 
 of motors, the electric activity at motor 
 terminals, per KW delivery at belt, would 
 be 1.111 KW. If now, a size of wire 
 which would expend in resistance at the 
 working pressure 10 per cent, of the 
 maximum pressure employed, the total 
 activity at the generator terminals would 
 be 1.235 KW and the power delivered 
 to the generator shaft assuming 90 per 
 
 cent, efficiency would be KW = 
 
 0.9 
 
 1.372 KW. Consequently, we have, under 
 these conditions, to supply 1.372 KW 
 to the generator shaft in order to 
 obtain 1 KW from the motor shaft. The 
 total annual charge of the system will be 
 the interest and depreciation on the invest- 
 ment, added to the cost of superintendence 
 and repairs and the cost of the power 
 supplied at the generator shaft. If the 
 power be obtained from a waterfall, which 
 
THE T&ANSMISSION OF POWER. 239 
 
 is not limited in supply, then a little extra 
 loss of power in the line will not be a 
 matter of serious consequence, since it will 
 only involve the use of a correspondingly 
 larger generator and turbine, so that the 
 cost will only be increased by the fixed 
 charges on the extra investment. If, how- 
 ever, the power to be transmitted is from a 
 steam plant, not only will the engines and 
 boilers and generators at the transmitting 
 end have to be larger, by reason of a 
 greater waste of power in the line, but also 
 the coal consumed at the generating end 
 will be increased. We, have, therefore, to 
 find by trial and estimate such a size of wire 
 as will make the total annual cost of the 
 power delivered a minimum. If we make 
 the wire too small and its resistance too 
 great, its first cost will be reduced and the 
 annual interest on the wire will be reduced. 
 There will practically be no depreciation 
 
240 THE ELECTRIC MOTOR. 
 
 on copper wire, although there will be 
 some depreciation on the poles, supports or 
 insulation which must be maintained about 
 the wire. On the other hand, the engines, 
 boilers and generators will cost more, and 
 the coal per horse-power hour, or per KW 
 hour, delivered will cost more. If we 
 make the wire too large, we reduce the 
 cost of coal in the generating station, and 
 also the fixed annual charges of interest, 
 depreciation, superintendence and repairs 
 on generating plant which is now smaller, 
 but we have an increase in the fixed 
 charges upon the greater investment in the 
 line conductors. Economy requires that 
 the total charges or total annual expense 
 shall be as small as possible, and, con- 
 sequently, the size of the wire must be so 
 chosen that under the estimated conditions 
 of load the total cost of wire, power and 
 generating apparatus shall be a minimum. 
 
PROPERTY OF 
 
 CHAPTER IX. 
 
 ALTERNATING -CURRENT MOTORS. 
 
 CONSIDERABLE attention has been paid 
 of recent years to the development of 
 alternating-current machinery, owing to 
 the facilities which such machinery pos- 
 sesses for the long-distance transmission 
 of power. While it will be necessary to 
 refer briefly to the differences between the 
 alternating and continuous current, space 
 will not permit the discussion of the 
 peculiarities of alternating currents to any 
 great length, and the reader is therefore 
 referred to the authors' volume on "Alter- 
 nating Electric Currents," in the Ele- 
 mentary Electro-Technical Series, for more 
 complete particulars in that direction. 
 
 241 
 
242 THE ELECTRIC MOTOR AND 
 
 A continuous E. M. F., that is ati 
 E. M. F. which always acts in the same 
 direction, establishes, or tends to establish, 
 a continuous electric current in its circuit. 
 An alternating E. M. F. y that is an 
 E. M. F. which at regular successive in- 
 intervals reverses its direction, establishes, 
 or tends to establish, an alternating current 
 in its circuit. A continuous-current cir- 
 cuit has its analogue in a reservoir, which 
 discharges through a pipe or hydraulic 
 conductor. An alternating-current circuit 
 has its analogue in a hydraulic circuit in 
 which a pump drives water alternately 
 backwards and forwards at regular inter- 
 vals. The tidal flow in a river is another 
 example of alternating water currents. 
 
 A complete to-and-fro motion or double 
 alternation constitutes a cycle. The num- 
 ber of cycles per second, or per minute, con- 
 
THE TRANSMISSION OF POWER. 243 
 
 stittites what is called the frequency. In 
 commercial practice the frequency varies 
 between 25 cycles per second, or 50 rever- 
 sals of E. M. F. and current per second, 
 (1,500 cycles per minute, or 3,000 re- 
 versals or alternations per minute) and 140 
 cycles, or 280 alternations per second, 
 (8,400 cycles, or 16,800 alternations per 
 minute). 
 
 The current strength in an alternating- 
 current circuit, unlike that in a continu- 
 ous-current circuit, does not depend only 
 upon the E. M. F. and the resistance as 
 related by Ohm's law. To determine the 
 current strength in alternating-current cir- 
 cuits, it is necessary to take into account a 
 new quantity called reactance. Reactance 
 is a quantity similar to resistance, and like 
 it, is capable of being expressed in ohms. 
 Its value increases directly with the fre- 
 
244 THE ELECTRIC MOTOR AND 
 
 quency. A coil of wire, for example, 
 either with 01* without an iron core, having 
 a resistance of 3 ohms, will permit a cur- 
 rent of 3 1/3 amperes to flow through it 
 under a continuous pressure of 10 volts; 
 but, if the E. M. F. applied to its termi- 
 nals, instead of being continuous, alter- 
 nates with a frequency of say 50 cycles 
 per second, the coil will possess not only 
 a resistance of 3 ohms, but a reactance 
 which might be, at this frequency, say 4 
 ohms. This reactance has to be consid- 
 ered as to its effect of reducing the current 
 strength. If the frequency were doubled ; 
 that is, increased to 100 cycles per second, 
 or 200 reversals of E. M. F. and current 
 per second, the reactance would be 
 doubled, or increased to 8 ohms, and if 
 the frequency were made 150 cycles per 
 second, the reactance would be increased 
 to 12 ohms. 
 
THE TRANSMISSION OF POWER. 245 
 
 The amount of the reactance depends 
 not only upon the number of turns in the 
 coil but also on their ability to produce 
 magnetic flux through the coil. The 
 greater amount of magnetic flux which 
 will be produced by the current in passing 
 through the coil, the greater will be the 
 reactance of the coil for a given frequency. 
 The reactance is sometimes described as 
 the choking effect of the current, since it 
 tends to check or choke the current which 
 flows ; but the amount of this choking, 
 that is the total effective resistance, cannot 
 be determined by simply adding together 
 the resistance and reactance. Thus, in the 
 case of the above coil, having 3 ohms 
 resistance and 4 ohms reactance, at a 
 frequency of 50 cycles per second, gener- 
 ally represented thus, 50~, the effective re- 
 sistance of the coil will not be 7 ohms, but 
 can be obtained by drawing the resistance 
 
246 THE ELECTRIC MOTOR AND 
 
 as the base, and the reactauce as the per- 
 pendicular of a right-angled triangle as 
 in Fig. 60. The combined influence of re- 
 actance and resistance will then be repre- 
 
 B 
 
 A 
 
 f 
 
 IS 
 
 IS 
 
 V RESISTANCE 3 OHMS A 
 
 FIG. 60. DIAGRAMS INDICATING RELATION OP IMPED- 
 ANCE TO RESISTANCE AND REACTANCE. 
 
 sented by the length of the hypothenuse 
 OB, which in this case will be 5 ohms, so 
 that the current strength passing through 
 the circuit will be 10 volts, divided by 5 
 ohms = 2 amperes. 
 
THE TKANSMISSION OF POWER. 247 
 
 Ohm's law, as modified for alternating 
 current circuits, is, therefore, 
 
 Volts E. M. F. 
 ~ Ohms Impedance. 
 
 If the frequency of alternation be doubled, 
 so that the reactance is doubled, or be- 
 comes 8 ohms, the impedance, as shown in 
 Fig. 61, will be increased to 8.544 ohms, 
 and the current strength in the coil will, 
 
 therefore, be reduced to 5-^7, = 1.17 am- 
 
 0.544 
 
 peres. If the frequency of alternation 
 were made indefinitely small, so that the 
 current became continuous, the impedance 
 would become the simple resistance. 
 
 Reactance plays a prominent part in all 
 alternating-current circuits. It is usefully 
 employed in apparatus called alternating- 
 current transformers, which consist essen- 
 tially of coils of wire wound upon a 
 
248 THE ELECTRIC MOTOR AND 
 
 common core. One of these coils is con- 
 nected with the driving or primary circuit, 
 
 O RESISTANCE $ OHMS A 
 
 FIG. 61. DIAGRAM INDICATING RELATION OF IMPED- 
 ANCE TO REACTANCE. 
 
 while the other coil is connected with the 
 driven or secondary circuit ; i. e., the circuit 
 
THE TRANSMISSION OF POWER. 249 
 
 to which the activity has to be transferred. 
 When the secondary circuit is opened and 
 is, therefore, devoid of activity, the react- 
 ance of the coil in the primary circuit has 
 a maximum value depending upon the fre- 
 quency, the number of turns, and their 
 arrangement upon the iron core, so that 
 the impedence of the primary coil has a 
 definite and usually a large value in ohms. 
 Consequently, the primary coil takes a very 
 small current when supplied at a given 
 pressure. When, however, the secondary 
 circuit is closed through incandescent 
 lamps, motors, or other devices, the effect of 
 the activity, which is thus transferred from 
 the primary to the secondary coil is to 
 lower the reactance of the primary coil, and 
 thus reduce its impedance, permitting a 
 greater current strength and activity to 
 enter the primary coil from its supply 
 mains. 
 
250 THE ELECTRIC MOTOR AND 
 
 An alternating-current transformer is, 
 therefore, an apparatus, which, without 
 revolving parts, automatically transfers 
 energy from its primary to its secondary 
 circuit. At the same time, it possesses a 
 very valuable property of transforming the 
 energy, in regard to pressure and current, 
 in a manner depending upon the winding 
 of the primary and secondary coils. If the 
 primary and secondary coils have the same 
 size and the same number of turns, the 
 primary and secondary E. M. F.'s will be 
 practically the same, but if the primary 
 winding has, say 10 times the number of 
 turns as in the secondary winding, the E. 
 M. F. acting in the secondary circuit will be 
 
 TTjth of that in the primary circuit. Such 
 
 a transformer is called a step-down t/rans- 
 former, because the pressure is reduced 
 in the secondary circuit. If, however, 
 
THE TRANSMISSION OF POWER. 251 
 
 the secondary winding has, say 10 times the 
 number of turns as in the primary wind- 
 ing, the secondary E. M. F. will be 10 times 
 as great as the primary E. M. F. and the 
 current strength will be, approximately, 
 
 rth of the primary current strength. 
 
 Such a transformer is called a step-up 
 transformer, because it effects an increase 
 in pressure in its driving circuit. 
 
 It is obvious, that if no activity were 
 absorbed in a transformer, the activity in 
 the secondary circuit would be equal to 
 the activity received by the transformer at 
 its primary terminals. As a matter of fact, 
 the loss in a transformer, although com- 
 paratively small, is nevertheless quite 
 appreciable. A large transformer will 
 deliver, at its secondary terminals, about 
 98 per cent, of the activity it receives at its 
 
252 THE ELECTRIC MOTOR AND 
 
 primary terminals, or will absorb as heat, 
 about 2 per cent, of its maximum received 
 activity. This loss of 2 per cent, will be 
 only slightly reduced at no load, or on 
 open secondary circuit, so that, if a 10 
 KW transformer ; i. <?., a transformer cap- 
 able of delivering steadily an activity of 
 10 KW in its secondary circuit, absorbs 
 300 watts at full load, it will require to be 
 supplied with 10.3 KW at its primary 
 
 terminals, and its efficiency will be - = 
 
 lu.o 
 
 97.09 per cent. Usually, the greater part 
 of this loss of 300 watts will occur at all 
 loads, so that roughly say 200 watts will 
 have to be expended in operating the 
 transformer, when it is delivering no 
 power to its secondary circuit ; i. e., when 
 its secondary circuit is open. 
 
 We have seen that in a continuous-cur- 
 
THE TRANSMISSION OF POWER. 253 
 
 rent circuit the activity is always expressed 
 as the product of the amperes and the 
 volts, or in other words, on the rate of sup- 
 ply of current, and the pressure at which 
 that current is supplied. In an alternat- 
 ing-current circuit, however, this relation 
 ceases, as a general rule, to be strictly ap- 
 plicable. This is for the reason that the 
 impulses, or waves of current, do not, as a 
 rule, exactly coincide with the impulses or 
 waves of E. M. F. When the current 
 waves do coincide, or keep exactly in step 
 with the E. M. F. waves, then the activity, 
 in watts, is the product of the amperes and 
 the volts, as in continuous-current circuits, 
 but it usually happens that the current 
 waves do not coincide, or are out of step 
 with, the E. M. F. in the circuit, and gen- 
 erally lag behind the latter. If we could 
 watch the waves of E. M. F. and current, 
 we should find that the crests of the E. M. 
 
254 THE ELECTRIC MOTOR AND 
 
 F. waves usually arrived ahead of the cur- 
 rent waves, although under certain circum- 
 stances the reverse may be true, and the 
 current wave crests may arrive in advance 
 of the E. M. F. wave crests. The current 
 in these cases is described as lagging or 
 leading respectively. 
 
 The effect of a lag or a lead is to pro- 
 duce an opposition between the E. M. F. 
 and the current which it drives, since it is 
 evident, that during the entire cycle, the 
 E. M. F. will not be in the same direction 
 as the current, but during a portion of 
 the cycle, the current and the E. M. F. 
 waves will have opposite directions. For 
 this reason the activity of the E. M. F. 
 will not be so great as the product of the 
 volts and the amperes, but will have to be 
 reduced by a factor called the power factor, 
 always less than unity, and only reaching 
 
THE TRANSMISSION OF POWER. 255 
 
 unity when there is no lag or lead ; i. e., 
 when current and E. M. F. waves coincide. 
 In special cases the power factor may be 
 as low as say 1 per cent., in which case 
 the current and the pressure would be 
 nearly out of step, the crests of one nearly 
 coinciding with the mean levels of the 
 other. Under ordinary circumstances, the 
 power factor is usually more than 50 per 
 cent, or 0.5, and it is quite commonly over 
 90 per cent, or 0.9. In such cases we have 
 to multiply the volts by the amperes and 
 by the power factor, in order to obtain the 
 true activity. In other words, the volts 
 and the amperes, when multiplied together, 
 cannot be less and will generally be more 
 than the actual activity of the circuit in 
 which they are measured. 
 
 When a circuit has very small reactance, 
 relatively to its resistance, the power 
 
256 THE ELECTRIC MOTOR AND 
 
 factor will be large, or nearly 100 per cent. 
 On the contrary, when the reactance is 
 large relatively to the resistance, the power 
 factor will be small. Consequently, the 
 power factor of an incandescent lamp is 
 almost exactly 100 per cent., because the 
 filament, having only a single bend or loop, 
 possesses an extremely small reactance and 
 a relatively large resistance. Therefore, if 
 we multiply the volts and the amperes 
 observed at the terminals of an incan- 
 descent lamp, or group of incandescent 
 lamps supplied on an alternating-cur- 
 rent circuit, we obtain almost exactly the 
 real activity which is supplied to them. 
 If, however, we take a coil of wire having 
 a large number of turns and a small 
 resistance, the pressure and current, ob- 
 served at the terminals of this coil, may be 
 considerably out of step, or may be, as it 
 is frequently called, displaced in phase, so 
 
THE TRANSMISSION OF POWER. 
 
 257 
 
 that the product of the volts and amperes 
 may be considerably in excess of the real 
 activity expended in the coil. 
 
 FIG. 62. ALTERNATING-CURRENT DYNAMO. 
 
 Any dynamo for generating alternating 
 E. M. F.'s is called an alternator. Fig. 62, 
 represents an alternator employed for 
 electric lighting. Since every dynamo- 
 
258 THE ELECTRIC MOTOR AND 
 
 electric generator develops in its armature 
 E. M. F.'s which alternate, it is evident that 
 a continuous-current machine differs from 
 an alternator principally in the fact that it 
 employs a commutator to direct all the 
 alternating-current impulses in the same 
 direction, so far as the external circuit is 
 concerned. In Fig. 62, is shown a sexti- 
 polar machine, driven by a pulley JP 9 and 
 provided with a pair of collector rings r, r, 
 for delivering the alternating E. M. F. to 
 the external circuit. The machine also 
 drives by the pulley P^ a small continuous- 
 cur rent generator 6r, called the exciter, the 
 function of which is to produce a suffi- 
 ciently powerful continuous current to 
 excite the field-magnet coils J/, M, M, of 
 the alternator. 
 
 When two ordinary alternators are con- 
 nected by a pair of wires, with the object 
 
PROPERTY C 
 
 THE TRANSMISSION O^JO^ER. 259 
 
 of employing one as a generated 
 other as a motor, it is found that the motor 
 will not start from rest when connected to 
 the running generator. This is for the 
 reason that before the armature of the 
 motor has had time to start up at full 
 speed in one direction, by the action of 
 any particular wave of current, the next 
 and opposite wave of current has reversed 
 the electro-dynamic force and arrested the 
 motion. If, however, the motor armature 
 be brought, by an externally applied force, 
 up to the speed at which it should run in 
 order to develop the same frequency as the 
 generator, then if its field magnets are ex- 
 cited, its armature circuit may be closed in 
 such a manner that the armature will fall 
 into step with the impulses received from 
 the generator, and the motor will commence 
 to be driven. This is because the arma- 
 ture of the motor reverses the direction of 
 
260 THE ELECTRIC MOTOR AND 
 
 its C. E. M. F. nearly in synchronism with 
 the reversal of the direction of the cur- 
 rent. The two machines then keep in 
 step, or are said to run synchronously. 
 The motor may exert a powerful torque 
 and exert a considerable mechanical activ- 
 ity; but, provided that it be not too 
 heavily overloaded, it will maintain its 
 synchronism with the generator. On 
 being subjected to an excessive load, it will 
 fall out of step, will fail to receive activity 
 from the generator, and will then rapidly 
 come to rest. 
 
 The practical difficulty experienced with 
 alternating-current motors, until recent 
 times, was that they would not start from 
 rest, so that a prime mover of some kind 
 was necessary in order to bring the alter- 
 nating-current motor up to speed before 
 it could be usefully connected with the 
 
THE TRANSMISSION OF POWER 261 
 
 circuit. Synchronous alternating-current 
 motors of this type have been brought 
 up to speed in a variety of ways. In 
 some cases, this is effected by means of 
 special windings on the armature, capable 
 of acting as continuous-current machines 
 under light loads, and sometimes by storage 
 batteries and auxiliary motors. In other 
 cases continuous-current exciters are em- 
 ployed at each end of the line, as ordi- 
 nary continuous-current generators and 
 motors, thus obtaining sufficient power 
 from the line circuit from the generating 
 exciter to the motor exciter, to be able to 
 run the motor armature unloaded, up to 
 synchronous speed when the exciters would 
 be disconnected from the circuit and the 
 alternating-current armatures connected 
 thereto. The inconvenience, however, of 
 having to bring the motor armature up to 
 speed, where frequent stoppages are neces- 
 
262 THE ELECTRIC MOTOR AND 
 
 sary, becomes so great that the synchro- 
 nous alternating-current motors have never 
 come into extended commercial use. A 
 device, however, which is sometimes used, 
 is to provide the motor-armature with a 
 double winding, one winding having a 
 commutator for the production of con- 
 tinuous currents, and the other winding 
 arranged, like that of an alternator arma- 
 ture, for the passage of alternating currents. 
 By connecting the continuous-current 
 winding with the alternating-current 
 mains, the motor may be started and 
 brought up to speed by allowing the field 
 magnets to reverse their polarity at each 
 alternation of the current, so that the 
 magnetic flux reverses coincidently in both 
 field and armature at every alternation 
 of current. After full speed has been 
 attained, the alternating-current winding 
 is connected to the circuit, so that the 
 
THE TRANSMISSION OF POWER. 263 
 
 motor runs synchronously, while the con- 
 tinuous-current winding supplies the cur- 
 rent necessary to steadily energize the field 
 magnets. 
 
 The difficulty of starting and operating 
 synchronous alternating-current motors, 
 has, however, led to the introduction and 
 development of multiphase alternating- 
 currents and multiphase motors. 
 
 A multiphase alternating-current system 
 is a system of two or more circuits tra- 
 versed by independent alternating currents, 
 possessing a definite difference of phase. 
 
 A diphase system, or two-phase system, 
 is a system consisting of circuits having 
 two alternating currents differing in phase 
 by one quarter of a cycle. 
 
 A triphase system, or three-phase system, 
 is a system of circuits having three alter- 
 
264 THE ELECTRIC MOTOR AND 
 
 nating currents, differing in phase by one- 
 third of a cycle. 
 
 Multiphase systems of any complexity 
 may exist, but in practice not more than 
 three separate currents are employed. 
 
 B 
 b 
 
 FIG. 63. DIAGRAM OF DIPIIASE SYSTEM WITH FOUR 
 CONDUCTORS. 
 
 Fig. 63, represents the simplest form of 
 diphase system, comprising two distinct 
 circuits supplied with alternating currents 
 from a common source at A. The circuit 
 ab, cd, taken by itself is a simple alter- 
 nating-current circuit. The circuit ef, gh, 
 taken similarly is also a simple alternat- 
 ing-current circuit, but these circuits, taken 
 
THE TRANSMISSION OF POWER. 265 
 
 together, constitute a dipJiase system, for 
 the reason that the waves of E. M. F. 
 and current generated in the circuit abed, 
 differ in phase by one quarter of a cycle 
 from those generated in the circuit efgli. 
 The impulses reach their crests in one 
 circuit, when at their zero or mean levels 
 in the neighboring circuit. This result 
 may be obtained by employing either two 
 ordinary or Uniphase generators, rigidly 
 coupled together on the same shaft, in 
 such a position that the E. M. F. waves 
 in one are generated one quarter cycle 
 ahead of the E. M. F. waves in the other ; 
 or, by employing two windings on the 
 armature of one alternator so arranged as 
 to produce the necessary difference in 
 phase. 
 
 Instead of employing two entirely sepa- 
 rate circuits for the two alternating cur- 
 
266 
 
 THE ELECTRIC MOTOR AND 
 
 rents of a diphased system, as shown in 
 Fig. 63, a common return conductor may 
 be employed and only three wires used as 
 in Fig. 64. In such cases, the third, or 
 middle conductor, is made about 40 per cent. 
 
 B 
 b 
 
 FIG. 64. DIAGRAM OF DIPHASE SYSTEM WITH THREE 
 CONDUCTORS. 
 
 heavier in order to carry the increased cur- 
 rent strength. The diphase system requires 
 that the waves of current and E. M. F. in 
 the conductors a b d, shall be a quarter 
 cycle out of step with those in the con- 
 ductor g h d. 
 
THE TRANSMISSION OF POWEK. 267 
 
 A triphaser is an alternator which pro- 
 duces three E. M. Fs. differing from one 
 another in phase by one third of a cycle. 
 Such triphase currents might be produced 
 by three Uniphase armatures rigidly 
 
 a 
 
 b 
 
 hi 2 
 
 E 
 
 FIG. 65. TRIPHASE Six- WIRE SYSTEM. 
 
 clamped together on a single shaft, but so 
 set that the E. M. Fs. differ in phase by 
 one third of a complete cycle. Such a com- 
 bination is diagranimatically represented 
 in Fig. 65, where the three separate circuits 
 have Uniphase currents, but the current 
 waves in the three circuits differ by one 
 
268 THE ELECTRIC MOTOR AND 
 
 third of a cycle. In practice, however, six 
 wires are never used for a triphaser, but 
 three wires only, each wire serving in turn 
 as the return of the other two. This ar- 
 rangement is represented in Fig. 66. 
 
 
 o 
 
 1 
 
 f ! 
 
 1 
 
 
 D 
 
 i 
 
 3 B 
 
 r 
 
 
 Jcl 
 
 
 
 E 
 
 j 
 
 3 
 
 
 
 ft* 
 
 
 FIG. 66. TRIPHASE THREE- WIRE SYSTEM. 
 
 Fig. 67, shows a form of triphaser having 
 40 poles and capable of maintaining an 
 activity of 500 KW; 166 2/3 KW in each 
 of its three circuits. The pressure is 500 
 volts between each pair of terminals. The 
 armature is driven at 108 revolutions per 
 minute. The frequency is 36 ~ per sec- 
 ond. The dimensions of this machine are 
 
THE TRANSMISSION OF POWER. 269 
 
 FIG. 67. THREE-PHASE ALTERNATOR, 40 POLES, 500 KW, 
 
270 THE ELECTRIC MOTOR. 
 
 107" x 213" and its height 150". The 
 total weight is 108,000 pounds, or about 
 216 pounds per KW of output. The 
 armature has three separate windings in 
 which tri phase E. M. Fs. are developed. 
 The three main leads are shown in the 
 figure. 
 
 Fig. 68, shows another form of belt- 
 driven triphaser, having 10 poles and mak- 
 ing 600 revolutions per minute. The 
 frequency is 50 ~ per second, the activity 
 250 KW; or, 83 1/3 KW, in each cir- 
 cuit. This machine is seen to be sepa- 
 rately excited. Its weight is about 30,000 
 pounds, or 120 pounds per KW. 
 
 Another type of multiphase system is 
 the monocydic system. This system has 
 been designed for use in central stations 
 where the main load is that of lighting, 
 
272 THE ELECTRIC MOTOR AND 
 
 but where alternating-current motors re- 
 quire to be operated from the circuit. The 
 armature is wound with two sets of coils, 
 one constituting the main winding, which 
 corresponds to that of an ordinary uni- 
 phaser, while the second winding is of 
 smaller cross-section and fewer turns, and 
 is connected to the centre of the main 
 winding as shown in Fig. 69, at A, where 
 a o b, represents the main armature wind- 
 ing, and o c, the short coil or teaser winding. 
 Three terminals are thus led out from the 
 the armature at a, b and c. The terminals 
 a and J, connected by means of collector 
 rings and brushes to the external circuit, 
 constitute the lighting circuit, while a 
 third wire from <?, enables an alternating- 
 current motor to be operated in conjunction 
 with the other two. The windings are so 
 arranged that the E. M. F. in C I), is in 
 diphase relation to that in A B, as rep- 
 
m. J 
 
 resented diagrammaticallyNtt;', jn Fig. 
 69, the loop a o b, being woiilid on the 
 drum at right angles to the half loop o c. 
 
 FIG. 69. DIAGRAMS OF MONOCYCLIC ARMATURE WINDING. 
 
 A inonocydw armature is represented in 
 Fig. 70. A, B and C\ are the three col- 
 
 FIG. 70. MONOCYCLIC ARMATURE. 
 
 lector rings, forming the main terminals 
 of the armature. The windings are just 
 
274 THE ELECTRIC MOTOK AND 
 
 visible in the slots left between the teeth 
 or iron armature projections. The shape 
 of the coils is represented in Fig. 71. The 
 main coils are flat, while the teaser coils 
 
 FIG. 71. MAIN AND TEASER COILS. 
 
 are bent in such a manner as to permit 
 them to be laid across the main coils in a 
 midway position, so as to generate their 
 E. M. Fs. a quarter cycle out of step with 
 those in the main coils. 
 
THE TRANSMISSION OF POWER. 275 
 
 A form of 'monocyclic alternator is rep- 
 resented in Fig. 72. This is a 120 KW 
 
 FIG. 72. MONOCYCLIC ALTERNATOR, 40 POLES, 120 KW. 
 
 machine, wound for 60 ~ per second, and 
 a pressure of 1,1 50, 2,300 or 3,450 volts 
 between the main terminals, according to 
 
276 THE ELECTRIC MOTOR. 
 
 requirements. This machine weighs about 
 15,000 pounds or 125 pounds per KW. 
 
 The connections for use with a mono- 
 cyclic system are shown in Fig. 73. Here 
 the generator terminals A and J3, are con- 
 nected with the mains for lighting. T^ 
 represents a step-down transformer whose 
 primary terminals P^ and P^ are con- 
 nected to the mains A and B, respec- 
 tively, at a pressure, of say 2,200 volts. 
 The secondary terminals s iy s 2 and s 3 , of 
 this transformer constitute a Uniphase 
 three-wire system, having 220 volts be- 
 tween Si or .<? 3 or 110 volts between s^ and 
 S 2 ; and 110 volts between s 2 and s 3 , with- 
 out any difference in phase. This is ob- 
 tained by dividing the secondary coil into 
 halves. The secondary circuit is connected 
 with lamps on each side of the three-wire 
 system as shown. T, is a step-down trans- 
 
278 THE ELECTRIC MOTOR AND 
 
 former, transforming from 2,200 to say, 
 50 volts, for operating two arc lamps in 
 parallel. The primary terminals of this 
 transformer are connected to the main 
 leads A and B. r l\, is a transformer 
 whose primary terminals are also con- 
 nected with A and B, while the sec- 
 ondary coil in this case, having a single 
 pair of terminals, is connected directly 
 with incandescent lamps, and also with 
 a small fan motor, which being of small 
 size can be operated without the use of 
 multiphase currents. T 6 , is also a uni- 
 phase transformer connected with the pri- 
 mary mains A. and B, and feeding in its 
 secondary circuit 110- volt lamps, as well as 
 two arc lamps through a compensator. 
 
 Hitherto we have simply examined the 
 devices which have been operated from 
 the mains A and B, without the use of 
 
THE TRANSMISSION OF POWER. 279 
 
 the poiver wire, the dotted line connected 
 with the terminal C, and all that we have 
 yet examined might have been obtained 
 from an ordinary uniphaser. To operate 
 an induction motor, two transformers have 
 to be employed, such as 2\ and T 2 , the 
 primary terminals of one being connected 
 between A and C, and those of the other 
 between B and C. The secondary termi- 
 nals, when connected with the motor, as 
 shown, generate a system of triphase cur- 
 rents in the motor a. Similarly, the two 
 transformers T 7 and T 8 , one connected 
 with its primary terminals between A and 
 B, and the other transformer connected 
 with its terminals between O, and the 
 centre of the primary in T 8 , produce in 
 their secondary circuits a system of tri- 
 phase E. M. Fs. and currents, capable of 
 operating the induction motor as well as 
 the incandescent lamps. 
 
280 THE ELECTRIC MOTOR AND 
 
 A monocyder, therefore, produces a uni- 
 phase main E. M. F. in its main circuit, 
 which is employed for all uniphase pur- 
 poses, such as lighting, or for the operation 
 of synchronous motors. It also generates 
 in a subsidiary, or auxiliary coil, an 
 E. M. F. in diphase relation with the main 
 E. M. F. and, by combining these two 
 diphase E. M. Fs. through the connec- 
 tion of the third wire, triphase E. M. Fs. 
 can be produced in the secondary circuits 
 of suitably connected transformers. 
 
 Fig. 74, shows the connections employed 
 for the distributing circuit of a triphaser. 
 Here any pair of conductors may be re- 
 garded as an independent uniphase circuit, 
 from which step-down transformers for 
 uniphase work may be operated. Thus 
 TI, T 2 and T 3 are step-down transformers, 
 each connected with one pair of high-pres- 
 
THE TRANSMISSION OF POWER. 
 
 281 
 
 sure wires. A pair of transformers, how- 
 ever, operated from any two of the three, 
 as shown at ^ and 3 , will produce in their 
 secondary circuits, when united in the 
 manner represented, a triphase system of 
 
 FIG. 74. CONNECTIONS OF TRIPHASE SYSTEM. 
 
 E. M. Fs. and currents suitable for operat- 
 ing a triphase alternating-current motor 
 MI, but three transformers may also be 
 employed, each connected across a pair of 
 high-pressure wires as shown at t a , t and 
 t s . Their secondary circuits are connected 
 
282 
 
 THE ELECTRIC MOTOR AND 
 
 with the three terminals of the triphase 
 induction motor M. 
 
 Fig. 75, similarly represents the connec- 
 tions of a diphaser. Here two independ 
 
 FIG. 75. CONNECTIONS OF DIPHASE SYSTEM. 
 
 ent circuits are shown, each of which may 
 be treated as a uniphase circuit, as seen 
 at T^ and T 2 . By operating two trans- 
 formers, one from each circuit and connec- 
 ting their secondaries together, as shown 
 at ^ and t 2 , a diphase system of E. M. Fs. 
 
THE TRANSMISSION OF POWER. 283 
 
 and currents may be obtained, capable of 
 operating a diphase motor M. As already 
 pointed out three wires are theoretically 
 sufficient for the operation of this system. 
 
 The triphase system of three wires pos- 
 sesses a distinct saving in copper over an 
 ordinary Uniphase, or a diphase system, 
 for a given maximum pressure between 
 any pair of conductors and a given per- 
 centage of drop in the lines. The saving 
 in copper amounts to 25 per cent, of that 
 required for a four- wire diphase, or a two- 
 wire Uniphase system. 
 
CHAPTER X. 
 
 ROTATING MAGNETIC FIELDS. 
 
 IT now remains to explain the manner 
 in which a multiphase alternating-current 
 motor operates when its stationary, or 
 stator coils, are traversed by multiphase 
 currents. 
 
 Let us suppose that a field frame is ar- 
 ranged with four poles and four coils, as 
 shown in Fig. 76. Let coils 1 and 3, be 
 joined together in series in one circuit, and 
 coils 2 and 4, be also joined together in 
 series in another circuit ; moreover, let 
 these two circuits be connected to the two 
 windings of a diphaser ; then, when one 
 circuit has its full current strength, the 
 
 284 
 
THE TRANSMISSION OF POWER. 285 
 
 other circuit will have no current passing 
 through it. Let us suppose that at the in- 
 terval of time represented at A, Fig. 76, 
 
 FIG. 76. DIAGRAM ILLUSTRATING A ROTATING MAG- 
 NETIC FIELD. 
 
 coils 1 and 3, are receiving a wave of cur- 
 rent which produces a north pole at 1, and 
 a south pole at 3. At this instant there 
 will be no current in the coils 2 and 4. A 
 
286 THE ELECTRIC MOTOR AND 
 
 small compass needle, pivoted at the centre 
 of the field frame, would, therefore, point 
 to pole 3. 
 
 Next suppose, that a quarter cycle 
 elapses, as at B / then the current in the 
 coils 1 and 3, will have disappeared, and 
 the current in 2 and 4, will have attained 
 its maximum strength. Under these con- 
 ditions, a north pole will be developed at 
 4, and a south pole at 2, so that the com- 
 pass needle will have to rotate through 
 90, and will now point to 2. Again, at 
 the next quarter cycle represented at (7, 
 the current in 2 and 4, will have died 
 away, but the current in 1 and 3, will 
 have the opposite direction to that at A ; 
 that is to say, if A, represents the effect of 
 the positive wave (7, represents the effect 
 of the negative wave. A north pole will, 
 therefore, be formed at 3, and a south pole 
 
THE TRANSMISSION OP POWER. 287 
 
 at 1 . The compass needle will, therefore 
 be rotated to 1, having described 180. 
 Again, Z>, represents the condition at the 
 next quarter cycle, when the current flows 
 through 2 and 4, producing a north pole 
 at 2, and a south pole at 4. The needle 
 will now be pointing to 4, and will have 
 rotated through 270. Finally, after a 
 complete cycle has elapsed the condition 
 at A, will be reproduced, when the needle 
 will have completed a revolution. It is 
 evident that the effect of the diphase cur- 
 rents in the field frame has been to pro- 
 duce a rotation of the magnetism of the 
 field, in obedience to which the compass 
 needle rotates once to each complete cycle. 
 
 If the frequency in the circuits be, say 
 50 cycles per second, the compass needle 
 may be expected to make 50 complete 
 revolutions per second, and would consti- 
 
288 THE ELECTRIC MOTOR AND 
 
 tute a diminutive moving part or rotor. 
 We have explained the successive steps of 
 this rotating field that occur in Fig. 76, on 
 the supposition that they take place in 
 positions 90 apart. In practice, however, 
 motors are frequently so constructed that 
 the magnetic field rotates almost uniformly 
 around the frame, instead of by jumps. 
 
 The motor constituted by the field frame 
 and the rotating compass needle would ob- 
 viously be very feeble. Magnetic action, 
 however, may be intensified in various 
 ways, either by employing a larger or more 
 powerful compass needle, such, for ex- 
 ample, as a suitably pivoted electromagnet, 
 or, by employing a mass of iron for the 
 rotating part, wound with coils of wire 
 forming closed circuits, so that the moving 
 or rotating magnetic field may induce in 
 these coils powerful currents, whose mag- 
 
THE TRANSMISSION OF POWER. 289 
 
 netic flux will be attracted by the rotating 
 field, thus turning the armature around. 
 
 There are thus two classes of multiphase 
 motors, both of which employ a rotating 
 field. In one class the rotating field acts 
 upon a magnetized armature, which, after 
 being set in rotation, keeps in step or in 
 synchronism with the rotating field. In 
 the other class, the rotating field acts so as 
 to induce currents in the armature by the 
 difference of speed between the rotating 
 field and the rotating armature, so that the 
 armature never quite attains the speed of 
 the field, and lags behind it by an amount 
 sometimes called the slip, which depends 
 upon the torque or load. The first class 
 embraces what are called synchronous mul- 
 tiphase motors ; the second class, are called 
 induction multiphase motors, or simply 
 induction motors. 
 
290 THE ELECTRIC MOTOR AND 
 
 There is a marked difference between 
 synchronous multiphase motors and syn- 
 chronous Uniphase motors. The latter are 
 incapable of starting under ordinary practi- 
 cal conditions, since the magnetic field pro- 
 duced by a Uniphase current does not 
 rotate, but merely oscillates to-and-fro. 
 The former are so designed as to be capa- 
 ble of self-starting, owing to the influence 
 of the rotating magnetic field, which pulls 
 the armature around with it. If one of 
 the diphase circuits of the field frame be re- 
 versed it will be found that the effect is to 
 reverse the direction of rotation of the field 
 and, therefore, the direction of rotation of 
 the armature. 
 
 Fig. 77 represents diagram rnatically the 
 action of a triphase rotating field. Here 
 six poles 1, 2, 3, 4, 5 and 6, are represented, 
 with their coils so arranged that 1 and 4, are 
 
THE TRANSMISSION 
 
 in series in one circuit, and u 2 and 5, i$fsoO, ^ 
 series in the second circuit, and 3 and 6, in 
 series in the third circuit. Six conditions 
 
 & DIESEL /,'; 
 
 PROPERTY ( 
 
 291 
 
 FIG. 77. DIAGRAM OP TRIPHASE ROTATING FIELD. 
 
 are represented at A, B, C, D, E, and F, 
 during successive sixths of one complete 
 cycle. At A, the compass needle is shown 
 
292 THE ELECTRIC MOTOR AND 
 
 pointing to pole 1, the current being a 
 maximum in coils 1 and 4. At B, the 
 needle is shifted to pole 6, the current 
 being now a maximum in coils 3 and 6. 
 Similarly, at each successive sixth of a 
 period, the needle will have shifted around 
 one-sixth of the revolution as the current 
 successively rises and falls in different cir- 
 cuits. It will be seen that the difference 
 between a diphase field frame, and a 
 triphase field frame, consists in the number 
 and arrangement of the coils, but that the 
 effect is otherwise the same, the result of 
 combining the effects of successive current 
 waves being to produce a rotary magnet- 
 ism. The armature, as before, may be of 
 the synchronous, or of the induction type. 
 It will be readily understood that Fig. 7V 
 is diagrammatic only. The actual rotation 
 of the field being usually obtained by a 
 somewhat different winding. 
 
THE TRANSMISSION OF POWER. 293 
 
 A synchronous multiphase motor has 
 the same speed at all loads. If overloaded 
 it will come to rest, but will start again 
 from rest when the load is removed. An 
 induction motor will very nearly reach the 
 full rotary speed of the field at light load, 
 but will be retarded, or will slip, as already 
 mentioned, at full load. The amount of 
 slip is comparatively small, being only 
 about 3 per cent, in large motors, and 
 about 5 per cent, in small motors. Induc- 
 tion motors may be designed which will 
 start from rest under a very powerful 
 torque. It is usually necessary, especially 
 with large motors, to insert resistances into 
 the armature circuit at starting, in order to 
 check the very powerful currents which 
 tend to be developed in them when started 
 from rest ; for, since the E. M. Fs. induced 
 in the armature are proportional to the 
 difference in speed between the armature 
 
294 THE ELECTRIC MOTOR AND 
 
 and the rotary field, it is evident that when 
 just starting this difference of speed will 
 be a maximum, and the current will 
 be very powerful, producing reactionary 
 effects that are disadvantageous. The 
 effect of inserting resistance in the arma- 
 ture circuit is to check the strength of 
 these currents and so improve the starting 
 torque of the motor. 
 
 A form of tri phase motor, of 15-horse- 
 power capacity, is represented in Fig. 78. 
 The three main terminals are seen at A, B, 
 and C. The field frame F, is of laminated 
 iron. W, is a portion of the field winding. 
 The lever Z, is provided for the purpose of 
 starting the motor effectively. When the 
 lever is in the position shown, resistances 
 are left in the armature circuit as above 
 described, so as to obtain, when starting, a 
 more powerful and less wasteful torque, 
 
THE TRANSMISSION OF POWER. 
 
 295 
 
 and a reduced current in the armature 
 coils, which are hidden from view. As 
 soon as the armature has come up to speed, 
 
 FIG. 78. MULTIPHASE INDUCTION MOTOR. 
 
 the lever Z, is pushed in toward the arma- 
 ture, thereby bringing a metal collar into 
 contact with the strips S, thus short-circuit- 
 ing the resistance, and improving the action 
 of the motor for full speed. In order to 
 
296 
 
 THE ELECT RfC MOTOR AND 
 
 reverse the direction of motion of the 
 armature, it is sufficient to reverse any pair 
 
 FIG. 79. HOIST, WITH 10 KILOWATT MULTIPHASE MOTOR. 
 
 of wires on the terminals A, B and G. 
 This has the effect of reversing the direc- 
 tion of the rotating field. By examining 
 
THE TRANSMISSION OF POWER. 297 
 
 the figure, it will be seen that the dimen- 
 sions of this motor are relatively very 
 small as indicated by the foot rule that lies 
 extended at its base. 
 
 In Fig. 79, a 10 KW triphase motor M, 
 is shown, connected to a hoist. Here F, is 
 the field winding, and A, the winding on 
 the rotating armature. 
 
 A marked advantage possessed by mul- 
 tiphase motors, either of the diphase or 
 triphase type, lies in their simplicity. 
 They require no commutator, and their 
 winding is of a very simple descrip- 
 tion. They are compact and require the 
 minimum amount of attention. These 
 facts, taken in connection with the facility 
 of transforming alternating-current pres- 
 sures, have given a great impetus to the 
 manufacture and use of multiphase motors. 
 
THE TRANSMISSION OF POWEK. 299 
 
 Fig. 80 shows a form of tripliase motor 
 suitable for driving line shafting. It is 
 secured in an inverted position to a ceiling 
 or elevated beam. 
 
 The multiphase motor is sometimes used 
 as a starter for a large Uniphase syn- 
 chronous motor. Fig. 81 represents such 
 an arrangement. Here the diphase motor 
 M, is capable of being moved forward on 
 its base by the wheel H, so that its pulley 
 , engages by friction with the pulley R, of 
 the large synchronous motor S. This is 
 done in order to bring the large synchronous 
 motor up to, or slightly in excess of, its syn- 
 chronizing speed. As soon as this speed 
 has been attained, the circuit of the uni- 
 phase motor is closed, enabling it to be 
 operated from that circuit and to absorb 
 energy from the generator at the transmit- 
 ting end of the line. The friction clutch (7, 
 
THE TRANSMISSION OF POWEK. 301 
 
 is then operated to connect the pulley P, 
 and its load with the synchronous motor, 
 which torque can now be taken by the 
 motor without its falling out of synchron- 
 ism. The diphase motor M, is then with- 
 drawn and stopped. 
 
CHAPTER XL 
 
 ALTERNATING-CURRENT TRANSMISSIONS. 
 
 As we have already pointed out, 
 economy in electric transmission necessi- 
 tates the use of high pressure in the line 
 when the distance between generating and 
 receiving station is great, and that con- 
 siderable practical difficulty exists in 
 obtaining continuous-current translating 
 devices which may be operated by it. 
 
 The use of alternating currents for the 
 transmission of power obviates the diffi- 
 culty as regards high-pressure translating 
 devices, since by means of the alternat- 
 ing-current transformer, the high pressure 
 
THE TRANSMISSION OF POWER. 303 
 
 on the line can readily be transformed at 
 the generator and motor to any desired 
 low pressure. 
 
 Alternating-current systems of transmis- 
 sion may be classified as Uniphase or multi- 
 phase. The use of any uniphase power 
 system is open, however, to the objection 
 that, as yet, no electric motor of any con- 
 siderable size has been designed, which 
 will start from rest when directly con- 
 nected with such circuit. For this reason 
 the tendency of recent engineering prac- 
 tice has been towards multiphase trans- 
 mission systems. 
 
 In order to compare the relative advan- 
 tages of economy between uniphase and 
 multiphase systems, so far as relates to the 
 weight of the conductors employed, some 
 common criterion must be adopted as 
 
304 THE ELECTRIC MOTOR AND 
 
 a basis of comparison. It is obvious, if a 
 given weight of copper be employed in a 
 Uniphase system of transmission, at a pres- 
 sure of say 4,000 volts, that it would be 
 possible to reduce this weight of copper 
 either on a uniphase or a multiphase system 
 by employing a higher pressure. Conse- 
 quently, the basis of comparison must be a 
 given maximum effective pressure. This 
 maximum permissible pressure might be 
 measured between any wire in the system 
 and the ground, or, between any pair of 
 conductors independently of the ground. 
 The latter is usually the basis of compari- 
 son, since, when circuit wires are buried 
 side by side in a conduit, or are suspended 
 side by side from poles, it is the insulation 
 between these wires which determines the 
 electric security of the system and this in- 
 sulation is not from a practical standpoint 
 to be regarded as the mere number of ohms, 
 
THE TRANSMISSION OF POWER. 305 
 
 or megohms, existing between the con- 
 ductors, but in their latent capability of 
 maintaining this degree of insulation under 
 all normal circumstances. 
 
 Let us suppose that the maximum per- 
 missible pressure between any pair of wires 
 
 FIG. 82. UNIPHASE CIRCUIT. 
 
 is fixed at 10,000 volts effective, as indicated 
 by a voltmeter connected between them; 
 then the uniphase system would have 
 10,000 volts between its single pair of 
 wires, as shown in Fig. 82, where G, is the 
 generator, M y the motor and 1 1 and 2 2, the 
 wires. A four-wire diphase system would 
 have 10,000 volts between the wires of each 
 circuit, as shown in Fig. 83. The three- 
 
306 THE ELECTRIC MOTOR AND 
 
 wire diphase system would have 10,000 
 volts between the outside wires and 7,070 
 
 5 
 
 f 
 
 1 
 
 < 
 
 A 
 
 i 
 
 Q,| 
 
 1 
 
 4 
 
 2 
 
 V 
 
 2l 
 
 
 4 4 
 
 FIG. 83. FOUR- WIRE DIPHASE CIRCUIT. 
 
 volts between neighboring wires, as shown 
 in Fig. 84, and a triphase system would 
 
 3 3 
 
 FIG. 84. THREE-WIRE DIPHASE SYSTEM. 
 
 have 10,000 volts between any two of the 
 three wires, as shown in Fig. 85. Under 
 
THE TRANSMISSION OF POWER. 307 
 
 these conditions the Uniphase, and the in- 
 dependent-circuit dipkase or, the four-wire 
 dipkase, possess the same relative economy 
 in conductors. The triphase system, how- 
 ever, requires 25 per cent, less copper, 
 altogether, than either the uniphase, or the 
 
 FIG. 85. TRIPHASE SYSTEM. 
 
 independent-circuit diphase, while the inter- 
 linked, or three-wire dipliase, requires 45 per 
 cent, more copper than the uniphase, on 
 the basis of Fig. 84, since when the maxi- 
 mum effective pressure is reached between 
 wires 1 and 3, the working pressure is only 
 7,070 volts. If the pressure between out- 
 side conductors could be neglected, and 
 
308 THE ELECTRIC MOTOR AND 
 
 10,000 volts retained between working 
 wires, then the three-wire diphase would 
 save 27 per cent, in copper over either the 
 uniphase, or the four-wire diphase, and 
 
 FIG. 86. STAR CONNECTION. 
 
 thus slightly exceed the triphase system 
 in economy. 
 
 There are two methods of connecting 
 the circuits of a triphase system; namely, 
 the star method, and the triangle method. 
 
THE TRANSMISSION OF POWER. 309 
 
 These are illustrated in Figs. 86 and 87, 
 respectively. Both methods have been 
 used. The E. M. Fs. in each branch differ 
 in phase by l/3rd cycle, in each case. 
 
 D E 
 
 FIG. 87. TRIANGLE OR DELTA CONNECTION. 
 
 The connections employed for step-up 
 and step-down transformers, at each end of 
 a transmission line, are outlined in Figs. 88 
 and 89, where Fig. 88 indicates a uniphase 
 and Fig. 89 the triphase system. Here the 
 pressure generated by the alternator and 
 
310 
 
 THE ELECTRIC MOTOR AND 
 
 motor may be, say 1,000 volts, while tliat 
 on the line may be 10,000 volts. Ob- 
 
 FIG. 88. STEP-UP AND STEP-DOWN TRANSFORMERS 
 WITH UNIPHASE SYSTEM. 
 
 viously, however, the pressure between the 
 line terminals, at the step-up transformer, 
 
 FIG. 89. STEP-UP AND STEP-DOWN TRANSFORMERS OF 
 TRIPHASE TRANSMISSION SYSTEM. 
 
 will be greater than the pressure at the line 
 terminals at the receiving end, owing to 
 the drop in the line. 
 
THE TRANSMISSION OF POWER. 311 
 
 No better illustration can be given of 
 methods of alternating-current power trans- 
 mission than that afforded by the system 
 now in operation at Niagara Falls. Here 
 energy, taken by turbines from water fall- 
 ing through a vertical shaft, is delivered 
 to alternating-current circuits for transmis- 
 sion. 
 
 In the case of a powerful stream like 
 Niagara, since it would be impossible to 
 set a wheel at the foot of the falls, tur- 
 bines are placed at the bottom of a pit 
 178 feet deep, situated a mile and a half 
 up the river. The water that falls 
 through the penstocks is discharged 
 through a tunnel at the foot of the falls. 
 The total available capacity of the tunnel 
 is about 100,000 horse-power. 
 
 The capacity of each turbine is 5,000 
 
QQ 
 
 rfl 
 
 a 
 
 SI 
 
 
THE TRANSMISSION 
 
 horse-power at the 
 Consequently, it would be necessary to 
 install 20 turbines in all in order to utilize 
 the full capacity of the tunnel. Fig. 90 
 gives a bird's-eye view of the arrangement 
 with the wheel pit and tunnel in section. 
 Fig. 91, shows the short canal leading in 
 from the river, and feeding the various 
 wheels through their separate penstocks. 
 P P P, is the penstock, or vertical iron 
 feed water pipe through which the water 
 falls on to the turbine. T, is the turbine, 
 R R, the tail race, that is a large exit 
 pipe through which the water passes to 
 the tunnel after leaving the turbine. The 
 tunnel is 7,250 feet long, 14 to 18 feet 
 wide, and 21 feet in height, its gradient 
 being about 1 in 150. Since a part of the 
 tunnel passes under the city of Niagara it 
 was necessary to prevent all possibility of 
 eroding the walls. In order to effect this, 
 
314 
 
 THE ELECTRIC MOTOR AND 
 
 the entire tunnel 
 was lined with vit- 
 rified brick, and 
 about 13 millions 
 of bricks were used 
 for this purpose. 
 8, S, is the turbine 
 shaft, which drives 
 the generator 6r, in 
 the power house 
 above. 
 
 An inspection of 
 Fig. 92 will show 
 in greater detail 
 
 
 K 
 
 FIG. 91. WHEEL PIT. 
 
THE TRANSMISSION OF POWER. 
 
 315 
 
 the manner in which the lower end 
 of the penstock delivers its \vater to 
 the turbine wheel. After falling through 
 
 FIG. 92. ONE OF THE NIAGARA POWER COMPANY'S 5,000 
 HP TURBINES DESIGNED BY FAESCH <fe PICCARD, 
 GENEVA, SWITZERLAND. BUILT BY THE I. P. MORRIS 
 COMPANY, PHILADELPHIA, PA. 
 
 the vertical pipe P, P, of Fig. 91, it 
 passes through the inclined pipe P, P, 
 at the lower part of the penstock, entering 
 the body of the turbine at r l] and is dis- 
 
316 
 
 THE ELECTRIC MOTOR AND 
 
 charged therefrom into the tail race below. 
 The vertical axis of the shaft of the tur- 
 
 FIG. 93. SECTION OF THE TUHBINE. 
 
 bine AS; passes upwards to the generator, as 
 shown more completely in Fig. 91. 
 
THE TRANSMISSION OF POWER. 317 
 
 A vertical section to the parts shown in 
 Fig. 92, is given in Fig. 93, together with 
 the upper portion of the penstock and 
 turbine shaft. In this figure the same 
 letters refer to the same parts. 
 
 Coming to the top of the turbine shaft, 
 we find the generator which it drives. In 
 this form of generator it is the field mag- 
 nets which move, the armature remaining 
 at rest. The armature is shown in Fig. 
 94. A, A, is the Gramme-ring diphase 
 armature of the iron-clad type, resting 
 upon the pedestal JP, and having 187 slots 
 cut in its surface in which the conductors 
 are placed. There are two conductors in 
 each slot, each conductor formed of a 
 copper bar 1.34" X 0.44" in cross-section. 
 The winding of the armature is in two 
 separate circuits, so arranged that the 
 alternating E. M. F. is generated one 
 
318 
 
 THE ELECTRIC MOTOR AND 
 
 quarter of a wave apart in the two cir- 
 cuits, so that the two E. M. Fs. are in 
 diphase relationship. 
 
 FIG. 94. ONE OF THE 5,000 HP ARMATURES. 
 
 The revolving field ring, with its 12 
 poles, is represented separately in Fig. 95. 
 The poles N, /#, are of soft steel, rigidly 
 
THE TRANSMISSION OF POWER. 319 
 
 bolted on the interior of the solid nickel 
 steel ring, and the field spools are repre- 
 sented in position. These field coils are 
 wound on brass spools and are all perma- 
 
 FIG. 95. FIELD RING WITH POLES AND BOBBINS IN PLACE. 
 
 nently excited by a continuous current 
 from a separate generator. The field ring 
 is 11' 7" in diameter, and revolves at 250 
 revolutions per minute. The cover of the 
 field ring is shown in an inverted position 
 
320 THE ELECTRIC MOTOR AND 
 
 in Fig. 96. A, A, A, are ventilating aper- 
 tures in the cover, intended to draw in 
 cool air for the ventilation of the armature 
 during rotation, while C, is a central aper- 
 ture for the reception of the turbine shaft. 
 
 FIG. 96. THE DRIVER FOR THE FIELD RING. 
 
 Since the field magnets revolve around 
 the fixed armature, it is necessary to 
 firmly attach the field to the shaft. This 
 is effected by means of the cover just de- 
 scribed. A completed machine is repre- 
 sented in position in Fig. 97. 
 
 A vertical cross-section of the machine 
 
THE TRANSMISSION OF POWER. 
 
 321 
 
 tli rough the axis of the shaft is shown in 
 Fig. 98. s, ,y, $, is the turbine shaft to the 
 top of which is firmly secured the moving 
 
 FIG. 97. THE FIRST GENERATOR IN POSITION IN THE 
 POWER HOUSE AT NIAGARA. 
 
 field ring F. H., through the driver D. 
 The poles p, p, have their coils excited by 
 current supplied through the collector rings 
 
322 THE ELECTRIC MOTOR AND 
 
 $ Brushes, not shown in the figure, rest 
 on these rings, supported on the brush 
 
 FIG. 98. VERTICAL SECTION OP ONE OF THE 5,000 HP 
 GENERATORS. 
 
 holder bars b, b, attached to the platform 
 over the machine. The current is supplied 
 
THE TRANSMISSION OF POWER. 323 
 
 to these brush holders through conductors 
 6r, leading to an independent generator at 
 175 volts pressure, a, a, is the fixed 
 armature ring supported on the cast-iron 
 base B. 
 
 The electric connections necessary for 
 the local and long distance distribution of 
 power are represented in Fig. 99, for two 
 5,000 horse-power generators. The pres- 
 sure supplied by the alternators in each of 
 their two separate diphase circuits is from 
 2,000 to 2,400 volts, according to require- 
 ments. The two generators are indicated 
 at 1 and 2. Their four wires are led to 
 separate switches 8 and S". Each switch 
 is arranged so that it can either be discon- 
 nected altogether, as shown in the diagram, 
 or can make connection between the gener- 
 ator and either of the sets of bus-bars A 
 and B. Thus, if the switch be thrown on 
 
324 
 
 THE ELECTRIC MOTOR AND 
 
 one side, it will connect the four generator 
 wires to the four bus-bar wires A, while 
 
 FIG. 99. DIAGRAM SHOWING THE CONNECTIONS OF 
 THE GENERATORS WITH LOCAL AND LONG DISTANCE 
 FEEDERS. 
 
 if it be thrown on the other side, it will 
 connect the generator wires to the four 
 bus-bar wires B. 
 
THE TRANSMISSION OF POWEK. 325 
 
 The two sets of bus-bars are arranged so 
 as to enable the two separate generators 
 to be employed independently ; one, for ex- 
 ample, to supply local distribution, and the 
 other, to supply long distance distribution. 
 The switch 8' 8', in the centre of the figure, 
 enables connection to be made between the 
 long distance wires Z, and the bus-bars B, 
 or the local circuit wires L, L', and the bus- 
 bars A. For local distribution, a pressure 
 of 2,000 volts is sufficient without the inter- 
 vention of any step-up transformers ; but 
 for long distance transmission, as, for 
 example, to Buffalo, the step-up trans- 
 formers T, T', would be employed. These 
 are so arranged, that when connected in 
 
 o ' 
 
 the proper manner, having their pri- 
 maries supplied by diphase currents, their 
 secondaries will generate tri phase currents. 
 The three long-distance mains are rep- 
 resented on the secondary side. This 
 
326 THE ELECTRIC MOTOR AND 
 
 FIG. 100. THE INTERNAL CONSTRUCTION OF A LARGE 
 STATIC TRANSFORMER. THIS TRANSFORMER REDUCES 
 THE PRESSURE OF THE TWO-PHASE ALTERNATING 
 CURRENT FROM 2,400 TO 200 VOLTS. 
 
 transfer from the diphase to the triphase 
 system is introduced for the purpose of 
 saving copper in the line transmission. 
 
THE TRANSMISSION OF POWER. 327 
 
 FIG. 101. 1,000 HP TRANSFORMER. 
 
328 THE ELECTRIC MOTOR. 
 
 Fig. 100, shows the internal parts of a 
 large 1,000 horse-power transformer, in- 
 tended for the reduction of pressure from 
 2,200 to 200 volts, but it would, of course, 
 be possible to employ similar transformers 
 for raising the pressure, the secondary 
 windings then being altered. This trans- 
 former belongs to the type of oil-cooled 
 transformers. It is set in an iron case, 
 represented in Fig. 101, through which oil 
 is pumped. 
 
 An excellent illustration of the capa- 
 bilities of long-distance alternating-current 
 transmission is seen in Fig. 102. Here the 
 power station, which might be a station like 
 that at Niagara Falls, is represented in the 
 lower, left-hand corner, with triphasers 
 driven by water-wheels and supplying a 
 pressure of 2,000 volts. The pressure is 
 raised to 10,000 volts by means of three 
 

 
 !,; 
 
 
 
 ill 
 
 
 { 
 
 o w 
 
 
 3 S 
 
 ~ DD 
 
 14 
 
 H 
 
 ^ r 
 
 > *~* 
 
 
 5 
 
 
 0! $ 
 
 
 ^ ^ 
 
 L 
 
 i ^ 
 
 S 
 
 3 H 
 P 
 
 
 > s 
 
 
 ^ ^3 
 
 
 a w 
 
 
 3 
 
 
 33 * 
 
 
 2? 
 
 
 
 
 
 13 
 
 
 ^ 3 
 
 
 hi 
 
 
 aj 
 
 
 o 
 
 
 a 
 
 
330 
 
 THE ELECTRIC MOTOR AND 
 
 step-up transformers, and is transmitted 
 through the three long-distance wires to 
 the receiving station, where it is reduced 
 
 FIG. 103. A TYPICAL ALTERNATING-CURRENT INDUCTION 
 MOTOR OF 125 HP. 
 
 through step-down transformers to a pres- 
 sure of 310 volts, in a circuit intended for 
 street railway power transmission, and to 
 2,000 volts, in another circuit intended for 
 
THE TRANSMISSION OF POWER. 331 
 
 city distribution. The 3 10- volt triphase- 
 circuit is led to a rotary converter / i. e., a 
 triphase motor carrying a commutator upon 
 which brushes rest in such a manner that 
 as the motor armature revolves, the alter- 
 nating current received at the collector 
 rings on one side is redistributed through 
 the commutator as a continuous current 
 of 500 volts pressure on the other, which 
 pressure is conveyed to the street railway 
 mains. The 2,000-volt secondary circuits 
 are carried through the city, and are either 
 employed to drive triphase motors of the 
 synchronous or non-synchronous type, or 
 through local transformers to distribute 
 light and power in 110-volt triphase or 
 Uniphase circuits. 
 
 A form of triphase motor of 125 horse- 
 power, or about 94 KW, is represented in 
 Fig. 103. Here the current is supplied 
 
332 
 
 THE ELECTRIC MOTOR AND 
 
 through three terminals at the top of the 
 field frame. The armature carries a collar 
 which is so arranged that when disengaged 
 
 FIG. 104. A 250-HP THREE-PHASE ALTERNATING- 
 CURRENT MOTOR. 
 
 from its receptacle, a certain resistance is 
 inserted in the armature circuit, but when 
 the motor has attained full speed, the collar 
 
THE TRANSMISSION OF POWER. 333 
 
 is thrown into its receptacle by the use of 
 the projecting handle at the side, when 
 this resistance is cut out of the armature 
 circuit. 
 
 Fig. 104, represents a form of more 
 powerful tri phase motor, being adapted 
 to supply 250 HP, or about 188 KW. 
 Here the current is supplied through 
 the three collector rings of the rotat- 
 ing portion or rotor. This produces 
 a rotating field in the armature, under 
 the action of which the armature attracts 
 the field frame and is set in rotation. 
 After the armature has reached full 
 speed the machine acts as a synchronous 
 motor in step with the triphase impulses 
 received on the line. 
 
 If the motor were a uniphase machine, it 
 would not be able to start itself from a 
 
334 THE ELECTRIC MOTOR. 
 
 state of rest, but once brought to full 
 speed it would also be able to run in 
 synchronism, although it would, probably, 
 be more easily thrown out of step by a 
 sadden variation of load. 
 
 The torque which a multiphase ; that is, 
 of a diphase or triphase induction motor, 
 can exert at starting; i. e., its starting 
 torque, is often considerably greater than 
 the torque which it will have to exert 
 when running at full speed under full load. 
 The starting torque of a multiphase syn- 
 chronous motor is usually much less than 
 its full load torque, but its power factor 
 at full load is greater than that of an 
 induction motor. This is often an advan- 
 tage to the alternating-current distributing 
 system. 
 
CHAPTER XII. 
 
 MISCELLANEOUS APPLICATIONS OF ELECTRIC 
 MOTORS. 
 
 ONE of the principal advantages of the 
 electric motor is the ease with which it 
 can be directly applied to machinery. It 
 has been customary, in large machine 
 shops, to employ long lines of shafting, 
 receiving power from an engine or other 
 prime mover, and transmitting this power 
 to the driving pulleys of machines, either 
 directly, or through the intervention of 
 counter-shafts. The use of the electric 
 motor enables each machine to be operated 
 independently of all the others, thus 
 avoiding the continuous expenditure of 
 
330 THE ELECTRIC MOTOR AND 
 
 power in overcoming the friction of line 
 shafts. Moreover, the requirements of 
 each machine as to speed and regulation 
 may be more readily dealt with by this 
 means. In some cases, where machinery 
 lias to stand at an angle with the line 
 shafting, the difficulty which would be 
 experienced in belting to the same are 
 entirely overcome. In other cases groups 
 of machines may be operated each from a 
 single motor, by the use of short lengths of 
 counter-shaft. This is known as the group 
 system. 
 
 , The number of machines to which elec- 
 tric motive power has been applied is so 
 great that space will prevent more than 
 a cursory description of them. We will, 
 therefore, select some of the more promi- 
 nent of these applications, although many 
 others will occur to the reader. 
 
THE TRANSMISSION OF POWER. 337 
 
 The application of the electric motor to 
 the driving of a screw machine is shown 
 
 FIG. 105. ELECTRIC MONITOR OR SCREW MACHINE. 
 
 in Fig. 105. Here the armature of the 
 electric motor, mounted on the lathe 
 head, is shown at A. A switch is pro- 
 
338 
 
 THE ELECTRIC MOTOll AND 
 
 vided at S, for starting the motor, which, 
 is an ordinary continuous-current machine. 
 
 Fig 106, shows the application of a con- 
 tinuous-current electric motor directly 
 
 FIG. 106. ELECTRIC PIPE CUTTING MACHINE. 
 
 coupled to a pipe cutting machine. Fig. 
 107, shows the application of a continuous- 
 current electric motor, to a punch press. 
 
THE TRANSMISSION OF POWER, 339 
 
 Here the motor is geared to the shaft of 
 the machine. 
 
 The electric motor is particularly 
 adapted for driving such machinery as is 
 used at irregular intervals, and where but 
 little power is required. Of course, under 
 these circumstances, it would not be 
 economical to install a steam engine 
 and boiler. An instance of this kind is 
 found in the driving of the bellows of 
 church organs. Water motors, formerly 
 employed for this purpose, have been 
 largely superseded by electric motors. 
 An electric motor attached to a house or 
 church organ is represented in Fig. 108. 
 M, is a small continuous-current motor, 
 belted to the pulley of the bellows 
 mechanism. A regulator 7?, is so ar- 
 ranged, that if the rate of pumping is not 
 sufficient to maintain the full wind pres- 
 
340 
 
 THE ELECTRIC MOTOR AND 
 
 sure, a resistance will be cut out of the 
 circuit and the motor will be accelerated. 
 The starting box S, is placed by the side 
 
 
 I 1*1 
 
 I ,v~ 1 
 
 FKL 107. ELECTRIC PUNCH PRESS WITH DIVIDING 
 HEAD OR INDEX. 
 
 of the keyboard, so as to permit the organ- 
 ist readily to start and stop the motor at 
 will. 
 
THE TRANSMISSION OF POWER. 341 
 
 FIG. 108. ELECTRIC MOTOR APPLIED TO ORGAN 
 BELLOWS. 
 
 The application of the electric motor to 
 the pumping of water is shown in Fig. 
 109, Here a continuous-current motor M 
 
342 THE ELECTRIC MOTOR AND 
 
 < 109. ELECTRIC MOTOR APPLIED TO PUMPING IN 
 DWELLING HOUSE. 
 
THE TRANSMISSION OF POWER. 343 
 
 operated from incandescent electric light 
 mains, is belted to the pump pulley. The 
 supply wires to the motor are led through 
 a fuse block F, to the double-pole snap 
 switch S, from which they proceed to an 
 automatic switch. This latter is provided 
 for the stopping and starting of the motor, 
 under the control of a ball float in a water 
 tank. When the water in the tank 
 reaches a certain height, the rising of the 
 ball lowers the weight and suddenly opens 
 the armature circuit. On the contrary, 
 when the water in the tank falls too low, 
 the descent of the float raises the weight, 
 and starts the motor slowly. In all such 
 cases, where motors are installed under 
 conditions where they are likely to run 
 for weeks without attention, it is advisable 
 to employ motors of as slow a speed and 
 substantial a construction as possible, so as 
 to diminish the wear and tear, and hence 
 
344 THE ELECTRIC MOTOR AND 
 
 the attention required. It is, for this 
 reason, even advisable to employ a motor 
 of more than sufficient size to do the work 
 required, since under these circumstances 
 it will run with very little effort. 
 
 The motors, above illustrated, have 
 been all of the continuous-current type. 
 It is needless to say, however, that alter- 
 nating-current motors could be employed 
 in their stead, provided that they are of 
 the multiphase type, so as to permit them 
 to start from rest. 
 
 Fig. 110 shows a Gatling gun, in which 
 an electric motor is employed for the pur- 
 pose of operating the breech mechanism. 
 The certainty and precision with which 
 the motor will introduce and release the 
 cartridges, renders this application of the 
 electric motor very advantageous. 
 
THE TRANSMISSION 
 
 The applications of the 
 for prospecting in mining districts 
 known. The electric motor provides an 
 
 FIG. 110. GATLING GUN. OPERATED BY ELECTRIC 
 MOTOR. 
 
 exceedingly convenient means for driving 
 such drills, when electric power is avail- 
 able. Their use in mining districts has 
 
346 
 
 THE ELECTRIC MOTOR AND 
 
 come into favor, owing to the fact that the 
 solid core of the rock mined is brought 
 out by this drill. Fig. Ill, shows a form 
 
 FIG. 111. ELECTRIC DIAMOND PROSPECTING DRILL. 
 
 of this machine with a continuous-current 
 electric motor applied to drive it. 
 
 Electric motors are often applied both 
 
THE TRANSMISSION OF POWER. 347 
 
 to elevators in buildings, and to hoists in 
 mines. In the latter case, the ease with 
 
 FIG. 112. THOMSON-HOUSTON PORTABLE ELECTKIC 
 HOIST. BAND CLUTCH TYPE. 
 
 which the power can be carried to different 
 parts of the mine renders the electric driv- 
 ing of such hoists very advantageous. An 
 
348 THE ELECTRIC MOTOR AND 
 
 illustration of a continuous-current motor, 
 connected with a portable electric hoist, is 
 
 FIG. 113. AN ALTERNATING-CURRENT INDUCTION 
 MOTOR GEARED TO A HOIST. 
 
 shown in Fig. 112. A similar form of 
 hoist driven by an alternating-current 
 induction motor is shown in Fig. 113, 
 
THE TRANSMISSION OF POWER. 
 
 349 
 
 In the commercial sale of electric power, 
 whether for lighting or for motive pur- 
 poses, a necessity exists for carefully 
 
 FIG. 114 1/8 HP ELECTRIC FAN. WITH WIRE GUARD 
 AND SWITCH FOR RUNNING FAST OR SLOW. 
 
 measuring the amount of supply to each 
 consumer. For this purpose a variety of 
 electric meters are employed. The electric 
 meters commonly in use employ a small 
 
350 
 
 THE ELECTRIC MOTOR AND 
 
 motor driven by the electric power, at a 
 speed proportionate to the rate of supply. 
 
 Probably there is no purpose for which 
 small powers are more required during 
 
 FIG. 115. FAN MOTOR. 
 
 certain seasons of the year, than for driving 
 rotary fans. A great variety of forms have 
 been devised, varying not only with the 
 character of the fan, but also with the posi- 
 
THE TRANSMISSION OF POWER. 351 
 
 tion in which it is located. Fan motors 
 are made to operate, both on continuous 
 and on alternating-current circuits. For 
 
 FIG. 116. FAN MOTOR BRUSHES IN DETAIL. 
 
 such small alternating-current motors mul- 
 tiphase circuits are not required. A 
 fan motor always starts with no load, be- 
 
352 
 
 THE ELECTRIC MOTOR AND 
 
 yond the friction of its own bearings, 
 but the load increases rapidly as the 
 speed increases, the activity developed 
 being, approximately, as the cube of the 
 
 FIG. 117. No. 3 FAN MOTOR. 
 
 velocity. The fan is generally attached 
 directly to the motor shaft. Fig. 114 is 
 an illustration of a continuous-current fan 
 motor, arranged for various speeds. Here, 
 
THE TRANSMISSION OF POWER. 353 
 
 as is usual where the motor is in a position 
 in which it may be touched, it is provided 
 with a wire guard. 
 
 FIG. 118. No. 1 FAN OUTFIT FOR ARC CIRCUITS 
 (CONSTANT CURRENTS). 
 
 The motor described in Fig. 114 is ex- 
 posed to view. Frequently, however, the 
 motor is inclosed in a cast-iron case, as 
 shown in Fig. 115. In such cases special 
 attention has to be paid to the brushes and 
 
354 
 
 THE ELECTRIC MOTOR AND 
 
 commutator, since they run out of view. 
 Fig. 116, shows the details of a form of 
 
 FIG. 119. CEILING FAN AND MOTOR. 
 
 brush employed in the motor of Fig. 115. 
 Here, it will be seen that carbon cylindri- 
 cal brushes are employed which are main- 
 
THE TRANSMISSION OF POWER. 355 
 
 tained in pressure upou the commutator by 
 the action of a spiral spring. 
 
 Fig. 117, shows an alternating-current 
 
 FIG. 120. No. 2 (1/4 HP) FAN OUTFIT, SET UP AS AN 
 EXHAUST. 
 
 fan motor, also enclosed. Fig. 118, shows 
 a form of fan motor intended to be oper- 
 ated on a series-arc circuit. Since the 
 pressure employed on such a circuit is 
 
356 THE ELECTRIC MOTOR AND 
 
 generally high, this motor requires to be 
 carefully insulated. 
 
 For the cooling of rooms, the fans are 
 
 FIG. 121. DIRECT-CONNECTED EXHAUST FANS AND 
 LUNDELL MOTORS. 
 
 sometimes suspended from the ceilings. 
 In this case the fan blades are driven in a 
 horizontal plane by a suitably supported 
 motor. Fior. 119, shows a form of ceiling 
 
THE TRANSMISSION OF POWER. 357 
 
 FIG. 122. ELECTRIC CAPSTANS. 
 
358 THE ELECTRIC MOTOli. 
 
 fan motor, adapted for continuous-cunvnt 
 circuits. Here the motor is placed below 
 the fau blades. 
 
 The electric motor is frequently used for 
 ventilating purposes. In Fig. 120 a motor, 
 is shown in position for driving an exhaust 
 fan. Another form of such motor is shown 
 in Fig. 121. 
 
 Fig. 122 shows the application of the 
 electric motor for driving a capstan on 
 board ship. In this particular case the 
 motor is operated on a 110-volt continuous- 
 current circuit, and has a capacity of about 
 5KW. 
 
INDEX. 
 
 Active Conductor, Circular Flux of, 84, 85. 
 Activity, 11. 
 
 of Electric Circuit, 53, 54, 55. 
 
 of Motor, 157, 158. 
 
 , Thermal, 55. 
 
 , Unit of, 11, 12. 
 
 , Wasted, 55. 
 Alternating-Current Dynamo, 257, 258. 
 
 Current Motors, 241 to 283. 
 
 Current Transformers, 247. 
 
 Current Transmission, 302 to 334. 
 
 E. M. F., 242. 
 Alternator, 257, 258. 
 
 , Collector Rings of, 258. 
 
 . Monocyclic, 275, 276. 
 
 Ampere, 35. 
 
 359 
 
360 INDEX. 
 
 Ampere Turns, 131. 
 
 Analogue of Electric Flow, 67 to 70. 
 
 Armature Core of Motor, 162. 
 
 , Monocyclic, 273. 
 
 of Motor, 110. 
 
 , Smooth-Core, 174, 175. 
 
 , Smooth -Core, Completed, 179, 180. 
 
 , Toothed-Core, 174, 175. 
 
 , Toothed-Core, Completed, 180. 
 
 Armatures, Disc, 171, 172, 173. 
 
 , Drum, 170. 
 
 , 5,000 Horse-Power, 318. 
 
 , Ring, 170. 
 
 Automatic Self-Oiling Bearings, 189, 190. 
 
 B 
 
 Babbitt Metal, 188. 
 
 Back Pressure, Electric, 49. 
 
 Barlow, 94. 
 
 Wheel Motor, 95. 
 
 Bar-Magnet, Flux of, 79. 
 Battery, Voltaic, 37. 
 
 , Voltaic, Series-Connected, 38. 
 
 Bearings, Automatic Self-Oiling, 189, 190. 
 , Self-Oiling, 163. 
 
INDEX. 361 
 
 Belt Tightener, 200. 
 
 Bluestone Voltaic Cell, 36. 
 
 Board of Trade Unit, 160. 
 
 Boiler and Steam Engine, Low Efficiency of, 26 
 
 to 28. 
 
 Box, Cut-Out, 208. 
 Broken Circuit, 32. 
 Brushes, Adjustment of, 211. 
 
 , Arrangement of, 186. 
 
 Brush Holders, 187. 
 
 c 
 
 C. E. M. F., 49. 
 
 Cell, Bluestone Voltaic, 36. 
 Choking Effect, 245. 
 Circuit, Broken, 32. 
 
 , Closed, 32. 
 
 , Completed, 32. 
 , Driven, 248. 
 
 , Driving, 248. 
 
 , Electric, 31, 32. 
 
 , Electric, Activity of, 53, 54, 55. 
 
 , Made, 32. 
 
 , Open, 32. 
 
 , Primary, 248. 
 
362 INDEX. 
 
 Circuit, Resistance of, 34. 
 
 , Secondary, 248. 
 
 -, Uniphase, 305. 
 
 Circular Flux of Active Conductor, 84, 85. 
 
 Mil, 42. 
 
 Mil-Foot, 42. 
 
 Closed Circuit, 32. 
 Commutation, Diameter of, 164. 
 
 , Sparkless, 212. 
 
 Commutator, Two-Part, 184. 
 Completed Circuit, 32. 
 Compound-Wound Motor, 156, 157. 
 Connections of Shunt-Wound Motor, 207, 208. 
 Conservation of Energy, Doctrine of, 2. 
 Constant-Potential Mains, 147. 
 Continuous-Current Motor, Forms of, 164 to 169. 
 
 - E. M. F-, 242. 
 Converter, Rotary, 331. 
 Core of Motor Armature, 162. 
 Cores, Laminated, of Motors, 176. 
 Coulomb, 44. 
 
 per-Second, 44. 
 
 Counter Electromotive Force, 49, 59, 60. 
 Current, Alternating, 242. 
 
 , Electric, 30. 
 
 Strength, 34. 
 
 Strength or Flow, Unit of, 35. 
 
INDEX. 363 
 
 Currents, Eddy, 175, 176, 215, 216. 
 
 , Stray, 215, 216. 
 
 Cut-Out Box, 208. 
 Cycle, 242. 
 
 D 
 
 Davenport, 104. 
 
 Density, Magnetic, Unit of, 134. 
 Diagrams of Torque, 123, 124. 
 Diameter of Commutation, 164. 
 Diphase Field, 292. 
 
 Field-Frame, 292. 
 
 , Four-Conductor, Diagram of System, 264, 
 
 265. 
 
 Four-Wire Circuit, 306. 
 
 , Independent Circuit, 307. 
 
 Motor, 283. 
 
 , Three-Conductor System, 266, 267. 
 
 Three- Wire System, 306. 
 
 System, 263. 
 
 System, Connections of, 282. 
 
 Disc Armatures, 171, 172, 173. 
 
 Dynamo, Faraday's, 98 to 101. 
 
 Double-Pole Switch, 208. 
 Driven Circuit, 248. 
 Driving Circuit, 248. 
 
364 INDEX. 
 
 Drop or Fall, 52. 
 
 Drum Armatures, 170. 
 
 Dynamo, Alternating-Current, 257, 258. 
 
 Electric Machine, 36, 37. 
 
 E 
 
 E. M. F., 33. 
 
 , Continuous, 242. 
 
 , Effective, 144. 
 
 Early Faraday Motor, 88, 89. 
 
 Eddy Currents, 175, 176, 215, 216. 
 
 Effect, Choking, 245. 
 
 Effective E. M. F., 144. 
 
 Resistance, 245. 
 
 Efficiencies of Motors, 159, 213. 
 
 Efficiency of Machine, 24, 25. 
 
 Electric and Hydraulic Resistance, Analogy Be- 
 tween, 39, 40. 
 
 Back Pressure, 49. 
 
 Circuit, 31, 32. 
 
 Current, 30. 
 
 Flow, 30. 
 
 Motor, Advantages of, 217, 218. 
 
 Motors, Miscellaneous Applications of, 
 
 335 to 358. 
 
INDEX. 3*35 
 
 Electric Pressure, 34. 
 
 Sources, 30. 
 
 Transmission, Commercial and Electric 
 
 Conditions of Problem, 223 to 240. 
 
 Transmission of Power, 217 to 241. 
 
 Electro-Dynamic Force, 97, 120, 121, 122. 
 Electromagnetic Rotation, 76. 
 Electromotive Force, 33. 
 
 Force, Counter, 49. 
 
 Force, Unit of, 35. 
 
 Elias' Motor, 108, 109. 
 Energy, Definition of, 3. 
 
 , Doctrine of Conservation of, 2. 
 
 , Hysteretic Loss of, 214. 
 
 , Indestructibility of, 2. 
 
 of Food, Transference of, 8. 
 
 , Rate-of-Expending, 11. 
 
 , Sources of, 19 to 28. 
 
 Entrefer, 182. 
 Ether Streams, 81. 
 , Universal, 80, 81. 
 
 F 
 
 Factor, Power, 254. 
 Fan Motors, 349 to 356. 
 
366 INDEX. 
 
 Faraday, 74. 
 
 Motor, Early, 88, 89. 
 
 Faraday's Disc, 98 to 101. 
 Field, Magnetic, 77. 
 
 Magnetic, of Motor, 110. 
 
 Rheostat, of Motor, 210. 
 
 , Triphase Rotating, 290, 291. 
 
 Fields, Diphase, 292. 
 
 Five-Thousand Horse-Power Armature, 318. 
 
 Flow, Electric, 30. 
 
 , Electric, Analogue of, 67 to 70. 
 
 Flux, Leakage, 136. 
 
 , Magnetic, 77. 
 
 , Magnetic, Unit of, 131. 
 
 , Stray, of Motor, 136. 
 
 Food, Transference of Energy of, 8. 
 Foot-Pound, 9. 
 Foot-Pound-per-Second, 12. 
 Force, Electro-Dynamic, 97, 120, 121, 122. 
 
 , Electromotive, 33. 
 
 , Magnetomotive, 130. 
 
 Forward Lead of Motor Brushes, 212. 
 Four- Wire Diphase Circuit, 306, 307. 
 Frequency, 243. 
 Froment's Motor, 114, 115. 
 Fuse, Safety, 208. 
 
Gauss, 134. 
 Gilbert, 131. 
 
 INDEX. 367 
 
 G 
 
 H 
 
 Holders, Brush, 187. 
 Horse-Power, 12. 
 
 Hydraulic Flow, Gradient of Water Pressure 
 During, 61, 62. 
 
 Transmission, 15. 
 
 Hysteresis, 214. 
 , Magnetic, 214. 
 
 Impedance, 247. 
 
 Independent Circuit, Diphase, 307. 
 Indestructibility of Energy, 2. 
 Induction Motor, 279. 
 
 Motors, 289. 
 
 Multiphase Motors, 289. 
 
 Installation and Operation of Motors, 200 to 216. 
 
 of Shunt- Wound Motor, 205, 206. 
 
 Intake of Machine, 22. 
 Inter-Linked Diphase, 307. 
 International Unit of Work, 9. 
 
368 INDEX. 
 
 J 
 
 Jacoby's Electric Motor, 101 to 104, 
 Joule, Definition of, 9, 10. 
 Joule-per-Second, 12, 48. 
 
 Laminated Cores of Motors, 176. 
 
 Law, Ohm's, 35. 
 
 Lead, Forward, of Motor Brushes, 212. 
 
 Leads, 52. 
 
 Leakage Flux, 136. 
 
 , Magnetic, 136. 
 
 M 
 
 M. M. F., 131. 
 
 Machine, Dynamo-Electric, 36, 3V. 
 , Efficiency of, 24. 
 
 , In-Take of, 22. 
 
 ' , Multipolar, 113. 
 
 , Output of, 23. 
 
 , Sextipolar, 113. 
 
 Made Circuit, 2. 
 
INDEX. 369 
 
 Magnetic Circuit of Motor, 28 to 130. 
 - Field, 77. 
 
 Flux, 77. 
 Hysteresis, 214. 
 
 Leakage, 136. 
 
 Resistance, Unit of, 132. 
 
 Saturation, 134. 
 
 Magnetism, Rotary, 292. 
 Magnetomotive Force, 130. 
 
 Force, Units of, 131. 
 
 Mains, Constant-Potential, 147. 
 
 Microhms, 41. 
 
 Mil, 42. 
 
 Miscellaneous Applications of the Electric Motor, 
 
 335 to 358. 
 Monocyclic Alternator, 275, 276. 
 
 Armature, 273. 
 
 Armature Winding, 273. 
 
 System, 270 to 279. 
 
 System, Diagram of Distribution by, 277, 
 
 278. 
 Motor, Activity of, 157, 158. 
 
 Armature, Core of, 162. 
 
 , Armature of, 110. 
 
 Brushes, Adjustment of, 211. 
 
 , Circumstances Affecting Speed of, 140 to 
 
 143. 
 
370 INDEX. 
 
 Motor, Circumstances Affecting Torque of, 138, 
 139. 
 
 , Classification of Losses of Energy in, 
 
 213. 
 
 , Compound-Wound, 156, 157. 
 
 , Electric, Advantages of, 217, 218. 
 
 , Elementary Theory of, 119 to 161. 
 
 , Froment's, 114', 115. 
 , Induction, 279. 
 
 , Magnetic Circuit of, 128. 
 
 , Magnetic Field of, 110. 
 
 -, Multiphase Induction, 294, 295. 
 
 , Quadripolar, 197. 
 
 , Separately-Excited, 111. 
 
 , Series- Wound, 154, 155. 
 
 , Shunt-Wound, 152, 153. 
 
 Motors, Alternating-Current, 242. 
 
 , Efficiency of, 159, 160, 213. 
 
 , Fan, 349 to 356. 
 
 , Induction, 289. 
 
 , Installation and Operation of, 200 to 
 
 216. 
 
 , Synchronous Multiphase, 289. 
 
 Multiphase Alternating-Current System, 263. 
 
 Induction Motors, 289, 294, 295. 
 
 Synchronous Motors, 289. 
 
 Multipolar Machine, 113. 
 
INDEX. 371 
 
 N 
 
 Negative Pole of Source, 31. 
 Niagara Transmission, 311 to 334. 
 
 o 
 
 Oersted, 90, 91, 132. 
 
 Oersted's Magnetic Experiments, 90 to 93. 
 
 Ohm, 35. 
 
 Ohm's Law, 35. 
 
 Oil-Cooled Transformer, 328. 
 
 Open Circuit, 32. 
 
 Operation and Installation of Motors, 200 to 216. 
 
 Output of Machine, 23. 
 
 Pacinotti, 115. 
 
 Pacinotti's Motor, 116 to 118. 
 Phase, Displacement of, 256. 
 Pneumatic Transmission, 15. 
 Pole, Negative, of Source, 31. 
 
 , Positive, of Source, 31. 
 
 Positive Pole of Source, 31. 
 
 Power, Electric Transmission of, 217, 241. 
 
372 INDEX. 
 
 Power Factor, 254. 
 
 Houses, 220. 
 
 Pressure, Back, Electric, 49. 
 
 , Drop or Fall of, 52. 
 
 , Electric, 34. 
 Primary Circuit, 248. 
 
 Q 
 
 Quadripolar Motors, 197, 198, 199. 
 Quantity, Electric, Unit of, 44. 
 
 K 
 
 Reactance, 243. 
 Reluctance, 132. 
 
 , Specific, 135. 
 
 Reluctivity, 135. 
 
 Resistance, Electric, Unit of, 35. 
 
 of Circuit, 34. 
 
 , Specific, 40. 
 
 , Total Effective, 245. 
 
 , Unit of, 35. 
 
 Resisting Torque, 143. 
 
 Resistivity, 40. 
 
 , Effect of Temperature on, 43. 
 
INDEX. 373 
 
 Rheostat, Field, of Motor, 210. 
 
 , Starting, 202, 203, 204. 
 
 Ring Armatures, 170. 
 Ritchie, 105. 
 
 Ritchie's Motor, 106, 107. 
 River, Energy of, 6. 
 Rope Transmission, 15. 
 Rotary Converter, 331. 
 
 Magnetism, 292. 
 
 Rotating Field, Triphase, 290, 291. 
 
 Magnetic Field, 284 to 301. 
 
 Magnetic Field, Diagram of, 285. 
 
 Rotation, Electromagnetic, 76. 
 Rotor, Definition of, 110. 
 
 s 
 
 Safety Fuse, 208. 
 Saturation, Magnetic, 134. 
 Secondary Circuit, 248. 
 Separately-Excited Motor, 111. 
 Series-Connected Voltaic Battery, 38. 
 Series Connection, 37, 38. 
 Series- Wound Motor, 154, 155. 
 Sextipolar Machine, 113. 
 Shunt- Wound Motor, 152, 153. 
 
374 INDEX. 
 
 Shunt- Wound Motor, Connections of, 207, 208. 
 
 , Installation of, 205, 206. 
 
 Smooth-Core Armature, 174, 175. 
 Solar Energy, Varieties of, 21, 22. 
 Sources, Electric, 30. 
 
 of Energy, 19 to 28. 
 
 of Energy, Classification of, 19. 
 
 Sparkless Commutation, 212. 
 Specific Reluctance, 135. 
 
 Resistance, 40. 
 
 Speed of Motor, Circumstances Affecting, 140 
 
 to 143. 
 
 Star Connection of Triphaser, 308. 
 Starting Rheostat, 202, 203, 204. 
 Stator, Definition of, 110. 
 
 Steam Engine and Boiler, Efficiency of, 26 to 28. 
 Step-Down Transformers, 250. 
 Step-Up Transformers, 251. 
 Stray Currents, 215, 216. 
 
 Flux of Motor, 136. 
 
 Stream Lines, 81. 
 
 Strength of Current, 34. 
 
 Structure and Classification of Motors, 162 to 
 
 199. 
 
 Sturgeon, 96. 
 Switch, Double-Pole, 208. 
 Synchronous Multiphase Motors, 289. 
 
INDEX. 375 
 
 System, Diphase, 263. 
 
 , Monocyclic, 270 to 279. 
 
 , Multiphase Alternating-Current, 263. 
 
 , Triphase, 263, 264. 
 
 Temperature, Effect of, on Resistivity of Metals, 
 
 43. 
 
 Theory, Elementary, of Motor, 119, 120. 
 Thermal Activity, 55. 
 Three- Wire Diphase, 307. 
 Toothed-Core Armature, 174, 175. 
 Torque, Definition of, 122. 
 
 , Diagrams of, 123, 124. 
 
 of Motor, Circumstances Affecting, 138, 
 
 139. 
 
 , Resisting, 143. 
 
 Total Effective Resistance, 245. 
 Transformer, Alternating-Current, 247. 
 
 , Oil-Cooled, 228. 
 
 Transformers, 247. 
 
 , Step-Down, 250. 
 
 , Step-Up, 251. 
 
 Transmission, Alternating-Current, 302 to 334. 
 , Hydraulic, 15. 
 
376 INDEX. 
 
 Transmission of Power, Electric, 217, 241. 
 
 , Pneumatic, 15. 
 
 , Rope, 15. 
 
 , Systems of, 14. 
 
 Triangle Connection of Triphaser, 308. 
 Triphase Alternator, 269, 270. 
 
 Motor, 297 to 299. 
 
 , Three-Wire System, 268. 
 
 , Six-Wire System, 267. 
 
 System, 263, 264, 306. 
 
 System, Connections of, 281. 
 
 Triphaser, 267. 
 
 Two-Part Commutator, 184. 
 
 Typical Electric Transmission System, 219, 220. 
 
 u 
 
 Uniphase Circuit, 305. 
 
 Unit, International, of Work, 9. 
 
 of Activity, 11, 12. 
 
 of Current Strength or Flow, 35. 
 
 of Electric Activity, 48. 
 
 of Electric Quantity, 44. 
 
 of Electric Work, 247. 
 
 of Electromotive Force, 35. 
 
 of Magnetic Density, 134. 
 
 of Magnetic Resistance, 132. 
 
INDEX. 377 
 
 Unit of Resistance, 35. 
 Units of Magnetic Flux, 131. 
 
 of Magnetomotive Force, 131. 
 
 of Work, 9. 
 
 Universal Ether, 80, 81. 
 
 V 
 
 Varieties of Solar Energy, 21, 22. 
 
 Vertical Section of 5,000 Horse-Power Generator, 
 
 322. 
 
 Voltage, 37. 
 Volt, 35. 
 
 Voltaic Battery, 37. 
 Volt-Coulomb, 47. 
 
 w 
 
 Wasted Activity, 35. 
 
 Watermotive Force, 60, 61. 
 
 Watt, 12, 48. 
 
 Weber, 131. 
 
 Winding, Teaser, of Monocycler, 272. 
 
 Work, International Unit of, 9. 
 
 , Rate-of-Doing, 11. 
 , Units of, 9, 
 
Elementa 
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THIRD EDITION. GREA TL Y ENLAR GED 
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 and Phrases. 
 
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ELECTRICITY AND MAGNETISM. 
 
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 By EDWIN J. HOUSTON, PH.D. (Princeton). 
 
 AUTHOR OF 
 
 \ 
 
 "A Dictionary of Electrical Words, Terms and 
 Phrases" etc., etc., etc. 
 
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The Measurement of Electrical Cur- 
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 AUTHOR OF 
 
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ELECTRICITY 
 
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THIRD EDITION 
 
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 THE UNIVERSITY OF CALIFORNIA LIBRARY