Class Book. K 18 Gopightl^'" COPYRIGHT DEPOSIT. vT" A L PRACTICAL ELECTRICITY Copyright 190I-I904-1908-I9II by QcveUnd Aimawre Works QUESTIO^IS AHP ANSWERS SIXTH EpmoN' \^ i ' Pv'ess of W. B. Conkcy Company Hammond, Ind. ©CI.A28r,221 INTRODUCTORY. In March, 1896, The Armature Winder made its first appear- ance, its attractive feature being the commencement of a series of lectures on designing dynamos and motors, these letters being written from daily shop practice, and made comprehensible by questions and their subsequent answers. As each paper with its lecture made its appearance, the interest manifested by readers became more pronounced, until we were flooded with inquiries for numbers which the various readers had missed. As we had only reserved a very few papers of each issue, our ability to supply the back numbers was limited. We consequently decided to print the lectures in book form, and so notified our readers of this decision, with the result that orders for the book came in, in quantities which were beyond anything we had anticipated. This evidence of the popularity of our efforts encouraged us in compiling a work much more extensive and valuable than had at first been our intention. In order to accomplish this, we felt the ne- cessity of associating with us a man of greater technical knowledge than we ourselves possessed, so that the work might be thoroughly criticised and enlarged. We selected Mr. John C. Lincoln, an electrical engineer of national reputation, who has contributed articles to this book covering matters of great interest, and, so far as we have been able to learn, ideas never before appearing in print. We are obligated to Mr. C. E. F. Ahlm for assistance rendered in preparing the chapter on electric automobiles. CLEVELAND ARMATURE WORKS. Clevelaiid. Ohio, 1911. James L. Mauldin / p^^p^ Alvin a. Pifer \ PROP^. PiRKFACE. This book was i^ritten especially to assist those who have some practical knowledge of electricity and who wish to learn more of the way in which wiring* is calculated and of the simpler and more important parts of dynamo electric machine design. Some of the methods used and explana- tions advanced in the book are, so far as the writers know, entirely new, and it has all been written with the idea of illustrating the subject and making it las simple and as easy of comprehension as possible. The only way to obtain a working knowledge of the subject is by careful study. The book has been arranged so that those who are willing to devote some effort to the work can get a clear conception of the more importlant ideas and laws that underlie the sub- ject. One who studies the text and answers the questions at the end of each chapter should be able to calculate a wiring job for lig-hts or power; to calculate the proper size and amount of wire for a dynamo when he has the dimen- Bions of the niaehine; to calculate the size and winding for 0, magnet to give a required pull, etc. The table of contents shows the scope of the work. The q''jestions which follow each chapter, in connection with the answers, will bring out the more important points treated in each chapter. It is believed that a careful study of the text and the working of the examples will serve to throi;^ a great deal of light upon a subject in which a grea/t many people are interested. Tlie dictionary in connection with this work is a valuable feature. Houston's Electrical* dictionary was largely used in the preparation of same. CLEVELAND ARMATURE WORKS. CLEVELAND. OHIO. TABLE OF CONTENTS CHAPTER I. II. III. IV. V. VI. VII. VIII. LX. X. XI. XII. XIII. XIV. XV. XVI. XVII. XVIII, XIX. XX. Wiring. Electric Batteries. Electro Plating. Magnetism. The Magnetic Circuit. Magnetic Traction. Magnetic Leakage. Energy in Electric Circuits, Calculation of Size of Wire for Magnetizing Coils. Calculation of E. M. F.'s in Electric Machines. Counter E. M. F. Hysteresis and Eddy Currents. Armature Reaction. Sparking. Winding of Dynamos and Motors. Proper Method of Connecting Dynamos and Motors. Self Excatation. Diseases of Dynamos and Motors, their Symptoms and how to cure them . Arc and Incandescent Lamps, Measuring Instruments. Alternating Current, Electric Automobiles. A CHAPTER I. VVIKIJVG. 1. It is very commonly said that nothing is known of electricity. Tliis is both true and false. We do not know what electricity is nor anything of its ultimate nature, but we do know a great deal about the laws which govern the action of electricity. For all ordinary purposes the action of electricity is very closely analogous to that of water. From the study of the principles which govern the flow and action of water a very great deal can be learned concerning the prin- ciples and laws governing the action of electricity. In this analogy the water represents electricity. When water flows from a higher to a lower level, it is capable of doing work by driving some kind of a water wheel. The greater the height through which the water falls, the greater the amount of work it can do. The same thing is true of electricity. The greater the difference in electrical level, or difference of potential, or the greater the voltage, the greater the amount of electrical work the electricity can do. The unit of difference of electrical level is the volt, and we may say that the volt corresponds to one foot of "head" in a system for developing power by water. The amount of power that can be developed from a water fall depends on two things; flrst, the fall in feet or the head, and second, the size of the stream. At Niagara Falls the power that can be developed is practically infinite, not because the height of the fall is so great, but because the size of the stream is so great. Any water fall is capable of developing power, depending on the size of the stream. The unit of flow may 2 be taken as one gallon per second. The corresponding- quantity in electricity is called current. The unit of cur- rent is called the ampere. The ampere then corresponds to the one gallon per second in a flow of water. The amount of water that can flow from a higher to a lower level depends on the size of the pipe line through which the water is led. Imagine a large pond of water twenty-five feet above the sea. The amount of water that will flow from the pond through a 4-inch pipe is very much greater than what will flow through a J^-inch pipe. Again if there are two pipes of the same size leading from the pond to the sea and one is twice as long as the other, afbout twice as much water will flow through the short pipe as through the long one. The friction of the water is greater in the long pipe, or the resistance to the flow is greater, and so less water flows. There is no convenient unit for the resistance of a pipe to the flow of water, but the unit of resistance of a wire to carrying a current is well defined and is called the ohm. Figure 1 Resistance offered to flow of water through a long crooked pipe. Discharge in gallons per minute corresponding to amperes. ^ 3 The resistance offered by the long, small, ^crooked pipe to the flow of the "water corresponds to the resistance of- fered by a wire to the flow of the electrical current. An in- spection of Fig. 1 will show that the flow depends on the head. If, instead of having a head of 25 feet, it was in- creased to 50 feet, the amount of water discharged would be doubled, so that the flow depends on the head or pressure. If on the other hand the discharge pipe was made larger, or shorter, even with 25 feet head, twice as much water could be made to escape, so that the flow or current is in- versely proportioned to the resistance. Putting this in the form of an equation we have: Discharge or current equals head or pressure divided by resistance or friction. In a circuit carrying electricity the same thing is true and we have: Electrical discharge or current equals electrical head or pressure, divided by elec- trical friction or resistance. Since the unit of electrical current is the ampere, and the unit of electrical pressure is the volt, and the unit of electrical resistance is the ohm, we have: Amperes equal volts divided by ohms, or putting it in the form of a fraction we have: volts Am.peres equals ohm; This relation is known as Ohm's law and is one of the most important that we shall consider. Since the electrical pressure is what causes the movement of the electrical cur- rent, it is called electro-motive force, and as this term is very long it is abbreviated to E. M. F. Since the amperes measure the amount of flow of electricity, such flow is called current, ^nd this is abbreviated to C. Kesistance is abbreviated to R., and we have our Ohms law E. M. F. ^ E C equals (1); or C equals — R R when E. is used in place of E. M. F. By the way in which Oh,ms law was deduced it is plain to see that is is only one form of a general and universal law. Ohms law is the statement for electrical quantities of the general law that the result produced is proportional to the effort expended, and inversely proportional to the re- sistance to be overcome. To get a general idea of these units we may say that a single cell of storage battery has a voltage of two volts. One hundred and ten volts is the electrical pressure usually employed for lighting incandescent lamps. Two hundred and twenty volts is very frequently used as the E. M. F. for driving motors. Five hundred volts is universally used on street railroads to propel street cars. An ordinary gravity batter3% such as is usually employed for telegraphic work- has an E. M. F. of one volt. Dynamos for electrotyp- ing usually employ two or three volts. Dynamos for elec- trcplating from ^ve to ten volts. The current taken by an incandescemt lamp is about Yo ampere. The current required by a street arc lamp is from ten to six amperes, depending on the br'illiancy of the light. The current used in a land telegraph wire is .003 to .005 amperes. The resistance of 1,000 feet of copper wire one-tenth of an inch in diameter is one ohm. Ten feei of German silver wire the size of the lead in a pencil has a resistance of one ohm. The resist- 5 ance of a mile of the heavy feed wire used propelling street ears is about one-tenth of an ohm. m Figure 2 System for distributing hot water at constant pressure. Suppose Fig. 2 to be part of the heating* system of a building'. The pump takes in the water from the low pressure pipe, and after passing* through a heater it is forced out into the high pressure pipe to the radiators over the building. If the pipes PI and PO are large enough there will be the same pressure practically at all parts of the pipe, and each radia- tor Rl, R2 and R3 will be exposed to the same pressure and receive the same amount of water provided they are simi- lar. If, however, the pipes PI and PO are small, some of the pressure on the water in the pipe PI will be lost in over- coming the friction of the pipe, so that radiator R3 farthest away from the pump would not get the same amount ol pressure as Radiator Rl nearest the pump. There would be a similar loss of pressure in pipe PO. If the pump produces a pressure of twenty pounds per square inch, and the fric- tion and resistance of the leading pipe PI is great enough to cause the pressure to fall to 19 pounds at the nearest radiator Rl, and causes it to fall to 18 pounds at R3, the 6 loss of pressure will be "two pounds at R3 in the pipe PO, and two pounds in the pipe P1 , if both PI and PO are ol the same size. The loss will be one pound at Kl in each pipe. Under these circumstances the pressure driving- water through El is 18 pounds and through R3 is 16 pounds, in- stead of 20 pounds as produced by the pump. Such a sys- tem for distributing water is closely analogous to a con- stant potential or constant electrical pressure system for distributing electricity. The pump takes the water from one main pipe and raises the pressure and delivers it to the other pipe. The radiators between t!hese pipes receive the water at practically constant pressure. The total stream in the main pipe is the sum of the individual currents in the radiators. The loss of head or pressure in t;he main pipes is greater as the flow of water is increased, and, if the radia- tors require practically constant pressure to work properly, soon reaches a limit. In each of these four respects such a water system is perfectly analogous to a constant potential lighting system. The pump corresponds to the dynamo in Fig. 3, which takes the electricity from one wire and raises its pressure so that it is 110 volts higher at one side of the dynamo than at the other. Figure 3. System for distributing electricity at constant pressure. The electricity is carried along the main wires Ml and MO, which correspond to the two pipes PI and PO in Fig. 2, to the incandescent lamps LI, L2, L3. It is evident that there is some loss of pressure in carrying the current along the main wires MO and Ml from the dynamos to the lamps, and that this loss of pressure depends on the amount of cur- rent or upon the number of lamps in use. The lamp L3 will get in any case some less pressure than the lamp Ll, and when this difference becomes great enough so that L3 burns perceptibly dimmer than Ll, the main lines Ml and MO are carrying more current than they properly can. In practice the number of radiators in such a heating system as shown in Fig. 2 would not probably be much over 100, and usually very much less, while for the electric system the number of lamps on the dynamo will be from five to ten times as great. f M. ^ O £3: 3, O o TT s -^r^^ . P' P 9 P § YO :0 O O O O O O Figure 4 Typical constant potential system. Fig. 4 shows the dynamo taking current from the main MO and delivering it at 110 volts higher pressure to the main Ml. Part of it leaves the main Ml for the branch Bl and flows through the seven lamps to the other main MO. The 8 voltage is lost in overcoming the resistance of the lamps. The resistance of .the lamps constitutes from 90 to 98 per cent, of the resistance of the circuit. A second part leaves the main at B2 and passes into the wires of this 'branch through the 17 lamps shown. The rest of the current passes to B3 and through the 8 lamps in that circuit. There will, of course, be some loss of pressure or "drop" in the branch circuits. The calculation required in wiring is needed to find out how large to make the main wires MO and Ml and how large the wire on the branch circuits should 'be. The whole system should be so designed that there should be a differ- ence of only a volt or two between the various lamps on the circuit. The point to be aimed at is even or constant volt- age for the lamps. We will take up three different forms of Ohm's law ttiat will be convenient for use in calculating wiring problems. E. M. F. We have seen that C equals , or, put into words^ R amperes equal volts divided by ohms. The two other forms of this most important equatioi* are volts equals amperes multiplied by ohms; or E. M. F. equals' C multiplied by E. (2) ; and third, ohma E. M. F. equal volts divided by amperes; or, R equals (3). C These three equations should be carefully studied and memorized. For our work in wiring, the second is the most 9 important. Equation (2) means that the loss in volts in any part of the circuit depends on the amount of current the wire is carrying, and also on the resistance of the wire. If the amount of current carried is doubled, the volts lost are doubled; and if a new wire is used of twice the resist- ance, the loss of volts is doubled, and in general the volts lost or the "drop" is equal to the amperes the wire is carry- ing multiplied by the ohms of resistance of the wire car- r^ung the current. Suppose there were 100 lamps on the three circuits shown in Fig. 4 and that they were very close together, so that they all received about the same E. M. F. from the mains Ml and MO, but that the dynamo was about 500 feet from the lamps, near an engine. In such a case the principal loss of pressure would be in the mains carr^n'ng current between the dynamo and lamps. If w^e use Xo. 6 wire, which is .162 inches in diameter, there would be a resistance of .395 ohms in the mains, for there are 1,000 feet in the two mains, and the table No. 1 shows this. Each lamp requires Vi ampere, so that 100 lamps twill require 50 amperes. By formula 2 we have volts lost in leads or mains equal amperes multiplied by ohms, or drop, equals 50 multiplied by .395 equals 19.75 volts. In this case, if the lamps were to be supplied with 110 volts, the dynamo would have to produce 110 volts plus 19.75 volts, or 129.75 volts. Circuits of this sort are frequent, and if carefully operated such a grpat loss as 20 volts in the mains may be allowed. The ordinary case, however, is one in which the lamps are about equally distributed between the dynamo and the end of the circuit. In such a case a drop of 20 volts in the mains would not be permissible, for then the lamps near the dynamo would get 130 volts and those at the end of the 9 10 circuit would get 110 volts. This is altogether too much varia- tion. The greatest variation that should ever be allowed is 8 volts, and all well-regulated plants do not have more than two. The reason that it is best to have the variation a mini- mum is that the incandescent lamps have a much longer life if the voltage is constant than if it is not. If a lamp has a life of 800 hours at 110 volts, it will not burn more than 200 hours at 115 volts, and if it is burned at 105 volts it will not give more than 2-3 of its rated light. The drop usually allowed in mains for a building does not exceed 3 per cent., and in the best plants is not over 2 per cent. Table 1 gives the properties of copper wire of ail the American or B. & S. (Brown. & Sharpe) gauge sizes. . TABLE 1. PKOPERTIES OF PURE COPPER WIRE. AT 75 DEGREES FAHRENHEIT R. Ohms per 1000 Feet 1^^ 1?^?. R. Ohms per 1000 Feet Ohms per Mile Feet per Ohm Ohms per Lb. ih ^%^ 150° ii'^ 0000 000 00 1 .04906 .06186 .07801 .09831 .12404 .25903 .32664 .41187 .51909 .65490 20383. • 16165. 12820. 10409. 8062.3 .000076736 .00012039 .00019423 .00030772 .00048994 .05675 .07160 .09028 .1161 .1435 1 = 1 2 3 4 5 .15640 .19723 .24869 .31361 .39546 .82582 1.0414 1.3131 1.6558 2.0881 6393.7 5070.2 4021.0 3188.7 2528.7 .00078045 .0012406 .0019721 .0031361 .0049868 .1810 .2283 .2879 .3630 .4577 6 7 8 9 10 11 .49871 .62881 .79281 1. 1.2607 2.6331 3.3201 4.1860 5.2800 6.6568 2005.2 1590.3 1261.3 1000.0 793.18 .0079294 .012608 .020042 .031380 .0.50682 .5771 .7278 .9175 1.157 1.459 ' 12 13 14 15 16 1.5898 2.0047 2.5908 3.1150 4.0191 8.3940 10.585 13.680 16.477 21.221 629.02 498.83 385.97 321.02 248.81 .080585 .12841 .20880 .31658 .51501 1.840 2.320 2.998 3.606 4.651 17 18 19 20 21 5.0683 6.3911 8.2889 10.163 12.815 26.761 33.745 43.765 53.658 ' 67.660 197.30 156.47 120.64 98.401 78.037 .81900 1.3024 2.1904 3.2926 5.2355 5.867 7.398 9.594 11.76 14.83 103.0 84.0 66.0 56.3 46.8 22 23 24 25 26 16.152 20.377 25.695 32 400 40.868 85.283 107.59 135.67 171.07 215.79 61.911 49,087 38.918 30.864 24.469 8.3208 13.238 21.050 33.466 53.235 18.70 23.59 29.73 37.50 47.30 39.3 33.5 27.4 24.4 19.6 27 28 29 30 31 51.519 • 64.966 81.921 103.30 127.27 272.02 343.02 432.54 545.39 671.99 19.410 15.393 12.207 9.6812 7.8573 84.644 134.56 213.96 340.25 528.45 59.64 75.20 94.82 119.5 147.3 17.0 14.4 11.8 10.0 8.6 32 33 34 35 36 164.26 207.08 261.23 329.35 415.24 867.27 1093.4 1379.3 1738.9 2192.5 6.0880 4.8290 3.8281 3.0363 2.4082 860.33 1367.3 2175.5 3458.5 5497.4 190.1 2.39.6 302.3 381.3 480.7 7.5 6.3 5.5 4.7 4.3 37 38 39 40 523.76 660.37 83?,.48 1049.7 2765.5 3486.7 4395.5 5542.1 1.9093 1.5143 1.2012 .9527 87421 13772. 21896. 34823. 606.1 764.3 963.6 1215. 4.0 3.7 3.6 3.0 73 > o O o ft -5 7.79 9.804 12.336 15.58 19.54 24.57 30.91 38.87 Lbs. per 1000 ft. 128.37 101.99 81.06 '0 o O o 'bo •i-H QQ tS 7.811 9.837 12.39 Lbs. per 1000 ft. 128.0 101.85 80.70 64.06 50.82 40.32 31.99 25.40 •qi jad %Q9^ 1-1 T-KNi CO eo CSS^OSOCD "^ «o t-' O C<1* O?00i-i00 »£:;doOOCi o t- CO "^ O irt CO to C- 1-1 c^ CDC 05 c la 00 CC C<1 iCO t— "^ _ J C<1 ^ o Sag: C^" 00 ?c ri rHOOQQO-^ Oi»«(MOOO «0 iO -^ 00 iJrtOO-MtC C-OOQOC I M 05 OC <£ c-^ »-i CO <:o »« -"^ o t-' i-H oi OO-rHlAOi »r: ■«* CO c66^^^i> n ^^^^^vi Figure 6 ' Figure 7 Drop in branch circtiit Drop in same circuit connected tapped at end. in center. 17 If possible, branch circuits should be tapped on to the mains at the center of the branch, in order to secure a more even voltage at the lamps. If the branch wires in Figs. 6 and 7 are both of the same size, it is easy to see that the drop in the branch wire as connected in Fig*. 6 is very much greater than in Fig. 7. In fact, the drop in Fig. 7 is only one-fourth of that in Fig. 6, for in Fig. 7 each branch carries half the current half the distance that it does in Fig. 6. Sometimes when from circumstances the drop in the branch circuits is bound to be very great, it is possible to connect them so that while there is a great deal of drop in each line all the lamps receive the same voltage. 1 666666666000000000 Figure 8 Method of connecting lamps so as to get even voltage at lamps even with great drop in the line. Fig. 8 shows such a connection. If the drop in each wire were five volts from one end to the other and the mains supplied 115 volts, each lamp would still get 110 volts. The great trouble with such schemes is that, although they work well when fully loaded, when partly loaded the volt- age on the lamps that do burn is excessive and certain io shorten the life of the lamps. The only way to install a plant that will be perfectly satisfactory in the way of drop in the lines is to use wire large enough, so that when fully loaded* the drop is small, then with light loads it will be still less. 18 CALCULATION OF FEEDERS FOR STREET RAILWAY WORK. In street railway wiring we have the peculiar ease that only one side of the line is wire and the earth is used for the return. FEEDER ^ TROLLEY Figure 9 Electric circuit of street car system. The rails are electrically connected to eacli other bj? bonding, and also are connected to the dynamo at the power house. It is usual to connect the dynamo to the gas and water pipes in the city, so as to take the current that naturally flows in them. In a well-bonded track there is not much loss of voltage in the return or ground circuit, and all the loss is figured in the overhead wire. The trol- ley wire is usually No. 1 or No. 0, so as to give mechanical strength. The trolle^^ wire is supplied from feeders, which are large wires running from the dynamos and connected to the trolley wires at various points. For the heaviest loads at least 10 per cent, loss or 50 volts is allowed in the feeder. HoTV large should a feeder three miles long be to carry 300 60 , amperes with 50 volts loss? Here we have equals* 300 19 ohms in feeder equals — . As there are three miles of feed- 6 1 1 er the resistance per mile ^vill be — multiplied by — 1 6-3 equals — , or .0555 ohms per mile. The table does IS not give the size of a wire so large as this, but it table does not give the size of a wire so large as this, but it will be ten times as large as one that has ten-eighteenths, or .555, ohms per mile, or a wire a little less than ten times as large as No. wire, is what we want. This will be a wire of about 105600x10 circular mils, or about 1,000,000 circular mils, or about one inch in diameter. Such a wire is very expensive to put up, so that it would be cheaper to install four wires i^ inch in diameter, as these would have the same size and carrying capacity as the single large wire. The calculations required in wiring are almost univer- sally used in connection with constant potential cii*cuits. cults. There are two ways in wliich electricity is distributed: First, constant potential; and second, constant current. In- Flgure 10 Arc light circuit. 20 candescent ligtiiog' and a great deal of arc lighting, street railway systems and all important plants for the transmis- sion of power are operated on the constant potential sys- tem. Most of the arc lights that are dn use, especially the older ones, are operated under the series system. In the first case, each lamp or motor receives the full voltage of the system and only part of the current. In the second, each lamp receives the full current flowing in the system, but only part of the voltage. Each arc lamp in a series system takes from 50 to 55 volts. Some of the latest arc dynamos will carry 125 or even 150 such lamps, which requires a 'pressure of nearly 8,000 volts. Such a voltage is very dangerous, and this is one reason -why the series system is not in general use. A 2,000 candle power arc lamp requires 9 to 10 amperes, and a 1,200 candle power from 6 to 61/2 . No. 6 B. & S. is usually used for 2,000 candle power arc light lines and No. 8 for 1,200 candle power. A convenient rule by which to calculate the resistance of copper wire in the absence of a table is R equals 10.8 multiplied by length in feet divided by diameter in rails, or one-thousandth of an inch squared, or 10.8 multiplied by L R equals ^ M2 in which L equals length in feet and M equals the diameter in mils. m QTJESTIONS ON WIRING. 1. What is known of the nature of electricity? 2. Whait is known of the laws governing its action? 3. What analogy may be used to illustrate the action of electricity? 4. In the analogy of the action of water and electric- ity, what corresponds to electric pressure? What to elec- tric current? What to electric resistance? 5. What is the unit of electric pressure? 6. To what unit in hydraulic work does it correspond? 7. What is the unit of electric current? 8. What is the unit of electric resistance? 9. What is Ohms Law? 10. Is Ohms Law peculiar to electricity or does the same general la-w hold in other work? Give an example. 11. How many volts does an ordinary storage battery produce? 12. What pressure is usually employed for incan- descent lamps? 13. How many amperes are used by an ordinary incan- descent lamp? How many by an arc light? 14. What is the resistance of 1,000 feet of copper wire 1-10 inch in diameter? 15. Give an example difiCerent from that in the text of the loss of pressure with the transmission of fluids. 16. On what does the loss of pressure in a pipe carry- ing a fluid depend? 17. To what does the pump in a system for distribut- ing fluids correspond in an electric system? 18. Give other points of analogy between the example you have selected and the electric system. 19. Upon what does the loss of pressure in a wire de- pend? 20. Draw a diagram of a constant potential electric system with four branch circuits and 38 lamps distributed ajnong them. 21. What part of the wholes resistance of a circuij should the lamps he? 22. What is "drop"? 23. What is the ideal condition as regards drop in wii^ ing up an electrical plant? 24. Why is it not possible to realize the ideal condition? 25. What are calculations in wiring required for? 26. What are the three different statements or forms of Ohm's law? 27. Which is the most important in wiring problems? 28. Write out in your own words what equation (2) means. 29. How many volts are lost in a circuit carrying 120 amperes and having a resistance of 1-30 of an ohm? 30. What sized wire would be required for such a cir- cuit if it were 400 feet long? 1 31. How many amperes are flowing in a wire of — ohm if there is a drop of two volts in it? 25 23 32. What is the resistance of a wire that has Syi volts drop when carrying 45 amperes ? 33. If a dynamo supplies current to its circuit at 114 volts and each main wire has a drop of three volts, what voltage is there on the lamps ? 34. A certain station fed a number of lamps at a consid- erable distance. The drop was 55 volts, the resistance of the 1 circuit was of an ohm. How many amperes was the 220 station carrying ? 35. What drop is allowed in the mains of the best plants ? 36. A dynamo in a basement is used to light a building. The wires are carried 100 feet before any branch circuits are taken off, and then one is taken off every 12 feet for 96 feet. What sized wire would be required to carry 400 amperes with a drop in the wires of three volts ? 37. Why is it best to attach a branch circuit to the main in the middle ? 38. A certain plant is used to light a building. It is de- sired to light another building 800 feet away and using 1,000 lamps. In order to save copper, 115 volt lamps are used in the first building and 100 volt lamps in the second building. At 15 cents per pound, how much less would the copper for the mains cost with 100 volt lamps in the second building than with 110 volt lamps ? 39. What are the objections to such a scheme as outlined in question 38 ? 40. In branch circuits carrying a large number of lamps, what table should be employed to determine the size of the wire ? 24 41. Haw many volts drop are usually allowed in the feed wires of street railway circuits? 42. How do the currents return from the street cars to the dynamo? 43. Why does such a return as is used ' in street railway work save copper? 44. How large a wire would be required to carry 500 amperes 1^^ miles with a drop of 75 volts? 45. Wha-t would such a wire cost at .14i/$ per pound? 46. If 125 volts drop were used, what current would this wire carry? 47. If 500 amperes were carried on a wire at 125 volts loss IVo miles, how much would the wire cost at .141^ per pound ? 48. What size of trolley wire is usually employed in street railway work? 49. Sketch out a system of wiring for street railway circuit hy which the voltage when near the power house is less than when at a distance from it. 50. In what two ways is electricity distributed? 51. For what is the series system used? 52. What is the characteristic feature of the constant potential system? 53. Of the series system? 54. What current is required for a 2,000 c. p. arc lamp? 55. What current is required for a 1,200 c. p. arc lamp? 56. What is a convenient rule for calculating the re- sistance of a copper wire in the absence of tables? CHAPTER IL ELECTRIC BATTERIES. m the year 1786 Galvani was making- some experiments with frogs' legs and had a number supported by the spinal cord from copper hoops attached to an iron railing. He noticed that when the muscles touched the railing that the frog's legs contracted spasmodically. This experiment led finall3' to the production of the electric battery. Volta, in the year 1800, produced the so-called voltaic pile, which is one of the simpler forms of a battery. The easiest and most simple way to make a battery is to insert in a jar partially filled with acidulated water, or even brine, a strip of zinc and one of copper. Upon joining the zinc and copper outside the solution by a metallic conductor, a current of electricity will flow from the copper to the zinc through the conductor and from the zinc to the copper through the acid. The way in which the current flows through the acid is not thoroughly understood, but this flow is accompanied by the oxidation or slow laming of the zinc and "by the evolution of hydrogen gas on the copper. The primary cause of the flow of the current is the com- bustion or oxidation of the zinc, and if the conditions are properly arranged the amount of current that flows is strictly proportional to the amount of zinc consumed. The appearance of the hydrogen gas on the copper re- duces the current which flows by covering it to a great ex- tent with a thin layer or coating of hydrogen gas. The battery will deliver much more current when means are provided to prevent the formation of gas upon the copper. 26 TABLE in. ELECTRO-CITEIVIICAL SERIES OF THE ELEMENTS. — + Oxygen Caesium Sulphur Potassium Nitrogen Sodium Flourine Zinc Chlorine Iron Bromine Copper Iodine Silver Phosphorus Mercury Carbon Platinum Antimony Gold Hydrogen The process of coating the copper with hydrogen gas is called polarization. The zinc plate is called the positive element, the copper plate is called the negative element. The binding post by vrhich the current leaves the copper is called the positive pole, because the current flov^s from this binding post through the outside circuit to the nega- tive pole on the zinc plate. Some metals may be used in place of the zinc as the positive element in the battery; among these the more important are potassium and sodium. Many medals may be used to take the place of copper, but the material most frequently employed is carbon. A battery composed of zinc arid carbon has a much higher electro-motive force than one in which the zinc and copper are used; in fact, the elements may be arranged in a series in which any one may be used as a positive element 27 in combination witli any below it, and as a negative ele- ment when used in combination with any above it. Table No. 3 is such a list. Zinc and copper in a solution of sulphuric acid give an elctro-motive force of about one volt. Zinc and carbon ffive about two volts. Zinc and carbon with an alkaline solution, such as salamoniac or potash, give about one volt and one half. Various means are employed to prevent the hydrogen from appearing or adhering to the negative ele- ment. Some of these are mechanical, such as the use of very fine metallic powder, such as platinum sponge, which permits the bubbles of gas to escape when very small, or by the use of a stream of air bubbles which mechanically carries away the hydrogen from the surface of the negative element. The first method is used in the Smee battery, in which the nej>"ative element is a thin plate of silver on which has been deposited a coating of very finely divided metallic platinum called platinum sponge. By all means the more important method for preventing the appearance of hydrogen on the negative element is t3ie use of some chemical which consumes the hydrogen before it reaches the negative element. This is usually accom- plished by inserting the negative element in a porous cup which is filled with a powerful acid or with some other ma- terial which burns up the hydrogen. When the zinc of a battery is consumed it combines with oxygen from the solution in which it is placed, and for every atom of oxygen which chemically unites v^ith the zinc two atoms of hydrogen are evolved, and these travel from the surface of the zinc through the solution in some wav toward the negative plate. If somewhere between 28 the positive and negative plates a porous cup is placed, the hydrogen will pass through the pores of this cup on its way toward the negative plate. If within the porous cup is placed a very powerful acid, the hydrogen is consumed or burned up as soon as it reaches this acid, and thus the polarization which would otherwise occur from the appearance of hydrogen gas on the negative plate is prevented. Zinc is used as the positive element in almost every battery. The reason wh}^ primary batteries are not used for the purpose of developing power is not that they could not be so used, but because the zinc and sulphuric acid which would be required to produce the power are so expensive as to be prohibitive. Efforts are being constantly made to produce a battery in which carbon may be used as the posi- tive element. If such a battery could be commercially pro- duced with an efficiency equal to the zinc battery, it would revolutionize the present methods of producing power and be one of the greatest inventions. If a plate of carbon be immersed in fused nitrate of soda and an iron plate be used as the negative element, current will be obtained. There is a dispute as to the source of this current, some claiming that it is electro-chemical and others that it is produced by electro-thermaH effects. In either case the battery has not been sufficiently effective to be practical. A very powerful battery for experiment«al purposes (see Fig. 11) may be constructed by using a number of oarbon brushes or plates' fastened parallel to and close to each side 29 of the zinc plates and arranged so as to be plunged into a solution of sulphuric acid, water and bi-chromate of pot- ash. Figure 11 Dip or plunge "battery. This solution may be made by adding to one quart of water one-half pint of commercial sulphuric acid and one- quarter pound of bi-chromate of potash. The writer has obtained a current of 30 amperes from a single cell of this battery, six inches in diameter and six inches deep. It is necessary to provide means by which the plates may be raised from the solution as soon as the occasion for their use is past. In order to get the best results from the use of the zinc plate when made of commercial zinc, it is necessary to amalgamate it or wet the surface with liquid mercury. This may be easily done by first mechanically cleaning the plate, next removing any grease by the use of potash or 30 scda, and third by immersing it for a few moments in an acid. The acid which is intended to be used as an electro- lite for the battery will answer. This will cause the zinc plate to present a perfectly clean surface, and the mercury will quickly spread all over it. This treatment prevents the acid from attacking the zinc when the outside circuit is not closed. Below is a table giving the names of a number of the more prominent cells m use, and the voltage on an open circuit, the electrolite used and the character of the plates. TABLE IV. DATA OF COMMON BATTERIES. Name of Cell. E.M.F. Plates. Electrolite. Bunsen 1.95 1.93 1.07 1.47 1.50 .90 2.00 Zinc <• a Lead Carbon Copper Carbon Copper Oxide r Nitric and t Sulphuric Acid 1 Nitric and I Sulphuric Acid ( Copper Sulphate t Zinc Sulphate Salamoniac Salamoniac Paste Groove Gravity Leclanche Dry Cell Edison Lelande Lead Storage Caustic Potash Sulphuric Acid It is a fact that with perfectly pure zinc and all condi- tions being perfect, the passage of a certain amount of current through a battery is invariably accompanied by the solution or consumption of a certain amount of zinc. Conversely, if a current from an outside source be passed through a battery from the zinc through the 31 electrolite to the carbon, metallic zinc will be deposited from the solution, provided the battery has been used before the experiment is made. In fact, the amount of electricity which passes through a properly arranged solution may be very accurately meas- ured by the amount of metal which is deposited from the solution. An instrument arranged to measure current in this way is called a volta-meter. Practical electricians will recall the old Edison meters, by which current was measured and sold to customers from the old Edison stations. In this instrument the current was caused to pass from one plate of zinc through a solution of sulphate of zinc and out through a second plate of zinc. The passage of ten amperes for ten hours through this meter causes the solu- tion of 4.33 ounces of zinc from the first plate by which the current enters the solution, and the deposit of an exactly equal amount from the solution upon the second plate. Every month these two plates were removed and weighed and the weight compared with what it was a month before. The amount of current that had passed was calculated from the change in weight. The plate \ which the current enters the solution is called the anode, and the plate by which the current leaves the solution is called the cathode. It will be convenient to remember that the current always carries the metal with it from the anode into the solution and from the solution on to the cathode. In fact, it is easy to determine the direction in which a current is flowing by causing all or a part of the current to pass through a glass tumbler partly filled with a solution of sulphate of copper or blue vitriol, in 32 which are immersed a couple of nails, one connected with each side of the circuit which is to be tested. On one of the nails will appear bubbles of gas, while the other will be more or less rapidly covered with a layer of metallic copper. The current will How from the first nail through the solu- tion to the second nail. A very great deal of attention is now being given to the chemical changes that are brought about by the ac- tion of electric current upon the various chemical com- pounds, and it is the writer's belief that the greatest ad- vances in electrical knowledge during the next few years will be made along this line. ELECTRO-PLATING. We have discussed above the principles upon which elec- tro-plating depend. The general scheme is to cover one mfetal with a thin layer of another metal by electro-chemical means. To do this a solution is prepared and in this solution are immersed a number of aaiodes, usually of nickel, silver, copper, gold or brass, with which it is desired tc plate the second metal. In the same solution is immersed the metal to be plated. A current is passed from the anode through the solu- tion to the metal to be plated, or cathode. The action of the current is to decompose the solution and deposit the metal from the solution on the cathode, at ihe same time forming a portion of acid which in some way passes through the solution to the anode and there dissolves just as much of the anode into the solution as was deposited by the cur- rent out of the solution. 33 The amount of metal deposited upon the cathode de- pends upn the amount of current which flows and upon the time it flows or upon the ampere hours of current. If the amount of current is properly arranged, the metal will be deposited from the solution in an even adhesive layer. If too much current flows, the metal will not be deposited in such a flrm layer and the corners will have a blackened appearance, when the work is said to be burned. The skill of the plater comes, first, in getting the work to be plated chemically clean; second, in arranging the solutions prop- erly; third, in adjusting the lamount of current to the so- lution and the amount of w^ork. One kind of solution is used with zinc, another ^^ith nickel, another with silver, and another wiih copper. Each solution requires special treatment, and to get good results, expert knowledge. It is a peculiar fact that a mixture of metals, such as brass, may be used in plating, but thiat the voltage required with such a solution is two or three times higher than that required by copper or nickel. Below will be found a table of the elements, giving their names, atomic weights, relative resistances by volume, rela- tive resistance by weight and weight deposited by ten am- peres in ten hours. 34 TABLE V. PROPERTIES OF METALS a: (V £ -c o -c >> n § -»-3 .i-H ^ o CO 3 (~> znJH . g o w P bC 1^ 5C Depo J ours peres £^ o "o u ^z< P. s S -^ r-i O ^ t* 8.94 10.5 19.26 e^c^S^ P^o < S.S^ Copper 1.00 1.113 2.203 1.06 1.00 1.27 63.4 108. 197. .2636 Silver .8980 Gold .5460 Aluminum 2.56 7.13 21.5 7.84 8.82 7.30 11.4 8.5 6.72 .526 2.732 13.62 5.33 7.69 6.75 15.55 12.16 16.69 1.95 3.74 6.02 6.46 8.28 8.78 13.05 13.92 23.60 27. 65.2 197. 56. 58.8 118. 207. 122. .0569 Zinc .2710 Platinum .4145 Iron .0776 Nickel .1222 Tin .2453 Lead .4303 German Silver Antimony .1863 Manganese Steel 7.8 13.6 9.8 34.82 89.76 89.92 42.43 62.73 87.23 200. 210. Mercury .8315 Bismuth .3492 STORAGE BATTERIES. When two plates of lead are immersed in a solution of sulphuric acid and a current is passed through the cell, there is a tendency to produce an oxide of lead on one plate and spongy or metallic lead on the other plate. If the plates are properly prepared and the current is sent through the battery repeatedly, first in one direction and then in the other, the cell will finally be completed or formed. This method of making a storage cell is called the Platite process. In a completed storage battery, passing the current through the battery is called charging it, and the charging produces chemical changes on the plates, which will pro- duce electric currents if the plates are connected by a wire outside the battery. When current is flowing from the battery it is said to be discharging. The battery will continue to discharge un- til the chemical products formed by the charging current have been reduced to their original state. The advantages possessed by the storage battery over the primary battery are that there is no polarization and the resistance of the battery may be made very much lower than that of a pri- mary battery. As its name indicates, the storage battery is practically a device for absorbing energy from an electric circuit at one time and restoring it to the electric circuit at some subsequent time. The charging current in a good battery may vary between wide limits, but the best results will be obtained from a moderately small amount of charging cur- rent. The same thing is true of the amount of the current Ji 36 during discharge. The best modern storage batteries use6 for horseless carriage work, where extreme lightness is es- sential, have a capacity of two ampere hours per battery for every pound of weight in the battery and a capacity of four watt hours per pound in the battery. The two principal uses for storage batteries at the pres- ent time are for storing power in central stations during times of light Joad, so that it can deliver the power during the time of the heaviest load, and second, for furnishing electric current for motors for horseless carriages and elec- tric launches. Storage batteries may also be used to great advantage near the end of a long line which has an inter- mittent load on it. The battery will absorb current during times of light load and deliver it during times of heavy load, thus making the current that comes over the line from the central station practically constant. The great objections to the storage battery are its cost and weight. So far. no one has succeeded in making a practical battery out of any other material than lead. QUESTIONS ON CHAPTER 11. BATTERIES. 1. What two men were chiefly instrumental in the early development of the electric battery? 2. Describe a way in which a simple battery may be constructed, 3. In which way does the current from a battery flow in the outside circuit? 4. What; is the real cause of the flow of <>urreiit in a battery? 5. What is polarization? 6. What is the positive element in a battery? What is the negative element? 7. What is the positive pole of a battery? 8. What metals may be used to advantag-e in place of copper in a battery? 9. Consulting table No. 2, why is it that zinc and car- bon produce a higher E. M. F. than zinc and capper? 10. What means are used to prevent hydrogen from aj)- pearing on the negative element? 38 11. Describe a chemical means for preventing* hydrogen from appearing on a negative element? 12. Why are primary 'batteries not used to develop power? 13. Describe a battery in which carbon is used as a positive element. 14. How may a powerful battery for experimental pur- poses be made? 15. In order to get the best results from a zinc plate when used in a battery, how must it be treated? 16. What is the relation* between the amount of zinc consumed in a battery and the amount of current it pro- duces? 17. What is a voltameter? 18. Describe the Edison current recording meter. 19. What is an anode? What is a cathode? 20. Does a current of electricity carry a metal with it or against it? 21. How may the direction of a current be determined by chemical means? ELECTRO-PLATING. 1. What is accomplished by electro-plating? 2. Describe the process of electro-plating. 3. On what does the amount of metal deposited depend? 39 4. What is the effect of having too much current in electro-plating? 5. lb it possible to plate with an alloy, such as brass? If so, how? STORAGE BATTERIES. 1. What is a storage battery? 2. Describe the process of charge and discharge. 3. What advantages does the storage battery possess over ordinary batteries? 4w For what are storage batteries usea/ y. CHAPTER m. MAGNETISM. If a hard piece of steel be brought into contact with a mag^net it will become magnetized and will retain more or less of the magnetism. If steel of the proper kind and which has had the proper treatment is chosen, the mag- netism will be constant, almost absolutely constant. Tung- sten steel, artificially aged, is used for volt meters and measuring instruments in which the accuracy of the instru- ment depends on the constancy of the magnetism of the steel, and the steel meets the requirements. If a magnet is supported so as to be free to turn in a horizontal plane, it will set itself north and south, as is seen in the mariner's compass. The pole that turns toward the north is called the north or N. pole and the other the south or S. pole. It is a fact that like poles repel each other and unlike poles at- tract each other. The earth on which we live is a great mag-net, and this has its S. magnetic pole at or near the north geographical pole, for if by definition a N. pole is one that points to the north and unlike poles attract each other, the N. pole of the compass must point toward the S. magnetic pole of the earth. 41 A magnet is surrounded by what is called a field of force. What are called lines of force are supposed to springs from the iron or steel at the north pole, pass through the air to the south pole, enter the iron and pass through it to the north pole. The lines of force are said to flow in the direction indicated. This should be carefully kept in mind, as it will be . used a great deal later. A line of force is always a closed curve, and if any one travels along the whole ^*.--v,----, of a line of force one will al- ways come to the -starting point. A line of force is the direction of the magnetic force at any point. The lines of force from the earth are flowing in the air from the south to the north. Near the equator the magnetic force acting on a horizontal compass needle is greater than in other parts of the earth. The earth as a magnet acts on a horizontal compass in the United States with a force corresponding to from one to two magnetic lines per square inch. If a bar raagnet be placed under a piece* of pasteboard or glass, and iron filings be sprinkled over the pasteboard or glass, they will arrange themselves along Figure 13 Bar magnet and field of force. 42 the lines of force. A picture of the mag-netic lines produced in this way is called a magnetic spectrum. A bar magrnet bent iniio a TT shape is called a horse-shoe magnet, and it is interesting -to get the magnetic spectrum of such a magnet. (See Fig. 20.) The region of powerful influence is smaller than with a bar magnet, but much more intense. The spectrum of two horse-shoe magnets attract- ing aind repelling each other is very instructive* A wire carrj/ing a current has a very peculiar si^ectrum. This spec- trum consists of concentric circles, denser near the wire than at a dis- tance form it, as indicated in the sketch. When the direction of the cur- renit is reversed, the direction of the lines is reversed. It is possible to find the direction of a current in a wire by the use of a compass by deter- mining in what direction the concentric mag- netic lines or magnetic whirl flows. A free north pole w^ould move in the direction in which the magnetic lines flow, or would revolve around the wire. . It is not possible, of course, to obtain a free north pole or a north pole with- out a south pole, so that all that can practically be discov- ered is the direction in which the north pole of a compass is moved. The direction in which the north pole is moved is the direction of the whirl, and the direction, of the whirl bears the same relation to that of the current that the direction of rotation of a screw bears to its motion back and forth. Figure 14 Magnetic spectum of wire carrying current. 43 If the north pole of a compass moves in a rig-ht hand direction, it shows that the lines of force flow right hand- ed and that the current is flowing away from the observer. If the north pole of a compass is moved to the right when placed over a wire carrying current, it shows that the whirl is right _ handed and the current is flowing away from the ob- ^, ^ -^ Figure 15 server. Direction of current indicated by motion of compass needle If, on the other hand, placed under a wire ^ ,, . - ^ - carrying current, it moves to the right when placed under the wire, it shows that the whirl is left handed and that current is trav- eling toward the observer. It is a fact that when current is caused to circulate around an iron or steel core, the core becomes magnetized, and if the current is strong Enough the core becomes much more strongly magnetized than is possible with permanent magnets. It is easy to get a magnet of such strength that the armature is attracted with a force of 125 pounds per square inch, and in extreme cases the magnetism of a piece of soft iron has been pushed to such an extent as to produce a magnetic pressure of 1,000 pounds per square inch. A piece of soft iron surrounded with such a circulating current becomes a powerful electro- magnet, but almost all the magnetism disappears when the current is withdrawn. There Ls a relation between the polarity of an electro- magnet and the direction in which the current circulates around the magnet core. When the current circulates 44 arouDd the magnet in 'the direction of the motion of the hands of a watch, the pole facing the observer in a S. pole. A little thought will show that the magnetism of an elec- tro-magnet may be regarded as the sum of the magnetic whirls of the wires surrounding the core. An inspection of Fig. 17 will show this. A helix is a coil of wire carrying a ^;^--r-r>--V2fr:^ current; the name is usually applied ; ^@' (^r i^ *^j t^))y only to a single long spiral of wire. piece of iron placed in a helix carry- current becomes an electro-magnet. A helix carrying current has all the properties of an electro-magnet, but the magnetic properties are not so pow- erful. Figure 16 Relation between polarity of electric magnet and direc- tion oi exciting current. ^^^^^^^ A pi Figure 17 Showing that the mag- netic lines of a helix or electromagnet are due to the addition of the mag- netic whirls of the wires carrying the exciting current. in an acid solution, copper are connected with a helix. This helix will turn and point north and south in the same way a com- pass would. It is attracted or re- pelled by a permanent magnet in the same way that a compass is. If there were two of them floating in the same vat they would arrange themselves end to end with N. and S. poles adjacent. Fig. 18 shows a zinc and copper plate attached to a cork and floating The zinc and Figure 18 Floating helix and electromagnet. 45 If now a piece of soft iron be placed in the helix all the above actions become much stronger, but this is the only difference. A piece of hard steel may be made into a permanent magnet by being inserted into a helix carrying current. A helix with a large number of turns is called a solenoid. A very important relation exists between a w^ire carry- ing a current and a magnetic field. A magnetic field is a space through w;iich the mangetic lines travel. Figure 19 . Magnetic spectrum of a helix ; compare with spectrum of bar magnet. ^^, Figure 20 Wire carrying current in a magnetic field tending to move in or out of the magnet- 46 Fig". 20 shows a liorse-shoe magnet and in such a mag- net the most powerful field exists betw^een the ends. Fig. 20 also shows a wire placed in this field and at right angles to the plane of the magnet. If, now, current be sent through this wire, it will experience a mechanical force tending t« move it sideways across the lines of force, either into or out of the magnet. Figure 21 Fig. 21 shows a method by which a wire carrying a cuiv rent and free to move may be arranged. This is a most important experiment, and, if possible, should be performed by every one interested in the study of electricity. The experiment shown in Fig. 21 is the fundamental experiment showing why it is that a motor will operate. By reversing the experiment shown in Fig. 21, and by causing the wire to move across the lines of force, it is possible to generate current in the wire. This Is a fundamental experiment, for it shows in the simplest possible manner how mechanical power can be transformed into electrical power, or how a dynamo works. The relations that exist between the direc- 47 tion of motion of the wire, the direction of lines of force and the direction of the current in the wire when moved by- hand or by mechanical force, is most easily remembered bv extending the thumb, first and second finger of Figure 22 Rotation of direction of lines, motion and current illustrated. • the right hand at right angles to each other. When so ex- tended the thumb points in the direction of the motion, the first finger points in the direction of the magnetic lines, a^d the second finger in the direction of the resulting current. The rule for remembering the direction of motion, lines and current when the wire is supplied with a current from 48 a battery or other source Is the same as the case of a wire moved by mechanical force, given above, except that the thumb, first and second fingers of the left hand are used instead of the right. DmeCTfON OF Figure 23 JpToduction of E. M. F. by moving wire in magnetic field. ' Figure 24 Passage of current through a loop in a motor and resulting motion. Fig. 24 shows an electric motor in which the rules given above may be applied. In Fig. 24 the N. pole is shown at the top and consequently the .magnetic lines flow downwards, across the upper air gap and through the ar- 49 mature iron and across the lower air gap. If, now, cur- rent flows from some external source through the loop from A to B, the wire iai the upper gap will be forced to the left. As the current in the other side of the loop will be flow- ing in the opposite direction to that in the upper side, this part of the loop will be forced to the right; thus the wire in "Ehe upper air gap and the wire in the lower gap both tend to rotate in a direction opposite to that of the hands of a watch. Since the direction of the current in all the wires in the upper air gap in an actual armature is the same, each of these wires will be forced to the left and in a similar manner each of the wires in the lower air gap will be forced to the right. The sum of the mechanical forces acting on the wires in the upper and lower air gaps is the torque or twisting effort of the armature. The mechanical force de- pends on two things, viz: the number of magnetic lines flow- ing across the air gap and the current flowing in each wire. When a wire one foot long is in a field of an intensity of 100,000 lines per square inch, there will be a mechanical force of ,106 pounds or 1.7 ounces pushing the wire sideways for every ampere of current flowing in the wire. It is clear now why it is so necessary to fasten the wires to the arma- ture by'bands, for it is not the iron which tends to move, but the wire on the outside of the iron, and in order to communicate the torque from the wire to the iron some such means are necessary. Fig. 25 shows the same machine as Fig. 24, except that the armature is driven in the opposite direction by me- chanical power. We have the north pole at the top and the current tending to flow through the wire in the same direction as in Fig. 24. There will be a drag on each wire 50 proiportional to the number of lines which flow across the upper air gap through the armature and across the lower air gap, and also proportional to the current which is flow- ing in each wire. Figure 25 Motion of a wire i*i a magnetic field and the resulting current. Since there is the same mechanical drag in each wire in the upper air gap and an equal mechanical drag in the opposite direction in each wire in the lower air gap, it re- quires a mechanical torque or twisting effort on the arma- ture to force the wires carrying the current through the air gaps. It sometimes happens that when very excessive currents pass through the wires on an armature the me- chanical drag is such that the wires slip over the surface of the iron, usually cutting through the insulation at some point and burning out the armature. This is one advantage of the modern tunnel wound armature, for its construction gives an almost perfect mechanical support to the armature wires. When a wire moves so as to cut 100,000,000 lines of force per second, there is produced in this wire an electro- motive force of one volt. It will pay the student to per- form the experiments illustrated in this chapter, as he can in this way gain a first-hand knowledge of the fundamental principles upon which the operation of motors and dynamos depend which can be secured in no other way. QUESTIONS ON CHAPTER III. 1. What happens if a hard piece of steel is brougiit eontact with a magnet? 2. What is a mariner's compass? 3. What is the north pole? The south pole? 4. What is a field of force? 5. In what direction do magnetic lines flow? 6. What is a magnetic spectrum? 7. What is peculiar in the magnetic spectrum of a horse-shoe magnet? 8. Describe the magnetic spectrum of a wire carrying a current. 9. What is a magnetic whirl? 10. What is the relation between the direction of flow of current in a wire and the direction of the magnetic whirl? i J * 11. If the current in a vertical wire moves the north pole of a compass to the right when the compass is held between the wire and the observer, in what direction does the current flow? 12. A wire running north and south causes the north pole of a compass placed over it to be deflected toward the west; which way is the current flowing in the wire? 13. A lineman wished to learn the direction of the current in a wire over his head and observed that the com- 52 pass needle when held over the wire face down was deflected toward the east, the wire running north and south. In what direction does the current flow in the wire? 14. What is an electro-magnet? 15. What is the difference between a permanent mag- net and an electro-magnet? 16. What is the relation between the polarity of aai elec- tro-magnet and the direction in which the current circu- lates around the iron core? 17. Is there any relation between the polarity of an electro-magnet and the magnetic whirls in the wires of which it is composed? If so, what? 18. What is a helix? What are its properties? 19. What is flie difference between a helix and an electro-magnet? 20. When a wire carrying a current is placed in the field of a horse-shoe magnet, what occurs? 21. Explain the action of the mechanism in Fig. 20 when it operates as a motor. 22. Explain its action when it operates as a dynamo. 23. What is the relation between the direction of the motion, direction of the lines and the direction of the cur- rent when the apparatus is used as a dynamo? 24. What is the relation between the direction of the motion, the direction of the lines of force and the direction of the current when the apparatus is being used as a motor? 25. Why will the armature in Fig. 21 reverse its direc- tion of motion if the north pole were placed at the bottom instead of at the top? 53 26. Why is it that both wires in the loop in Fig. 21 ten3 to rotate the armature in the same direction? • 27. We have seen that the earth is a great magnet, with its south magnetic pole near its north geographical pole. If a person is riding a biciycle toward the west, in what direction will the E. M. F. be generated in the vertical spokes in the moving wheel? 28. If a current is traveling in a coil of wire that is free to move, and the coil turns so that its plane is east and west, in what direction will a current be flowing in this coil? 29. Two men standing in an east and west line, 50 feet apart, raise a steel tape from the ground. In what direction does the current tend to flow along the steel tape? 30. In an Edison motor the armature is revolving right- handed as seen by the observer. If the pole on the left is a north pole, in which direction does the current flow in the wires under the north pole? 31. When a wire is in a field of 100,000 lines per square inch, what is the mechanical force acting on the wire per ampere per foot? 32. How many magnetic lines must be cut per second to produce one volt? 33. Is there any other reason for banding down arma* ture wires to the core except to prevent the action of centri- fugal force? / CHAPTER IV. THE MAG^^ETIC CIRCUIT. De La Rives' floating battery (Fig. 18) showed that a helix canying a current is a magnet. If the current is measured and the number of turns counted, it will be found that the strength of a given helix depends on the number of amperes of current that flow through it, and if a con- stant current is used the strength of the helix depends on the number of turns. Putting these two facts together, we see that ihe strength of any helix is proportional to the product of the number of turns times the number of amperes or the am- pere turns. The number of ampere turns is a measure of the magnetizing force. 'By producing the magnetic spec- trum of a helix (Fig. 19) it will be seen that all the lines traverse the center of the helix and return through the space outside of the helix. If the diameter of the helix is large, more lines will flow through it than if it is small. If it is short, more lines will flow through it, other things being equal, than if.it is long. A careful consideration of these experiments will show that there is the same relation be- tween the number of lines of force and the magnetizing force or number of ampere turns and the magnetic resist- ance that there is between the current, voltage and resist- ance in the electric circuit. If we allow N to represent the number of lines of force produced, A T to represent the 55 number of ampere turns, and M R to represent the mag- netic resistance or reluctance, we have N equals A-T divid- A T ed by M Jl, or . It will be noticed at once that this is M R Ohm's law transferred to the magnetic circuit. The magnetic resistance is proportional to .the length of the magnetic circuit and is inversely proportiomal to the 1 area of MR equals — , where 1 is the length of the magnetic A circuit and A equals the area. Substituting this in the for- mula we have A N equals A-T multiplied by — 1 If A and L be expressed in inch measurements, we have A-T multiplied by A X equals (4) 1 multiplied by .3132 We will now see what effect the introduc- tion of iron into the helix wili have. Figs. 18 and 19 show that current flowing in a helix produces lines of force in the helix and causes it to become a weak magnet. If a piece of soft iron be inserted in the helix, the iron becomes very strongly magnetized. It can be shown that a great many more magnetic lines of force traverse the helix when it has the ircm inside than before. Therefore the iron offers an easier path for the magnetic liues than the air did because more lines flow under the same circumstances when the helix is filled with iron than when the iron is absent. Under some circum^ m stances the iron will -transmit or allow to pass 3,000 times as many lines as the air The presence of the iron multiplies the numDer of mag- netic lines by offering an easier path for the flow of the lines. If it was not for this multiplying action of the iron, dynamo electric machinery would be impossible. That property of iron, in virtue of which it conducts magnetic lines, is called permeability. Now the permeability of iron is not constant. When ftnly a few lines are flowing in a piece of iron the perme- ability or multiplying power is greatest. If the iron is al- ready carrying a large number of lines the permeability will be small. The capacity of the iron for carrying lines may be com- pared to the capacity of a sponge for soaking up water. When the sponge has only a little water in it, it will readily absorb more, but when the sponge has taken up nearly as much water as it will, or is saturated, it will ab- sorb more water only with reluctance. When iron is car- rying about as much magnetism or as many magnetic lines as it will, it is said to be saturated. The permeability of iron at various numbers of lines per square inch in the iron or at various degrees of saturation has been measured, and the results obtained are shown in the following table: 5« ^ I'ABLE VI. TABLE OF PERMEABILITY WROUGHT IRON CAST IRON o < t-i o <5 u k: ^S|c J=! •iH ^^^A s: rmeab Multi gPow Iron el S fl Ampe Turns Inchi Lengt II Ampe Turns j Inch i Lengt ss 3 h5cq 5 30,000 3,060 9.8 3.06 25,000 833 300 9.4 <^,000 2,780 14.4 4.72 30,000 580 51.7 10.2 50.000 2,488 20.1 6.29 35,000 390 89.7 27.5 60,000 2,175 28.0 8.76 40,000 245 163. 51. 65,000 1980 32.8 10.26 45.000 135 333. 104. 70,000 1,920 40.7 12.7 50,000 110 454, 142. 75,000 1,500 50.0 15.6 60,000 66 90y. 284. 80,000 1,260 63.5 19.8 70,000 40 1750. 548. 85.000 1,030 830 82.5 108.0 25.8 33.8 90,000 95,000 610 156. 48 8 100,000 420 238. 74.5 105,000 280 375. 117. 110,000 175 629. 197. 115,000 95 1210. 378. 120.000 60 2000. 626. 125,000 40 3125. 978. 130,000 30 4333. 1356. 135,000 24 5626. 1761, * 140,000 18 7777. 2434. ^ 68 ;«060Cf}t4 iDOOoa 60OOO «0000 40000 Coooc 1600 B. H. Cnrve Curves showing the same relations graphically that the table gives numerically. This table vras calculated by measuring the number of magnetic lines flowing through an iron ring surrounded by a certain number of turns of wire (see Fig. 27) and comparing this with the number that would flow through the air when a wire coil of the same size, carrying the sama current, was tested in the air (see Fig. 26). Figure 26 Coil of wire in air. 59 The number of lines flo-\ving in the coil in Fig. 26 may- be ealcnlated by Formula 4, or measured by coil and gal- anometer as in Fig. 27. Fig. 27 shows the same coil as in Fig. 26, except that the coil is fiJled with iron instead of air. The number of lines flowing may be measured with a small coil and galvanometer. By passing the same currents through both coils in Figs. 26 and 27 and comparing the number of magnetic lines produced, the permeability of the iron is found. If there are 100 turns in each coil, and one ampere is flowing through each coil, suppose current in coil in Fig. 26 produces 100 lines and current in coil in Fig. 27 produces 185,000 lines, then the permeability of the iron is 185,000 divided by 100 equals 1,850 at this stage of saturation. Figure 27 Same coil as in Figure 26 with iron core. In the above table the first column represents the num- ber of lines of force which flow through the iron. The sec- ond column is the permeability or multiplying power of the iron. The third column is the number of magnetic lines 60 there would be in air. The fourth column is the ampere turns required to force the magnetic lines through one inch of iron at the given density. The first part of this table is devoted to ordinary wrought iron and may be used in a general way to represent the magnetic properties of char- coal and sheet iron, soft sheet steel and cast steel. The second part of this table represents the properties of ordinary cast iron. It must be carefully kept in mind that while these ta- bles give a general idea of the map-netic properties of iron, QO two specimens of iron are exactly alike, and if it is de- sired to get an accurate know^ledge of the magnetic quali- ties of any particular sample of iron, it is necessary to make a separate test for this sample and construct a table similar to table Xo. 5 for each sample. It will be noticed that in a general w^ay wrought iron conducts the magnetic lines about twice as well as cast iron. WTien formula (5) is revised, so as to introduce the per- a. t. X A X // meability of the iron, it becomes N equals (5) 1 X .3132 in which /z represents the value of the permeability. We will now take an example and calculate the ampere turns required to force a given number of magnetic lines through the various parts of the magnetic circuit. We will select the Edison type of bi-polar dynamo for this calcula- tion. The easiest way to' make this calculation is to find the number of ampere turns required in each part of the magnetic circuit and add together the numbers so found. 61 In this example we will find ithe number of ampere turns required in the yoke, which is of wrought iron, next that required in each magnet core, next that required in each pole piece, then that required in each air gap and last that required in the armature iron. In Fig. 28 the dimensions of the parts have been indi- cated and the approximate length of the average magnetic line is shown. Let us suppose that 4,500,000 magnetic lines flow through the magnetic circuit of this dynamo. This will cause 4,500,000 divided by 54, or 83333, to flow per sqi'.are inch through the yoke. The following formula may Nxlx.3132 be deduced from formula 4: A. t. equals (6), in A X // Figure 28 Magnetic circuit of Edison bipolar dynamo. t)2 which N equals the total flow of magnetic lines in the part of the magnetic circuit considered, 1 equals length in inches of this part of the magnetic circuit, A equals area in square inches of this part of the magnetic circuit; // equals the permeability of this part of the magnetic circuit, with the particular Talue of N that may exist and the value of u must in each casi be found from the table. Substituting these quantities in formula (6) we have for the yoke X equals 4,500,000; 1 equals 22 inches; A, or the area of the cross section of the magnetic circuit in square inches, which in this case equals 6 multiplied by 9, or 54; and fi, or the permeability, equals 1,107. This is found by consulting the table, in w^hich it is seen that the permeability of wrought iron equals 1260 at 80,000 lines per square inch. That the permeability at 85,000 lines per square inch is 1030. The permeability of 83,333 lines wdll be approximately 2-3 the difference be- tween these two permeabilities, or 1260 — 153 or 1107. 4,500,000x22x.3132 a. t. equals equals 520 54x1107 The a. t. required in the magnet core will be found by substituting for N, 4,500,000 as before, for 1 or length of this part of the magnetic circuit, 10 inches. For A, or the cross section of the magnetic circuit at this point, we have 50.26 square inches, which is the area of a circle 8 inches in diameter. To ascertain the value of fi it is necessary to find out how many lines per square inch flow through the magnet core. In order to do this, divide 4,500,000 by 50.26, which g-ives 89,534 lines per square inch. This is sufficiently close 63 to 90,000 lines to take the permeability of 90,000 lines from the table, and, substituting* 830 for the value of ^i, we have 4,500,000xl0x.3132 a. t. equals equals 338 50.26x830 Xext we take up the number of a. t. required in the pole piece. This is of east iron and the area of cross sec- tion is indicated in the sketch as being 12 inches x 12 inches, or 144 square inches. The flux per square inch is 4,500,000 divided by 144 equals 31,?50. The ampere turns required in this part of the magnetic circuit would be 4,500,000x9x.3132 a. t. equals equals 166 144x532 It must be kept in mind that the pole pieces are of cast iron and therefore the permeability is much lower than if they were of wrought iron. The ampere turns required in the air gap are 4,500,000xlx.3132 a. t. equals equals 10,313 138x1 The air gap in an actual dynamo is partly filled with copper wire and insulation, but this conducts magnetic lines no better than air. The area of the air gap is calculated on the assumption that the pole pieces embrace two-thirds of the circuniler- ence of the armature. As per the sketch, the pole piece is 12 inches long and the average diameter of the air gap is 64 11 inches, and the circumference of a circle 11 inches in diameter is 34.54 inches. One-third of this is 11.5 and the area of the air gap is 11.5x12 equals 13S square inches. It will be noticed that the numoer of ampere turns re- quired in the air gap is vastly greater than that required in any other part of the magnetic crrcuit, and is a good example of how much better a conductor of magnetic lines iron is than air or any ordinary material. The ampere turns required in the armature iron are 4,500,000x9x.3132 a. t. equals equals 84 72x2077 In this part of the circuit the area of cross section of the magnetic circuit is taken as 6 multiplied by 12 inches equals 72 square inches, because the shaft is 4 inches in diameter, and for reasons that will appear later the lines cannot flow across the shaft when the armature is in motion. There are two coils on the dynamo, one on each magnet core,, and each of these two are of equal power and each does half the work of driving the magnetic lines around the circuit. If we wish to find the number of ampere turns that each should supply, we must add together half those required for the yoke, all in one magnet core, all in one pole piece, all In one air gap, and half those in the armaturS iron. Gathering these results together, we have: Half a. t. required in yoke ' 260 All a. t. required in magnet core 338 All a. t. required in pole piece 166 All a. t. required in one air gap. .... .10,213 Half a. t. required in armature iron.. 42 Total a. t. required in half of mag- netic circuit 11,019 65 Each of the two coils will then be required to produce 11,019 ampere turns in order to force 4,500,000 magnetic lines around the magnetic circuit. The method of calculating the size of wire required in the coil to produce this number of ampere turns will be explained in one of the succeeding chapters. The Edison type of dynamo is an excellent example of the older style of dynamos that were built eight or ten years ago. The prevailing style for large machines at the present time has the multipolar field and ironclad armature. The ironclad armature is well adapted for all 'sizes of machines, while the multipolar construction is especially advantageous in machines of large output, but for machines of less than 10 H. P. is not so good as the bipolar construc- tion, as will be explained in the chapter on Hysteresis and Eddy Currents. Figs. 29 and 30 show diagrams of the two styles of ar- mature in the same field frame. Figure 29 Smooth core armature. 66 The chief reason tha.t ironclad armatures have come into use is that by means of this device the magnetic re- sistance of the air gap is very much reduced. The practical effect of the introduction of the ironclad armature is to make the carrying capacity of the iron of the magnetic circuit the limit of the flux through the cir- cuit. The resistance to the magnetic flux in the air gap of the ironclad armature is not over one-fifth that in a smooth core armature of the same capacity. The ironclad arma- ture may be run so that there is only enough room between the armature iron and the iron of the field frame to permit of mechanical rotation- It will be noticed that the wire on the ironclad arma- ture is buried in slots, cut in the armature. This protects them from mechanical injury, and, more important still. FignreSO Iron clad armature. 67 gives them perfect mechanical support, so that there is no tendency to slide or move from their places as there is in the smooth core armature. 'Practically all of the magnetic flux that passes into the armature must get through the bottom of the iron teeth of the armature, and the area of this part of the magnetic cir- cuit determines the total flux that can be used. We w^ill now calculate the ampere turns required in a bi-polar machine v^ith an ironclad armature, and also the ampere turns required in a six-pole field with ironclad ar- mature. Figure 31 Magnetic circuit of 5 H. P. bipolar machine with iron clad armature, and cast iron field frame. 68 The bipolar machine is shown in Fig*. 31 and the dimen- sions are those actually used in a 5 H. P. motor. It will be noticed that in this machine the yoke is in two parts and half of the flux flows through each part. The frame is so designed that the fliix is most dense in the frame in the pole pieces. The sectional area of the pole pieces is show^n in Fig. 32. The area will be 9x51/, or 49f/C, less what is cut off of the corners. A circle 3 inches in diameter has an area of about 7 square inches, which is 2 square inches less than a surface 3 inches square, so that the area of the pole piece will be 491/2 minus 2 equals 4714 square inches. This machine has a flux of 2,100,000 lines. At this flux the density in the pole piece will be 2,100,000 divided by 47^^ equals 44,210. Oi SI Figure 32 Calculation of Sectional area of pole piece. The average length of the magnetic line in each pole piece is 4 inches. The permeability of cast iron at 44,1^0 is 153. Substi- tuting in the formula Ko. (6) we have 2,100,000x4x.3132 a. t. equals equals 362 in each m.agnet core. 47.5x153 The flnx in the yoke can all be calculated at the same time, for the density all through the yoke is the same, and consequently the value of the permeability or /i is the same. aux is 2,100,000 divided by (2%xl0x2) equals 2,100,000 divid- ed by 52.5 equals 40,000. The permeability at 40,000 lines per square inch in cast iron is 245. Substituting we have 2,100,000xl2x.3132 a. t. equals equals 613 52.5x245 in each half of the yoke. The area of the air gap is not the whole area of the pole face, for with an air gap 1-16 inch long there is a bunch- ing of the lines to a greater or less extent, as shown in Fig. 33. It is important to calculate the area of the air gap carefully, for on this will depend the number of a. t. in the air gap, and this number is much greater than that for any other part of the circuit, and an error in this calculation will have a greater effect on the total result than in any other. There are 48 sloits in a disc 7l^ inches in diameter and each slot is .230 inches wide; the circumference of the disc is 23.55. Each slot and tooth take up 23.55 divided, by 48 equals .491. This leaves the top of the tooth .491— .230 equals .261 wide. The lines will spread from the top of the teeth to the iron pole piece. Each pole piece embraces or covers 16 teeth. Experience teaches 'that it is safe to assume that the lines spread from the top of the teeth, so that the top of the tuft is equal in width to the ^op of the tooth plus twice the width of the air gap, but the average Figure 33 Bunching of magnetic lines in air gap. 70 width will be only half this. The average width of the tuft will be .261 plus .062 equals .323. Since the length of the armature is 51/2 and there are 48 teeth in the armature, we have 16 tufts of lines each 5^^ inches long x .323 wide. The area of the air gap is then 16x5.5x.323 equals 28.4. Substituting w^e have 2,100,000xlx.3132 a. t. equals equals 1447 28.4x16 The magnetic lines are very much crow^ded in the arma- ture teeth, and the density changes at each point in the length of the teeth, so that theoretically a separate calcu- lation w^ould have to be made for each part in the length of the tooth. A sufficiently close approximation, however, may l)e made by making two calculations, one for the ampere turns required for a length of i/g inch at the bottom of the teeth and the other for the rest of the tooth. It is first necessary to find the area of the "bottom of the teeth. The slots are % inch deep, .230 inches wide a.nd round at the bottom. This being so, the narrowest place in the tooth will be .750 minus .115 equals .635 from the outside of the disc, for there is a circle .230 in diameter at the bottom of the slot. The circumference of a circle whose periphery passes through the narrowest part of the tooth is 3.i416x[7.5— .0:55x2] equals 3.1416x6.23 equals 19.57. 1-48 of this circumference equals .408. .408 — .230 equals .178 inches, which is the width of the tooth at its thinnest point. 71 The area of the tooth at the bottom is .178x5.5x16 equals 15.66. The flux at the bottom of the teeth is 2,100,000 divided by 15.66 equals 134,100. The permeability at this flux is 30 — 4-5(30 — ^24) equals 25. Substituting 2,100,000xlx.3132 a. t. equals equals 210 15.66x8x25 As indicated above, the ampere turns in the rest of the tooth may be found in one calculation. The width of the teeth !n the narrowest place is .178 and in the widest place .2614-.178 is .261. The average width is then equals .219. 2 The average area of the teeth will be .219x5. 5x'l'6 equals 19.3 square inches. This area gives a flux of 2,100,000 divided by 19.3 equals 109,000, and the permeability at this density is 280 — 4-5 (280 — 175) equals 19G. Substituting we have 2,100,000x5x.3132 a. t. equals equals 108 19.3x8x196 The last calculation to make is ampere turns required for the armature iron. The area of iron carrying lines is 5V3x[7i^ — (IVs-j-lVi)] equals 4%x5i/< equals 26.1. The flux per square incTf ^vTif he 2,100,000 divided by 26.1 equals 80,460. The permeability at this density equals 1,237. The a. t. required for armature iron 2,100,000x5x.3132 a. t. equals equals 102 26.1x1237 72 Collecting" our results we have: A. t. required in eaeli mag-net cdre composing the magnetizing coil will be greater than that assumed in the formula. Wire enough should be put on the coil so that the watts lost will not be over .8 per square inch, and much more satisfactory results will be obtained if enough are used so that only .5 watts will have to be radiated per square ii^ch. In the coil for the Edison dynamo the radiating surface is 10 inches x the circumference of a circle 12 inches in diameter, or 10x37.64 equals 376.4 sq. in. While a large part of the heat radiated from the coil will escape from the outside, almost as much will be radiated from the ends of the coil and into the iron core inside. The iron core will conduct the heat to the heavy pole piece and yoke, where it is quickly radiated. im It is safe to allow three-fourths as much radiating sur- face for the rest of the coil as it has direct radiating sur- face, so the total radiating surface is 376-j-%(376) equals 658 square inches. At % watt per square inch we have wasted in this coil 329 watts, and at 110 volts this means a current of 329 divided by 110 equals 3.0 amperes. We have seen that if the coil has only one pound of wire 344 amperes will flow. If only three amperes are wanted, we will have to make the coil weigh 344 divided by 3 equals 115 pounds. The final result as to the winding for the magnetizing coil for the Edison dynamo is then 115 pounds of Xo. 15 B. & S. wire. The next question is, will the space allowed for the winding take so much wire as this? The cross section of the coil was 2 inches x 10 inches and the average length of each turn was 2.62 feet. The number of turns in each layer would be 10 inches divided by .065, for No. 15 wire is .057 under the insulation and will be about .065 over the insulation if single cotton-covered wire be used. 10 divided by .065 equals 153 turns per layer. The number of layers will be 2 divided by .065 equals 31. The number of feet on the coil -will be 153x31x2.62 equals 13.427 feet. Table No. 1 shows that single cotton-covered magnet wire weighs 10.13 pounds per 1000 feet, and 12,427 feet will weigh 12.43x10.13 equals 126 pounds. We can get in 126 pounds of wire in the space that 115 pounds should be put in. 108 What sized wire and how much should be used to wind the ironclad dynamo shown in Fig. 31. Here the ampere turns required are 2791; the coil was 3 inches wide x 2 inches thick. The average length of this coil may be found from Fig-. 44. The aver- 6|- ^ age length of the turn is 6 plus 21/^ plus 6 plus 2y/plus (3.1416x5) or the circumference of a cir- cle 5 inches in diameter equals Dimenslons^oTmfg^Detizing coil- 32.7 inches equals 2.72 feet. average length of turn. Suppose this is to be a 500- volt motor, then each of the two coils will be exposed to 250 olts. Substituting in the formula, we have: 11 V. X 2789 X 272 A eouals 250 equals 337.8 or a little larger than No. 25. Xo. 24 will have to be used. No. 24 or .020 wire has 819.2 feet per pound, and 819.2 divided by 2.72 equals 301 turns per pound. Also it has 21 ohms per pound and a one-pound coil allows 250 divided by 21 equals 12 amperes to pass; 12x301 equals the ampere turns of No. 24 wire equals 3612. The coils for this motor are wound on forms and slipped over the pole piece. This allows all the outside and both sides to rarJiate heat, and we may allow one-half the inside surface of the coiJ as a radiating surface. 109 Radiating surface equals (32.7x2x2)-f(39x3)+y2 (26.5x3) equals 288 square inches. At i/o watt per square inch the current will be 144 divided bj^ 250 equals .58 amperes. If a one-pound coil passes 12 amperes, the coil must weigh 12 divided by .58 equals 20.6 pounds to cut the current down to .58 amperes. The winding- for the magnetizing coil for the motor in Fig. 25 for 500 volts is 20.6 pounds of No. 24 wire. It is clear that in a coil exposed to a constant potential the size of the wire and not the amount of wire or number of turns is what determines the magnetizing power. In a constant current dynamo, such as one used for arc lighting, the number of turns determines the magnetizing power, and the size of the wire simply -determines the amount of heating or the energy wasted in the coil. In a coil using constant current it is only necessary to divide the number of ampere turns required by the number of amperes. This gives the turns required. Then select a wire of such size that the coil will not g-et too warm. o The same rule should be followed in calculating the size of wire required for the series coil of a compound wound dynamo. It should he kept in mind that the heating of a shunt coil on a constant voltage raises the resistance and prevents more current from flowing, thus tending to pre- vent the coil from over-heatmg. In the series coil the reverse is true, for the heating of the coil makes the resistance higher and so increases the heating with a given current. J QUESTIONS FOR CHAPTER VIII, 1. In calculating the ampere turns for a magnetizing- coil of any given size of wire, what is the first thing neces- sary to know about the dimensions of the coil? 2. Describe how the number of ampere turns that will be produced by a coil of given dimensions and size of wire may be determined. 3. How many ampere turns will be produced by a ceil whose average diameter is 10 inches, size of w^ire No. 20, coil exposed to an electro-motive force of 110 volts? 4. What size of wire will be required to produce the same number of ampere turns as in preJ, the total flux through the armture, will remain constant as long as the voltage on the exciting coils does not cliange,and T, the number of turns on the armature cannot be changed after the armature is wound. The counter E. M. F. plus the volts lost in the armature must always be equal to the applied E. M. F., and if the resistance of the armature is low, so that onl}'- tw^o or three volts are lost in it at the heaviest load, the counter E. M. F. must remain constant, and if the counter E. M. F. is con- stant, the speed must remain the same. •> Looking at this in another way, the voltage forcing current through the armature is the difference between the applied and the counter E. M. F. If a heavy load is thrown on a motor that requires a heavy current, the first effect will be to reduce the speed. Reducing the speed lowers the counter E. M. F. and this causes a greater E. M. F. to iorce current through the arma- ture. If the applied E. M. F. is 110 volts and the resistance is .01 ohm, and the current required to run the armature with- out any load on it is 6 amperes, the counter E. M. F. is 109.94 volts. If full load is thrown on, which may be' 100 amperes, the loss of voltage in the armature is one volt and the coun- ter E. M. F. is 109 volts. These figures are about what ob- tain in practice. Thus by a change of less than 1% in speed the motor has taken its full load current. In a shunt wound motor the field is constant and the speed is consequently almost perfectly constant. In a series motor, however, the current that supplies the armature and fields is the same, and anything that alters the current in t.he armature alters the current in the field and changes the flux through the armature. Figs. 49 and 50 show a diagram of the winding of a shunt and series motor respectively. I- ^" *■ ^ — - Figure 49 Diagram of connections of shunt motor 125 In the shunt motor the amount of current passing through the armature does not directly affect the amount of magnetic flux which passes through the armature. In the series motor, however, the -amount of current passing through the field coil is directly proportional to the load on the motor. Since in a general way the amount of magnetic flux through the armature is proportional to the magnetiz- ing power of the field coil, the heavier the load on the motor the greater the magnetic flux, and consequently from equa- tion (i-i) the speed drops on account of greater magnetic flux. Figure 50 Diagram of connections of series motor. Another thing which causes the speed to drop is the v^oltage lost in the resistance of the field coil and armature. Due to these two causes the speed of the series motor ia exceedingly variable, being high when the load is light apd the magnetic flux is small, and low when the load is heavy and the magnetic flux is great. 127 Equation (14) put in another way says that the product Df the. speed and the magnetic flux must always be a con- stant quantity as long as the E. M. F. of supply does not change. Consequently, when one of these two quantities (speed and magnetic flux) is large, the other must be smalL When constant current is supplied to a series motor the speed of the armature will tend to become very high and means must be provided for either weakening the field or rocking the brushes so as to prevent tcwD great a rise in the speed of the armature. The old "Baxter arc motors used the first of these meth- ods of controlling the speed, and the Brush arc motors used the second. The transmission of power by constant current machin- ery has been, however, almost entirely abandoned and con- stant current arc dynamos are not nearly so much used as formerly. The constant potential system having taken its place very largely, even for arc lighting. QUESTIONS ON CHAPTER X. :*, What is counter eleotro-motive force? 2. Is there any difference between the counter electro- motive force produced in a motor and the E. M. F. produced in a dynamo? 3. Why will 110 volts force only a few amperes through an armature when it is runmn-g having a resiistance of 1-100 of an ohm? 4. How may the flux through a motor armature be measured by the speed of the armature? 5. A bi-polar motor armature has 66 slots; each coil has thre^ wires; the flux through the armature is 3,600,000 lines. What will be the speed of the armature on 220 volts? 6. If the speed of the armature should be 1,050 revolu- tions, what would the flux be? 7. Why does the speed of a motor increase as the field coils get warm? 8. Give another instance beside that in the text of the identity of ordinary and counter electro-motive force. 9. What makes the shunt motor constant in speed, even under greatly varying loads? 10. Why does the speed in a large armature change less with change of load than in a small armature? 11. Why does rocking the brushes to an extreme back- ward position raise the speed of a motor? 129 12. A two-horse power armature "has a resistance of 8-100 of an ohm; it is designed to run on 80 volts; one am- pere is required to run it at no load; at the heaviest load it is designed to take 30 amperes. What would be the drop of speed in per cent.? 13. Why does the speed of a series motor vary so great- fy with the load? 14. Why does the speed of the series motor change so much less with the load after the iron becomes saturated? 15. Why is the speed of a 500-volt shunt motor with unsaturated magnetic circudt almost as high when running on 110 volts as on 500 volts? 16. How will the speed of a compound wound motor vary ? 17. As long as the magnetic circuit is unsaturated, why is the torque of a series motor proportional to the square of the current? 18. To what is the torque of a shunt motor propor- tional? 19. Why does the speed of a series motor tend to be- come excessively high? 20. How is the speed of constant current motors gov- erned ? r CHAPTER XI. HYSTERESIS AND EDDY CURRENTa When iron is magnetized it tends to retain its magnet- ism, and when the direction of the magnetization is re- versed pow»?r is required to affect this reversal. Hysteresis may be called molecular friction caused by a reversal in positon of the minute molecular magnets of which the iron is supposed to be constituted. If the core of an electro-magnet should be composed of hard steel fil- ings and the direction of current through the magnetizing coil should be reversed, it is clear that there w^ould be an effort on the part of the steel filings to twist around end for end and in doing so there would be more or less fric- tion. Something of this same sort takes place when the direction of magnetization in a piece of iron takes place. It is easy to see that the direction of magnetization in l bi-polar motor armature changes twice every revolution. An examination of Fig. 31 \\ill show that if the left- hand pole be a north pole the magnetic lines will flow through the bottom of the teeth on tlie left-hand side of the armatdre from the top of the teeth to the bottom, and on the right-hand side of the armature from the bottom of the teeth to the top, but when the armature has made a half revolutiofn the direction of the magnetic lines will be reversed in any particular tooth. 1^ 131 Table No. 9 gives Ithe loss in waitts per cubic foot at a speed of 1,200 revolutions per minute in a bi-polar field with various magnetic fluxes per square inch. This table is for g-ood soft wrought iron and the hysteresis loss in the iron of which ordinary armatures are made, is probably higher than that given in the table. TABLE No. IX. HYSTERESIS IN SOFT IRON. Lines uer sn in ^^"^ wasted per cu. ft. at 1200 Lanes per sq. in revolutioDS per miuute in two-pole dynamo. 25,000 73 30,000 108 35,000 130- 40,000 155 45,000 . 182 50,000 216 55,000 238 60,000 275 65,000 ^ 314 70,000 348 75,000 395 80,000 431 85,000 472 90,000 512 95,000 564 100,000 520 105,000 670 110,000 780 115,000 964 120,000 1124 132 It will be noted that in a four-pole field the directiov of magnetization is reversed twice in every revolution, and if the armature in a four-pole machine runs at the same speed that it does in a two-pole, the loss by hysteresis will be twice as great with the four-pole machine as with the two-pole. EDDY OR FOUCAULT CURRENTS. It is clear that there is the same tendency to produce current in the iron part of the armature due to the cutting of the magnetic lines as there is in the copper wire which is wound on its surface. Ji in Fig. 31 the iron core was solid, there would be a very large current circulating in the iron core in the same direction as that which flows through the wire^ in the air gap. Such a current as this would be entirely useless and, worse still, would heat the armature core very hot; consequently, the armature, in- stead of being solid, is built up of thin sheet iron discs. These discs carry the magnetic lines without difficulty and an armature built up of these discs has the same mag- netic properties as a solid wrought iron armature would have. Fig. 51 shows the direction in ^vhich the currents tend to circulate around the armature, land show^s how these cur- rents are prevented from flowing by the ins>ulation between the discs. 133 The discs in Fig*. 51 may be insulated with paper, but la practice it is found that the thin coasting- of ox^de on the outside of each disc is enoug^h to accomplish the same purpose and produces an armature which will always re- main as solid as when first put up. The use of paper be- tween the discs is dangerous, because in time the paper charrs and crumbles to pieces, leaving the discs loose. The best way to treat the discs is to give them a thin coating of linseed oil; this forms a surface having the same insulating properties as paper, and the heat -to whiioh the armature as subjected will not affect it. In practice the discs for arma- tures run from ten to twenty-five thousandths of an inch in thickness. Even in the thinnest disc there are small eddy currents circulating which take power to produce and which heat ihe armature core. The loss by eddy currents is proportional to the square of the speed at which the arma- ture is run, because at double speed, other things being equal, the E. M. F. is twice as great, and this double E. M. F. produces double current. Figure 51 Circulation of eddy currents stopped by lamination of the iroxi. 134 Formula 8 shows that the loss in watts with double volts and double current is four times as great as with the given voltage. It is because of the loss by eddy currents that would occur with solid pole pieces that pole pieces are laminated. A consideration of the way in which E. M. F. is produced shows that when the number of lines of force en- closed by circuit is changed there is an E. M. F. produced which tends to send current around the circuit in such a direction as to oppose the change. When an ironclad armature with a short air gap is re- volved the magnetic lines flow from the pole piece into the armature in tufts or bunches. These bunches of lines pass across the pole piece with the motion of the armature and set up currents in the solid pole piece. It is possible by the use of a long air gap to cause the lines to flow from the pole piece uniforml3\ But vv'ith short air gaps it is necessary to laminate the pole piece in order to get rid of eddy currents. (See Fig. 33). QUESTIONS ON CHAPTER XI. 1. What is nysteresis? 2. What would be the difference in passing an alternat- ing- current and a direct current around an iron core ajs far as hysteresis is concerned? 3. Why is the hysteresis in a four-pole motor (twice as great as in a two-pole? 4. Why is there hysteresis in a revolving* armature? 5. What are eddy currents? 6. In what diirection would the eddy currents tendi to flow in the drum armature shown in Fig*. 46? 7. Why is the iron in an armature laminated? 8. Why are cables used on surface wound armatures instead of solid wires? 9. Wliy does the pole piece of a motor get warm if an iron clad armature is used with too short an air gap? 10. Why will the heating in such a case be much great- er with steel pole pieces than with cast iron? 11. What will be the loss from the eddy current that flows clear around the armature in Fig. 31 »if the flux through the armature is 1,200,000 lines, the speed of the armature is 1,200 revolutions per minute, the resistance of the armature between end plates 1-10 of an ohm and the end plates are so large as to ihave a megligible resisitance ? 136 12. Is there* any difference in their nature between eddy currents and the useful current produced by an arma- ture? 13. Why was paper formerly used between armature discs? . 14. Why has this practice been abandoned? 15. In what way do the watts lost from eddy currents vary with the speed? CHAPTER Xn. ARMATURE REACTION. When a dynamo produces current these currents flow around the armature in such a direction as to magnetize the armature at right angles to the main field magnets. A consideration of Fig. 52 shows this, and if the direction of circulation of current in Figs. 45 and 46 be worked out, the result will be the same. The position of the brashes en the commutator determines ►There the current which flows through the armature shall enter and leave the armature, and so determines the direction of the polarity of the armature as an electro-magnet. If the brushes in Fig. 45 be moved around the commutator the point at which the current divides to pass around the two halves of the Gramme ring will move with it. It is clear that the pole of the armature will be at the point at which the current divides. The strength of the armature as an electro-ipagnet is directly proportional to the amount of current which is drawn from the armature. The practical ett'ect of the arma- ture becoming a powerful magnet is to cause more magnetic lines to pass into the armature at one side of the pole piece Figure 52 Armature reaction in a dynamo. 138 than at the other, for a north pole in the armature wil] attract the lines from the south pole of the held and repel those from the north pole. When this action is sufficiently great, the axis along which the magnetic lines How is ro- tated so as to occupy a posifti'on between the polar- ity caused by the fields alone and that caused by the arma- ture alone. When the brushes are placed as in Fig. 52 mid- way between the north and south poles of the field, the only effect of the magnetization of the armature is to cause more lines to flow into the armature from the top of the pole ^ piece than from the bo^om. The teai'- dency is to rota'te the a:xis of the magnetic lines which pass throuo-h the armature. It does r>r. + ^^^^,. ,. Connter magnetic motive not directly tend to decrease the force of armature reaction, flnx of the lines through the ar- mature. As will be seen in the next chapter, it is necessary in order to stop sparking in a dynamo to rotate the brushes a short distance in the direction of the rotafioTi of the armature. This produces the oomdition of things shown in Fig. 53, in which the armature reaction is such as to directly oppose to some extent the passage of the magnetic flux through the arma- ture. It will be seen that if the brushes were rotated si^il further forward that the magnetism in the armature would still further oppose that of the fields. In arc dynamos the armature is made relatively a very powerful magnet and its magnetizing action is fully equal that of the fields. By rotating the brushes it is easy to see that the amount of magnetic flux w^hich would pass through the armature could be very greatly altered. In the Wood arc dynamo the regu- 139 lation is entirely effected in this way. In the Brush arc dynamo part of the current is shunted by or around the neld coils; this makes the armature relatively muc^h strong er than the fields, and the armature reaction prevents mag- netic flux from flowing- through the armature, as will be more fully explained in the chapter on sparking. When the field is relatively weak, with reference to the armature, it is necessary to rotate the brushes through a considerable arc in order to stop sparking; the rotation of brushes makes the effect of the armature reaction much greater than it otherwise wpuld be. In fact, if the brushes of a Brush arc dynamo be always rotated to such a position that the spark is the same length, it is necessary to reduce the current in the fields only from 9^2 to 7 amperes, to re- duce the flux through the armature from a maximum to zero. The armature reaction with 10 amperes is equal in magnetizing force and opposite to that of the fields with 7 amperes. * If the brushes of a series. dynamo be rocked quite well forward in the direction of rotation and current be sent through the armature alone, the magnetizing force of the armature will set up a powerful magnetizing flux through the armature and fields; and, if the machine be run as a motor, it will operiaite as if Itlhe field coils were in ^aidtiilooi, with the exception that it will spark furiously. In this case the armature reaction furnishes the magnetic field. In ordinary constant potential dynamos and motors the armature reaction is a necessary evil, and the dynamo shoula be carefully designed so that the armature magnetizing force shall never reaoh more than from 1-2 to 2-3 the mag- 140 netizing power of the fields. That is, the ampere 'turns on the armature at full load should be from 1-2 to 2-3 the am- pere turns on the field at full load. As was noticed in Chapter IX, there are twice as many tarns tof wire required on a Gramme ring armature as on a drum armature -to produce the .same number of cfonduc- tors, in which the E. M. F. is set up by means of the rota- tion of the armature; that is, the same number o-f amperes produce twice as many ampere turns in a Gramme ring armature as in a dm of a siix-pole dynamo with a drum armature, and shows the direction in which the cur- rents in the armature flow. It will be seen that the number of turns under each pole may be made quite small, but that the number of ampe-re -turns required on the fields will be larger on the multi-polar machine than on the bi-polar, be- cause the area of iihe. air gap is relatively much smaller. The small number of turns on the arfmature and the largpe number of ampere turns required on the field make it pos- sible for the aiynature to carry very heavy currents, without allowing the number of ampere turns in the armature un- der each pole to become great euough to seriously distort the field. QUESTIONS ON CHAPTER XII. 1. What is ar-mature reaction? 2. On wbat does the strength of the arma;ture as a magnet depend? 3. In wihat way is the armature m-agneti^ed with ref- erence to its field? 4. Why is the pole piece whioh the armature is leav- ing in a dynamo magnetized more strongly than the oppo- site one? 5. Why does -the movement of (the brushes affect the armature reaction? 6. Why does armature reaction usually reduce the amount of flux? 7. H-o^^ would the brushes have to be set in a dynamo to increase -the amount of flux through the armature? 8. In wO^at kind of dynamos is it desirable to have ar- ■natare reaction? 9. How is the regulation of the Wood arc dynamo effected? 10. How is 'the regulation of a Brush arc dynamo ef- feoted? 11. How sbocld the brushes on a motor be set in order to dispense w^th the field coil? 12. In Oonstant potential machinery, how strong is it best to make the magnetizing power of the armature at lull load wi-th reference to the fields? ^ 143 13. Wliy is the Gramme ring* anexcellent form of ar- m'atfurie for a eonstamt current machine aind a poor form for a oonstanit poten'tdal machine as compared with a drum armature ? 14. What device is used to prevent the effect of arma- ture reaction in larg-e machine's? 15. With the siame mumber of turns on the armafture, how much will the farmarture reaction be reduced by chang- ing from "two to fooir pole? CHAPTER Xin. SPARKING. Intimately connected with armature reaction is the sparking" that occurs on the commutator of the direct cur- rent dynamo or motor. Every ordinary machine has a load at ^^^hjch it will spark. Consid- eration of Fig. 55 shows that the current is flowing through the coil in one direction just before it reaches the brush and is flowing through it in the oppo- site direction just after it leaves the brush. During the i'me that the coil is short circuited by the brush, the direc tion of the curreni: is completelj^ reversed. Fig. 55 shows Figure 55 Comnmtation in Gramme ring armature. this in detail. Three coils are shown, a, b and c. In c the current is traveling through the coil in one direction; (he coil b is short circuited by the brush. In c the curreuc /s traveling through the coil in the oppos-ite direction tc that in a. 145 The currents in coils e and a are each equal tto half the total armature current. The current in the short circuited coil will depend ooi the magnetic field in which it is moving- while it is short circuited. If it is still under the influence orf the north pole which it is leaving, the current will immediately increase as soon as it is short circuited by the brush, and may continue quite large until it is about to leave the brush. Then the resistance in its circuit, due to the small surface of the brush which rests on the commutator bar, reduces it to zero. A current must now in a very small space of time increase in the coil b from zero to the full value of half the armature current. The self-induction of the coil b prevents this from being done and the commutator bar c, leaves the brush before the current in coil b has reached its full value. A short arc is now formed between the extremity of the brush and the bar c, w^hich lasts until the electro- motive force has overcome the self-induction of the coil b and raised the current in it to half the armature current. It should be explained here that the self-induction of a coil is of the same nature as inertia in a weight. The inertia tends to prevent motion from being imparted to the weight, but when once in motion the inertia tends to prevent the weight from coming to rest. The self-induction in a coil acts the same way with ref- erence to the electric current. It tends to prevent the cur- rent from being established in the coil, but, when once es- tablished, tends to prevent it from changing value or from dying out. The self-induction of a coil surrounding an iron core is very much greater than that of the same coil in the air; furthermore, the self-induction of a coil increases as the square of the number of turns in the coil. 146 We have traced the acttoin in the commutaftion of the coil b where the brush is rocked so far back in the direc- tion opposite to thait of rotaitdooi that the coil b is still cut- ting* the lines whion flo-w from the pole which it is leaving. Under these circumstances it is seen that tihe self-induction of the coil prevents the current froTQ being reversed until so late tha-t a small arc forms between the point of the C'ommurtator brush a.nd one oif the commutator bars to which it is attached. This continual 'arcing- is called spark- ing. When, however, the brush is rocked forward 'in the direction of rotation until 'the coil b is coitting the lines of force which flow from the lyole which it is 'approaching, the action is very different. Fig. 56 shows the relative position of the poles and the coil being commutated. When the brushes are rocked into the position shown in Fig. 56 the coil b is short circuited while it is cutting lines from the south pole, or the pole toward which it is ap- proaching. The E. M. F. generated in the coil b will be op- posite to that generated while the coil was under the influence of the north pole; therefore, as soon as the coil b is short circuited by the brush theE.M.F.set up therein tends to reduce the current in the coil to zero and next to generate a current in the coil to the reverse direction. If all the conditions are just right this current wHill be equal to half the armature current at the moment the bar c' leaves the brush. When these con- Flgure 56 Diagram of correct and sparkless commutation. 147 ditions obtain, there is no possibility of any arcjng" between the commntator bars and the brush, and consequently the commutation is sparkless. It is necessary that the coil b should be in a field which will not tend to increase the current that is already flowing in it at the moment that the coil is first short circuited. It is clear that the exact con- ditions which would make sparkless commutation possible if sparkless commutation depended only upon magnetic con- ditions can only exist for one particular position of the brushes and one particular load on the armature. For, sup- pose the coil b were short circuited in a quite powerful field of the pole toward which it is approaching-, then a current flowing in it at the instant it was first short circuited would die out almost immediately and a large current would be sQt up in the opposite direcftion, amd woaild 'tend to increase until broken by the bar c, leaving the brush. This would produce an aire dua to over-commutaltion. A factor of very great importance in commutation is the resistance between the brush and the commutator baj's. It must be carefully kept in mind that while the current in the coil b is being reversed by the small E. M. F. generated in it, the main current of the dynamo is passing from the cammut-ator bars b, ajid c, to the brusih. There will therefore be a greater or less difference of potential between the bars b, and c, and the brush. This difference of potential or voltage wall depend on the resistance be- tween the brush and commutator bars and also upon the current. It is clear that if there should be a tendency in the coil b to over-commutate by being placed in too strong a south field, this local current must flow through, the leads c„ and b„ across from the bar b, tlirough the brush to the bair c, and to the ooil. In order to do this the current which J48 naturally fjows from the bar b' into the armatufre will be increased. ^Vhile the current which naturally runs from the brush throug^h the lead or connection c'' to the arma- ture is reduced by the same quantity. This consideration w!ll show that there is very little danger of over-commuta- iion when the armature carries a fairly large load. The tendency of a considerable armature current trav- eling from the brush into the bars and so into-the armature is to immediately stop any current which might flow in the coil b, because the tendency is for the leads or connec- tions c" b" to carry the -same amount of current. And this tendency is increased if there is considerable resistance in the two leads c" and b". When these two leads are carrying the same amount of current it is manifestly im- possible for any local current to circulate in the coil b. As the bar c' moves away from the brush the resistance thait the current me^ts in flowing from the bar c' increases on account of the smaller surface of contact between the brush and the commutator bar c'. This tends to reduce the cur- rent in the lead c", but such a reduction of the current must be accompani 'l by a corresponding increase of the current in the coii ^, This is becauise the current dm the doiil b plus the current in the lead c" must -always equal heres and into bar b', 25 amperes. Current through iDOth c" and b", 25 amperes each. Current in coil b, none. Current in coils a and c , 25 amperes each. the brush would rest equally on the bars a' and h\ 25 am- peres would flow into each bar, 25 amperes would flow into each lead a" and b" and the current in the coil a w^ould be reduced to zero, or it would be half commutated (see Fig. 59.) The objection to the copper brush is that the resistance between the copper brush and the commutator is ^o low 151 that the current can easily bunch up on one side of the brush; for instance, when the commu'tator bar c' had moved to such a position that only one-third of its -surface rested under the brush, the resistance of contact would be so low that the 25 amperes of armature current could easily flow into it. If this should be the case the current in the coil b would have to be built up almost instantly and a large cur- rent would flow from the tip of the brush into the com- mutator bar c' just as the bar was leaving* the brush. Enough current would flow, in fact, to fuse the very tip of the brush and bar at the edge of the bar, and the fused bit of copper would appear as copper dust thrown off from the commu- tator. This fusing action roughens the bars, which tends Figure 58 Current from armature 50 amperes. Brush covers half bar e all of b' and half of a'. Current into bar c', 12>^ amperes. Current into bar b', 25 amperes. Current into bar a', 12}4 amperes. Current through coil b, 12j^ amperes. Current through coil a, 12^ amperes. to make commutation still more imperfect. Trouble of this kind once started grows rapidly worse, until it is necessary to put on new brushes or to retrim them and to true up the commutator. The higher resistance of carbon makes it impossible for enough current to pass from the edge of the 152 copper bar to the tip of the carbon brush to fuse the copper. The action just described, viz: the distribution of the current over the surface of the brush is the most important one in the progress of commutation. The only thing which prevents this from always producing spairkless commufcatiKDoi is Ithe self- induction of the coil to be commutated. It is clear that if commutation is to take place easily this self-induction should be as low as possible. If three-tenths of a volt ap- plied for 1-100 of a second is sufficient to overcome the self- induction of a coil of one turn on a given armature, 1 2-10 volts, or four times as much as would be required to over- come the self-induction and reverse the crrrent in a coil of two turns on the same armature. Nine times 3-10 would be Figure 59 Current from armature 50 amperes. Brush covers all bars a' and b'. Current into bars a' and b', 25 amperes each. Current in coil a=0. Current in coil b=25 amperes. Coil b completely commutated. required with three turns, and so on, for the self-induction of a coil on any given armattire is proprtional to, the square of the number of turns on the armature coil. It will be noticed that the effort to commutate the short circuited coil due to the resistance of the brush in- 153 creases with heavy loads; thus there is twice as much ten- dency for the ourrent to flow into the brusii eve«nly with 50 amperes as there is witli 25. This gives us twioe the voltage for commutating the current in a sihort circuited coil when 50 amperes are flowing than is^aviailable when a current of 25 amperes is being produced by the armature. On the other hand, the commutation which is prt>duced by the short circuited coil cutting the lines of the field toward which it is approaching, grows weaker and less perfect as the load increases, because the increasing load increas.es the a/rraature reaction and the increased armature reaction weakens the field which the coiil is approaching, while strengthening the pole from w^hioh the coil is receding. TJierefore the commutation produced by the cutting of lines of force is strongest when it should be weakest and weakest when it sho Figure 63 Lap winding on four pole dynamo 163 This is on account of the fact that there are only two paths for the armature current. The lap winding shown in Fig. 63 is perfectly analogous to the winding shown in Figs. 60 ana 61. In this machine there are four paths for the current through the windings of the armature, and the connections, instead of being com- plicated as with the wave winding, are as simple as with the Iwo-pole winding. By cro^s connecting opposite bars of the commutator it is possible to use either two or four brushes on a four-pole armature with a lap winding. In the wave winding the commutator bars are cross connected by the armature wires themselves. In the lap winding there are four paths for the arma- ture current through the armature. There must neces- sarily be four brushes on the commutator, unless the commutator is cross connected, and the voltage produced in each of the four circuits depends on the magnetic flux of its respective pair of poles. It may happen in this way, that after the armature has worn the bearings so as to be out of center in the fields that the E. M. F. in one circuit maj^ be considerably higher than that in the circuit on the opposite side of the arma- ture. • In a bi-polar machine the two sides of the coil must fpan nearly or quite 180 degrees of the armature in order that one side of each coil may be under a north pole while the other is under a south pole. In a four-pole machine each armature coil must span nearly or quite 90 degrees for the same reason. In a six-pole machine a *span in each coil of 60 degrees is required. 164 One peculiar thing is noticed in a wave windl^^ on a four-pole machine, when there are about half as man}' slots in the armature as there are bars in the commutator. One coil cannot be connected to the commutator and must be taped up and left in the armature without any electrica\ connection with the rest of the armature winding*. Tap- ing- up this coil makes the number of bars in the commu- tator one less than twice the number of slots in the arma- ture. Table Xo. 10 gives the armature windings and the size of the wire required for a number of the armatures most commonly used in the United States. 165 TABLE ]So. X, EDISON GENEEATOR WINDING. o 1 Kind of 08- bo- Si go QQ O o o u^dg snoo rt fl f= Pi Oj 0^ ^ c8 'C "^ "TJ 'C Ti 'C "^ C G fl f3 C C fl 53 c3 c3 cj 03 cj ^ 00 oo 9-1 1 Ai JO 9ZTS '■^OOi-t 2 ^ogSoO b s^^ ^'1 OOh* c^^'*rL,a-SXOOTH'^^ ^Hh:i 0?H Brush No. 7 30 .0?3 8 17 36 2000 Brush No. 8 65 .083 12 21 30 2000 Brush No. 9 85 .08:3 24 23 19 2000 Brush No. 10 100 .083 24 Zi 21 2000 Brush No 11 125 .083 24 22 24 2000 T. H. Rine M. D. Schuyler 50 .072 30 15 11 2000 50 .057 8 8 37 1200 Wood No. 8 60 .064 120 11 6 1200 Wood No. 9 80 .072 120 13 6 1200 J, 168 COMPOUNDING OF DYNAMOS. We have considered heretofore two general methods of field winding, viz: shunt and series. A combination of these two methods is called compound winding. In a shunt wound dynamo the excitation is almost constant, but the voltage produced by the dynamo decreases as the load in- creases, due to four causes: First, in order to obtain sparkless commutation the brushes are rocked forward into such a position that the coil, while short circuited by the brush, is under the influence of the pole toward which it is approaching. The armature reaction with the brushes in this position decreases the magnetic flux. This lowers the voltage. Second, the armature reaction tends to bunch the lines very greatly under one side of the pole and to thin them out under the other side of the pole. In a surface wound armature this action does not greatly alter the total magnetic flux, but when an ironcl'id armature is employed the armature teeth are satu- rated by the action of the normal fleld, and the effect of the armature reaction cannot greatly increase the flux of the lines under the dense end of the pole piece. Consequently all the lines which are prevented from passing into the ar- matiire at the other end of the pole piece practically dimin- ish the total magnetic flux by just this amount. Third, the current flowing through the shunt fields is decreased, owing to the loss of voltage produced ?n the armature by the effect of the armature reaction. Fourth, a rea- son which in large armatures is of practically^ little import- ance is the loss of voltage due to the resistance of the arma- ture. The combined efl:ect of these actions is to reduce the voltage from 5 to 25 per cent, between no load and full load. 169 It is desirable, of course, that the dynamo produce at the lamps a perfectly constant voltage. To satisfy this condi- tion the voltage at the dynamo at full load must be greater than the voltage at no load by the amount of the loss of voltage in the line. In order to accomplish this result and counteract the effect of armature reaction, a series winding is put on to the fields of the d^mamo. The effect of this series winding is to increase the ampere turns on the tield coils in proportion to the load. Therefore, when the arma- ture reaction tends to reduce the voltage by the greatest amount the series coils tend to increase the voltage to the greatest extent. By using the proper number of series turns the effect of armature reaction can be overcome and the voltage increased as the load increases, thus making up 12 x-x-x-x-x- Figure 64 Diagram of compound winding in a dynamow 170 for line loss. Fig. 64 is the diagram of compound winding on a dynamo. Fig. 65 shows the effect of the series coil. Compound winding can be used on motors as well as dynamos. The effect here is to increase the torque and decrease the speed of the motor as the load increases. A little thought and a consideration of Fig. 20 will show that the torque or twisting effort is proportional to the current IZO to ^^'*'"^'*"«*».^^ n — ^ 3 ^ -^^ N AMPERES Zoo BOO 400 Saa Figure 65 Upper line shows the current and voltage when series coil is used. Lower line shows current and voltage when plain shunt winding is employed. which flows through an armature as long as the field is constant, and is always proportional to the product of the current through the armature and the strength of the field. An advantage of compound wound motors is that the speed variations which will occur when a plain series wound motor is used are confined within definite limits. At the same time the advantages of the series motor are obtained, viz: First, powerful starting torque; second, the decreased effect 171 of armature reaction, which shows itself in freedom from sparking at heavy loads. In calculating the number of am- pere turns required on a compound wound dynamo, it is necessary to calculate the number of ampere turns that would be required 'to force five or ten per cent, additional flux through the circuit. The effect of the shunt coils is usually sufficient in an ironclad armature to saturate to a considerable extent parts of the magnetic circuit. This makes it necessary that the ampere turns of the series coil should be much greater than would otherwise be necessary. In practice the ampere turns of a series coil at full load vary from one-third to one-half the ampere turns of the shunt coil. QUESTIONS OX CHAPTEK XIV. t. For what two purposes is wire used on a dynamo or motor? 2. Why is it desirable to make the section of the field coil circular? 3. What advantage is gained by placing the field coil near the air gap? 4. In order to have a motor winding properly arranged, what must be the direction of the current in all the wires under each pole piece? 5. Why does the coil winding on a four-pole dynamo span one-quarter of the circumference of the armature? 6. How many degrees will a coil span in an armature intended for a ten-pole machine? Why? 7.' Why is it necessary for the current in all the wires under the north pole of a motor to fiow in one direction and in the opposite direction under the adjacent pole? 8- "What is the difference of potential between the first and last coils in fhe same layer of a two-pole, two-layer horizontally wound armature intended for 500 volts? 9. If the armature has 64 sections, what would be the difference of potential between the third and fourth coils? Eleventh and twelfth? 173 10. In the same armature, what would be the differ- ence of potenftial between the upper and lower layers of wire? « 11. What is a horizontally wound armature? 12. What is a vertically wound armature? 13. How is it possible to connect the armature to the commn'taitor so as to have the brushes set in any desired position? 14. What is a wave winding? What is a lap winding? 15. What are the advantages of wave winding for ma- chines up to 100 horse power? 16. Why are the brushes in a six-pole dynamo placed 60 degrees apart? 17. Explain why a six-pole armature with a wave wind- ing may have its brusihes placed in the saime position as a bi-polar machine? 18. A four-pole wave wound armature has a flux of one and a half millions of lines; the speed is 1,200 revolu- tions per minute; there are 45 slots in the armature and each coil has four turns in it. What will be the voltage produced? 19. What will be the voltage produced bj the same armature if lap winding is used? 20. What will be the relative resistance of the arma- tures with wave and lap windirg? 21. How may a lap wound armature for a four-pole machine be connected so as to operate with two brushes? 174 22. What will be the difference in operation of a wave and a lap wound armature when the armature is not central in the pole pieces? 23. Why is it impossible to use an armature in a four- pole wave "wound machine with an even number of slots if there are the same number of commutator bars as arma- ture slots? 24. Make a diagram for a wave winding- for a four-pole armature having 12 slots in the armature and 23 bars in the commutator? 25. 'What is a compound wound dynamo? 26. What is the object of putting a series coil on a dynamo? 27. Wliy does the voltage of a plain siiunt wound dynamo decrease with the load? 28. If a bi-polar dynamo produces 200 amperes and the shunt ampere turns are 2,600 on each coil and there are eight turns in the series coil, what will be the total ampere turns on each field coil at full load? 29. What is the effect of compound winding on motors? 30. What are the advantages of compound wound mo- tors over plain s-hunt wound motors? 31. Why will a 500-volt compound wound dynamo that operates very well on 500 volts greatly over-compound whea operated at 250 volts? CHAPTER XV. PROPER METHODS OF CONNECTING UP DYNAMOS AND MOTORS. It is a factj and one which for a long time remained undiscovered, that a dynamo will excite itself when run at the proper speed and with proper connections between ar- mature and fields. It is also true that in order that a ma- chine may excite itself or excite its own field magnets, it is first necessary to send a current from an external source around the field magnets. This current drives a certain amount of flux through the magnetic circuit, and since most of the magnetic circuit is composed of iron, a part of this ^ux does not disappear when the current is cut off. This permanent magnetism is called residual magnetism. The residual magnetism will be greater in a dynamo with an ironclad armature than in one with a smooth core, because the magnetic circuit is so much more perfect. The residual magnetism in most cases will be greater with cast iron field cores than with wrought iron or soft steel. ' The amount of this residual magnetism with an ironclad armature varies from one to five per cent, of the total fiux with fully excited fields. The writer has seen a 500-volt street railway gen- erator w^hich had a residual magnetism such that it pro- duced 25 volts when the armature was run at full speed. This residual magnetism produces a voltage in a certain direction depending upon the way in which the current has 176 been flowing through the field coils and upon the way in which the armature is connected up to the commutator. In order that a d3^namo may excite itself, it is necessary that the current produced by the residual magnetism shall flow in such a direction as to sitrengthen this re- sidual magnetism. If the eurremt produced by the residual magnetism flows through the field coils in the oppo- site direction this wull tend to weaken the residual mag- netism and consequently to reduce the current which flows. If, on the other hand, the current produced b}^ the residual magnetism flow^s through the fleld coils in such a direction as to strengthen it, the greater magnetism which results will strengthen the current, and this in turn strengthens the field, and this process goes on until further increase in the magnetism is prevented by the saturation of some part of the magnetic aircuit. It often -happens that when an armature is re-wound tihe conneotions between the winding and the commutator are made in such a way as to reverse the direction in which current fiows from the armature; that is, the brush which before the armature was re-w^ound w^as a positive brush may become a negative brush. This reversal of the direction in which current flows in connecting up an armature is easily made and very frequently occurs. The re-wound armature when put into the old field 'produces a current which tends to flow in the opposite direction from that of the old armature. This current tends to reduce instead of strengthen the residual magnetism, and the result is that the machine will not excite itself or refuses to build up. In order to correct this difficulty, it is only necessary to reverse the connections between the armature and the field coil, so that the current produced by the residual magnetism may flow in suoh a 177 direction as to strengthen this residual magnetism. To do this either the leads from the armature may be crossed or the leads from the field may be reversed. When the fields have both series and shunt coils it is usually more conven- ient to reverse the armature leads than it is to reverse the leads from both series and shunt coils. When, however, the field has only a single winding it will usually be found to be more convenient to reverse the field leads. An excel- lent method of determining whether the armature and fields are connected in such a way that the machine will not build up is to measure the residual magnetism with a volt meter with the field circuit open, then close the field circuit, and if the voltage drops it is almost a certain indication that the armature and field connections are reversed. In con- necting up a compound wound dynamo to its circuit it is necessary to be sure that the shunt coils and series coils tend to drive the lines around the magnetic circuit in the same direction. If the series coil is connected up in the opposite direction to -the shunt coil the dynamo will build up all right and will work satisfactorily on very light loads. When, however, the load becomes even, five or ten per cent, of full load, the voltage drops off very rapidly and it is im- possible to get full voltage with even half the load on. This is because the ampere turns due to the series coil decrease the total ampere turns acting on the magnetic circuit in- stead of increasing them as the load comes on. This lowers the magnetic flux and of course lowers the resulting volt- age. All shunt and compound wound dynamos are provided with a rheostat, which is placed in series with the shunt field magnetizing circuit. This rheostat is a resistance capable of adjustment by hand by means of which the current flow- 178 ing" throug'h the shunt first coils may be regulated. Wlien this resistance is all cut out tne maximum current flows through the shunt fields and they consequenftly have a max- imum magnetizing- power and the maximum voltage is pro- duced. If this voltage is too high, it is necessary only to insert more resistance in the shunt fields by a movement of the rheostat and thus cut down the magnetizing power of the fields and therefore the voltage produced by the dy- mamo. It sometimes (happens that a dynamo refuses to build up because there is 'so much resistance in the rheostat that the current produced 'by the residual magnetism is not powerful enough to sufficiently increase the magnetism of the fields to begin 'the building up process. Therefore if a machine refuses persistently to build up it is a good plan to short circuit the rheostat. This cuts out the resistance and at the same time bridges any possible open circuit that there may be in the rheostat. The rheostat should be ar- ranged 90 that the field circuit can never oe suddenly brok- en. This is to avoid the possibility of breaking down the insulation of the field coils by the so-called field discharge. A field discharge is said to occur when the shunt circuit of a dynamo in operaftion is suddenly opened. Anyone who has done this knows that a yery lomg thin arc is produced; the length of the arc indicates the high voltage produced by the discharge and the small size of the arc shows that the current is comparatively weak. A calculation will show w^hat the voltage produced by such a field discharge may be. Suppose a shunt field of a 110-volt dynamo is composed of two coils each of 1,500 turns, also that the magnetic flux passing thrugh these coils amounts to 4,500,000 lines. Tf this circuit is opened in one second, the voltage which would be produced will be 2x1,500x4,500,000 divided by 100,000,000 179 (>r 135 vcfltts. When the field dircuit is opened in 1-100 of a .second, tihe voltage will be 1,500x2x4,500,000 100,000,000 l,500x'2x4,500,0O0x!l0O equals 1 100,000,000 100 or 13,500 volts. Such a voltage as this is very apt to punc- ture the insulation of a field coil and care should be taken that the circuit is never opened in such a way as to expose the insulation to such a strain. The production of an ex- tremely high voltage in this manner is simply a reproduc- tion on a larger scale of the ordinary battery and spark coil used for igniting gas engines. In the ordinary spark coil the current from a battery of two or three volts is passed around a magnet and then suddenly opened with the production of a spark from one-fourth to one inch in length. Here we have the production of many hundreds of volts from two or three. The same multiplication takes place when a shunt field is opened suddenly. Rheostats for the shunt circuit of a dynamo should have sufficient resistance, so that when it is all inserted the volt- age in the dynamo will slowly sink to zero. This method of stopping the action of a dynamo is perfectly safe and should be followed wherever possible. Fig. 66 shows an- other diagram of the connections of a compound wound dynamo. Almost all stationary motors are plain shunt wound machines. Fig. 67 is a diagram of the way in which these 180 motors should be connected up. The essential point in this scheme is that the shuht field circuit be always closed through the rheostat and armature so that a field discharge is impossible. The rheostat is inserted for the purpose of not permitting too great a rush of current through the armature before it has attained its speed and consequently its counter E. M. F. Figure 66 Biagram of connections of compound wound dynamo It this rheostat were arranged so that when it wds thrown off, the armaiture circuit should be lopened, the open- ing of the main switch would break the current through the shunt fields and produce a field discharge. An arrangement of a starting rheostat like this has been )the cause of numberl^ burn-outs in field coils. If, however, the resistance of the starting rheostat is simply sufficient to choke the current 181 back to the desired amount and does never open tlie arma- ture circuit, the opening" of the main switch simply cuts the current oif the motor. The instant after the main switch is opened the motor armature becomes a dynamo armature at practically the same voltage and supplies the field trolls with current almost as long as the armature continues to revolve. In this way there is absolutely no possibility of such a disturbance of the shunt circuit such as will produce any abnormal strain on the insulaltioa. Figure 67 Diagram of connections of plain shunt wound motoTo An automatic rheostat or starting box is one which is provided with a spring, which tends to throw the handle back to the position of greatest resistance. (See Fig. 68.) A magnet holds the handle in opposition to the spring in that position in which all the resistance is cut out^ The IB2 mag-net is usually energized by the current which passes through the shunt coils on the motor. If, for any reason, the power which op'erates the motor should fail, the mag- net will weaken and rele-ase its hold. The spring will foice the handle back to the position of greatest resistance, and when the power is again thrown on the line the motor wili start up in the ordinary way. Figure 68 Blagvam of automatic starting box showing coniiGetSo53S If the resistance in the starting rheostat were entirely cut out and the power was thrown onto the motor from ten to a hundred times full load current would flow through the armature, causing very bad sparking and almost cer- tainly blowing the fuses which protect the motor. Overload rheostats are those in which the resistance is cut in where the current exceeds a certain ajciount. 183 In one design of overload rheostat the mag-net spok- en of above has two windings, a shunt winding which is the more powerful and a series winding in oppositon to it. With normal load the series winding does not diminish the strength of the magnet sufficiently to release the rheostat handle, but with an overload the magnet is weakened suffi- ciently so as to release tli'e rheostat handle and insert the resistance of the starting rheostat in t-he armature circuit A QUESTIONS OX CHAPTER XV. 1. What is the effect of residual magnetism in the self- excitation of dynamos? 2. Would a dynamo in which there was no residual magnetism excite itself? 3. Why will reversing the connections of the shunt coil prevent a dynamo from generating? 4. What is the amount of residual magnetism in or "Jinary iron-clad dynamos? 5. When a machine begins to build up, vsKhat causes the voltage to stop rising? 6. Tf a dynamo could be made without iron that would build up if supplied with a residual field from an external source, what ^vould be true of the voltage generated by such a dynamo? 7. If an armature fails to build up, wha-t course should be pursued? 8. How is it possible to be certain that the armature and field magnet connections are properly made with refer- ence to the residual magne-tism? 9. How w;ill a compound wound dynamo act when the series and shunt coils are reversed? 10. W%y does moving the arm of a rheostat' raise or lower the voltage cf a shunt or compound wound dynamo? 11. What is a field discharge? 185 12. What will be the voltage Irom a field discharge from the Edison dynamo on Fig. 26, df there are 1,500 turns on each coil and the circuit is broken in 1-50 of a serious trouble. B. — Short Circoiits. If, in a properly wound and connected armature, two of the commutator bars be connected together, the voltage which is produced in the coil connecting these bars will produce -a very great local current, which will flow through the coil and complete its circuit acress the two commutator bars. Such a co>nnection would be a short circuit, and any connection that allows a local current to flow through a part of the armature winding is called a short circuit. Suppose an armature with a resistance of 1-10 of an ohpa has fifty coils; the resistance oi each path in the ar- 188 mature will be 1-5 of an ohm and the resistance of each coil Avill be 1-25 of 1-5, or 1-125 of an ohm. If, now, this armature is capable of producing 250 volts each coil in it generates 10 volts on the average. When the armature is working properiy this 10 volts simply adds itself to the voltage produced by the other coils »a.nd is expended in forcing the armature current thro'ugh the external resist- ance. If, however, the t^vo bars to which thi-s coil is con- nected be short circuited, this 10 volts will expend itself in producing a \ery great local current through this short circuited coil. The coil generates 10 volts and its resist- ance is 1-125 of an ohm. The current which will flow then will be 1,250 amperes; this is enough to heat the eoil red hot and entirely destroy the insulation in its neighbor- hood. Trouble of this sort is the most destructive that can occur in an armature, for it usually cbmpels the re-winding of the whole armature. If the short circuit is discovered before the coil has been sufhciently heated to destroy the insailation, and it is absolutely necessary to use the arma- tnre temporarily and the point at which the coil is short circuited cannot be discovered, -each turn of the short cir- cuited coil may be cut in two and then the two commuta- tor bars between which this coil is connected may be sold- ered together. It often happens that one wire in a coil touches its neighbor at some point, and when this occurs only one turn of the coil will be short circuited and only one turn will get hot. A shorrb circuited coil always shows itself by getting warmer than its neighbors at first, and if not soooi discov- ered will smoke and finally set fire to the insnlation. If an armature is completely short circuited, as, for instance, from top to bottom layers in a horizontally wound armature or fro.m coil to coil in a vertically wound arma- 189 tuTe, it will refuse to build up if it is a g-eneraitor and will turn >a half revolution at a time if it is a two-pole motor, or a quarter revolution if it is a four-pole motor. In a bi- polar machine the short circuit of the armature will not affect the distribution of the current when the short cir- cuit is 90 degrees fromi the brushes, for then the two oppo- site, sides of the commutator are at no difference of poten- tial and no current \Aall flow in the short circuit. C. — Sparking. The principles which govern perfect commutation were explained in the chapter on "Sparking," but many other causes beside imx^roper design of the dynamo may cause a machine to spark. When the commuta»tor is in good con- dition, trueand smooth, and the brushes have a firm con- tact against it and the m'achine invariably sparks at a heavy load, the trouble may be attributed to a poor design. In a well designed machine 'the causes for sparking will be a rough commutator, a commutator out of round, or brushes not having sufficient contact against the commu- tator. In fact, the causes of sparking may be divided into two classes — sparking from electrical causes and sparking from mechanical causes. The cause of the electrical sparking was explained in Chapter XV. In most machines built at the present time any spark- ing that there may be is principally due to mechanical causes. It is clear that in order to have sparkless running the brushes must at all times touch the commutator. The fact that from some cause or other the brushes do not touch the commutator all the time is the cause of most cases of sparking. If the brush is not free to move, sparking will 190 result, for even in the best machines there will be some movement of the commutator with reference to the brush, and if the brush cannot follow it there will be a very short arc that maybe will n'ot be seen unrbil the oommuta'tor is blackened and burned at one spot. When an armature is slightly out of balance and is Tun- ing at a very high speed, there will be a vibration of the commutator, and if the machine is to run sparkless the brushes will have to follow this vibration of the commu- tator. In order that the brushes may follow the movements of a commutator that is not running perfectly true, the mov- ing part of the brushholder should be as light as possible and the spring tension that holds the brush against the commu- tator should be as heavy as possible. This condition is best fulfilled in a brushholder in which the brush alone moves, for in such a brushholder the inertia of the moving part is as small as it is possible to obtain, and consequently a com- paratively small pressure will enable such a brush to follow the uneven motions of the surface of the commutator. The writer once saw a motor which ran at 3,700 revolu- tions per minute, which could not be prevented from spark- ing when solid brushes were used, owing to the fact that the commutator did not run perfectly true. When leaf cop- per brushes were employed on this same commutator the motor ran almost sparkless, due to the fact that the copper, with its large number of separate leaves, always made con- tact with the commutator. Another cause which prevents the brush from touching the metallic part of the commuta- tor is the use of insulation between the commutator bars that does not wear down as fast as the commutator bars themselves. After the machine has run for a time these 191 insulations project above the copper bars and produce both heating- and sparking. Poor construction of the commu- tator is another prolific cause of sparking. If the commu- tator is not perfectly tight the centrifugal force will throw out one bar more than its neighbor, and consequently there will be spots on the commutator that the brush cannot make contact with. A commutator must be mechanically clean in order to run sparklessly. Spots of paint or dirt may be on a coimmutator and get between the brush and the copper bar, and so prevent perfect contact at one point in the commutator and produce sparking. A cause which produces as much sparking as improper mechanical arrangement of the brushholder is improper set- ting of the brushes. As explained in the chapter on spark- ing, there is a proper place for the brushes, and if they are not placed in this position there will be a tendency to spark. The brushes being in a wrong position will first heat the commutator and roughen it, and when the surface of the commutator is impaired, sparking will result. In a dynamo the brushes should be rocked forward in the direction of rotation into such a position at no load that the voltage is two or three per cent, lower than the maximum voltage. In a motor the brushes should be rocked backward into such a position thai at no load the speed is increased about two per cent, above tfhe lowest speed. 1). — ^H'eating the Commutaitor. Abnormal heating of th^ commutator is due tO One of four causes: First, friction of the brush against the com- mutator; second, improper position of the brushes SO that there is forced commutation; third, abnormally heavy €ur« rents being taken from the armature; fourth, poor contact 192 between brushes and commutator. As soon as it is deter- mined to widch of t'heise four causes the heating- is due, the remedy in each case is obvious. The heating of the com- mu'tator in many iTistamces may be remedied by the substi- tution of copper brushes for carbon brushes. First, because the friction between the commutator and the coppe-r brush need not be so great as between the commutator and the carbon brush, and still more important because the electri- cal resistance between the co-mmutator and the brush is yery much less with the copper than with the carbon,* The objection to the use of the copper brush on any commuta- tor is that unless it is given very careful attention it will cut the comjmiutator in the same way and for the same reason that a bearing without oil will cut. E. — Grooinds, When a machine is out of order the first thing to do in testing it is to find whether or no there is a connection be- tween the "winding and the frame of the dynamo or motor. Such a connection is called a ground. A single ground on a machine does not of itself impair its action; ix only ren- ders the insulation in some other part of the machine very liable to break down. When there are two grounds on a machine there will be a short circuit of more or less of the winding, for the current will run from one part of the T\*inding through one ground through the frame oi the machine through the second ground to the other part of the winding. Such a short circuit usually shofws itself very plainly by burning the insulation and usually stop- ping the operation of the machine. Some motors, as, for instance, street car motors, are built with one end of the winding grounded to the frame. The object of this is to allow the current after it has pass- 193 ed througli the motor and done its work to escape tlhrongh the motor frame, axles and wheels of the car to the rails. When guch a motor as this is to be tested for a ground it is necessary to open the connection between the winding- and field frame before the test is made. Testing for ground is usually done with a small dynamo provided with a field made of permanent magnets and operated by hand. When current passes through the circuit its presfence is made known by the ringing oi a pair of smiali bells. Partial grounds, as, for instance, in the mica insulation of a commutator, may cause isevere heating of a part of the commutator, due to the arc that is formed between the commutator bars and the commutator core. It is possible by the use of a- Wegton volt m-eter to determine just where the ground is in an armature, provided the ground is per- fect or nearly so. Pass current from an external source between the armature core and the winding, and tesft the voltage when the wire osts A and C, but, before passing through the wire on the bobbin, the current must traverse the very high re- sistance R; this resistance is from 65,000 to 75,000 ohms for a volt meter intended for a 600-volt circuit. Therefore the 210 current whicl] passes through the wires on the bobbin, even with full voltage, is very small, and with 100 volts will be not much over 1-700 of an ampere. Yet this small current is ab]e to produce very considerable deflection in the two hair springs which resist the motion of the bobbin. An- other very excellent point in the design of this meter is the Figure 73 Magnetic vane voltmeter depending on repulsion of two similarly magnetized iron strips. Tvay in which it is made deadbeat, or the way in which the needle is prevented from vibrating back and forth on each side of the point at which it will finailly come to rest. The bobbin B is made of copper, and when it moves there will be generated in it aurrents which, according to Lentz's law,tend 211 to prevent its motion. The mechanical momentum given to the bobbin by the action of the current in the wires thgt are wound on it is absorbed by these Foucault or eddy cur- rents in the copper bobbin. The Weston direct current me- ters are almost perfectly deadbeat. Figure 74 Western electric meter depending on effort of iron strip to get into as powerful fielA as possible, or to get as near to the wire carrying current as possible. In Fig. 72 is a sketch of the Weston di- rect current ammeter. The working parts 'are precisely the same, the principle of operation is identical, and it would be impossible to tell the two dnstruments apart, so far as the actual indicating mechanism is concerned, if it were not that the bobbin is wound with coarser wire. 212 The wire on the bobbin is a shunt on the resistance 'R. The wiiole current to be measured passes through the meter from binding- post A to post C. In doing- so it has to pass through the resistance E. The voltage at the extremities of this resistance is, according to Ohm's law, proportional Figure 75 ^ Brush Electric Co. voltmeter and ammeter in which the attraction of a Solenoid for an iron core is weighed. to the current; or, looking at it in another way, the current will divide between the resistance R and the bobbin B in- versely proportional to their resistances. Therefore, when a large current is passing through H, d oorrespomdirigly iarge current is passing thrmigh bobbin B. As we have 213 seen in Fig-. 71, the posdtion of the pointer registers th« amount of current passing through the bobbin, fndTt wH be seen that the position of the pointer may be read off directly as amperes. ..J.^^'^l "■^'" "* *^' ""'"P"" measuring instruments de- pend for their action upon the attraction of a solenoid for i 214 a piece of iron. The attraction of the solenoid is balanced by a spring or gravity and the position at which equilibrium occurs is a measure of the attracting force, and therefore a measure of the ampere turns in the solenoid. Whether the position of the pointer is to be read off as volts or amperes depends on whether the coil is wound with fine wire of coarse wire. A serious objection to these instruments in so far a9 their accuracy is concerned, is that they will record highei Talues on descending amperes or volts than on ascending* This is due to the residual magnetism. When a current oi 25 amperes would pass through the meter this would cause a certain number of lines of force to pass through the iron part of the meter. When the current sank to 23 amperes a certain number of lines due to the 25 ampere currenV would still remain in the iron, laind this number would b^ greater when the current would pass from 25 amperes io 23 amperes than when it passed from 21 to 23 amperes. The mechanical force acting on the iron would be greater in the first than in the second case and therefore the am- peres indicated will be higher. Error due to this cause amounts to from 2 to 10 per cent., depending on the con- struction of the meter. Fig. 73 show^s one style of mag- netic vane meter. Fig. 74 shows the meter built by the Western Electric to. Fig. 75 shows a style of meter for- merly built by the Brush Electric Co. Fig. 76 shows the type af meter built by the Westinghouse Electric Co, 215 THOMPSON REiCORDING WATT METER. Mo&t of tihe recording meters in use in this country are of this type. In general, the meter is simply an ordinary motor, except that it is built without iron, as sihown in Fig. 77. Attached to the shaft of H Figure 77 Diagram of connections and operation of Thompson's recording wattmeter. and is connected up to a sonall commuitator co-mposed of silver bars. Two thin silver brushes touch this comanuta- tor and carry the current to and from the armature. The torque on the motor is proportional to the product of the current in the fields and armature. In well regulated sys- tems, the voltage supplied is so nearly constant that the currenit in the armature is practically the same for any load. 216 It shoiiid be remarked that, in order fto reduce the ctirrent wasted in passing through the armature to the smallest possible amount, there is in series with the arma- ture a very large external resistance. The voltage supply being practically constant, the current through the arma- ture v^ll also remain constant. The only factor thait varies much is the current in the field. Eddy currents are gener- ated in the copper disc by its motion between the poles of the permanent magnets, and doubling the speed doubles the voltage produced and therefore doubles the current or quad- ruples the watts lost in the disc. In order to make the instrument register correctly, the speed must be twice as great w'hen 20 amperes are passing through the field as when only 10 amperes are passing through. Doubling the current through the field doubles the mag- netic field through which the armature revolves, and this doubles the torque on the armature. Doubling the speed doubles the current produced in the retarding disc, so that the increased torque is balanced by an equally increased resistance or counter torque in the disc. If the armature speed is doubled its counter electro-motive force will be quadrupled, because it is revolving at double speed in a field of double strength. Since in anj- case the counter electro-motive force is extremely small, the current passing through the armature 5s not varied appreciably by the variation in the counter electro-motive force. We have then, by dou'bling the speed, quadrupled the watts lost in the revolving copper ring and at the same time have quadrupled the energy imparted to the armature by quadrupling its electro-motive fore© 217 against a constant current. Since these same relations al- ways hold, it is clear that the speed of the instrument will be alwaj^s proportional to the current passing- tTirough it. Consideraition will show .'that a change in the voltage while the current remains cooistan twill change 'the counter electro- motive force of the armature and its speed in the same way that change of current does. If the voltage alone should change and the current be constant, the same relation is true. Suppose the voltage to he doubled; the current through the armature would be doubled and there would be twice the torque on the arma- ture. This double torque would produce double speed and consequently double counter E. M. F. acting against double current, or it would exert four times as much energy as at the lower speed. Thus, for either case 'of change of volitage or current ihe sneed of rotation is a correct measure of the energy passing through it. 15 QUESTIONS ON CHAPTER XVIli;. T, What does a common volt meter really measure** 2. On whart law doets 'the accuracy of tlli'e common voit meter depend? 3. If, in Fig. 68, tbe righit-lia.njd pole is moo-tlh, which way does the current flow through the right-hand side of the bobbin w^hen the needle registers voltage? 4. What makes the Weston volt meter dead beat? 5. What is the object of the iron core between the poles of the horse-shoe magnet? 6. WTien the meter registers the voltage and comes to rest, what tw^o forces are equal? 7. On what does the permanent accuracy of this meter depend? 8. What is the difference between tn.e Weston am- meter and volt meter? 9. Describe the electrical connections in the ammeter. 10. Describe the action of the magnetic vane instru* ment. 11. Wliat is the objection to measuring instruments using soft iron? 12. Wliy is the speed of the Thompson recording meter proportional to che watts in the circuit to which it is con- nected ? 13. If the voltage of th-e circuit supplying the current is constant, and the power required to rotate the copper disc is proportional to the square of the speed, why will doubling the current double the speed? CHAPTER XIX ALTERNATING CURRENTS. The currents that have been previously considered in this v^ork have been direct; that is, constantly fiov^ing in one direction. An alternating current is one which changes its direction many times every second; that is, the current flows first in one direction and then in the opposite, the time required for alternation or reversal varying from 1-50 to 1-275 of a second. In the older lighting dynamos the number of alternations usually employed was irom 250 to 266 per second. Modern alternating current machinery op- erates from 50 to 125 alternations per second. Figure 78 Two successive alternations or one cycle. Fig. 78 is the diagram of two successive alternations an a circuit. Two successive alternations, such as shown in this figure, are called a period or a cycle. A two-pole ma- chine will produce one cycle every revolution. Fig. 79 220 shows a bi-polar dynamo with a single coil wound on it, with the two ends of the coil connected to a pair of rings on which brushes make contact. As this coil revolves between the poles of the dynamo there will be a certain E. M. F, produced at each point. The E. M. F. will be a maximum when the coil is horizontal and the plane of the coil and plane of the poles coincide. From this point on the volt- age decreases graduailly until the coil is vertical, and at this point Decomes zero. As the coil moves on voltage is Fignre 79 Alternating cuirent produced in a bipolar field. again generated, but now^ in the opposite direction. When the coil reaches the horizontal position the voltage will be a neo-ative maximum, wiiich graduahy diminishes until the coil has reached the vertical position again and the voltage sunk to zero. The voltage will now be produced in a posi- tive direction and again increased to a maximum. 221 A cycle is usually considered to begin at the point at which the voltage is at zero and at which the current which is to be generated in the next half revolution will be posi- tive. Fig. 80 shows -a coil revolving in a uniform field. Such a coil will generate w^hat is known as a sine wave; this is the form of the current w^ave that is sought in all power transmitting m-achinery, Flig. 78 shows the sine wave. ^B ^ Figure 80 Coll revolving in uniform field and producing a sine wave. The old Westinghouse alternating current dynamos used for lighting were run at 133 cycles per second. The Thomp- son-Houston were run at 125 cycles per second. Most of the modern alternating current machinery is run at 7,200 alternations per minute, or 60 periods per second. The great plant at Niagara Falls, which transmits power to Buffalo, runs at 3,000 alternations per minute, or about 25 per second. An ordinary alternating current is called a- single phase current. Such a current as would be gener- ated in the mechanisan shown in i^'igs. 79 and 80 would be a single phase current. 222 A two-phase current is really not one current, but two separate currents produced from one dynamo. One of these currents succeeds the other in such a way that when the first current is at a maximum the other current is at zero; in other words, they are* a quarter cycle apart. Figure 81 One current of a two phase current. 7/ O* 9»' Figure 82 The other current ic a two phase current. ^g. 81 shows one of the currents in a two-phase dy^ nanio; Fig. 82 -shows the other. Fig. 83 show^s the two com- bined in one diagram. Fig. 84 shows a w^ay in w^hich a two- phase current may be taken from a direct current commu- ^ 2'^'6 tator. It will be seen by an examination of Fig. 84 that the two currents which are taken from the commutator of the two-pole dynamo are connected to bars which are 00 de- grees apart; thus when the current in circuit No. 1 is at zero, the commutator bars to which it is attached are on a hori- zontal line and. there is no difference of voltage between the ♦ MAX. ♦MA)t -MAX. -.>1AX Figure 83 Diagram of two phase currents or Figures 81 and 82 on one diagram. ///J. BRUSH RING INSUL' Figure 84 Method of producing two phase current from the commutator of a bipoxctr armature. 224 two bars, and therefore there is no current in the circuit. The circuit No. 2 is attached to bars which are in a vertical line, and the voltage between these bars is at a maximum. Fig*. 84 makes it clear why it is that the iw^ currents in a two-phase circuit are said to- be 90 degrees apart. A three- phase current is one in which, there are three currents, but they can hardly be called three separate currents. If the •••MAX WAX Figure 85 A diagram of the currents in a three phase line. three sliding rings shown in Fig. 86 be connected to three commutator bars 120 degrees apart on the commutator of a two-pole dynamo, the current which is taken from these three sliding rings is a three-phase . current, as shown in diagram in Fig. 85. Thus, if there were 36 bars in the commutator of a two-pole dynamo, one slide ring would be attached to commutator bar No. 1. The second slide ring will be attached to commutator bar No. 13 and the third slide ring would be attached to commutator bar No. 25; or, each slide ring is attached to a point 1-3 the circumference of the commutator away from its neighbor. Since there are 360 degrees in a circle, these currents are said to be 120 degrees apart. If a two-phase current were 226 to be taken from this same commutator, circuit No. 1 would be attached to bars Nos. 1 and 19; circuit No. 2 wouM be attached to bars Nos. 10 and 28. By a proper combination of two-phase or three-phase currents it is possible to pro- duce a revolving pole. By placing inside of the apx)iaratus which produces this revolving pole a short circuited arma- ture, this will be dragged around by the revolv- ing pole in the same way that a short circuited armature in a direct current machine would be dragged around if the fields were revolved about such an armature. Such a ma- chine is called an induction motor. ^I, ^'^\ ^3 Figure 86 iH^eUiod of producing three phase current from the commntatof of a bipolar armature. The great advantage that alternating currents possess over direct currents is that they can be transformed from a low voltage and a large current to a high voltage, and imiall current without any moving mechanism, or vice versa. 226 Alternating current is tistially generated for lighting purposes in a dynamo at from 1,000 to 2,000 volts. A small current at this high voltage will transmit a large number of watts, and only small wires will be needed to transmit this small current; one ampere, for instance, of this cur- rent at 1,000 volts is received in the primary coil of a trans- former, which changes it into 10 amperes at 100 volts, or 20 amperes at 50 volts, depending upon the winding of the transformer. This low voltage current is distributed Figure 87 Diagram of alternating current transformer. 'through the building 'to be lighted and operates 20 incan- descent lamps. Fig. 87 is; a diagram of a transformer; P is the primary coil which receives the high voltage current, S is the secondary coil which delivers the low voltage current, I is an iron core passing through both coils. According to Lentz's law, current will be generated in the secondary coil in opposition to that of the primary. The number of turns on the primary and on the secondary coils is in the ratio of their voltages. Thus, if there are 100 turns on the primary coil and it is designed to receive current at 1,000 227 volts, there will be five turns on the secondary coil if it is desired to have it deliver current at 50 volts. The transformers are connected in parallel across the main circuit and the self-induction of the primary coil pre- vents excessive current from flowing" through it when the secondary circuit is open. Thus, suppose current is supplied at 125 periods per second and that there are 100 turns on the transformer and that 2,000,000 lines flow through the core of the transformer on an average. A little study will show that the voltage produced in a coi^ having 100 turns placed around this iron core would be 100x125x4x2,000,000 100,000,000 Solving this equatioin, ^Ye find that there will be 1,000 volts produced in such a coil. If 1,000 volts would be produced in a separate coil, there must be the same voltage produced in the coil which is attached tO' the 1,000 volt line wires. In this coil the vol/tage will appear as counter electro-motive force oppos- ing the voltage of the 'main circuit. This E. M. F. is al- most precisely equajjo the E. M. F. on the large line wires, and, in fact, the only current that leaks through the pri- mary coil is jus't enough to- produce ampere turns suffi- cient to cause 2,000,000 magnetic lines to flow through the iron core of the transformeir. When the secondary circuit is closed, however, the cur- rent in it tends to de-magnetize the iron core, because, ac- cording to Lentz's law, it flows in the opposite direction to that in the primary coil. There will be, therefore, a certain number of counter magnetizing turns due to the ciurent in the secondary coil, and there must be always 228 jusit e-nough more magn'etiziiig turns in the primary coil to overcome the de-magnetizing tuims in the secondary coil and still force the magnetic flux through the iron core, and so produce the counter E. M. F. in its own coils sufficient to oppose the E. M. F. of the main line. It will be noted that the transformer receives and de- livers the same number of watts, but that this number of watts may be made up volts and amperes in almost any ratio that we please by properly choosing tlie number of turns on the two coils. 3?he Ruhmkorff coil is an example of this, in which a battery current of a few volts and eight or ten Amperes is transformed into an exceedingly small current, but having a voltage of hundreds of thousands of volts. It is to be kept in mind that the battery current is interrupted or, in effect, made alternating by the circuit breaker on the coil. The alternating current system of transmitting power is without doubt destined to come into very extensive use on account of the ease of transformation with a transformer without any moving parts and on ac- count of the cheapness of the line over which the power can be efficiently transmitted after being transformed with such little expense. Lines are in use in this country in w^hich power is transmitted 40 miles at a pressure of 40,000 volts. In an experimental plant in Germany power was transmitted 130 miles with a loss in the line amounting to only 13 per cent. Without doubt power electrically trans- mitted by alternating currents of high voltage is destined to play a very large part in the industrial development of this country. QUESTIO^s^S ON CHAPTER XIX. 1. Wihat is an alternating current? 2. How many alternaitions per second were used in the older lig*hting systems? 3. What is a period? 4. A four-pole machine is running 1,100 reTolutionp per minute; if it is producing alternating current, iiow many cycles per second will this current have? 5. How may an alternating currenl: be produced from an ordinary direct current motor or dynamo? 6. What is a sine wave? 7. What is a single phase alternating current? ^ 8. What is a two phase alternating current? 9. If a two phase current is taken from a direct cur- rent two-pole dynamo, to what points on the commutaitor will the four rings be attached? 10. What is a three phase alternating current? 11. How may a three phase current be produced from a direct current two-pole dynamo? 12. Why are the currents of a two-pha^e current said to be 90 degrees apart, while the currents of a three-phase current are said to be 120 degrees apart? 13. If possible, sketch the connections which would be necessary to produce a revolving pole with a two-phase cur- rent. 230 14. What advantages do alternating currents iiave over direct currents? 15. What is an alternating current transformer? 16. What is the object of a transformer? 17. How is current produced in the secondary coil from a primary coil with insulation of thousands of ohms between the two coils? 18. Why will a transformer connected across a thou- sand-volt circuit and having a resistance of only one ohm allow only a small part of an ampere to pass? 19. Why will the current in the primary coil increase vvhen the resistance of the secondary circuit decreases? 2Q. What is true of the watts received by the primary cofil and the watts delivered by the secondary coil? 21. What is a Rhumkorff coil? 22. Why is the alternating system of power transmis- sion rapidly coming into use? CHAPTER XX. ELECTRIC AUTOMOBILES. The practicability of the electric automobile was long ques- tioned, because of the severe duty imposed on the storage bat- tery; with the many improvements in the latter, which have taken place in the last few years, however, the development of the electric automobile has taken rapid strides, until to-day it stands in the front rank of automobiles. Batteries are now manufactured practically *'fool proof" and of capacity to run a vehicle under ordinary conditions 35 miles or more on one charge. The medium for transmitting the power or the Electric Motor is ideal for this purpose ; it is simple in con- struction, it is efficient, and it has a rotative movement which insures smooth running, free from vibrations of any kind, and Tt is easily controlled. There are principally two systems of Electric Automobiles : the one using a double motor equipment with each motor driv- ing a rear wheel through gearing, and the other employing a single motor which is connected by gearing or chain to a differential gear driving the rear axle. The two systems have each their advantages, but are in principle the same, though the single motor equipment is probably the one most extensive- ly used. The equipment of an Electric Automobile consists of the motor, the controller anc?" tjie storage battery. 282 THE MOTOR. The automobile motor, being exposed to all sorts of weather conditions, as well as liable to all sorts of abuse, must be particularly designed for these conditions. Also as the source of power, the storage battery, used in an automo- bile, must be kept down as low as possible on account of its comparatively great weight; the design of this type motor requires the greatest care and experience. The principal points to bear in mind when designing an automobile motor are that it must be weather-proof and accordingly entirely enclosed, it should be as light in weight as possible, it should have a large overload capacity and a good efficiency over a wide range of loads. As in street car service, the power required for starting is very large as is also the power required for climbing hills, and for this reason the same type motor has been selected for automobiles, that is, the series motor. In this motor, the fields being connected in series with the armature, the same current will flow through both, therefore the torque of the armature will be proportional to the square of this current. According- ly, when starting the motor, the armature then being at rest, there will be no counter electromotive force to oppose the current flowing, this current will be comparatively large and the torque great. In the same way when climbing hills the speed will be low and the counter electromotive force low and the torque large. After the start, and when running on a level road, the torque required is small and accordingly the current small and the speed high. In point of efficiency, however, the automobile motor dif- fers in design from the street car motor, the work of the automobile motor being a great deal more uniform, that is, 233 it is not called upon to render as frequent overloads or as frequent changes in load as the street car motor, but is run at a fairly constant load most of the timiC. Accordingly, the fixed losses are kept as low as possible, that is, losses due to hysterises and eddy currents in the armature iron, brush fric- tion and bearing friction. Figure 88 Outline drawing of automobile motor. In mechanical design, the automobile motor practically stands as a type of its own. It is made "fool proof,[' dust p^oof and weather proof, and all working parts that generally need attention are made most simple in construction so as to require the least amount of care. Ball bearings are used throughout, reducing bearing friction to a minimum, but in- creasing the life of the bearings, though requiring very little care. For reasons of keeping the weight down to the lowest possible for the largest output, the utmost care should be exer- cised in the distribution of the material needed, as well as the selection of same. 16 s ^ *^ 'I ^1 -I 'I ^1 ^t i 1 ''I ^^ '^ "« *^ ^)^ ^ 235 The magnet frame is usually of cylindrical shape of small diameter, resulting in a compact design; its material is cast steel or wrought iron forging and sometimes laminated steel built up in the same manner as the armature core. The end housings, which contain the ball bearings, are cast of alum- inum ; only the commutator end housing being supplied with a small water-tight lid which enables examination of commuta- tor and brushes. Fig. 88 shows the outlines of a small auto- mobile motor, illustrating in a general way the principles em- bodied in its design. The horse power required to propel a carriage weighing (w) tons at a speed of (v) miles per hour on a grade of (p) per cent, or number of feet rise or fall respectively in a length of lOo feet, may be found from formulae w X (50 4- 20 X p) X V H. P. eouals 375 In Fig. 89 this formuxae has been used in calculating the power required to propel a vehicle weighing 1,000 lbs. or Y^ ton at various speeds and grades from 0% or level to 20%. The same Fig. 89 also gives revolutions per minute of various sizes of driving wheels most commonly in ase. To illustrate the use of these curves, we will assume a carriage weighing 1,500 lbs. and desire to know the amount of power required for this carriage climbing a hill of 8% grade at a speed of 16 miles per hour. • From above formulae we have : i§H(50 + 20x8)xl6 H. P. equals equals 6.75 . • 675 This would have been found from the curves in the fol- lowing way: The horizontal line marked 16 miles per hour intersects the diagonal line marked 8% at a certain point : from 236 this point follow a vertical line down, and read off the result, which is 45 H. P.; this is, however, for a vehicle weighing 1,000 lbs., and as the carriage in our example weighs 1,500 lbs., the above result must be multiplied with 1.5, which gives us 6.75 H. P. as before. In the same way, if our vehicle has 30" driving wheels and it is desired to know the revolutions per minute of the horizontal line marked 16 miles per hour, con- tinue the horizontal line marked 16 miles per hour until it intersects the diagonal line marked 30" wheel; from this point follow a vertical line upwards and read the result, which gives us 180 revolutions. From this the proper gearing be- tween motor and driving axle may be selected. •S • E ■ 6 B-^-Q-B-g • B 1 - iTTin ? — AV^»^- Figure 90 Diagram of controller connections. 237 THE CONTROLLER. The automobile controller is generally of the drum type, having one large drum with contacts arranged for two or three speeds and on small drum for reversing; in some types of controllers the two are combined in one single drum ope- rated by a handle placed in some convenient position under the seat of the carriage. Fig, 90 shows a diagram of controller connections for a vehicle motor using a single motor and is arranged for a separate reversing drum and a speed drum giving three speed positions and one charging position. All contacts marked with the same number are electrically connected. In the diagram contacts illustrated on the dotted lines i, 4, 5, 6, all belong to the speed drum and must be considered moving together, as this drum is rotated. In the same way contacts illustrated on dotted lines 7 and 8 belong to the reversing drum and rotate with this drum. Further, contacts on dotted lines 3 and 9 repre- sent springs or controller ''fingers" which are stationary and permanently connected to the various apparatus, as batteries, motor, etc. Suppose the reversing drum to be in the position of "ahead" that is moved so that the dotted line 7 is under the dotted line 9, and further that the speed drum is moved to the position of "ist speed" or so that the dotted line 4 is under the dotted line 3, and we trace out the connections thus estab- lished, we find that the current from the four sets of batteries unite, flowing through the watt meter or combined ampere and volt meter, thence through the circuit breaker or fuse through the series f:eld of the motor, the armature and back to the speed drum, there splitting to the different batteries. We have thus a parallel connection of the batteries or the lowest voltage available; if the capacity of the storage battery when connected in full series is 80 volts, we would have 20 volts at the terminals of the meter with the controller in this position. 238 By similarly tracing the connections for other positions, the 2nd speed position will give us a series parallel connection of the batteries or a voltage of 40 at the terminals of the motor, and, lastly, the 3rd speed position gives us the straight series connection or the full voltage of 80 at the motor terminals. When the speed drum is on the charging position the motor is entirely disconnected and the batteries arranged in full series, connected through the meters to the charging terminals. The particular controller just described had a brake attach- ment applied to the controller handle whereby with one move- ment of the handle power might be turned off and brake ap- plied; this position is marked in the diagram by dotted line 2 as "maximum brake." Such an arrangement has the advan- tage of being less confusive than the employment of a separate brake handle, especially rn emergency cases where quick stops are necessary and the time which would be lost in fooling with separate handles as a rule is very valuable. THE BATTERY. The automobile storage battery does not, in principle, differ from the stationary storage battery; it is a lead battery formed according to the Plante or the Faure method. The Plante process, which was briefly mentioned under Chapter IT, requires for the complete formation of the battery a repeated reversal of the current and is very tedious and expensive. By treating the plates with certain acids, however, the forming may be accomplished in a comparatively short time. The Faure process consists of applying or pasting already formed materials to the lead plates. The materials used for this purpose are red lead and litharge mixed with sulphuric acid and water to make a paste; plates made up in this manner 239 need then simply be charged to be ready for use. In both cases the electrolyte used is diluted sulphuric acid. In the following we will make a brief description of the Chloride, the Willard and the Edison auto-batteries as being of three distinct types in regard to construction and forma- tion. THE CHLORIDE ACCUMULATOR. The positive plate of this battery is cast of lead in the shape of a grid whose perforations are round holes some- what less than M" in diameter and about i" between centers; these holes taper to a smaller diameter from the outside sur- face to the middle of the plate, making, in fact, countersunk holes from both surfaces of the plate. The active material consists of pure lead in the form of ribbons, the width of which are equal to the thickness of the plate. These ribbons are wound into spirals which are pushed into the holes of the grid. The negative plates are made by casting under heavy pressure around pellets of active material placed in the mould, a grid of an alloy of lead and antimony. The pellets are made of finely powdered lead dissolved in nitric acid; by adding hydrochloric acid to this solution a precipitate of lead chloride results. This precipitate after being washed is then melted with zinc chloride and poured intb moulds to ^orm the pellets, which are about 54" square and of the same thickness as the plate. The finished plates are then placed between zinc plates and immersed in a zinc chloride solution; the electro- chemical action resulting from short circuiting these plates are to remove the chloride, leaving the pellets in the form of pure lead in a highly porous state. There are several types manufactured, of which the fol- lowing are examples : 240 TABLE XXII. ELEMENTS OF TYPE M. V. Number of Plates: 5 7 9 '' 13 15 Discharge in amperes for 3 hours. 18 27M S6H 45M 55 64 Weight in lbs. of com- plete cell with electro- lyte. 19^8 28 36 44^ 53K 61H THE WILLARD BATTERY. The plates of this battery are of the Plante type and are made up of lead sheets ridged or grooved across the whole width of the plate ; the grooves are cut in a downward direc- tion from the surface of the plate to its center, thereby form- ing V-shaped pockets or shelves which greatly increase the active surface of the plate and after forming serve to retain the active material. It is claimed that the Willard plates are not subject to any deterioration or buckling as the active oxides when formed between the ribs, by their expansion, only cause these thin ribs or shelves to open up and slightly separate from each other. The internal resistance of this cell is very low as its construction gives a plate without any joint whatever between the active and the conducting ma- terials. The positive and negative plates in each cell are separated by hard rubber discs which are perforated to allow free circulation of the electrolyte. Following are two tables giving some data of the Willard batteries : 241 TABLE XXIII. WILLARD STANDARD BATTERY. Weight in Ampere Hour Capacity when Discharged in Pounds. 3 hrs 4 hrs. 5 hrs. 6 hrs. 13 34 38 40 42 16 45 50 53 55 19 56 63 67 70 22 66 73 78 81 28 84 93 99 103 35 112 124 132 137 TABLE XXIV WILLARD SPECIAL BATTERY. Weight in Ampere Hour Capacity when Discharged in Pounds. 3 hrs. 4 hrs. 5 hrs. 6 hrs. 18 48 53 56 59 25 72 80 85 89 31 96 106 112 117 37 120 132 140 147 44 144 158 167 175 50 168 180 196 205 THE EDISON STORAGE BATTERY. The batteries described in the foregoing were all lead-lead batteries. The Edison battery is distinctly different from these in that it employs no lead whatever in its construction. The 242 plates are made up of steel and nickel, each individual plate consisting of 24 little cups or pockets pressed of thin steel heavily plated with a coat of nickel, which is afterwards fused to the steel. These little cups, which are made in two sec- tions, one engaging within the other like a capsule, are filled with the active materials — consisting of specially prepared oxides of nickel and iron — are placed in corresponding open- ings in a thin grid and the whole is subjected to a very high pressure. This locks the two sections of each cup firmly Figure 91 Finished Plate, Grid and Group of pockets containing active material. together and fastens them securely to the grid. Fig. 91 shows the construction of aiT Edison plate. This construction results in an extremely strong and light plate, having good electrical contact between active and conducting materials. The finished cell consists of a number of such plates loaded with nickel oxide alternating with plates loaded with 243 iron oxide; the nickel oxide plates form the positive pole and the iron oxide plates the negative pole of the cell. To prevent the plates from coming in contact with each otlier, hard rub- ber rods are placed between same and sheets of hard rubber, as well as rubber supports, are used to separate the plates from the containing jar, which is made of steel in this battery. The electrolyte used is a 20 per cent solution of potash. The Edison battery is made m three sizes, of which data is given below : TABLE XXV. Type of Cell: E-18 E-27 E-45 Capacity in ampere hours 105-115 105-115 260-280 Average discharge voltage per hour 1.25 1.25 1.25 Rate of discharge in amperes 30 45 75 Satisfactory rate ot charging in amperes. 40 65 100 Suitabl timeof charging in hours 3K m 334 Weight in pounds per cell in- cluding so ution 13 i:k 28 The manufacturers claim that any desirable rates of charge and discharge may be employed without fear of injury to the cell. THE CHARGING OF AUTO BATTERIES. The voltage per cell of the lead batteries — which is as yet the most extensively used — is about 2 volts and it should never be allowed to discharge below 1.8 volts and rather not below 1.9 volts. 244 When we wish to charge an automobile battery, we must first make sure of the charging current available, the voltage of the same, whether direct or alternating current, and if direct current, whether arc or incandescent. The next im- portant point to establish is the polarity of the terminals of our charging circuit as the positive and negative terminals of the same must be connected to corresponding terminals of our battery. On the battery the poles are usually marked with a + or ■ — and to ascertain the poles of our charging circuit we may connect the two terminals of the same to two lead plates immersed in a crock containing water and a little sul- phuric acid. The lead plate which turns brown is the one connected to the positive terminal and this is the one which must be connected to the terminal marked -{- on our battery. The other lead plate will take on a bluish color and is the negative terminal. If a series arc circuit is available and the battery consists of 20 to 30 cells, connect as per diagram. Fig. 92, where A-A is the ^ H-^ Figure 92 Auto charging connections for arc circuit. arc circuit, B is the battery terminals on the carriage, and C is a crock or small wooden trough containing water and some sulphuric acid. By varying the distance of the two lead plates in the crock, any desirable charging current may be had. The current and voltage taken is read off on the meters in the car- riage. 245 If the battery consists of 40 or more cells connections should be m.ade as shown by the dotted lines in Fig. 92. Should the charging circuit be a no volts incandescent, connections should be made as in Fig. 93, which may be F^ Figure 93 Auto charging connections for incandescent circuit. used for any number of cells. If the only charging current available is alternating, it will be necessary to use a rotary transformer or some other apparatus for rectifying of the current, as storage batteries cannot be charged directly from alternating current. As there are several points of importance to take into ac- count when dealing with storage batteries, we will in the fol- lowing lay down a few general rules in the caretaking of the same, and also discuss some of the principal troubles which might be encountered. A battery should never be discharged below 1.8 volts at the very most and better not lower than 1.9 volts ; when this voltage is reached the battery must be re- charged, the charging-voltage per cell to be from 2.4 volts to 2.6 volts. If while recharging the cells should get hot and the electrolyte boil, the charging current should be reduced. Should it be -desired to charge rapidly the current may be started at a high value and gradually tapered off as the charging proceeds. For a three-hour charge, for , example, charge with 50% of the total current during the first hour, 33^4% during the second hour and i6j^% during the third hour. 246 The battery should never be allowed to stand discharged for any length of time : when not in use give it a short charge about once a week. If it is to be laid up for a longer period, charge fully, take out the plates and wash and dry them thor- oughly. After a battery has been in use for some time part of the electrolyte has been lost through spilling or evaporation, and it must be replenished to such an extent as to always stand somewhat over the tops of the plates, about Yz" or so. Either solution or only water is added until the density of the electro- lyte reaches i.i to 1.2 and it should never be allowed to ex- ceed 1.26, as this may cause corrosion of the grids. The density is measured by a hydrometer on which it may be read off directly. Fig. 94 shows a hydrometer made especially for use with automobile batteries, which are always covered. The hydrometer proper is enclosed in a syringe ; Figure 94 Automobile Hydrometer. if the tip of this syringe is inserted in the vent hole in the cover of the cell and the bulb compressed, enough electrolyte will be drawn up into the syringe to float the hydrometer and the density may be read through the glass tube of the syringe. The electrolyte is made up of about one part sulphuric 247 acid to six parts distilled water, By measure. When mixing the solution it must be remembered to pour the acid into the water, and never vice versa; if it be desired to add more water to the solution introduce same at the bottom of the cell by a tube or small hose. A common trouble with batteries is buckling of the plates; this is mostly caused by sulphating. A white sulphate of lead is formed between the supporting grid and the active material and if excessive will cause an expansion of the {)late, buckling or warping same. If sulphating should be discovered before buckling has already set in it may be cured by charging of the battery at a somewhat higher rate than usual, urtil the cells emit gas. A battery which is allowed to stand idle for a long time without being charged will invariably sulphate ; an over- discharge will cause the same trouble; this discharge may be through over-load or through short circuit between the in- dividual plates. Short circuit between the positive and negative plates in a cell is another common trouble which most always .is caused by active material shedded from the plates ; the only remedy is to remove the cause of the trouble. 248 QUESTIONS OX CHAPTER XX. 1. What causes vibrations in other automobiles— not elec- tric ? , 2. Is there any other automobile motor besides the elec- tric which has a rotative movement ? 3. :Mention some advantage of single motor equipment over double motor equipment. 4. ^Mention some advantage of double motor equipment over single motor equipment. 5. Explain the reason for using a series motor for auto- mobile work. 6. Required, the horse power necessary to propel a car- riage weighing 2,oco lbs. when running on a level road and at a speed of 12 miles per hour. 7. What is the revolutions per minute of the driving wheels for carriage m example 6, if diameter of wheels is 36 inches? 8. What is the speed of the motor in example 6, if the gearing is 8:1? 9. If a carriage is running at a speed of 20 miles per hour with controller in position of full voltage on the motor, what will the speed be with controller in ist and 2d speed position it conditions otherwise remain the same? 10. If the hydrometer registers a density of 1.3 what should be done? 11. Describe the color of the plates in a storage cell. 12. How does the color of the plates change with dis- charge of cell? 13. How are acid fumes from batteries neutralized and acid spots on clothes removed? 14. How may *'sulphating" of a battery be prevented or sulphate removed? ANSWERS TO QUESTION'S ON CHAPTER I, 1. Nothing of its ulimmate nature. 2. They are probably better understood than, the laws gioverning heat land light. 3. The operation of an hydraulic system. 4. (a) The water pressure or head, (b) The amount of flow or number of gallons per minute, (c) The frietion- al resistance of the x>ipes oarrying the water. 5. The volt. 6. To one foot of head or pressure. 7. The ampere. 8. The ohm. 9. Amperes equal volts divided by ohms. 10. Ohm's law is only the application of a general law to electrical action. The How of heat thi*ough a wall is an example. 11. About two. 12. Usually 110. 13. (a) One-«half ampere, (b) From six and a half to ten. 14. One ohm. 15. Loss of pressure bert:.ween boiler and engine in steam pipes. 250 16. On the amouiit of fluid carried iiirongh tJhe pipe and on the straig^tness and general character of the pipe line. 17. To tihe dj'namo. 18. To be filled in by student. 19. Upon the amount of current transmitted and on the resistance of the wire. 20. Draw a diagram and compare with Fig. 4. 21. From 95 to 98 per cent. 22. It is the loss of voltiage due to the resistanae of the wires over wMch the current niu!^t travel. 23. The use of wires of such size that t4ie loss of voltr age shall be practically zero. 24. On account of the great size of conductors needed and the consequent expense. 25. To select wire of such size that tihe lamps shall at all times receive the same voltage. 26. See text, page 8. 27. No. (2). 28. Write out and compare with text. 29. Four volts. 30. Such a circuit would require 800 feet of No. 0000 wire. 31 > I'ifty amperes. 32. .077 ohms. 33. 108 volts. 251 < 34. 12,100. 35. Abou't two vdlts. 36. Wire twice ais large as No. 0000. 37. So as to reduce 'the drop to as small an anDount as possible. 38. $806.00. 39. A'Mien only a few lamps are bnrning- on a distanrt circuit, the voltage on this circuit is practically that of the dynamo, and tends to burn out the lamps. 40. Table 2, page 16. 41. At least 50 volts. 42. Through the rails and ground. 43. Because the copper used in bonding t.he track is not nearly so great in amount as that required by the trol- ley wires and feeder. 44. 2.50 times the size of a No. 0000 wire. 45. $1,900.00. 125 46. x500 equals 833. 75 47. $1,141.00. 48. No. 1 lor No. 0. 49. SucJh a sj'Sftem would leave the trolley wire discon- nected near the power house. Power would be supplied to the line from the dynamos by feed wires connected at a distance from tiie power station. 252 50. By the oonstanrt: pot-en'tiial amd oonstaiut current systems. 51. For operating the older arc lamp systems. 52. Each device for receiving electricity ds exposed to the same electro-motive force. 5ii. Each device for receiving electricity must carry the same current. 54. From 9^^ to 10 amperes. 55. About 6^2 amperes. 56. The resistance of the wire in ohms equals 10 8-10 times the length in feet divided by the square of the diam- eter of the wire in thousandlths of an incn. ANSWERS TO QUESTIONS IN CHAPTiJR 11. 1. Galvani and Volta. 2. Write the answer and compare with the text. 3. From the negative plate through the outside circuit to the positive plate. 4. The chemical action of the electrolite upon the posi- tive plate. 5. The counter electro-motive force caused by the pro- duction on the negative plate of some gas, usually hydrogen. 6. The positive element is the one on which the elec- trolite acts cheraiaally; the negative element Is -the remain- ing one upon which the electrolite has less or no chemical action. 7. The terminal on the negative plate from which the current flows into the outside circuit. 8. Platinum, carbon and silver. 9. Because zinc and carbon are farther apart in the electro-chemical series than zinc and copper. 10. Both mechanical and chemical means are employed. The mechanical means consists of blowing air or some other gas across the negative plate, or of providing numerous small points from which the gases may escape. 11. Write the answer and compare with text. 12. They cost too much. 254 33. Write description of Jablockoff battery and com- pare with text. 14. Write description of plunge battery and compare with text. 15. It should be amalgamated 16. Directly proportional. 17. An instrument in which the amount of current that has passed in a given time is measured by the amount of de- composition effected. 18. Write answer and compare with text. 19. An anode is the plate or electrode by which cur- rent enters the solution. A cathode is the plate or electrode by which current leaves the solution. 20. With it. 21. Write answer and compare with text. ELECTRO-PLATING. 1. Metal is taken from the anode and deposited in a thin even layer on the cathode or work to be plated. 2. See text. 3. On the ampere hours or on tlie amount of current flowing multiplied by the length of time it flows. 4. The work is burned. 6. Yes. See text. 255 STORAGE BATTERIES. 1. A storage ba'ttery is one in iwhich electrical energiy is consumed in producing* chemical change and which will return the energy so stored as electrical energy upon de- mand. 2. See text. 3. It does no>t polarize, has a very low resistance, and so is capable of producing heavy discharges, and has a high- er voltage than most primary batteries. 4. For running horseless c|arriaiges and electric launch- es, and for absorbing the energy of a dynamo or circuit at times of light load and restoring it at times of heavy load. A battery may be very advantageously placed at or near the end of a long feeder line, so as to make the current that flows over the line nearly constant. ANSWERS TO QUESTIONS ON CHAPTER HI. 1. It is magnetized. 2. A small magnet is supported in such a manner as to be free to turn in a horizontal plane. 3. A north pole is one that points to the geographical north. A south pole is one that points to the geographical south. 4. The region of magnetic influence surrounding the poles of a magnet. 5. From the north pole into the air into the south pole and through the iron to the north pole. 6. The figure formed usually by iron filings in a field of magnetic force, showing the direction and intensity of magnetic force. 7. It is much more concentrated than that of a bar magnet. 8. See text. 9. The circular and concentric lines surrounding a wire carrying a current. 10. The same as between the direction of rotation of a righl hand screw and its direction of motion forwarrl oi backward. 11. Up. 12. South. 13. North* 257 14. A piece of magrnetic metal around which, a current is circulating. 15. See text. 16. That end of an electro-magnet around which the current circulates in the direction of motion of the hands of a watch, as seen by the observer, is the south pole. 17. Yes. The lines of force flowing from the electro- magnet may be considered as the sum of the magnetic whirls of the wires which surround the core. IS. A coil of wire in w^hich a current flows. It is a weak magnet. 19. An electro-magnet without a metallic or iron core would be a helix. 20. Tt expenences a mechanical force that pulls it side- ways across the magnetic lines. 21. Current and fieldin proper relation are supplied and motion results. 22. Motion and magnetic field properly related are sup- plied and electro-motive force which may produce a current is the result. 23. Thumb, first and second fingers of the right hand are extended at right angles to each other, and point in the directions respectively of motion, lines and current. 24. Extend the thumb, first and second fingers of the left hand at right angles to each other, and they will point respectively in the directions of motion, ISnes and current. 25. "Because the direction of lines would be reversed without reversing anything else. 258 26 The wire on top moves in one direction, tlie wire od tbe bottom in the opposite direction, both of which tend to produce rotation in one direction. 27. Current will tend to flow from the top to the bot- tom of the wheel. 28. Current will flow in the direction of the hands of a watch, as seen by the observer on the south side of the loop. 29. Current will flow from east to west. 30. Current flows away -from the observer. 31. About 1-10 of a pound per foot. 32. 100,000,000. 33. Yes. To provide sufficient friction between the wire and the armature core to prevent the wires moving from the mechanical force exerted between the current in the wire and the magnetic field. AiNSWERS TO QUESTIONS ON CHAPTER IV 1. On tihe a.mpe 110 6. .0663. 6. 134. 7. 4.97 per cent. 8. No. 32 9. — amperes. 55 10. On 110 volts 6.782, on 220 volts 3.391, on 500 volts 1.492, on 1000 volts .746, on 10,000 volts .0746. 11. On no volts 9.09, on 220 volts 4.545, on 500 volts 2, on 1,000 volts 3, on 10,000 volts .1. 12. Because the voltage Is hig-her and the current lower than if the dynamos were in parallel. 13. More economical because the voltage would be still further raised and the current reduced in the same ratio. 14. Because dt permits of the use of a cheap line with only small loss of power. 267 15. It could not be aooomplislied with 250 voUts. 16. It could noit 'be aooomplished with 500 watts. Abon^. 95 per cent of the 100 horse power would be losit in the line at 1,000 volts; 49 volts or ISO waitts or 14 of 1 per cent, with 20,000 volts. 17. Because with the same copper cost the amount or weight used is the same, and if this is run two inches in- stead of one, the resistance of each mile is doubled and the miles of line are doubled, and therefore the resistance quad- rupled. 18. As the square of the voltage. 19. The distance varies directly as the voltage. 20. 0000 wire is the nearest stankiard size, and this will cost $506.40. 21. Three No. 000 wires can be used, and this 'will cost $1,140.75. 22. The drop s-pecified in 'this question should have been omitted, and then the current would be 123.3. 23. Because tihe armature generates voltage and when it is in operation there is no way of measuring what is used in the armature resistance. Therefore the other two for- mulae that contain the voltage lost cannot be easily applied. ANSWERS TO QUESTIONS ON CHAPTER VIIL 1. To know the length of the average turn, 2. See text. 3. 4129. 4. No. 17. 5. 32,400. 6. Because the number of a. t. is increased with the same size of wire if it is small in diameter, and a small wire and small power will therefore produce more a. t. if of small circumference than if of large. 7. In order to have section enough of iron to allow the magnetic flux to pass. 8. Because an increa.se in the amount ocf itlhe wire de- creases the current that flows through 'the coil in the same proportion tha^t it increases the turns. 9. Yes. A heavy coil requires only a small amount of current to produce a given magnetizing power, an^ there- fore runs cooler. 10. For 6-volt plafting dynamo No. 6 wir-e gives 2788c For 110-volt dynamo No. 18 givels 3150. For 220-volt dynamo No. 21 gives 3165. For 500-violt dynamo No. 24 gives 3612. 11. For plating dynamo No. 6 wire req'uires 1214 poundis. For 110-volt dynamo No. 18 requires 16 pounds. For 220-volt dynamo No. 21 requires 16 poumds. For 500-vdlt dynamo No. 24 requires 20i/> pounds. 269 12. One watt per square inch. 13. If thicker than this the heat from the inside layers of wire has difficulty in getting" away to the outside surface. 14. .21 of 1 per cent, per degree F. 15. Divide the number of amperes that a coil of one pound will pass by the number of amperes it is desired to have the finished coil pass, and the result is the desired weight. 16. iSize of wire required ds No. 20. Wedght of wire re- quired is 14 pounds per coil. 17. 20.9 x>ounds of Xo. 21 wire gives 3,600 a. t. at full pressure of 250 volts and a heat loss of l^ watt per sq. in. 13. Divide number of ampere turns required by num- ber of amperes that wili flow, and the result is the number of turns. 19. It decrease the current by increasing the resist- ance through the coil and so decreases the power lost in the coil. 20. It increases the resistance and so increases tne power lost. a:n^swers to questions in chapter IX. 1. 100,000,000. 2. See text. 3. It is a device by which direct current is obtained irom an armature in the wire of which the current is alter- nating. 4. Because there must be two paths for the passage of the current through a direct current armature, and each path contains only half the amount of wire that is used on the whole armature. 5. 120 volts. 1,500 revolutions. 6. See text. 7. 1,3S8,SS9. 8. The best winding will be two parallel of .072 wire, and the resistance of the armature will be .0816 ohms. Di- mensions of arm'ature will be found in Fig. 29. 9. If the motor is of the same size it will only be neces- sary to double the number of iturns on the -armature. 10. Twice as many turns are required on a gramme ring armature as oai a drum armature. 11. In the gramme ring method of winding, adjacent coils are at a small difference of potential, and ft is easy to repair a coil if one gets out of order. 12. 223.2 square inches. 13. The number of wires will be doubled, (the seictional mrea will be halved, thus quadTupling the resistance. ANSWERS TO QUESTIONS IN CHAPTER X. 1. The electro-motive force produced in an electrical device which tends to reduce the current which the rprim'ary electro-motive force would tend to produce. 2. No. 3. Because the counter electro-motive force is very nearly equal to the primary elect-ro-motive force. 4. By an application of formula (14). 5. 925.8 revolutions per minute. 6. 3,174,600. 7. Because as the temperature of the fields rise the resistance rises and the ampere turns decrease, consequently the flux decreases and the speed increases in the same ratio as the flux decreases. 8. The Patton street car was an example of this, in which a gas engine drove a dynamo which on light loads and down grades charged la storage 'battery, while on heavy loads and up ^grades it became a motor and absorbed power from the storage battery. 9. The fact that the flux through the armature is con- stant and the voltage lost due to the resisance of the arma- ture is very small, even at heavy load. 10. Because the voltage lost in a large armature is rela- tively less for the same heating than in a smaller armature. 11. Because it decreases the counter electro-motive force by decreasing the effective flux through the armature. .272 12. Volts lost in armature with one ampere equal .08 volts. Volts lost in armature with 30 amperes equal 2.4 volts. The drop in speed in per cent, will be 2.4 divided by 79.92 equals 3 per cent^ 13. Because the ampere, turns on the field coil of a series motor, and therefore the magnetic flux through the armature, depend upon the load on the armature. 14. Because the flux through the field magnets tends to become constant after the iron becomes saturated. 15. The magnetic flux across an air gap is strictly pro- portional to the ampere turns expended in the air gaip, and if the iron is unsaturated at the highest voltage, practically all the ampere turns will be expended in the air gap and the flux through the armature will be proportional to the volt- age, thus making the speed constant. 16. In the same way that the speed of a series motor does, but not in the same degree. There will be an upper limit set to the speed on account of the flux produced by the shunt coil. 17. The torque of an armature is proportionial to the product of the current and magnetic flux through it. "When the iron is unsaturated the flux through the armature will be doubled by doubling the current, and the double flux, acting on the double current, produces four times the torque. 18. To the current passing through the armature. 19. On a constant potential circuit with no load on the armature the increasing speed produces an increasing coun- ter electro-motive force, which reduces the current ^SWEiT^S TO QUESTIONS ON CBDAPTBR XVni. 1. A current proportional to the voltage. 2. Ohm's law. 3. Down through the plane of the paper, 4. The eddy currents generated in the copper coil on n-h'ch the wire carrying* the current is wound. 5. Magnetic field uniform. 6. The mechanical force lacting on the w^ires carrying current and the reaction of the hair springs. 7. On the constancy of the permanent magnet. 8. A difference in the si^e of wire on the movable coil which in the ammeter is adapted to receive much larger cur- rents at a correspondingly lower voltag-e. 9. See text. 10. See text. 11. The error introduced by the hysteresis of the soift iron. 12. Write answer and compare with text. 13. Write answer and compare with text. ANSWERS TO QUESTIONS ON CHAPTER XIX. 1. A cnirent -which is cans tan tly reversing its direotion. 2. From 12 to 16,000 per minute. 3. The time required for two successive alternatioois. 4. 36 2-3. 5. By connecting a circuit to tv^o rings att|aohed to op- posite points on a direct current bi-polar commutator. 6. The form of alteirnating current wave produced by a coil revolving in a uniform field. 7. A single alternating current. 8. Two alternating currents produced or used by the same machine in such relation to each other that when one is zero the other is maximum. 9. To four- points 90 degrees apart. 10. Three alternating currents having a certain rela- tion to each other set forth in answer to question 11. 11. By taking current from three rings attached to three points on a two-pole direct current dynamo 120 de- grees apart, 12. Because two-phase circuits are attached to points 90 degrees apart on a direct current bi-polar commutlator, and to produce a three-phase to points 120 degrees apart. 13. Fig. 86. 14. The volts and amperes can be transformed by static apparatus. 290 15. A device of iron and copper by wliicli electric energy is transferred from one circuit o another without metallic contact. 16. To receive a small current at a high, voltage and produce a large current at a correspondingly lower voJ't|age, or vice versa. 17. On account of -the magnetic flux which is common to both the primary and the secondary coils. 18. The self-induction of the coil produces a counter electro-motive force, which is very nearly equal to the pri- mary electro-motive force. 19. The ampere turns' of the secondary coil oppose those of the primary, but the primary coil must always have enough ampere turns to force sufficient ma*tr-iH iH T-l tH 1-t T-t C0 CO 05 T-< '^. ^ ^. ^. 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C. — Abbreviation for alternating" current. ACCELERATION— The rate of change of speed or velCKjity. ACCUMULATOR, A SECONDARY OR STORAGE CELL— Two inert plates partially surrounded by a fluid inca- pable of acting chemically on either of them until after the passage of an electric current, when they become capable of furnishing an independent electric current. AFFINITY, CHEMICAL— Atomic attraction. The force which causes atoms to unite and form chem- ical molecules. ALARM, BURGLAR — A device, generally electric, for auto- matically announcing the opening of a door, window, closet, drawer, or safe, or the passage of a person through a hallway, or on a stairway. ALARM, ELECTRIC— An automatic device by which atten- tion is called to the occurrence of certain events. ALLOY — A combination, or mixture, of two or more metal- lic substances. ALLOY, GEEMAN SILVER— An alloy employed for the v-zires of resistance coils, consisting of 50 parts of cop- per, 25 of zinc, and 25 of nickel. AMP ^06 ALPHABET, TELEGRAPHIC: MOESE'S— Various group- ings of dots and dashes, which represent the letters of the alphabet or other signs. ALTEKXATIONS— Changes in the direction of a current in a circuit. A current that changes its direction 300 times per sec- ond is said to possess 300 alternations per second. ALTERNATIONS, COMPLETE— A change in the direction of a current in a circuit from its former direction and back again to that direction. A complete to-and-fro change. Complete alternations are sometimes indicated by the symbol. 0^ ALTERNATOR — A name commonly given to an alternate current dynamo. AMALGAM — A combination or mixture of a metal with mercury. AMEER~A resinous substance, generally of a transparent, yellow color. AMMETER — A form of galvanometer in which the value of the current is measured directly in amperes. AMMETER, MAGNETIC- VANE— An ammeter in which the strength of a magnetic field produced by the current that is to be measured is determined by the repulsion exerted between a fixed and movable iron vane, placed :n said field and magnetized thereby. AMxMETER, PERMANENT-MAGNET— A form of ammeter in which a magnetic needle is moved against the field of a permanent magnet by the field of the current it ^ measuring. AMPERAGE — The number of amperes passing in a given circuit. 307 ARC AMPERE — The practical unit of electric current. Such a current as would pass with an electromotive force of one volt through a circuit whose resistance is equal to one oinn. A current of such strength as would deposit .005084 grain of copper per second. AMPERE-TURN— (See Turn, Ampere). ANION — The electro-negative radical of a molecule. An anion is that group of atoms of an electrically de- composed of electrolyzed molecule which appears at the anode. • ANNUNCIATOR, ELECTRO-MAGNETIC— An electric de- vit^e for automatically indicating the points or places at which one or more electric contacts have been closed. ANNUNCIATOR, HOTEL— An annunciator connected with the different rooms of a hotel. ANODE — The conductor or plate of a decomposition cell connected with the positive terminal of a batterj^ or other electric source. That terminal of an electric source out of which the current flows into the liquid of a decomposition cell. ARC— A voltaic arc. ARC — To form a voltaic arc. ARC, ALTERNATING—A voltaic arc formed by means of an alternating current. ARC, HISSING OF--A hissing sound attending the forma- tion of voltaic arcs when the carbons are too near to- gether. ARM 3U» AEC, VOLTAIC — The source of lig-ht of the electric arc lamp. ARM BRIDGE— One of the sections in a Wheatstone bridge for necessary resistance. ARM-CROSS— A transverse piece attached to a pole for the support of wires, ARM, ROCKER— An arm on v.'hich the bru-^hes of a dynamo or motor are mounted for the purpose of shifting thefr position on the commutator. ARMATURE— A mass of iron or other magnetizable mate- rial placed on or near1:he pole or poles of a magnet. ARMATURE, BI-POLAR — An armature of a dynamo-elec- tric machine the polarity of which is reversed twice in every revolution through the field of the machine. ARMATURE, DRUM — An armature of a dynamo-electric machine, in which the armature coils are ^\ound longi- tudinally over the surface of a cylinder or drum. AR:MATURE, DYXAMO-ELECTRIC machine— That part of a dynamo-electric machine in which the differences of potential which cause the useful currents are gen- erated. ARMATURE, POLARIZED— An armature which possesses a polarity independent of that imparted by the magnet pole near which it is placed. AR!N MATURE, RIXG — A dynamo-electric machine armature, the coils of which are wound on a ring-shaped core. ARMATURE, SPHERIC Ali— A dynamo-electric machine ar- mature, the coils of which are wound on a spherical Iron core. 309 BAG ARRESTEE, LIGIITNTNG— A device by means of which the apparatus placed in any electric circuit is protected from the destructive effects of a flash or bolt of light- ninor. ASTATIC — Possessing no directive power. Usually applied to a magnetic or electro-magnetic device which is free from any tendency to take a defi- nite position on account of the earth's magnetism. ATMOSPHERE, AJN"— A unit of gas or fluid pressure equal to about 15 pounds to the square inch. ATTRACTION, MAGNETIC— The mutual attraction exert- ed between unlike magnet poles. AURORA BOREALIS— The Northern Light. Luminous sheets, columns, arches, or pillars of pale, flashing light, generally of a red color, seen in the northern heavens. AUTOMATIC CONTACT BREAKER— (See Contact Breaker, Automatic). AUTOMATIC CUT-OUT— (See Cut-Out, Automatic). B B — A contraction used in mathematical writings for the internal magnetization, or the magnetic induction, or the number off lines of force per squaire inch or per square centimetre in the magnetized material. B. A. OHM— (See Ohm, P. A.) B. W. G. — A. contraction for Birmingham wire gauge. BACK ELECTROMOTIVE FORCE— (See Force, Electromo- tive. Bacl<). BAT 310 BALANCE, COULOMB'S TORSION— An apparatus to meas- ure the force of electric or magnetic repulsion between two similarly charged bodies, or between two similar magnet poles, by opposing to such force the torsion of a thin wire. The two forces balance each other; hence the origin of the name. B.^ LANCE, INDUCTION, HUGHES'— An apparatus for the detection of the presence of a metallic or conducting substance by the aid of induced electric currents. BALLS, PITH — Two balls of pith, suspended by conducting threads of cotton to insulated conductors, employed to show the electrification of the same by their mutual repulsion. BARS, BUS— Omnibus bars. (See Bars, Omnibus). BARS, OMNIBUS — Main conductors common to two or more dynamos in an electrical generating plant. The terms bus and omnibus bars refer to the fact that the entire or whole current is carried hy them. BATH, COPPER — An electrolytic bath containing a readily electrolyzable solution of a copper salt, and a copper plate acting as the anode, and placed in the liquid near the object to bo electro-plated, which forms the kath- ode. BATH, ELECTRO-PLATING -Tanks containing metallic solutions in which articles are placed so as to be elec- tro-plated. BATH, NICKEL — An electrolytic bath containing a readily electrolyzable salt of nickel, a plate of nickel acting as the anode of a battery and placed in the liquid near the object to be coated, which forms the kathode. 311 BAT BATTEKY, CLOSED-CIRCUIT— A voltaic battery which may be kept constantly on closed-circuit without seri- ous polarization. BATTERY, ELECTRIC— A general term applied to the combination, as a single source, of a number of sepa- rate electric sources. BATTERY, GAS— A battery in which the voltaic elements are gases as distinguished from solids. BATTERY, LEYDEN JAR— The combination of a number of separate Leyden jars so ^ to act as one single jar. BATTERY, LOCAIi— A voltaic b^tttery used at a station on a telegraph line to operate the Morse sounder, or the registering or ^recording apparatus, at that point only. BATTERY, OPEN-CIRCUIT— A voltaic battery which is normally on open circuit, and which is used continu- ously only for comparatively small durations of time on closed-circuit. BATTERY, PLUNGE- A number of separate voltaic cells connected so as to form a single cell or electric source, the plates of which are so supported on a horizontal bar as to be capable of being simultaneously placed in, or removed from, the exciting liquid. BATTERY, PRI:MARY— The combination of a number of separate primary cells so as to form a single source. BATTERY, SECONDARY— The combination of a number of separate secondary or storage cells, so as to form a single electric source. BATTERY SOLUTION— (See Solution, Battery). BATTERY, STORAGE— A number of separate storage cells connected so as to form a single electric source. BATTERY, VOLTAIC— The pombination, as a single source, of a number of separate voltaic cells. BOM 312 BELL MAGNETO ELECTRIC— A • bell rung by tlie move- menit of the arina.ture of an- electro magnet. BELL, TELEPHONE-CALT^A call bell used to call a cor- respondent to the telephone. BI-POLAK— Ha^-ing two poles. BLASTTXC, ELECTETC— The electric ignition of powder or other explosive material in a blast. BLOCK, BIaANCH — A device employed in electric wiring for taking off a branch from a main circuit. BLOCK, EUSE — A block containing a safety iuse or fuses for incandescent light circuits. BOAELj, HANGEE— a form of board provided for the ready placing or removal of an arc lamp from a circuit. BOAHD, ISrULTIPLE SWITCH— A board to which the nu- merous circuits employed in systems of telegraph}', telephony, annunciator or electric light and power cir- cuits are connected. 20AED, SWITCH— A board pro\dded wdth a smtch or switches, by means of which electric circuits connected therewith may be opened, closed, or interchanged. BOBBIN. ELECTRIC— An insulated coil of wire for an electro-magnet. BODY, ELECTRIC RESISTANCE OF— The resistance of the humian body measured from hand to Jiand varies from 3,000 ohms to 15,000 ohms. BOLO^IETER — An apparatus devised by Langley for meas- uring small differences of temperature. BOMBARDMENT, MOLECULAR— The forcible rectilinear projection from the negative electrode, of the gaseous molecules cf the residual atmospheres of exhausted ves- sels on the passage of electric discharges. 313 BRI BORE, ARMATURE — The space provided between the pole pieces of a dynamo or motor for the rotation of the armature. BOX, DISTRTCT-CALL— xV box by means of which an elec- tric signal is automatically sent over a telegraphic line and received by an electro-magnetic device at the other end of the line. BOX, FIRE-ALARM SIGNAL— A signal box provided for the purpose of automaticalh'' sending an alarm of fire. BOX, FUSE — The box in which the fuse-wire of a safety- fuse is placed. BOX, JUXCTIOX — A moisture-proof box provided in a sys- tem of underground conductors to leceive the termi- nals of the feeders, in which connection is made be- tween the feeders and the mains, and from which the * current is distributed to the individual consumer. BOX, RESISTANCE — A box containing a number of sepa- rate coils of known resistances employed for determin- ing the value of an unknovvn resistance, and for other purposes. BRAKE, ELECTRO-MAGNETIC— A brake for car wneels, the braking power for which is either derived entirely from electro-magnetism, or is thrown into action by electro-magnetic de\dces. BRAKE, PRONY — A mechanical device for measuring the power of a driving shaft. BRANCH-BLOCK— (See Block, Branch). BREAKER, CIRCUIT— Any device for breaking a circuit. BRIDGE-ARMS -(See Arms, Bridge or Balance). 21 BRU 314 BEIDGE, ELECTEIC— A device for measurino- the value of electric resistances. The electric brirlge is also called the Electric 13alanc§: BEIDGE, MAGNETIC— An apparatus invented by Edison for measuring" magnetic resistance, similar in principle to Wheatstone's electric bridg-e. BRUSH, DISCHARGE— (See Discharge, Brush). BRUSH-HOLDERS EOR DYNAMO-ELECTRIC J\L\CIIINES — Devices for supporting the collecting JDrushes of dy- namo-electric machines. BRUSH ROCKER— (See Rocker, Brush). BRUSHES, ADJUSTMENT' OF DYNAMO-ELECTRI6 MA- CHINES — Shifting the brushes into the required posi- tion on the commutator cylinder, either non-automatic- ally by hand, or automatically by the current itself. BRUSHES, CARBON, FOR ELECTRIC MOTORS— Plates of carbon for leading current to electric motors. These are generally known simply as brushes. BRUSHES, LEAD OF— The angle through which the brushes of a dynamo-electric machine must be moved forward, or in the direction of rotation, in order to diminish sparking and to get the best output from the dynamo. BRUSHES OF DYNAMO-ELECTRIC MACHINE— Strips of metal, bundles of wire, slit plates of metal, or plates of carbon, that bear on the commutator cylinder of a dynamo-electric machine, and carry off the current generated. 315 C. G. S. BUCKLING — Irreg-ularities in ^he shape of the surfaces of the plates of storage cells, following- a too rapid dis- charg*e. BUG — A term originally employed in quadruplex telegra- phy to designate any fault in the operation of the ap^ paratus. BUNSEN VOLTAIC CELL— (See Cell ,Voltaic, Bunsen's). BURGLAR ALARM ANNUNCIATOR— (See Annunciator^ Burglar Alarm). BURNER, AUTOMATIC-ELECTRIC— An electric device for both turning on the gas and lighting it, and turning it off, by alternately touching different buttons. BUS— A word generally used instead of omnibus. BUS-BARS— f See Bars, Bus). BUTTON, CARBON— A resistance of carbon in the form of a button. BUTTON, PUSH — A device for closing an electric circuit by the movement of a button. BUZZER, ELECTRIC— A call, not as loud as that of a bell,, produced by a rajjid automatic make-and-break. C — An abbreviation for centigrade. C — A contraction for current. C. C. — A contraction for cubic centimetre. C. G. S. UNITS — A contraction for centimetre-gramme-sec- ond units. CAL 316 C. P. — A contraction for candle power. CABLE — To send a telegraphic dispatch, by means of a cable. CABLE, BUNCHED — A cable containing more than a single wire or conductor. CABLE, CAPACITY OF— The ability of a wire or cable to permit a certain quantity of electricity tc>be passed into it before acquiring a given dift'erence of potential. CABLE, ELECTKIC— The combination of an extended length of one or more separately insulated electric con- ductors, covered externally vnth a metallic sheathing or armor. CABLE, SUBMARINE— A cable designed for use under . water. CABLEGEAM — A message received by means of a subma- rine telegraphic cable. CALIBRATE — To determine the absolute or relative value of the scale divisions, or of the indications of any elec- trical instrument, such as a galvanometer, electrome- ter ,voltameter, wattmeter, etc. CALL-BEIX, MAGNETO-ELECTBIC— An electric call-bell operated by currents produced by the motion of a coil of wire before the poles of a permanent magnet. CALOEIE, GBEAT— The amount of heat required to raise the temperature of one kilogramme of water from degree C. to 1 degree C. CALOPJE, S:MALL- — The amount of heat required to raise tue tem.peratnre of one gramme of water from degree C, to 1 degTee C. 317 . CAU CANDLE — The unit of photometric intensity. Such a light as would be produced by the coQsumx-»tion of two grains of a standard candle per minute. CAXDLE, JABLOCHKOFF— An electric arc light in which the two carbon electrodes are placed parallel lo each other and maintained a constant distance apart by means of a stieet of insulating material placed betv/een them. CANDLF-POWEK— (See Power, Candle). CAOUTCHOUC, OR IXIJIA-RUBBER— A resinous substance obtained from the milky juices of certain tropical trees. CAPACITY, ELECTROSTATIC— The quantity of electricity Avhich must be imparted to a given body or conductor as a charge, in order to raise its potential a certain amount. CAPACITY, ELECTROSTATIC, Ul>n:T OF— Such a capacity of a conductor or condenser that an electromotive force of one volt will charge it with a quantity of electricity equal to one coulomb. The farad. CAPACIl'Y, SPECIFIC INDUCTIVE— The ability ot a di- electric to permit induction to take place tnrough its mass, as compared with the ability possessed by a mass of air of the same dimensions and thickness, under pre- cisely similar conditions. CARBON — An elementary substance which occurs naturally in three distinct allotropic forms, viz: charcoal, graph- ite and the diamond. CARBON POINTS— (See Points, Carbon). CAU * 318 CAEBOX TEA?s"SMlTTEE FOR TELEPHONES— (See Transmitter, Carbon, for Telephones). CARBONIXG LAVlPS— (See Lamps, Carboning). CARBOXJZE — To reduce a earbonizable material to carbon. CAPBOXS, AETIFICIAIi-— Carbons obtained by the carboni- zation of a mixture of pulverized carbon with diiferent carboniza}>]e liquids. CAPBOXS, COPEI)--A cylindrical carbon electrode for an arc lamp that is molded around a central core of char- coal, or other softer carbon. CAPBOXS, ELASIITXG PPOCESS FOP— A process for im- proving* the electrical uniformity of the carbon conduc- tors employed in incandescent lighting, by the deposi- tion of carbon in their pores, and over their surfaces at those places where the electric resistance is relatively great. CAPD, COMPASS — A card used in the mariner's compass, on which are marked the four cardinal points of the compass X, S, E and W, and these again divided into thirty-tw^o points called Rhumbs. CAPDEW YOLT^IETEP— (See Voltmeter, Cardew). CATAPHOPESIS — A term sometimes employed in place of electric osmose. (See Osmose, Electric). CATHOBE — A term sometimes used instead of Kathode. CAUTEPTZATIOX, l^LECTPTC— Subjecting to cauterization by means cf a wire electrically heated. 319 OEL CAUTERY, ELECTRIC— An instrument used for electrio craiterization. "Jn electro-theraT)eutics, the application of vaiio'.isl}' shaped platinum wires heated to incan- descence by the electric current in place of a knife, for remo\ing" diseased growths, or for stopping- hemor- rhag-es. CELL, ELECTEOLYTIC— A cell or vessel containing- an electrolyte, in which electrolysis is carried on. CELI:, POROUS — A jar of ung-lazed earthenware, emj)loyed in double-fiuid voltaic cellSj to Iceep the two liquids sep- arated. CELL, SECONDARY — A term sometimes used instead of storage cell. CELL, SECONDARY OR STORAGI], CAPACITY OF— The product of the current m amperes, by the number of hours the battery is capable of furnishing said current, when fully charged, until exhausted. CELL, SELENTIL^L — A cell consisting of a mass of selenium fused in between two conducting wires or electrodes of platinized silver or other suitable metal. CELL, ST07LAGE— A single one of the cells required to form a secondary battery. CELL, VOLTAIC— The combination of two metals, or of a metal and a metalloid, which, when dipped into a liquid or liquids called electrolj^tes, and connected outside the liquid or liquids by a conductor, will produce a current of electricity. CELL, VOLT-A.IC, BICHROMATE— A zinc-carbon couple used with an electrolyte known as electropoion, a solu- tion of bichromate of potash and sulphuric acid in water. CEL 320 CELL, VOLTAIC, BUNSEN'S— A zinc-carbon couple, the elements of which are immersed respectively in electro- lytes of dilute sulphuric and strong- nitric acids. CELL, VOLTAIC, CLOSED-CIRCUIT— A voltaic cell that can be left for a considerable time on a closed circuit of comparatively small resistance without serious polari' zation. CELL, VOLTAIC, CONTACT THEOEY OF— A theory which accounts for the production of difference of potential or electromotive force in the voltaic cell by the contact of the elements of the voltaic couple with one another by means of the electrolyte. CELL, VOLTAIC, DANIELL'S— A zinc-copper couple, the elements of which are immersed respectively in electro- lytes of dilute sulphuric acid, and a saturated solution of copper sulphate. CELL, VOLTAIC, DOUBLE-FLUID— A voltaic cell in which two separate liuids or electrolytes are employed. CELL, VOLTAIC, DEY— A voltaic cell in which a moist ma- terial is used in place of the ordinary fluid electrolyte. CELI<, VOLTAIC, FULLEK'S :MERCUEY BICHROMATE— A zinc-carbon couple imn-ersed in an electrolyte of elec- tropoion liquid. In w^hioh ithe zinc is in contact with liquid mercury. CELL, VOLTAIC, GRAVITY— A zinc-copper couple, the ele- ments of which are employed with electrolytes of dilute sulphuric acid or dilute zinc sulphate, and a concentra- ted solution i>»f copper sidphate respectively. 321 CHA CELL, VOLTAIC, GKOVE— A zinc-platinum couple, the ele- ments of which are used with electrolytes of sulphuric and nitric acids respectivel5\ CELL, VOLTAIC, LECLAXCHE— A zinc-carbon couple, the elements of which are used in a solution of sal-ammo- r.iac and a finely divided \ayec of black oxide of man- ganese respectively. CELL, VOLTAIC, OPEX-CIKCUIT— A voltaic cell that can 7iot be kept on closed circuit, with a comparatively small resistance, for any considerable time without serious polarization. CELL, VOLTAIC, POLAEIZATIOX OF— The collection of a g-as, generally hydrogen, on the surface of the negative element of a voltaic cell. CELL. VOLTAIC, SILVEE CHLOEIDE— A zinc and silver couple immersed in electrolytes of sal-ammoniac or common salt, in which chloride of silver is used as the depolarizer. CELL, VOLTAIC, SMEE— A zinc-silver couple used with an electrolyte of dilute sulphuric acid. CELL, VOLTAIC, STANDARD, CLARK'S— The form of standard cell designed by Latimer Clark, having an E. M. F. of 1.438 volts at 57 degrees F. CHARACTERISTIC CURVE— (See Curve, Characteristic). CHARGE, DISSIPATION OF— The gradual but final loss of any charge by leakage, which occurs even in a well in- sulated conductor. CIR 322 CIIAPtGE, DISTEIBUTIOX OF— The variations that exist In the density of an electrical charge at different por- tions of the surface of all insulated conductors except spheres. » CHAEGE, ELECTETC— The quantity of electricity that ex- ists on the surface of an insulated electrified conductor, CHAEGE, EESIDUAT. — The charge possessed by a charged Leyden jar for a few moments after it has been disrapt- zTelj discharged by the connection of its opposite coat- ings. CHAEGE, EETUEX — A charge induced in neighboring con- ductors by a discharge of lightning. CHAEGIXG ACCOIULATOES— Sending an electric current into a storage battery for the purpose of rendering it an electric source. CHOKIXG COTL— (See Coil, Choking). CIECUIT, CLOSED — A circuit is closed, completed, or made when its conducting continuity is such that the current can pass. CIECUIT, CLOSED-MAGNETIC— A magnetic circuit whic& lies wholly in iron or other substance of high magnetic permeability. CIECUIT, CONSTANT-CUEEENT— A circuit in which the current or number of amperes is maintained constant notwithstanding changes occurring in its resistance. CIECUIT, CONSTANT POTENTIAL— A circuit, the poten- tial or number of volts o? which is maintained approxi- mately constant. 323 CIR CIECUIT, EARTH— A circuit in which the ground or earth forms part of the conducting* Dath. CIRCUIT, ELECTliTC— The path in which electricity circu- lates or posses from a given point, a>r?und or through a conducting path, back again to its starting point. CIRCUIT, EXTERNAL— That part of a circuit which is ex- ternal to, or outside the electric source. CIRCUIT, GROUND— A circuit in which the ground forms part of the path through which the current passes. CIRCUIT, INDUCTIVE— Any circuit in which induction takes place. CIRCUIT, INTERNAL— That part of a circuit which is in- cluded within the electric source. CIRCUIT, LOCAL-BATTERY— The circuit, in a telegraphic system, in which is placed a local battery as distin- guished from a main battery. CIRCUIT, AIAGNETIC— The path through which the lines of magnetic force pass. CIRCUIT, METALLIC— A circuit in which the ground is not employed af, any part of the path of the current, metal- lic conductors being employed throughout the entire circuit. CIRCUIT, MULTIPLE— A compound circuit, in which a number of separate sources or separate electro-receptive devices, or both, have all their positive poles connected to a single positive lead or conductor, and all their neg- ative poles to a single negative lead or conductor. CIR 324 CIECUIT, MULTlPLE-SEPtlES— A compound circuit in which a number of separate sources, or separate elec- tro-receptive devices, or both, are connected in a num- ber of separate groups in series, and these separate groups subsequently connected in multiple. CIECUIT, OPEN— A broken circuit. A circuit, the con- ducting* continuity of which is broken. CIKCUIT, KETUBN— That part of a circuit by which the electric current returns to the source. CIRCUIT, SERIES—A compound circuit in which the sep- arate sources, or the separate electro-receptive devices, or both, are so placed that the current produced in each, or passed throusfh each, passes successively through the entire circuit from the first to the last. CIRCUIT, SERIES-MULTIPLE— x\ compound circuit, in which a number of separate sources, or separate elec- tro-receptive devices, or both, are connected in a num- ber of separate groups in multiple-arc, and these sepa- rate groups subsequently connected in series. CIRCUIT, SHORT— A shunt, or by-path, of comparatively small resistance, around the poles of an electric source, or around any portion of a circuit, by which so much of the current passes through the new path, as virtualh^ to cut out the part of the circuit around which it is placed, and so prevent it from receiving an appreciable current. CIRCUIT, SHUNT— A branch or additional circuit provided at any part of a circuit, through which the current branches or divides, part flowing through the original circuit, and part through the new branch. 325 COI CLARK'S STANDARD VOLTAIC CELL— (See Cell. Voltaic, Standard, Clark's). CL;e:aRAXCE-SPACE— (See Space, Clearance). CL]i?ATS, ELECTRIC— Suitably shaped pieces of wood, porcelain, hard rublDcr or other non-conducting material used for fastening- and supporting electric conductors to ceilings, walls, etc. CLOCK, ELECTRIC— A clock, the works of which are mov- ed, controlled, regulated or wound, either entirely or partially, by the electric current. CLUTCH, CARBON, OF ARC LAMP- A clutch or clamp at- tached to the rod or other support of the carbon of an arc lamp, provided for gripping or holding the carbon. CODE,. CIPHER — A code in which a number of words or phrases are represented by single words, or by arbitrary words or syllables. COIL, CHOKING — A coil of wire so wound on a core of iron as to possess high self-induction. COIL, IMPEDANCE— A term sometimes applied to a chok- ing-coil. COIL, INDUCTION — An apparatus consisting of two paral- lel coils of insulated wire employed for the production of currents by mutual induction. COIL, INDUCTION, MICROPHONE— An induction coil, in which the variations in the circuit of the primary are obtained by means of microphone contacts. (See Mi- crophone). colli, KICKING — A term sometimes applied to a Choking- Coil. COM 326 UOJL, MAGNET — A coil of insulated wire surrounding the core of an electro-magnet, and through which the mag- netizing current is passed. COIL, PKIMATiY — That coil or conductor of an induction coil or transformer, through which the rapidl^^ inter* rupted or alternate inducing currents are sent. COTL, EESTSTAXCE— A coil of wire of known electrical resistance employed for measuring resistance. COIL, RESISTANCE, STANDARD— A coil the resistance of which is that of the standard ohm or some multiple or sub-multiple thereof: COTL, RUIIMKORFF — A term sometimes applied to any in- duction coil, the secondary of which gives currents ot higher electromotive force than the primary. COIL, SECONDARY— That coil or conductor of an induc- tion coil or transformer, in which alternating currents are induced by the rapidly interrupted or alternating currents in the x^^'iniary coil. COTL, SHUNT — A coil placed in a derived or shunt circuit. DOIL, SPARK — A coil of insulated wire connected with the main circuit in a system, of electric gas-lighting, the extra spark produced on breaking the t^ircuit of which is employed for electrically igniting gas jets. COILS, ARMATURE, OF DYNAMO-ELECTRIC MACHINE — The 'vioils, strips or bars that are wound or placed on the armature core. COMMERCIAL EFFICIENCY— (See Efficiency, Commercial). COMMERCIAL EFFICIENCY OF DYNAMO— (See Efficien- cy, Commercial, of Dynamo). 327 COM COAOrUTATlOX, DIAMETER OF— In a dynamo-electric machine a diameter on the commutator cylinder on one side of which the difOerences of potential, produced by the movement of the coils through the magnetic field, tend to produce a current in a direction opposite fo those on the other side, COMMUTATOE — In general, a device for changing the di- rection of an electric current. COMMUTATOPi, DYNAMO-ELECTRIC MACHINE— That part of a dynamo- electric machine which is designed to cause the alternating currents produced in the arma- ture to flow in one and the same direction in the ex- ternal circuit. COMPASS, AZIMUTH— A compass used by mariners for measuring the horizontal distance of the sun or stars from the magnetic meridian. A mariner's Compass. COMPASS, INCLINATION"- A magnetic needle moving freely in a single vertical plane, and emploj^ed for deter- mining the angle of dip at any place. CO:NrPONENT, HORIZONTAL, OF EARTH'S jSEAGNETISM — That portion of the earth's directive force which acts in a horizontal direction. That portion of the earth's magnetic force which acts to produce motion in a com* pass needle free to move in a horizontal plane only. COMPOUND-WINDING OF DYNAMO-ELECTRIC MA- CHINES— (Sec \Alnding, Compound, of Dynamo-Elec- tric Machines). COMPOUxN"D-WOrND DYNAMO-ELECTRIC MACHINE— (See Machine. Dynamo-Electric, Compound-Wound). C0:>'' 328 COMPOUND- WOUND :M0T0E— (See Motor, Compound- Wound). CONDFXSEK \ device for increasing the capacity ot an insulated conductor by bringing- it near another insu- lated 'earth-ccnnected conductor, but separated there- from by any medium that will readily permit induction to take place through its mass. COXDENSEK, CAPACITY OF— The quantity of electricity in coulombs a condenser is capable of holding before its potential in volts is raised a given amotmt. CONDUCT — To i)ass electricity through conducting sub- stances. CONDUCTANCE — A word sometimes used in place of con- ducting power. Conductivity. CONDUCTING POWEE— (See Power, Conducting). CONDUCTION, ELECTEOLYTIC— A term sometimes em- ployed to indicate the passage of 'electricity through an electrolyte. CONDUCTmTY, ELECTEIC— The reciprocal of electric resistance. CONDUCTOE— A substance which will permit the so-called passage of an electric current. A substance which pos- sesses the ability of determining the direction in whicB electricity shall pass through the ether or other dielec- tric surrounding it. CONDUCTOE, LIGIITNING — A term sometimes used for a lighlning rod. i529 CON CONDUCTORS, SERVICE—Conductors employed in sys- tems of incandescent lig-hting- connected to the street mains and to the electric apparatus placed in the sepa- rate building's or areas to be lig-hted. CONDUIT, TJNDEEGEOTJND ELECTRIC— An underground passageway or space for the reception of electric wires or cables. CONNECT — To place or bring- into electric contact. CONNECTOR — A. device for readily connecting or joining" the ends of two or more wires. CONSEQUENT POLES— (See Poles, Consequent). CONSERVATION OF ENERGY— (See Energy, Conservation of). CONSTANT-CURRENT— (See Current, Constant). CONSTANT-CURRENT CIRCUIT— (See Circuit, Constant Current). CONSTANT POTENTIAL— (See Potential, Constant). CONSTANT-POTENTIAL CIRCUIT— (See Circuit, Con- stant-Potential) . CONTACT-BREAKER, AUTOMATIC— A device for causing- an electric current to rapidly make and break its own circuit. , CONTACT, METALLIC— A contact of a metallic conductor produced by its coming* into firm connection with an* other metallic conductor. 22 COK 330 CONTACT, SLIDING— A contact connected with one part of a circnit that closes or completes an electric circuit by being- slid over a conductor connected with another part of the circuit. CONTROLLER— A mag-net, in the Thomson-Houston sys- tem of automatic regulation, whose coils are traversed by the main current, and by means of which tlie regu- lator magnet is automatically thrown into or out of the main circuit on changes in the strength of the cur- rent passing. CONVECTION, ELECTROLYTIC— A term proposed bv Helmholtz to explain the apparent conduction of elec- tricity by an electrolj'te, without /consequent decom- position. CONVERTER— The inverted induction coil employed in systems of distribution by means of alternating- cur- rents. A term sometimes used instead of transformer. CONVERTER, EFFICIENCY OF— The efficiency of a trans- former. CONVERTER, PTEDGEHOG— A form of transformer. (See Transformer, Hedgehog). COPPER, STRAP — Copper conductors in the form of straps or flat bars. CORD, ELECTRIC— A flexible, insulated electric conductor, g-enerally containing at least two parallel wires. CORE ,AR:NLATUKE, H— An armature core the shape of tiie letter H, generally known as the shuttle armature, and sometimes as the g-irder armature. 331 COU COEE, ARMATUKE, LAMINATION OF— The subdivision of the core of the armature of a dynamo-electrie machine \ into separate insulated plates or strips for the purpose of avoiding eddy or Foucault currents. COEE. ARMATURE, OF DYNAMO-ELECTRIC MACHINE— The iron core, on, or around, which the armature poils of a dynamo-electric machine are wound or placed. CORE, ARMATURE, VENTILATION OF— Means for pass- ing* air through the armature cores of dynamo-electric machines in order to prevent undue accumulation of heat. CORE, LAMINATED— A core of iron which has been divid- ed or laminated, in order to avoid the injurious produc- tion of Foucalt or eddy currents. CORE, STRANDED, OF CABLE— The conducting \%dre or core of a cable formed of a number of separate conduc- tors or wires instead of a single conductor of the same weight per foot as the combined conductors. CORED CARRONS— (See Carbons, Cored). COULO^IB — Such a quantity of electricity as would pass in one second in a circuit whose resistance is one ohm, under an electromotive force of one volt. COUNTER- ELECTROMOTIVE FORCE- (See Force, Elec- tromotive, Counter). COUPLE, ASTATIC— Two magnets of exactly equal strength so placed one over the other in the same ver- tical plane as to completely neutralize each other. CUR 332 COUPLE, MAGNETIC— The couple which tends to turn a magnetic needle, placed in the earth's field, into the plane of the magnetic meridian. COUPLE, THERMO-ELECTRIC— Two dissimilar metals which, when connected at their ends only, so as to form a completed electric circuit, will produce a difference of potential, and hence an electric current, when one of the ends is heated more than the other. COUPLE, VOLTAIC— Two materials, usually two dissimilar metals, capable of acting- as an electric source when dipped in an electrolyte, or capable of producing* a dif- ference of electric potential by mere contact. CROSS ARM— (See Arm, Cross). CROSS, ELECTRIC— A connection, generally metallic, acci- dentally established between two conducting lines. CRUCIBLE, ELECTRIC— A crucible in which the heat of the voltaic arc, or of electric incandescence, is employed either to perform difScult fusions, or for the purpose of effecting the reduction of metals from their ores or the formation of alloys. CUP, POROI'S— A porous cell. CURRENT, ALTERNATING— A current which flows alter- nately in opposite directions. A current whose direc- tion is rapidly reversed. CURRENT, CONSTANT— A current that continues to flow for some time without varjdng in strength. CURRENT, CONTINUOUS— An electric current which flows in '>F)e and the same direction. 333 CUR CURRENT DENSITY— The current of electricity which passes in any part of a circuit as compared with the area of cross-section of that part of the circuit. CURRENT, DIRECT— A current constant in direction, as distingniished from an alternating current. CURRENT, DIRECTION OF— The direction an electric cur- rent is assumed to take out from one pole of any source through the circuit and its translating* devices back to the source through its other pole. CUBRENT, ELECTRIC- The quantity of electricity which passes per second through any conductor or circuit. The rate at which a definite quantity of electricity passes or fiows through a conductor or circuit. CURRENT, GENERATION OF, BY DYNAMO-ELECTRIC MACITINP" — The difference of potential developed in the armature coils by the cutting of the lines of n\ag- netlc force of the field by the coils, during the rotation of the armature. CURRENT, INDUCED— The current produced in a conduc- tor by cutting lines of force. CURRENT, PULSATORl'— A current, the strength of which changes suddenly. CURRENT, ROTATING— A term applied to the current which results by combining a niimber of alternating currents, whose phases are displaced with respect to one another. CURRENT STRENGTH— The product obtained by dividing the electromotive force by the resistance. The current strength for a constant current accord- ing to Ohm's law is — E C equals — R CCJl 334 CUREEXT, TO TEAXSFORM A— To change the electromo- tive force of a current by its passage through a convert- er or transformer. To convert a current. CUEEEXT, UXIT STEEXGTH OF— Such a strength of cur- rent that when passed through a circuit one centimetre in length, arranged in an arc one centimetre in radius, will exert a force of one dyne on a unit magnet pole placed at the center. This absolute unit is equal to ten amperes or practical units of current. CUEEEXTS, CO XM^ETED— Electric currents changed either in their electromotive force or in their strength, by passage through a converter or transformer. CUEElvN"TS, EDDY — Useless currents ]>roduced in the pole pieces, armatures, field-magnet cores of dynamo-electric machines or motors, or other metallic masses, either by their niotion througli magnetic fields, or by variations in tftie strength of electric currents flowing near them, CUEEEXTS, EXTEA— Currents produced in a circuit by the induction of the current on itself on the opening or closing of the circuit. CUEEEXTS, FOUCAULT— A name sometimes applied to eddy currents, especially in armature cores. CUEEEXTS, HEATIXG EFFECTS OF— The heat produced by the passage of an electric current through any cir- cuit. CUEEEXTS, SFNIPLE PEETODIC— Currents, the flow o9 which is variable, both in strength and duration, and irt which the flow of electricity;, passing any section of the conductor, may be represented by a simple periodic curve. 335 CUT CURVE, CnAEACTEETSTIC— A diagTam in which a curve is employed to represent the ratio oi: volts and am- pheres' in a dynamo or motor. CUEVE, CHARACTErJSTIC, OF PARALLEL TRANSFOR* MER — A curve so drawn that its ordinate and abscissa at any point represent the secondary electromotive force and the secondary current of a multiple connected trnnsformer, when the resistance of the secondary eir« cuit has a certain definite value. CURVE. PERMEABILITY— xA. curve representing- the mag- netic permeability of a magnetic substance. CURVE, SIMPLE-HARMONIC— The curve which results when a simple-harmonic motion in one line is com- pounded with a uniform motion in a straight line, at right ang-les thereto. A harmonic curve is sometimes called a curve of sines because the abscissas of the curve are proportional to the times, while the ordinates are proportional to the sines of the angles, which 5re themselves proportional to the times. CUT-OUT, A — A device by means of whi<6h an electro-re- ceptive device or loop may be thrown out of the circuit of an electric source. CUT-OUT, AUTOMATIC, FOR MULTIPLE-CONNECTEI> ELECTRO-RECEPTICE DEVICES— A device for auto- matically cutting an electro-receptive device, such as a lamp, out of the circuit of the leads. Automatic cut-outs for incandescent lamps, when connected to the leads in multiple-arc, consist of strips of readily melted metal called safety-fuses, which on the passage of an excessive current fuse, and thus auto- matically break the circuit in that particular branch. DEC 336 CUTTING LmES OF FORCE— (See Force, Lines of Cutting) CYCLE — A period of time within which a certain series of phenomena regularly recur, in the same order. CYCLE, MACrNETIC— A single round of magnetic changes to which a magnetizable substance, such as a piece of iron, is subjected when it is magnetized from zero to a certain maximum magnetization, then decreased to zero, reversed and carried to a negative maximum, and then decreased again to zero. DAIMPEE — A metallic cylinder provided in an induction coil so as to partially or completely surround the iron core, for the purpose of varying the intensity of the currents induced in the secondary. DAMPING — The act of stopping vibratory motion such as bringing a swinging magnetic needle quickly to rest, so as to determine the amount of its deflection, without waiting until it comes to rest after repeated swingings to and fro. DEAD-BEAT — Such a motion of a galvanometer needle in which the needle moves shary^ly over the scale from point to point and comes quickly to rest. DECLTXATION — The variation of a magnetic needle from the true geographical north. DECLINATION, ANGLE OF— The angle which measures the deviation of the magnetic needle to the east or west of the true geographical norfh. 337 BIE DECOMPOSITION, ELFXTEIC— Chemical decoinposition by means of an electric discharge or current. DEMAGNETIZATION — A process, g-enerally directly oppo- site to that for producing- a magnet, by means of which the magnet may be deprived of its magnetism. DENSITY, MAGNETIC— The strength of magnetism as measured by the number of lines of magnetic force that pass through a unit area of cross-section of the magnet, i. e., a section taken at right angles to the lines of force. DEPOSIT. ELECTPO-METALLURGICAL— The deposit of metal obtained by an^' electro-metallurgical process. DETECTOE, GEOUND— In a system of incandescent lamp distribution, a device placed in the central station, for shovs^ing by the candle-power of a lamp the approxi- mate location of a ground on the s^^stem. DEVICE, ELECTEO-EECEPTIYE— Various devices placed in an electric circuit, and energized by the passage through them of the electric current, DEVICE, TRANSLATING— A term embracing electro-re^- ceptive and magnefo-receptive devices. (See Device, Electro-Eeceptive) . DIAMAGNETIC — The property possessed by substances like bismuth, phosphorus, antimony, zinc and numerous others, of being apparently repelled when placed be- tween the poles of powerful magnets. DIELECTEIC — A substance which permits induction to tak^ place through its mass. DIS 338 BTELECTETC, POLAPJZATTOX OF— A molecular strain produced in the dielectric of a Leyden jar or other con- denser> by the attraction of the electric charges on its opposite faces, or by the electrostatic stress. DI^niEH — A choking coil or resistance employed for regu- lating* the potential of the feeders, which usually carry incandescent lamps. DIP, MAGXETIC— The deviation of a magnetic needle from a true horizontal position. The inclination of the mag- netic needle towards the earth. DIEECT CUREEXT— (See Current, Direct). DIEECT-CUEEEXT ELECTEIC MOTOE— (See Motor. Elec- tric, Direct-Current). DIEECTIOX OF LIXES OF FOECE— (See Force, Lines of, Direction of). DISC, AEAGO'S — A disc of copper or other non-magnetic metallic substance, which, when rapidly rotated under a magnetic needle, supported independently of the disc, causes the needle to be deflected in the direction of rotation, and, when the velocity of the disc is sufficient- ly great, to rotate with it. DISC, FAEADAY'S — A metallic disc movable in a magnetic field on an axis parallel to the direction of the field. DISCHAEGF>— The equalization of the difference of poten- tial between the terminals of a condenser or source, on their connection by a conductor. DISCHAEGE, BEUSH— A faintly luminous discharge that occurs from a pointed positive conductor. 339 BIS DISCTTARGE, DISEUPTIVE— A sudden, and more or less complete, discharge that takes place across an inter- vening* non-conductor or dielectric. DISCHARGE, LUMINOUS EFFECTS OF— The luminous phenomena attending- and produced by an electric dis- charg-e. DISCHARGE, OSCILLATING— A njiimber of successive dis- charges and recharg-es w^hich occur on the disruptive discharge of a Lej^den jar, or condenser. DISCHARGE, VELOCITY. OF— The time required for the passage of a discharge through a given length of con- ductor. DISCHARGER, UNIVERSAL— An apparatus for sending the discharge of a powerful Leyden battery or condens- er in any desired direction. DISCONNECT— To break or open an electric circuit. DISTANCE, SPARKING— The distance at which electrical sparks will pass through an intervening air space. DISTILLATION, ELECTRIC— The distillation of a liquid in which the effects of heat are aided b}^ an electrification of the liquid. DISTRIBUTION, CENTER OF— In a system of multiple- distribution, any place where branch cut-outs and switches are located in order to control communication therewith. The electrical center of a system of distxi- liution as regards the conducting network. DISTRIBUTION OF ELECTRICITY— (See Electrcity, Dis- tribution of). DYN 340 DISTRIBUTION OF ELECTRICITY BY CONSTANT PO- TENTIAL CIlCCITri'— (See Electricity, Multiple Distri- bution of, by Constant Potential Circuit). DOUBLE-CARBON ARC LAMP— (See Lamp, Electric Arc, Double-Carbon ) . DOUBLE-EIUID VOLTAIC CELL— (See Cell, Voltaic, Dou- ble-Fluid). DOUBLE-TOUCH, MAGNETIZATION BY— A method for producing magnetization by the simultaneous touch of two magnet poles. DROP, ANNUNCIATOR— A movable signal operated by an electro-magnet, and placed on an annunciator, the drop- ping of which indicates the closing or opening of the circuit with which the electro-magnet is connected. DROP, AUTOMATIC— A device for aiitomaticallv closino- the circuit of a bell and holding it closed until stopped bj^ resetting a drop. ' DRUM ARMATURE— (See Armature, Drum). DRY VOLTAIC CELL- (See Cell, Voltaic, Dry). DUPLEX TELEGRAPHY— (See Telegfaphy, Duplex). DYEING, ELECTRIC— The application of. electricity eithef to the reduction or the oxidation of the salts used in dyeing. DYNAMICS, ELECTRO— That branch of electric science which treats of the action of electric currents on one another and on themselves or on magnets. DYNAMO — The name frequently applied to a dynamo-elec- tric machine used as a generator. 341 DYN DTN-AMO, COMPOSITE FIELD— A dynamo whose field coils are series and separately excited. DYXAMO, COMPOUND-WOUND— A compound-wound dy- nam^o-electric machine. (See Machine, Dynamo-Elec- tric, Compound- Wound). DYN AMO-ELECTKTC MACHINE, BI-POLAE~(See Ma- chine, Dynamo-Electric, Bi-Polar). DYNAMO-ELECTEIC MACHINE, MULTIPOLAR— (See Ma- chine, Dynamo-Electric, Multipolar). DYNAMO, INDUCTOPt— A dynamo-electric machine for al- ternating* currents in which the diiferences of potential causing the currents are obtained by magnetic changes in the cores of the armature and field coils by the move- ment past them of laminated masses of iron inductors. DYNAMO, MULTIPHASE— A polyphase dynamo. (See Dy- namo, Poh'phase. Dynamo, Rotating Current). DYNAMO, POTiYPHASE— A dynamo producing two or more currents differing in phase. A name sometimes applied to a rotating current dynamo, (See Dynamo, Rotating Current). DYNAMO, PYBOMAGNETIC— A name sometimes applied to a pyromagnetic generator. DYNAMO. SEPARATELY EXCITED— A separately-excited dynamo-electric machine. DTr^AMO, SERIES — A series-wound dynamo-electric ma- chine. DYNAMO. SHUNT — A shunt-wound dynamo-electric ma- chine. EFF 342 DY1S^4M0jV[ETFK, electro— a form of galvanometer for the measurement of electric currents. DYNE — The unit of force. The force which in one second can impart a Telocity of one centimetre per second to a mass of one gramme. E. — A contraction sometimes used for earth. A contraction sometimes used for electromotive force, or E. M. F., as in the well-known formula for Ohm's law, E C equals — R E. M. r. — A contraction generally used for electromotive force. p]ARTH-7A fault in a telegraphic or other line, caused by accidental contact of the line with the ground or earth, or with some conductor connected with the latter. EBONITE — A tough, hard, black substance, composed of india rubber and sulphur, which possesses high powers of insulation and of specific inductive capacity. EDDY CURRENTS— (See Currents, Eddy). EEL, ELECTRIC — An eel possessing the power of giving powerful electric shocks. The gyinnotus electricus. EFFECT, EDISON--An electric discharge which occurs be- tween one of the terminals of the incandescent, filament of an electric lamp, and a metallic plate placed near the filament but disconnected therefrom, as soon as a certain difierence of potential is reached between the lamp terminals. 343 -EiFW EFFECT. FEEHANTI— An increase in the electromotive force, or difference of potential, of mains or conductors towards the end of the same farthest from the termi- nals that are connected with a source of constant pc5* tential. EFFECT, HALL — A transverse electromotive force, pro- duced by a magnetic field in substances undergoing' electric displacement. EFFECT, JOULE— The heating eifect produced by the pass- age of an electric current through a conductor, arising" merely from the resistance of the conductor. EFFECT, PELTIER— The heating effect produced by the passage of an electric current across a thermo-electric ■junction or surface of contact .between two different metals. EFFECT, THEFtMO-ELECTETC— The production of an elec- tromotive force at a thermo-electric junction by a dif- ference of temperature between that junction and the other junction of the thermo-electric couple. EFFECT, THOMSON— The production of an electromotive force in unequally heated homogeneous conducting sub- stances. A. term also applied to the increase or decrease in the differences of temperature in an unequally heat- ed conductor, produced by the passage of an electrical current through the conductor. EFFECT, VOLTAIC— A difference of potential observed at the point of contact of two dissimilar metals. EFF 344 EFFICIENCY, COMMERCIAL— The useful or available en- ergy produced divided by the total energy absorbed by any machine or apparatus. The Commercial Efficiency equals W W — equals M W+w+m, when W equals the useful or available energy; M equals the total energy; w, the energy absorbed by the ma- chine, and m, the stray power, or power lost in friction of bearings, etc., air friction, eddy currents, etc. I:FFICIENCY, COMMEECIAL, of dynamo— The useful or available electrical energy in the external circuit, divided by the total mechanical energy required to drive the dynamo that produced it. EFFICIENCY, ELECTRIC— The useful or available electric- al energy of anj^ source, divided by the total electrical energy. W The electric efficiency equals , where W, equals W-fw the useful or available electrical energy, and w, the electrical energy absorbed by the. machine. EFFICIENCY OF CONVERSION— The ratio between the energy present in any result and the energy expended in producing that result. EFFICIENCY, QUANTITY, OF STORAGE BATTERY— The ratio of the number of ampere-hours, taken out oi a storage or secondary battery, to the number of ampere- hours put in the battery in charging it, 345 ELE EFFICIENCY, KEAL, OF STORAGE BATTERY— The ratio of the number of watt-honrs taken out of a storage battery, to the number of watt-hours put into the bat- tery in charging it. ELECTRIC— Pertaining to electricity. ELECTRIC ARC— (See Arc, Electric). ELECTRIC BATTERY— (See Battery, Electric). ELECTRIC BOBBIN— (See Bobbin, Electric). ELECTRIC BUZZER— (See Buzzer, Electric). ELECTRIC CANDLE— (Se^ Candle, Electric). ELECTRIC CHARGE— (See Charge, Electric). ELECTRIC CIRCUIT -(See Circuit, Electric). ELECTRIC CLOCK— (See Clock, Electric). ELECTRIC COIL— See Coil, Electric). ELECTRIC CURRENT— (See Current, Electfte). ELECTRIC EFFICIENCY— (See Efficiency, Electric). ELECTRIC ENERGY— (See Energy, Electric). ELECTRIC FIELD— (See Field, Electi^ Magnetic.) ELECTRIC FORCE— (See Force, Electric). ELECTRIC FURNACE— See Furnace, Electric). ELECTRIC FUSE— (See Fuse, Electric). ELECTRIC HEAT— (See Heat, Electric). ELECTRIC HORSl^: PO\YEPx-- (See Po^er, Horse, Electric). ELECTRIC INSULATION— (See Insulation, Electrio). ELECTRIC LAMP, ARC— (See Lamp, Electric, Arc). 23 ELE 346 EI.ECTETC LAMP, INCANDESCENT— (See Lamp, Electric, Incandescent). ELECTRIC LAUNCfi— (See Launch, Electric). ELECTRIC LIGHT— (fsee Light, Electric). ELECTRIC LIGHTING, CENTRAL STATION— (See Sta- tion. Central). ELECTRIC LOCOMOTIVE— (See Locomotive, Electric). ELECTRIC METER— (See Meter, Electric). ELECTRIC MOTOR— (See Moto^, Electric). ELECTRIC OSCILLATIONS— (See Oscillations, Electric). ELECTRIC POTENTIAL— (See Potential, Electric). ELECl^RIC POWER— (See Pcwef, Electric). ELECTRIC RESISTANCE— (See Resistance, Electric). ELECTRIC RESONANCE— (See Resonance, Electric), ELECTRIC SHOClv-(See Shock, Electric). ELECTRIC TRAMWAY— (See Tramway, Electric). ELECTRIC WELDING— (See Welding, Electricj. ELECTRIC WHIRL- (See Whirl, Electric). ELECTRIC WORK -(See Work, Electric). ELECTRICALLY— In an electrical manner. ELECTRICIAN — One versed in the principles and applica- tions o1: electricaJ science. ELECTRICITY— The name given to the unknown thing, matter uv ^orce, or both, w^hich is the cause of electrfc phenomena. Electricity, no matter how produced, is believed to be one and the same thing. 347 ELB ELECTRTCJTY, AM i:\rAL— Electricity produced during- life m the bodies of animals. All animals produce electricity during life. In some, such as the electric eel or torpedo, the amount is com- parativelj^ large. In others, it is small. ELECTRTCITV, ATMOSPHEHIC— The free electricity al- most always present in the atmosphere. ELECTEICITY, ATMOSPHERE, ORIGIN OF— The exact cause of the free electricity of the atmosphere is un- known. ELECTRICITY, CONTACT— Electricity produced by the mere contact of dissimilar metals. ELECTRICITY, DISTRIBUTION OF— Various combina- tions of electric soiirces, circuits and electro-receptive devices whereby electricity generated by the sources is carried or distributed to more or less distant electro- receptive devices by means of the various circuits con- nected therewith. ELECTRICITY, DISTRIBUTION OF, BY ALTERNATING CURRENTS— A system of electric distribution by the use of alternating currents. ELECTRICITY, DISTRIBUTION OF, BY CONSTANT CUR- RENTS — A S3^stem for the distribution of electricity by means of direct, i. e., continuous, steady or non-alter- nating currents, as distinguished from alternating cur- rents. ELECTRICITY, DOUBLE FLUID HYPOTHESIS OF— A hypothesis which endeavors to explain the causes of electric phenomena by the assumption of the existence of two different electric fluids. ELE 34S ELECTRICITY, FRICTIOXAL— Electricity produced by friction. ELECTRICITY, GALYAXIC— A term used by some in place of voltaic electricity. ELECTRICITY, HERTZ'S THEORY OF ELECTRO-MAG - XETIC RADIATIOXS OR WAYES— A theory, now gen- erally accepted, which regards light as one of the ef- fects of electro-magnetic pulsations or waves. ELECTRICITY, MAGNETO— Electricity produced by the motion of magnets past conductors, or of conductors past magnets. Electricity produced by magneto-elec- tric induction. ELECTRICITY, MULTIPLE-DISTRIBUTIOX OF, BY CON- STANT POTENTIAL CIRCUIT— Any system for the distribution of continuous currents of electricity in which the electro-receptive devices are connected to the leads in multixjle-arc or parallel. ELECTRICITY, NEGATI\'E— One of the phases cf electri- cal excitement. The kind of electric charge produced on resin when rubbed with cotton. ELECTRICITY, POSITIYE— One of the phases of electric excitement. I'he kind of electric charge produced on cotton when rubbed against resin. ELECTRICITY, PYRO— Electricity developed in certain crystalline bodies by Unequally heating or cooling them ELECTRICITY, SERIES DISTRIBUTION OF, BY CON- STANT CURRENT CIRCUIT— Any system for the dis- tribution of constant currents of electricity in which the electro-receptive devices are connected to the line- wire or circuit in series. 349 ELE ELECTRICITY, SINGLE-FLUID HYPOTHESIS OF— A hy- pothesis which endeavors to explain the cause of elec- trical phenomena by the assumption of the existence of a sing-le electric fluid. ELECTRICITY, STATIC— A term applied to electricity pro- duced by friction. ELECTRICITY, STORAGE OF— A term improperly employ- ed to indicate such a storage of energj^ as will enable it tc directlj^ reproduce electric energy. ELECTRICITY, THERMO- Electricity produced by differ- ences of temperature at the junctions of dissimilar metals. ELECTRICITY, UNIT QUANTITY OF— The quantity of electricity conveyed bj' unit current per second. The practical unit quantity of electricity is the cou- lomb, v/hich is the quantity conveyed by a current of one ampere in one second. ELECTRICITY. VOLTAIC— Differences of potential pro- duced by the agency of a voltaic cell or battery. ELECTRIFICATION— The act of becoming electrified. The production of an electric charge. ELECTRIFY— To endow with electrical properties. ELECTROCUTION— Capital punishment by means of elec- tricity. ELECTRODE— Either of the terminals of an electric source. ELECTRODE, NEGATIVE— The electrode connected with the negative pole of an electric source. ELECTRODE, POSITIVE— The electrode coi^uected with the positive xjole of an electric source. ELE 350 ELECrrwODE, SPONGE— A moistened sponge connected to one of the terminals of an electric source and acting* as the electro -therapeutic electrode. ELECTRODES— The terminals oi an electric source. ELECTRODES, CARBON, FOR ARC-LAMPS— Rods of arti- ficial carbon employed in arc lamps. These are more properly called simply arc-Jamp car- bons. ELECTRODES, CORED— Carbon electrodes of a cylindrical shape provided with a central cylinder of softer carbon. ELECTROLIER— A chandelier Tor holding electric lam^s, as distinguished from a chandelier for holding gas- lights. ELECTROLYSIS— Chemical decomposition effected by means of an electric current. ELECTROLYTE, TOLARIZATION OF— The formation of molecular groups or chains, in which the poles of all the molecules of any chain are turned in the same direction, viz: with their positive poles facing the neg'i- tive plate, and their negative poles facing the positive plate. ELECTROLYTIC OR ELECTROLYTICAL— Pertaining to electrolysis. ELECTROLYTIC CELL— (See Cell, Electrolytic). ELECTROLYTIC DECOMPOSITION— (See Decomposition. Electrolytic). ELECTR0-:NL\GNET— (See Magnet, Electro). ELECTRO-METALLURGY— (See !^fetallargy, Electro). 351 ELE ELECTRO:NrETEH— An apparatus for measuring- differ- ences of potential. ELECTEOAfETEIi, CAPILLAKY— An electrometer in wMch a diSerence of potential is measured by the movemenr of a drop of sulphuric acid in a tube filled with mercury ELEClT.O^rETEK, QUADrvAT^T— An electrometer in which an electrostatic charge is measured by the attractive and repulsive force of four plates or quadrants, on a light needle of aluminum suspended within them. ELECTEOMOTIVE FORCE— (See Force, ElectromotiveJ. ELECTROMOTIVE FORCE, BACK OR COUNTER— (See Force, Electromotive, Back). ELECTRO PnORUS— An apparatus for the production of electricitj' by electrostatic induction. ELECTRO-PLATING— (See Plating, Electro). ELECTRO-PLATING BATH— (See Bath, Electro-Plating). ELECTROPOTON LIQUID— (See Liquid, Electropoion). ELECTROSCOPE— An apparatus for showing the presence of an electric charge, or for determining its sign, whether positive or negative, but not for measuring its amount or value. ELECTROSCOPE, GOLD-LEAF— An electroscope in which two leaves of gold are* used to detect the presence of an electric charge, or to determine its character wheth- er positive or negative. ELECTROSCOPE, PITH-BALL— An electroscope which shows the presence of a charge by the repulsion of two similarlj' charged pith-balls. ELE 352 ELECTEOSTATIC CAPACITY— (See Caijacity, Electro- static). ELECTKOTONUS— A condition of altered functional acfiv- iij which occurs in a nerve when subjected to the action of an electric current. ELECTROTYPE— A type, cast or Impression of an object obtained by means of electro-metallurgy. (See Metal- lurg-y, Electro. ETectrotyping*) . ELECTROTYPING, OE THE ELECTROTYPE PEOCESS— Obtaining casts or copies of objects by depositing met- als in molds by the agency of electric currents. The molds are made of wax, or other plastic sub- stance, rendered conducting by coating it with po^v- dered plumbago. ELEMENT, NEGATRT:, OF A VOLTAIC CELL— That ele- ment or plate of a voltaic cell into which the current passes from the exciting fluid of the cell. The plate that is not acted on by the electrolyte during the gen- eration of current by the cell. ELE:MEXT, POSITTYE— That element or plate of a voltaic cell from which the current passes into the exciting fluid of the cell. The element of a voltaic couple which is acted on by the exciting fluid of the cell. ELEMENT, THEEMO-ELECTEIC— One of the two metals or substances which form a thermo-electric couple. ELEMENT, VOLTAIC— One of the two metals or sub- stances which form a voltaic couple. ELEV VTOE, ELECTEIC— An elevator operated by electric power. L 353 ENB ELONOATIOX, MAGNETIC— An increase in the length of a bar of iron on its magnetization. ENDOSMOSE, ELECTRIC— Differences in the level of li- quids capable of mixing through the pores of a dia- phragm separating them, produced by the flow of on electric current through the liquid. ENERGY— The power of doing work. ENERGY, CONSERVATION OF— The indestructibility of energy. The total quantity of energy in the universe is un-il- terable. •ENERGY, DISSIPATION OF— The expenditure or loss of available energy. ENERGY, ELEC^nUC— The power which electricity pos- sesses of doing work. ENERGY, ELECTRIC, TRANSMISSION OF— The transmis- sion of mechanical energy between two distant points connected by an electric conductor, by converting the mechanical energy into electrical energy at one point, sending the current so produced through the conduc- tor, and reconverting the electrical into mechanical en- ergy at the other point. ENERGY, KINETIC— Energy which is due to motion as distinguished from potential energy. ENERGY, POTENTlAI^Stored energy. Potency, or capa- bility of doing work. Energy ]30sses??ing the power or potency of doing work, but not actually performing strch work. The capacity for doing work possessed by a body at rest, arising from its position as regards the earth, or from the position of its atoms as regards other atoms, with which it is capable of combining. EVA 354 ENERGY, RADIANT— Energy transferred to or charged on the universal ether. ENERGY. STATIC — A term used fo express the energy- possessed by a body at rest, resulting from its position as regards other bodies in controdistinction to kinetic energy or tLe energy possessed by a body whose atoms, molecules or masses are in actual motion. Potential energy. EQUATOR, ALAGXETIC— The magnetic parallel or circle on the earth's surface where a magnetic needle, suspended so as to be /ree to m'ove in a vertical as well as a hori- zontal plane, remains horizontal. EQUIVALENT, ELECTRO-CHEMICAL— A number repre- senting the weight in grammes of an elementary sub- stance liberated during electrolysis by the pasi^age of one coulomb of electricity. EQUn^ALENT, JOULE'S— The mechanical equivalent of heat. ERG — The unit of work, or the work done when unit force is overcome thrrAigh unit distance. The work accom- plished when a body is moved through a distance of one centimetre with the force of one dyne. KTIIER — The tenuois, highly elastic lluid that is assumed to fill all space, and by vibrations or waves in which light and heat are transmitted. EVAPORATION, ELECTRIC— The formation of vapors at the surfaces of substances by the influence cf negative elect r if. cat ion. 355 FAR EVAPOKATION, ELECTRIFICATION BY— An increase in the difference of potential existing-, m a niijss of vapor attending* its sudden condensation. EXCHANGE, TELEPHONIC, SYSTEM OF— A combination of circuits, switches and other devices, by means of which any one of a number of subscribers connected with a telephonic circuit, or a neighboring t^elephonic circuit or circuits, may be placed in electrical communr- cntion with any other subscriber connected wdth stieh circuit or circuits. EXPLODER, ELECTRIC MINE— A small mag'neto-electric machine used to produce the currents of high , electro- motive force employed in the direct firing of blasts. EXPLODER, ELECTRO-MAGNETIC— (See Exploder, Elec- tric Mine). EXPLORER, MAGNETIC— A smalh flat coil of insulated wire, used, in connection with the circuit of a tele- phone, to detennine the position and extent of the mag- netic leakage of a dynamo-electric machine ov other similar apparatus. FAPIRENHEIT'S THERMOMETER SCALE— (See Scale, Thermometer, Fahrenheit's). FALL OF POTENTIAT.— (See Potential, Fall of). FAN GUARD— (See Guard, Fan). FARAD — The practical unit of electric capacity. Such a capacity of a conductor or condenser that one coulomb of electricity is required to produce in the con- ductor or condenser a dijlerence of potential of one volt. FIB 356 FARAD. MICRO— The millionth part of a farad. FAULT — ^Any failure in the proper working of a circuit due to ground contacts, cross-contacts or disconnec- tions. FEED, CLOCKWORK, FOR ARC LAMPS— An arrangement of clochwork for obtaining a uniform feed motion of one or both electrodes of an arc lamp. FEED, TO — To supplj^ with an electric current, as by a dynamo or other source. FEEDER. — One of the • conducting wires or channels through wh'ch the current is distributed to the main conductors. FEEDER, STANDARD OR MAIN- -The main feeder to which the standard pressure indicator is connected, and whose pressure controls the pressure at the ends of all the other feeders. FEEDERS — In a system of distribution by constant poten- tial, as in incandescent electric lighting, the conducting wires extending between the bus-wires or bars, and the junction boxes. FEET, AMPERE— The product of the current in amperes by the distance in feet through which that current passes. FIBRE, QUARTZ— A fibre suitable for suspending galvx- ]:ometer needles, etc., made of quartz. FIBRE, VULCANIZED— A variety of insulating material suitable for i^arposes not requiring the highest insu- lation. 357 FIE FIELD, AIR — '.riiat portion of a magnetic field in which the lines of force pass through air only, FIELD, ALTERNATING— An electrostatic or magnetic field the positive direction of the lines of force in which is alternately reversed or changed in direction. FIELD, ALTERNATING MAGNETIC— A magnetic field the direction of whose lines of force is alternately reversed. FIELD, DENSITY OF— The number of lines of force that pass through any field, per unit of area of cross-sectioa. FIELD, ELECTRO-MAGNETIC— The space traversed by the lines of magnetic force produced by an electro-magnet. FIEID, ELECTROSTATIC— The region of electrostatic in- fluence surrounding a charged body. FIELD, EXCITER OF— In a separately excited dynamo- electric machine, the dynamo-electric machine, voltaic battery, or otner electric source employed to produce the field of the field mag-nets. FIELD, INTENSITY OF— The strength of a field as meas- ured by the number of lines of force that pass through it per unit of area of cross-section. FIELD, MAGNETIC- -The region of magnetic influence sur- rounding the x>f>les of a magnet. A space or region traversed by lines of magnetic force. A place where a magnetic needle, if free to move, will take up a definite position, under the influence of the lines of magnetic force. FIELD, MAGNETIC, OF AN ELECTRIC CURRENT— The magnetic field surrounding a circuit through which an electric current is flowing. An electric current produces a magnetic field. FIR 358 FIELD, MAGNETIC, PULSATORY— A field, the strength of which pulsates iu such manner as to produce' oscillatory currents by induction. FIELD, MAGNETIC, STRAY— That portion cf the field of a dynamo-electric machine which is not utilized for the development of differences of potential in the armature, because its lines of force do not pass thrcugh the arma- ture. FIELD, MAGNETIC, STRENGTH OF— The dynamic force acting on a free magnetic pole, placed in a magnetic field.^ FIELD, ROTATING CURRENT— A magnetic field produced by means ox a rotating current. FIGURES, MAGNETIC— A name sometimes applied to the groupings of iron filings on a sheet of paper so held in a magnetic field as to be grouped or arranged under the influence of the lines of force of the same. FILAMENT OF INCANDESCENT ELECTRIC LAMP— (See Lamp, Incandescent Electric, Filament of). FILAMENTS, FLASHED —Filaments fbr an incandescent lamp, that have been subjected to the flashing process, FINDER, RANGE, ELECTRIC— A device by means of which the exact distance of an enemy s snip or other target can be readil}^ determined. FIRE ALARM, AUT0:MATIC— (See Alarm, Fire, Automat- ic). FIRE ALARM SIGNAL BOX— (See Box, Fire Alarm Signal) 359 YLV FIRE, HOT, ST. EL^CO'S— A term proposed by Tesla for a form of powerful brush discliarg-e between the second- ary terminals of a high frequency induction coil. FITTINGS OE FIXTURES, ELECTRIC LIGHT— The sock- ets, holders, arms, etc., required for holding or suj)port- ing" incandescent electric lamps. FIXTURES, TELEGRAPHIC— A term generally limited to the variously shaped supports provided for the attach- ment of telegraphic ^^dres. FLASHED FILAMENTS— (See Filaments, Flashed). FLASHES, AURORAL— Sudden variations in the intensity of the auroral light. Intermittent flashes of auroral light that occur during the prevalence of an aurora. FLASHIXC OF DYXAMO-ELECTRIC MACHINE— (See Ma chine, Dynamo-Electric, Flashing of). FLATS — A name sometimes applied to those parts of com- mutator segments the surface of which, through wear, has become lower than the other portions. FLOW, MAGNETIC- The magnetic flux. FLOW OF CURRENT, ASSUMED DIRECTION OF— (See Current, Assumed Direction of Flow oi*). FLUID, DEPOLARIZING— An electrolytic fluid in a voltaic cell that prevents polarization. FLUORESCENCE— A property possessed by certaiu solid or liquid substances of becoming self-luminous while exposed to light. FOH 360 FLUX, MAG^^ETIC— The number of lines of magnetic force that pass or flow throug-h a magnetic circuit. The total number of lines of magnetic force in any magnetic field. The magnetic flux is also called the magnetic flow. FLYER, ELECTEIC— A wheel arranged so as to be set into rotation by the escape of convection streams from its points when connected with a charged conductor. FOCUS — A point in front or back of a lens or mirror, where all the rays of light meet or seem to meet. FOLLOWING HORX OF POLE PIECES OF DYNAMO- ELECTRIC MACHINE— rSee Horns, Followinff of Pole Pieces of a Dynamo-Electric Machine). FOOT-POUND— A unit of work. FORCE — Any cause which changes or tends to change the condition of rest or motion of a body. FORCE, CENTRIFUGAL— The force that is supposed to urge a rotating body directly away from the center of rotation. FORCE, COERCIVE —The power of resisting magnetization or demagnetization. FORCE, CONTACT-A difference of electrostatic potential, produced by the contact of dissimilar metals. FORCE, ELECTRIC— The force developed by electricity. FORCE, ELECTROMOTIVE— The force starting electricity in motion, or tending to start electricity in motion. The force which moves or tends to move electricity. FORCE, ELECTROMOTIVE, ABSOLUTE UNIT OF— A unit of electromotive force expressed in absolute or C. G. S. unit^. The one-hundred millionth part of a volt, since 1 volt equals 108 C. G. S. units of electromotive force. 361 FOR FORCE, ELECTROMOTIVE. AVERAGE OR MEAN— The sum of the \ allies of a nnmber of separate electromo^ tive forces divided by their number. FORCE, ELECTROMOTIVE, BACK— A term sometimes used for couuter electromotive force. Counter electromotive force is the preferable term. FORCE, ELECTROMOTIVE COUNTER— An opposed or re- verse electromotive force, which tends to cause a cur- rent in the opposite direction to that actually produced by the source. In an electric motor, an electrom'otive force contrary to that produced by the current which drives the motor, and which is proportional to the ve- locity attained by the motor. FORCE, ELECTROMOTIVE, DIRECT— An electromotive force acting- in the same direction as another electro- motive force already existing. FORCE, ELECTROMOTIVE. EFFECTIVE— The difference between the direct and the counter electromotive force. FORCE, ELECTROMOTIVE, IMPRESSED— The electromo- tive force acting on any circuit to produce a current therein. FORCE, ELECTROMOTIVE. INVERSE— An electromotive force which acts in the opposite direction to another electromotive force already existing. FORCE, ELECTROMOl IVE, OF INDUCTION— The electro- motive force developed by any inductive action. In a coil of wire undergoing induction, the value of the induced electromotive force does not depend in any manner on the nature of the material of which the coil is composed. 24 FOE 362 FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- AGE CELL, TIME-FALL OF— A gradual decrease m the potential dii^erence of a storage battery observed dur- ing- the discharge of the same. FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- AGE CELL, TIME-RISE OF— A g-radual increase in the potential diifcrence of a secondary or storage cell ob- served on beg-inning the discharge after a prolonged rest. FORCE, ELECTROMOTIVE, SECONDARY IMPRESSED— An electromotive force produced ^vhich varies in such manner as to produce a simple periodic current, or an electromotive force the variations of which can be cor- rectly represented by a simple-periodic curve. FORCE, ELECTRO.AIOTIVE THERMO— An electromotive force, or difference of potential, produced by dift'erences cf temperature acting at thermo-electric junctions. FORCE, ELECTROMOTIVE VIRTUAL, OR EFFECTIVE— The square root of the mean square of an alternating or variable current. FORCE, ELECTROSTATIC— The force producing the at- tractions or repulsions of charged bodies. FORCE, ELECTROSTATIC, LINES OF— Lines of force pro- duced in the neighborhood of a charged body by the presence of the charge. Lines extending in the direction in which the force of electrostatic attraction or repulsion acts. FORCE, LINES OF, CUTTING— Passing a conductor through lines of magnetic force, so as to cut to inter- sect them. 363 FOR FORCE LINES OF, DIRECTION OF— It is generally , agreed to consider the force lines of nuagnetic force as coming out of the north pole of a magnet and pas» ing into its south pole. FORCE, LOOPS OF— A term sometimes employed in the sense of lines of force. FORCE, MAGNETIC— The force which causes the attrac- tions cr repulsions of magnetic poles. FORCE, M-AGNETTC, LINES OF— Lines extending in the direction in which the magnetic force acts. Lines extending in the direction in which the force of magnetic attraction or repulsion acts. FORCE, MAGNETIC, LINES OF, CONDUCTING POWER FOR — A term employed by Faraday for magnetic per- meability. FORCE, MAGNETO-MOTIVE— The force that moves or drives the lines of magnetic force through a magnetic circuit against the magnetic resistance. FORCE, MAGNETO-MOTIVE, PRACTICAL UNIT OF— A value of the magneto-motive force equal to 4// multi- plied by the amperes of one turn, or to 1-10 of the abso- lute unit. FORCE, TUBES OF— Tubes bounded by lines of electro- static or magnetic force. FORCE, TWISTING— A term sometimes used for torque. FORCE, UNIT OF— A force which, acting for one second on a mass of one gramme, will give it a velocity of one centimetre per second. Such a force of unit is called a dyne. FED 364 FOECES, PAEALLELOGEAM OF— A parallelogram con- structed about the two lines that represent the direc- tion and intensity with which two forces are simulta- neously acting on a body, in order to determine the direction and intensity of the resultant force with which it moves. FOEK, TEOLLEY— The mechanism which mechanically connects the trolley whee] to the trolley jjole. FOEMIXG PLATES OF SECOND AEY OE STOEAGE CELLS— rSee Plates of Secondary or Storage Cells, Forming* of). FOEMULAE — Mathematical expressions for some general rule, law or principle. ' FOUCAULT CUEEEXTS— (See Currents, Foucault). FEEE MAGNETIC POLE— (See Pole, Magnetic, Free). FEEQUENCY OF ALTEENATIONS— (See Alternations, Frequency of). FEICTIOXAL ELECTEICAL MACHINE— (See Machine, Frictional Electric). FEICTIONAL ELECTEICITY— (See Electricity, Frictional) FEOG, GALVANOSCOPIC- The hind legs of a recently killed frog employed as an electroscope or galvanoscope by sending an electric current from the nerves to the muscles. FEOG, TEOLLEY— The name given to the device employed in fastening or holding together the trolley wires at any point where the trolley wire branches, and prop- erly guiding the trolley wheel along the trolley wire on the movement of the car over the track. 365 GAL FURNACE, ELECTRIC— A furnace in which heat gener ated electrically is employed for the purpose of effect^ ing difficult fusions for the extraction of metals froui their ores, or for other metallurg-ical operations. FL^E BLOCK— (See Block, Fuse). FUSE BOX— (See Box, Fuse). FUSE, BRANCH— A safety fuse or strip placed in a branch circuit. FUSE, CONVERTER— A safety fuse connected with the circuit of a converter or transformer. FUSE, ELECTRIC— A device for electrically igniting- a charge of powder. FUSE, MAIN — A safety fuse or strip placed in a main cir- cuit. FUSE, SAFETY— A strip, plate or bar of lead, or some readily fusible alloy, that automatically" breaks the cir- cuit in whijch it is placed on the passage of a current of sufficient power to fuse such strip, plate or bar, when such current would endanger the safety of other parts of the circuit. GAINS — The spaces cut in the faces of telegraph poles for the support or placing of the cross arms. GALVANIC BATTERY— (See Battery, Galvanic). GALVANIC CELL— (See Cell, Voltaic). GALVANIC POLARIZATION— (See Polarization, Galvanic). GAL 366 GALYAXTC TASTE— (See Taste, Galvanic). GALVANISM — A terra sometimes employed to express the effects produced by voltaic electricity. GALVAXIZATIOX, ELECTEO-METALLUEGTCAL — The process of covering" any condiictive surface with a me- tallic coating- by electrolytic deposition, such, for ex- ample, as the thin copper coating- deposited on the car- bon pencils or electrodes used in systems of arc light- ing". GALVAXOMETER — An apparatus for measuring the strength of an electric current by the deflection of a magnetic needle. The galvanometer depends for its operation on the fact that a conductor, through which an electric cur- rent is flowing, will deflect a magnetic needle placed near it. This deflection is due to the magnetic fleld caused by the current. GALVAXO:NrETEE, ABSOLUTE— A galvanometer whose constant can be calculated with an absolute calibration. GALVAXOMETEE, ASTATIC— A galvanometer, the needle of which is astatic. GALVAXO.AfETEE, BALLISTIC— A galvanometer designed to measure the strength of currents that last but a mo- ment, such, for example, as the current caused by the discharge of a condenser. GALVAXO:\rETEE CONSTANT— (See Constant, Galvanom- eter). GALVA1S0:METEE, IJEAD-BEAT — a galvanometer, the needle of which comes quickly to rest, instead of swi ag- ing repeatedly to-and-fro. (See Damping). 367 # GAL GALVANO^IETE'R, DEPREZ-D'ARSONVAL— A form of dead-beat galvanometer. GALYA>^0:METER, DIFFERET^TIAL— a galvanometer con- taining two coils so v^^ound as to tend to deflect the nee- dle in opposite directions. GALVANO]\rETER, FIGURE OF :MERIT OF— The recipro- cal of the current required to produce a deflection of the galvanometer needle through one degree of the scale. GALVANOMETER, MARINE— A galvanometer devised by Sir William. Thomson for use on steamships where the motion of magnetized masses of iron would seriously disturb the needles of ordinary instruments. GALVANOMETER, IStlRROR— A galvanometer in which, instead of reading the deflections of the needle directly by its movements over a graduated circle, they are read by the movements of a spot of light reflected from a mirror attached to the needle. GALVANOMETER, REFLECTING— A term sometimes ap- plied to a m.irror galvanometer. GALVANOMETER, SENSIBILITY OF— The readiness and extent to which the needle of a galvanometer responds to the j)assage of an electric current through its coils. GALVANOMETER, SINE— A galvanometer in which a ver- tical coil is movable around a vertical axis, so that it can be made to follow the magnetic needle in its deflec- tions. Tn the sine galvanometer, the coil is moved so as to follow the needle until it is parallel with the coil. Un- der these circumstances, the strength of the deflecting currents in any two differenf cases is proportional to the sines of the angles of deflection. GAS 368 GALYANOMETEE, l^ANGENT— An instrument in wliich tlie deflecting' coil consists of a coil of wire within which is placed a needle very short in proportion to the diameter of the coil, and supported at the center of the coil. The galvanometer acts as a tangent galvanometer only when the needle is very small as compared with the diameter of the coil. The length of the needle should be less than one-twelfth the diameter of the coil. GALVANOMETEK, TORSION— A galvanometer in which the strength of the deflecting current is measured by the torsion exerted on the suspension system. GAP, ATE — A gap, or opening in a magnetic circuit con- taining air only. GA.P, ATE, MAGNETIC— A gap filled with air which exists in the opening at any part of a core cf iron or other m.edium of high permeability. GAP, SPAEK — A. gap forming part of a circuit between two opposing conductors, separated by air, or other similar dielectric which is closed by the formation of a spark only when a certain difference of potential is attained. G^S, DIELECTEIC, STEENGTH OF— The strain a gas is capable of bearing without suffering disruption, or without permitting a disruptive discharge to pass through it. GAS-LIGHTING, MULTIPLE ELECTEIC— A system of electric gas-lighting in which a number of gas-jets are lighted by means of a discharge of high electromotive force, derived from a Euhmkorff coil or a static indue- tfon machine. 369 GEN GASSING — The evolution of gas from the plates of a stor- age or secondary cell. GAUGE, BATTEPY— A form of portable galvanometer, suitable for ordinary test work. GAUGE, WIRE, AMERICAN— A name sometimes applied to the Erown & Sharpe Wire Gauge. GAUGE, WIEE, ETEMTNGHAM— A term sometimes appliecl to one of the English wire gauges. GAUGE, WTEE. MICEOMETEE— A gauge employed for ac. cnrately measiiring the diameter of a wire in thou- sandths of an inch, based on the principle of the vernier or micrometer. GAUSS— The unit of intensity of magnetic field. GAi:^SS, FLEMING'S— Such a strength of magnetic field as is able to develop an electromotive force of one vot in a wire one million centimetres in length moved through the field with unit velocity. GAUSS, S. P. THOMPSON'S— Such a strength of magnetic field that^its intensity is equal to 108 C. G. S. units. GAUSS, SIE WILLIAM THOMSON'S— Such an intensity of magnetic field as would be produced by a current of one ampere at the distance of one centimetre. GENEEAl^OE, DYNAMO-ELECTEIC— An apparatus in which electricity is produced by the mechanical move- ment of conductors through a magnetic field so as to cut the lines of force. A dynamo-electric machine. GENEEATOE, [MOTOE— A dynamo-electric generator in which the power required to dri\'e the dj^namo is ob- tained from an electric current. GEA 370 GENERATOR, PYE0-:MAGXETIC— An apparatus for pro- ducing- electricity directly from heat derived from the burning" of fuel. GERMAX SHAHRR ALLOY— (See Alloy, German Silver). GIMBA.LS- Concentric rings of brass, suspended en pivots in a compass box, and on which the compass card is supported so as to enable it to remain horizontal not- withstanding the movements of the ship. GLOBE. VAPOR, OF IXCAXDESCEXT LAMP— A glass globe surrounding the chamber of an incandescent elec- tric lamp, for the purpose of enabling the lamp to be safely used in an explosive atm.osphere, or to permix the lamp to be exposed in places where water is liable to fall on it. GOVERNOR, CITRREXT— A current regulator. A device ' for "maintaining constant the current strength in any circuit. GOVERXOR, ELECTRIC— A device for electrically controll- ing the speed of a steam engine, the direction of cur- rent in a plating bath, the speed of an electric motor, the resistance of an electric circuit, the ilow of water or gas into or from a containing vessel, or for oiher similar purposes. GRAME— A unit of weight equal to 15.43235 grains. . The grame is equal to the weight of one cubic cen- tintetre of pure water at the temperaTure of its maxi- mum density. GRAMOPHOXE — An apx)aratus fop recording and repro- ducing articulate speech. 371 -GUT GRAPHITE — A soft variety of carbon suitable for writing" on paper or similar surfaces. GRAY'S HARMONIC TELEGRAPHY— (wSee Telegraphy, Gray's Harmonic Multiple). GRAYITATIOX — A name applied to vhe force which causes masses of matter to tend to move towards one another. GRAYTTY, CENTRE OF— The centre of weight of a body. GRID — A lead plate, provided with perforations, or other irregularities of surface, and employed in storage cells for the support of the active material. The support provided for the active material on the plate of a sec- ondary or storage cell. GROTHUSS' HYPOTHESIS— (wSee Hypothesis, Grothuss). GROUND DETECTOR— (See Detector, Ground). GROUND OR EARTH— A general term for the earth when employed as a conductor, or as a large reservoir of electricity. ^ GROUND-RETURN— A general term used to indicate the use of the ground or earth for a part of an electric circuit. The earth or ground which forms part of the return path of an electric circuit. GROUND-WIRE — The wire or conductor leading to or con- necting with the ground or earth in a grounded circuit. GUARD, FAN — A wire netting placed around the f^n of an electric motor for the purpose of preventing its revolv- ing arms from striking external objects. GUTTA-PERCHA —A resinous gum obtained from a tropi- cal tree and valuable electrically for its high insulating powers. H'AE 372 GYMNOTUS ELECTRICUS— The electric eel. H H. — A contraction for the horizontal intensity of the earth's magTietism. H. — A contraction used in mathematical writings for the TnagTietizing- force that exists at any point, or, gener- ally, for the intensitj^ of the magnetic force. The letter H, when used in mathematical writings or formulae for the intensity of the magnetic force, is always represented in bold or heavy faced type, thus: H KAIE, ELECTROLYTIC REMOVAL OF— The permanent removal of hair from any part of the body, by the elec- trolytic destruction of the hair follicles. HALF-SHADES FOR INCANDESCENT LAMPS—Shades for incandescent electric lamps, in which one-half of the lamp chamber proper is covered with a coating of silver, or other reflecting surface for reflecting the light, or is ground fdr the purpose of diffusing the light. HANDIIOLE OF CONDUIT— A box or opening commimi- cating with an underground cable, provided for readily tapping the cable, and of sufficient size to permit of the introduction of the hand. HANGER, DOUBLE-CURVE TROLLEY— A trolley hanger generally employed at the ends of single and double curves, and on intermediate points on double track curves, supported by lateral strain in opposite direc- tions. HANGER, TROLLEY— A device for supporting and prop- erly insulating trolley wires. HARMONIC RECEIVER— (See Receiver, Harmonic). 373 HEA HARMONIC TELEGEAPH— (See Telegraphy, Gray's Har- monic Multiple). • HEAD LIGHT, LOCOMOTIVE, ELECTRIC— An electric light placed in the focus of a parbolic reflector in front of a locomotive engine. The lamp is so placed that its voltaic arc is a little out oi the focus of the reflector, so that, by giving a slight divergence to the reflected light, the illumination extends a short distance on either side, of the tracks. HEAT— A form of energy. The phenomena of heat are due to a vibratory motion impressed on the molecules. Heat is transmitted through space by means of a wave motion in the univer- sal ether. This wave motion is the same as that caus- ing light. A hot body loses its heat by producing a wave mo- tion in the surrounding ether. This process is called radiation. (See Radiation). The energy given off by a heated body cooling is called radiant energy. HEAT ELECTRIC— Heat produced by means of electric current. HEAT, MECHANICAL EQUIVALENT OF— The amount of mechanical energy, converted into heat, that would be required to raise the temperature of 1 pound of water 1 degree Fahr. The mechanical equivalence between the amount of energy expended and the amount of heat produced, as measured in heat units. Rowland's experiments, the results of which are gen- erally accepted, gave 778 foot-pounds as the energy equivalent to that expended in raising the temperature of 1 pound of water from 39 degrees F. to 40 degrees F. BEN 374 HE VT SPECIFIC The capacity of a substance for heat as compared with the capacity of an eqnal quantity of some other substance taken as unity. Water is o-enerally taken as the standard for compari- son, because its capacity for heat is greater than that of any other common substance. HEAT UNIT— The quantity of heat required to raise a given weight of water through a single degree. (1.) The British Heat Unit, or Thermal Unit, or the amCTint of heat required to raise 1 poimd of water at greatest density 1 degree Eahr. This unit represents an amount of work equal to 778 foot-pounds. (2.) The Greater Calorie, or the amount of heat re- quired to raise the temperature of 1,000 grames of water 1 degree C ^See Calorie). (3.) The Smaller Calorie, or the amount of heat re- quired to raise the temperature 1 gramme of water 1 degree C. (4.) The Joule, or the quantity of heat developed in one second by the passage of a current of one ampere through a resistance of one ohm. HEATEE.ELECTRIC— A device for the conversion of elec- tricity into heat for purposes of artificial heating. HEDGEHOG TEANSFOKMEK— (See Transformer, Hedge- hog). HENKY, ^— The practical unit of self-induction. A circuit has a self-induction of one Henry when a change of one ampere per second produces in it a coun- ter E. M. F. of one volt. 375 HOR HIGH-BARS — A term applied to those commutator seg"- ments, or part? of commutator segments, which, throug-h less wear, faulty construction or looseness, are hii^her than adjoining' portions. HOLDERS, CARBON, FOR ARC LAMPS— A clutch or clamp attached to the end of the lamp rod or other support, and provided to hold the carbon pencils used on arc lamps. HOLDERS FOR BRUSHES OF DYXAMO-ELECTRIC MA- CHINE — A device for holding* the collecting brushes of a dynamo-electric machine. HOLTZ MACHINE— (See Machine, Holtz). HOOD FOR ELECTRIC LA:\[P— A hood provided for the double purpose of protecting the body of an electric lamp from rain or sun, and for throwing Its light in a general downward direction. HORIZONTAL COMPONENT OF EAR I^H'S :NL4GNETIS]Nr— (See Component, Horizontal, of Earth's Magnetism). HORNS, FOLLOWING, OF POLE PIECES OF A DYNAMO- ELECTRIC MACHINE— The edges or terminals of the pole pieces of a dynamo-electrical machine from which, the armature is carried during its rotation. HORNS, LEADING, OF POLE PIECES OF A DYNA:M0- ELECTRTC MACHINE— The edges or terminals of the pole pieces of a dynamo-electrical machine from which the armature is carried during its rotation, HORSE-POWER— A commercial unit for power or rate of doing work. HORSE-POWER, ELECTRIC— (See Power, Horse, Electric). HYS 376 HOESESHOE MAGNET— (See Magnet, Horseshoe). HOTEL ANNUNCIATOFv— (See Annunciator, Hotel). HOUE, AMPEEE— A unit of electrical quantity equal to one ampere flowing for one hour. HOUE, HOESE-POWEE— A unit of work. An amount of work equal to one-horse power for an hour. One horse power is equal to 1,980.000 foot-pounds, or 745.941 "watt hours. HOUE, KILO-WATT— A unit of electrical power equal to a kilo-watt maintained for one hour. HOUE, LAMP — Such a service of electric current as will maintain one electric lamp during one hour. HOUE, WATT— A unit of electrical work. An exjDenditure of electrical work of one watt for one hour. HUMAN BODY, ELECTEICAL EESISTANCE OF-(See Body, Human, Eesistance of). HYDEOGEN, ELECTEOLYTIC— Hydrogen produced by electrolytic decomposition. HYPOTHESIS, GEOTIIUSS— A hjrpothesis produced by GrothiTSS to account for the electrolytic phenomena that occur on closing the circuit of a voltaic cell. HYSTEEESIS— Molecular friction to magnetic change of stress. A retardation of the magnetizing or demagnetizing effects as regards the causes which produce them. The quality of a paramagnetic su,bstance by virtue of which energy is dissipated on the reversal of its mag- netization. 377 j^Q r I. H. P. — A contraction for indicated horse-power, or the horse-power of an engine as obtained by the means of an indicator card. IGNITION, ELECTRIC— The ignition of a combustible ma- terial by heat of an electric origin. ILLUMINATION, ARTIFICIAL— The employment of artifi- cial sources of light. ILLUMINATION, UNIT OF— A standard of illumination proposed oy Preece, equal to the illumination given by a standard candle at the distance of 12.7 inches IMPEDANCE— Generally any opposition to current flow. A quantity which is related to the strength of the impressed electromotive force of a simple periodic or alternating current, in the same manner that resistance is related to the siteady electromotive force of a con- tinuous current. IMPEDANCE COIIr-(See Coil, Imipedance). IMPRESSED FLECTROMOTIVB FORCE— (See Force, Elec- troanotive, Impressed). INCANDESCE— To shine or glow by means of heat. INCANDESCENCE, ELECTRIC— The shining or glowing of a substamce, generally a solid, by means of heat of elec- tric origin. INCLINATION, ANGLE OF— The angle which a magnetic needle, free to move im a horizontal plane, makes wit a a horizontal line passing through its^point of support. The angle of magnetic dip. 25 IND 378 IXiCAXDESCENT ELECTEIC T^\]MP— (See r>amp, Electric, Incandescent). IXCLIXATIOX, MAGXBTIC— The angular deviation from a horizontal position of a freely suspended magnetic needle. IXDIA EUBBEE — A resinous substance obtained from the milky juice of several tropical trees. IXDIOATOE, ELECTEIC— A name applied to various de- vices, generally operated by the deflection af a mag- netic needle, or the ringing of a bell, or both, for indi- cating, at some distant point, the condition of an elec- tric circuit, the 'Strength of current thaif is passing through it, the height of water or oth'er liquid, the p«ressure o'a a boiler, the tennperature, the speed of an engine or line of shafting, the working of a machine or other similar events or occurrences. IXDICATOE, ELBCTEIC, FOE STEAMSHIPS— An electric indicator operated by circuits connected with the throt- tle valve and reversing gear of the stea«m engine. IXDICATOE, LAMP— An apparatus used in the central sta- tion of a system of incandescent lamp distribution to indicate the presence o-f the proper voltage or potential •difference en the mains. IXDICATOE, POTEXTIAL— An apparatus for indicating the potential diffeience between any points of a circuit. IXDICATOE, SPEED— A name sometimes applied to a tachcgneter. A revolution counter. INDUCED CrEEEXT~(See Current, Induced). 379 IND INDUCTAiSrCE— The induction of a current on itself, or od other circuits. Self-induction. A term generally employed instead of self-induction. That property in virtue of which a finite electromo- tive force, acting on a circuit, does not im^mediately generate the full current due to its resistance, 'and when the electromotive force is withdrawn, time is re- quired for the current sitrength to fall to zero. — (Flem- ing.) A quality by \^rtue of which the passage of an elec- tric current is necessarily accomipanied by the absorp- tion of electric energy in the formation of a magnetic field. INDUCTANCE, CO-EFFICIENT OF— A constant quantity, such that when multiplied hy the current strength passing in any coil or circuit, "vvill represent numerlcal- 1}' the induction through the coil or circuit due 'to that current. A term sometimes used for co-efficient of self-induc- tion. INDUCTANCE, VARIABLE— The inductance .which occui-. in circuits formed partly or wholly of substances like iron or other paramagnetic substances, the magnetic permeability of which varies with the intenisity oif the magnetic induction, and where the lines of force have their circuit partly or wholly in soich material or vari- able magnetic peroneability. INDUCTION — An infiuence exertea by a charged body or by a magnetic field on neighboring bodies without ap- parent communication. IIN-U 380 INDUCTIOX, ELBGTEO— DYNAMIC— Electromotive forces set up by induction in conductors which are either ac- tually or practically moved so as to cut the lines of magnetic force. These electramo-tive forces, when permitted to act through a circuit, produce an eleciric current. I1SDUCTI0X, ELBCTRO-MAGXETIC— .A variety of electro- dynamic induction in which electric currents are pro- duced by the motion of electro-magnetic solenoids. INDUCTION, ELECTEOSTATIC— The production of an electric charge in a. conductor brought inito an electro- static field. INDUCTION, MAGNETIC— The pi:oduction of magnetism in a magnetizable subs»tance by bringing it into a mag- netic field. INDUCTION, MAGNETIC, CO-EFFICIENT OF— A term sometimes used instead of magnetic permeability. (See Permeabilit}', Magnetic). INDUCTION, MAGNETIC LINES OF— Lines which show * not only the direction in which magnetic induction takes place, but also the magnitude af the induction. This term is often loosely used for lines of force. INDUCTION, MAGNETIC-ELECTEIC— A variety of electro- djmamic induction in which electric currents are pro- duced by the motion of permanent magnets, or of con- ductors past permanent magnets. INDUCTION, MUTUAL— Induction produced by two neigh- boring circuits on each other by the mutual interaction of their magnetic fields. 381 iNr> INDUCTION, MUTUAL, CC-EFFICIENT OF— The quanti- ty which represents the numiber of lines of force which are common to or linked in with 'tw^o circuits, which are producing mutual induction on each other. INDUCTION, REFLECTION OF— A term proposed by Fleming" to express an action which resembles a reflec- tion of inductive power. INDUCTION, SELF— Induction produced in a circuit while changing- the current therein iby the induction o-f the current on itself. INDUCTION, SELF, CO-EFFICIENT OF— The amount of cutting of magnetic lines in any circuit due to the pas- sage of unit current. For a given coil the co-efficient of self-induction is, according to S. P. Thompson: (1.) Proportional to the square of the number of convolutions. (2.) Is increased by the use of an iron core. (3.) If the magnetic permeability is assumed as con- stant, the co-efficient of self-induction is numerically equal to the product of the number of lines of magnetic force due to the current, and the number of times they are enclosed by the circuit. INDUCTION, TOTAL INIAGNETIC— The total magnetic in- duction of any space is the number of lines of magnetic induction w^liich pass through that space, where the magnetizable material is placed together with the lines added by the magnetization of the magnetic material. INDUCTION, UNIPOLAIl— A term sometimes applied to the induction that occurs when a conductor is fjo moved through a magnetic field as to continuously cut- its lines of force. INK 382 IXDUCTIOiXLESS RESISTAXCE— (See Resistance, Induc- tionless.) INDUCTIVE CAPACITY, SPECIFIC— (See Capacit3% Speci- fic Inductive.) INDUCTIVE CIRCUIT— (See Circuit, Inductive.) INDUCTIVE RESISTANCE— (See Resistance, Inductive.) INDUCTOR DYNAISEO— (See Dynamo, Inductor.) INDUCTORIUM— A name sometimes applied to a Ruhm- korff induction coil: INEQUALITY, ANNUAL, OF EARTH'S MAGNETISM - Variations in the value of the earth's magnetism dur- ing' the earth's revolution depending on the position of the sun. Annual variations in the earth's magnetism. INERTIA— The inability of a body to change its condition of rest or motion, unless some force acts on it. INERTIA, ELECTRIC — A term sometimes employed in- stead of electro-magnetic inertia. A term employed to indicate the tendency of a cur- rent to resist its stopping or starting. INERTIA, ]MAGNETIC— The inability of a magnetic core to instantly lose or acquire magnetism. INFLUENCE, :\LACHINE— (See Machine, Electrostatic In- duction.) INK WRITER, TELEGRAPHIC— A device employed for recording the dots and dashes of a telegraphic message in ink on a fillet or strip of paper. 383 INT INSTALLATION — A term embracing the entire plant and its accessories required to perform any specified work. The act of placing, arranging- or erecting a plant or apparatus. INSTALLATION, ELECTRIC— The establishment of any electric plant. INSULATING STOOL— (See Stool, Insulating.) INSULATING TAPE— (See Tape, Insulating.) INSLT:.ATT0N; electric— Non-conducting material so placed vnih respect to a conductor as to prevent the loss of a charge, or the leakage of a current. INSULATOR, DOUBLE-CUP— An insulator consisting of two funnel-shaped cups, placed in an inverted position on the supporting pin and insulated from one another by a free air space, except near the ends, which are cemented. INSLILATOR, FLUTD- An insulator provided with a small, internally placed, annular, cup-shaped space, filled with an insulating oil, thus increasing the insulating power of the support. INSULATOR, OIL— A fluid insulator filled with oil. INSULATOR TELEGRAPHIC OR TELEPHONIC— A non- conducting support of telegraphic, telephonic, electric light or other wires. INTENSITY, MAGNETIC— Density of magnetic induction. INTENSITY OF CURRENT— (See Current, Intensity of.) INTENSITY OF FIELD— (See Field, Intensity of.) INTENSITY OF MAGNETIZATION— (See Magnetization, Intensity of.) ISO 384 IXTBXSITY, PHOTOMETRIC, UXIT OF— (The amount of light produced by a candle that- consumes two grains of spermaceti wax per minute.) INTEERUPTER, AUTOMATIC— An automatic contact breaker. INTERRUPTER, TUNIXG-FORK— An interrupter in which the successive makes and breaks are produced by the vibrations of a tuning-fork or reed. INVERSION, THERMO-ELECTRIC— An inversion of the thermo-electric electromotive force of a couple at cer- tain temperatures. IONS — Groups of atoms or radicals which result from the electrolytic decomposition of a molecule. TONS, ELECTRO-NEGATIVE— The negative atoms, or groups of atoms, called radicals, into which the mole- cules of an electrolyte are decomposed by electrolysis. IONS. ELECTRO-POSITIVE—The positive atoms, or groups of atoms, called radicals, into which the molecules of an electrolyte are decomposed by electrolysis. IRON-CLAD ELECTRO-MAGNET— (See Magnet, Electro, Iron-Clad.) IRON CORE, EFFECT OF, ON THE MAGNETIC STRENGTH OF A HOLLOW COIL OF WIRE— An iu- crease in the number of lines of magnetic force, be- yond those produced by the current itself, due to the opening out of the closed magnetic circuits in the atoms or molecules of the iron. ISOCHRONIS^Nl— Equality of time of vibration or motion. A contraction proposed for Joule. C85 JOI JABLOCHKOFF CAXDLE— (See Candle, Jablochkoff.) JAR, LEYDEN — A condenser in the form of a jar, in which the metallic coatings are placed opposite each other on the outside and the inside of the jar respec- tively. JAR, LEYDEN, CAPACITY OF— The quantity of electricity a Leyden jar will hold at a g-iven difference of poten- tial. JAR, LIGHTNING— A Leydon jar, the coatings of which consist of metallic filling's. As the discharge passes, an irregular series of sparks appear, which somewhat resemble in their shape a lightning flash. Hence the origin of the term. JAR OF SECONDARY CELL— The containing vessel in which ^he plates of a single secondary cell arc placed. JAR, POROUS— A porous cell. JAR,UNrT— -A small Leyden jar sf»metimes employed to measure approximately the quantity of electricity passed into a Leyden battery or condenser. JOINT, .-\MERTCAN TWIST— A telegraphic or telephoni • joint in which each of the two wires is twisted around the other. JOINT. P.RITANNIA — A telegraphic or telephonic joint in which the wires are laid side by side, bound together and subsequentlj" soldered. JOINT, MAGNETIC— The line of junction between two separate parts of magnetization material. KEK 386 JOINT, SLEEVE — A junction of the ends of conducting wires obtained by passing them through tabes and then twisting and soldering. JOINT, TESTING OF— Ascertaining the resistance of the insulating material around a joint in a cable. A contraction for electrostatic capacity. JOULE — TJie unit of electric energy or work. 1 joule equals .73732 loot-pounds. 1 joule per second equals 1 watt. The British Association proposed to call one joule the work done by one watt in one second. K K. W. — A contraction for kilo-watt. KAOLIN — A variety of white clay sometimes employed for insulating pui-poses. KAPP LINES— (See Lines, Kapp.) KAETAYERT— A kind of insulating material resembling fiber. KATHION — The electro-positive ion, atom or radical into which the molecules of an electroh'te is decomposed iby electrolysis. KATHODAL— Pertaining to the kathode. KATHODE — The conductor or plate of an elect- o-decom- position cell connected with the negative terminal or electrode of a battery or other source. KEEPER OF MAGNET— (See Magnet, Keeper of.) KERITE — An insulating material. 387 KIL KEY, DISCHARGE— A key employed to enable the dis- charge from a condenser or cable to be readily passed through a galvanometer for purposes oi measure- ment. KEY, IXCEEMEXT, OF QUADRUPLEX TELEGRAPHIC SYSTEiM — A key employed to increase the strength of the current and so operate one of the dlistant instru- ments in a quadruplex sj^stem by an increase in the streng^th of the current. KEY PLUG — A simple form of key in which a connection is readily made or broken by the insertion of a pkig' of metal between two metallic plates that are thus in- troduced into a circuit. KEY, RBVBRSIXG— A key inserted in the circuit of a gaL vanometer for obtaining deflections of the needle on either side of the galvanometer scale. KEY, REYERSIXG, OF QUADRUPLEX TELEGRAPHIC SYSTEM — A key employed to reverse the direction of the current and so operate one of the distant instru- ments, in a quadruplex system, by a chauige in the di- rection of the current. KEY, SHORT-CIRCUIT— A key which in its normal condi- tion short circuits galvanometer. KEY, TELEGRAPHIC- The key employed for sending over the line the successive makes and breaks that product- the dots and dashes of the Morse alphabet, or the de- flections of the needle of the needle telegraph. KICKIXG COIL— (See Coil, Kicking.) KILOAMPERE— One thousand amperes. KILOGRAMME— One thousand grammes, or 2.2046 pounds avoirdupois. LAG S88 KILOWATT— One thousand -^vatts. KILOWATT HOUR— (See Hour, Kilowatt.) KIXETIC ENERGY— (See Energ-y, Kinetic.) KINETOGRAPH — A device for the simultaneous reproduc- tion of a distant stage and its actors under circum- stances such that the actors can be heard at any dis- tance from the theatre. KITE, FRAXKLIX'S— A kite raised in Philadelphia, Pa., in June, 1752, by means of T\'hich Franklin experiment- ally demonstrated the identity between lightning* an«.l electricity, and which, therefore, led to the invention of the lightning rod. KNIFE, BREAK SWITCH— (See Switch, Knife Break.) L — A contraction for co-efficient of inductance. L — A contraction for length. LAG, ANGLE OF— The angle through which the axis of mas-netism of the armature of a dvnamo-electric ma- chine is shifted by reason of the resistance its core offers to sudden reversals of magnetization. LAG, ANGLE OF, OF CURRENT— An .angle (whose ta^igent is equal to the ratio of the inductive to the ohmic re- sistance. An angle, the tangent of which is equal to the induc- tive resistance of the circuit, divided by the ohmic re- sistance of the circuit. LAG, MAGNETIC--A magnetic viscosity as manifested by the sluggishness with which a magnetizing force pro- duces its magnetizing effects in iron. 389 LAM LAMINATE© CORE— (See Core, Lamicaled.) LAMP, ALL-XIGHT — A term sometimes applied to a double-canbon arc lamp. LAMP, AEC, ELECTRIC— An electric lamp in which the light is produced by a voltaic arc formed between two or more car'bon electrodes. LAMP, CHAMBER OF— The glass bulb or chamiber of an incandescing electric lam-p in which the incandescing conductor is placed, and in w^hich is maintained a high vacuum. LAMP, ELECTRIC, ARC, DIFFERENTIAL— An arc lamp in 'Which the movements of the carbons are controlled by the differential action of two magnets opposed to each other, one of whose coils is in the direct 'and the other in shunt circujit around the carbons. LAMP, ELECTRIC, ARC, DOUBLE CARBON— An electric arc lamp provided with two pairs of carbon electrodes, so arranged that ^vhen one pair is consumed, the cir- cuit is automatically completed through the other pair. LAMP, ELECTRIC GLOW— A term employed mainly in Europe for an incandescent electric lamj). LAMP, ELECTRIC, INCANDESCENT— An electric lamp in which the light is produced by the electric Incandes- cence of a strip or filament of some refractory sub- stance, generally carbon. LAMP, ELECTRIC, INCANDIZSCENT, LIFE OF— The num- ber of hours that an incandescent electric lamp, when traversed by the normal current, will continue to af- ford a sfooci commercial lig'lit. LAW 390 LAMP, ELECTEIC, SAFETY— An incrindesoent electnc lamp, wth thoroughlv insulated leads, employed in mines, or other similar places, where the exjjlosive ef- fects of readily ignitable substances are to be fear?d. LAMP, ELECTRIC, SERIES CONNECTED INCANDES- CENT — An incandescent electric lamp adapted for use in series circuits. LAMP, ELECTRIC, INCANDESCENT, ELECTRIC FILA- MENT OF — A term now generally applied to the in- candescing conductor of an incandescent electric lamp, whether the same be of very small cross-section or of comparatively large cross-section. LAMP, PILOT — In systems for the operation of electric lamps, an incandescent lamp emplpj^ed in a station to indicate the difference of potenial at the dynamo terminals, bj^ means of the intensity of its emitted light. LAMP ROD— (See Rod, Lamp.) LAMPS, BANK OF— A term applied to a number of lamps, equal to about half the load, that were formerly placed in view of the attendant in circuit \vith a dyna- mo that is to be placed in a parallel circuit with another dynamo, one of the lamps of which is also in view. LAMPS, CARBONTNG—Placing carbons in electric arc lamps. LAUNCH, ELECTRIC— A boat, the motive power for which is electricity, suitable for launching from a ship. LAW, JACOBI'S— The maximum work done by a motor is reached when the counter-electromotive force is equal to one-half of the impres<^ed electromotive force. 391 LAW LAW. JOULE'S — The heating- power of a current is pro- portional to the product of the resistance and the square of the current strength. LAW, NATURAL — A correct expression of the order in which the causes and elfects of natural phenomena fol- low one another. LAW OF OHM, OTJ LAW OF CURRENT STRENGTH- -The strength of a continuous current is directly propor- tional to the dilference of potential or electromotive force in the circuit, and inversely proportional to the resistance of the circuit, i. e., is equal to the quotient arising- from dividing- the electromotive force by the resisftance. LAW, YOLTAMERIC— The chemical action produced by electrolysis in any electrolyte is proportional to the amount of electricity which pasf^es through the elec- trolyte. LAWS, LENZ S — Laws for determining the directions of currents produced by electrodynamic induction. The direction of the currents set up by electrodyna- mic induction is always such as to oppose the motions by whch such currents were produced. LAWS OF COULOMB, OR LAWS OF ELECTROSTATIC AND MAGNETIC ATTRACTIONS AND REPULSIONS. — I^aws for the force of attraction and repulsion be- tween charged bodies or between magnet poles. Tlie fact that the force of electrostatic attraction or repulsion between two charges, is directly proportional to the product of the qualities of electricity of the two charges and inversely proportional to the square of the distance between them, is known as Coulomb's Lonv. LEG 392 LAWS 01 JOULE — La^vs expressing the (le^elopnient ol heat produced in a circuit by an electric current. LEAD, AXGLE OF— The angular deviation from the nor- mal position, which must be given to the collecting- brushes on tlie commutator cylinder of a dynamo-elec- tric ujachine, in order to avoid destrucr/ive burning. LEAD OF BRUSHES OF DYXA^^LO-ELEC'l'lJlC MACHl^JE — Tiie angular deviation from the normal position, ■which it is necessary to give ihe brushes on Ihe com- mutator of a dynamo-elect tic nia chine, iji order to ob- tain t fTicient action. . LEADING TIOl^X OF POLE PIECES OF DYNA?10-ELEC- TEIC MACIITXE— (See Horns, Leading, of Pole Pieces of a Dynamo-Electric ^lachine). LEADIXG-IX WIKES— (See Wires, Leading-In). LEx\DS — The conductors in any system of electric distribu- tion. LEAKAGE, ELECTKIC— The gradual dissipation of a cur- rent due to insufficient insulation. LEAKAGE. MAGXEjl...— A useless dissipation of the lines of magnetic force of a dynamo-electric machine, or other similar device, by their failure to pass through the armature where they are needed. Useless dissipation of ]ines of magnetic force outside * that portion of the field of a dynamo-electric machine through which the armature moves. LECLAXCHE'S VOLTAIC CELL— (See Cell, Voltaic, Le- clanche). 393 L.IG LEG — In a system of telephonic exchange, where a ground return is used, a single wire, or, where a metallic cir- cuit is employed, two wdres, for connecting a subscriber with the niain switchboard, by means ot which any sub??criber may be legged or placed directly in circuit with two or more other parties. LEGAL OHM— (See Ohm, Legal). LENGTH OF SPAEK— (See Spark, Length of). LENZ'S LAW— (See Law, Lenz's). LEYDEN JAR Bx^TTERY— (See Battery, Leyden Jar). LIGHT, ELECTRIC— Light produced hy the action of elec- tric energy, LIGHT, MA.X WELL'S, ELETRO-MAGNETIC THEORY OF - — A hypothesis for the cause of light produced by Max-- w^ell, based on the relations existing between the phe- nomena of light and those of electro-magnetism. LIGHT, SEARCH, ELECTRIC~An electric arc light placed in a focusing lamp before a lens or mirror, so as to ob- tain either a parallel beam or a slightly divergent pen- cil of light for lighting the surrounding space for pur- poses of exploration. LIGHTER, CIGAR, ELECTRIC— An apparatus for electric- ally lighting a cigar. LIGHTING, ARC— Artificial illumination obtained by means of an arc light. The term arc lighting is used in contradistinction to incandescent lighting. LIGHTING, ELECl^RIC, CENTRAL STATION— The light- ing of a number of houses or other buildings from a single station, centrally located. 26 LIG 394 LIGHTING, ELECTKIC GAS— Igniting gas jets by means of electric discharges. LIGHTING, ELFXTRIC, ISOLATED— A system of electric lightipg where a separate electric source is placed in each house or area to be lighted, as distinguished from the central station lighting, where electric sources are provided for the production of the current required for an entire neighborhood. LIGHTNING— The spark or bolt that results from the dis- ruptive discharge of a cloud to the earth, or to a neigh- boring cloud. LIGHTNING AEKESTER— (See Arrester, Lightning). LIGHTNING, BACK-STROKE OF— An electric discharge, caused by an induced charge, which occurs after the direct discharge of a lightning fiash. LIGHTNING, CHAIN— A variety of lightning flash in which the discharge takes a rippling path, somewhat resem- bling a chain. LIGHTNING, FORKED— A variety of lightning flash, in which the discharge, on nearing the earth or other object, divides into two or more branches. LIGHTNING, GLOBULAR— A rare form of lightning, in which a. globe of Are appears, which quietly floats for a while in the air and then explodes with 'great violence. LIGHTNING, HEAT— A variety of lightning flash in which the discharge lights up the surfaces of tTie neighboring clouds. LIGHTNING, SHEET— A variety of lightning flash unac- companied by any thunder audible to the observer, in which the entire surfaces of the clouds are illuminated. I 395 LIN ^T^rHTNING, VOLCANIC— The lightning discharges that attend most volcanic eruptions. LIGHTNING, ZIGZx\G— The commonest variety of light- ning flashes, in which the discharge apparently as- sumes a forked zigzag, or even a chain-shaped path. LINE-— A wire or other conductor connecting any two points or 5?tations. LIXE, AERIAL — An air line as distinguished from an un- derOTOund conductor. LINE, AKTIFICIAL — ^A line so made up by condensers and resistance coils as to have the same inductive eHects on charging or discharging as an actual telegraph line. LINE, CAPACITY OF— The ability of a line or cable to act like a condenser, and therefore like it to possess a ca- pacity. LIXE CIRCUIT— (See Circuit, Line). LINE, NEUTRAL, OF A :MAGNET— A line joining the neu- tral points of a magnet or points approximately mid- way between the poles. LINE, NEUTR.VL, OF COMMUTATOR CYLINDER— A line on the commutator cylinder of a dynamo-electric ma- chine connecting the neutral points, or the points of maximum positive and negative difference of potential. LIXEMAN — One who puts up and repairs line circuits and attends to the devices connected therewith. LTXES, KAPP— A term proposed by Mr. Gisbert Kapp for a unit of lines of magnetic force. One Kapp lire equals 6,000 C, G. S. magnetic lines. LOG 396 LINES OF FOPiCE, CUTTING— (See Force, Lines of, Cat- ting). LINES OF FOPvCE, DIRECTION OF— (See Force, Lines of, Direction of). LINES OF MAGNETIC FORCE— (See Force, Magnetic, Lines of). ' LINES, OVERHEAD— A term applied to telegraph, tele- phone and electric light or power lines that run over- head, in contradistinction to similar lines placed un- derground, LINKS, FUSE — Strips or plates of fusible metal in the form of links, employed for safety fuses for incandescent or other circuits. LIQUID, ELECTROPOION— A battery liquid consisting oi 1 pound of bichromate of potash dissolved in 10 pounds of water, to which 2% pounds of commercial sulphuric acid has been gradually added. LIQUID, EXCIXTNG, OF VOLTAIC CELL The electro- lyte or liquid in a voltaic cell, which acts on the posi- tive plate. LOAD, LIQUID RESISTANCE— An artificial load for^ a dynamo-electric machine, consisting of a mass of liquid interposed between electrodes. LOCAL BATTERY— (See Battery, Local). LOCOMOTIVE, ELECTRIC— A railway engine whose mo- tive power is electricity. LOCOMOTIVE HEAD LIGHT, ELECTRTC-(See Head Light, Locomotive), 397 MAO LODESTONE— A name formerly applied to an ore or iron (magnetic iron ore), that naturally possesses the power of attracting pieces of iron to it. LOOP, ELECTEIC — A portion of a main circuit consisting- of a wire going out from one side of a break in the main circuit and returning to the other side of the break. M MACHINE, AEMSTEONG'S HYDRO-ELECTKIC— A ma- chine for the development of electricity by the friction of a jet of steam passing over a water surface. MxiCHIXE, DYXAMO-ELECTEIC— A machine for the con- version of mechanical energy into electrical energy, by means of magneto-electric induction. MACHINE, D YNA MO-ELECTRIC, ALTERNATING-CUR- RENT — A dynamo-electric machine in which alternat- ing currents are produced. MACHINE, DYNAMO-ELECTRIC, BI-POLAR— A dynamo- electric machine, the armature of which rotates in a field formed by two magnet poles, as distinguished from a machine the armature of which rotates in a field formed by more than two magnet poles. Mi\ CHINE, DYNAMO-ELECTRIC, CLOSED-COIL— A dyna- mo-electric machine, the armature coils of which are grouped in sections, communicating with successive bars of a collector, so as to be connected continuously together in a closed circuit. MACHINE, DYNAMO-ELECTRIC, CLOSED-COIL DRUM— A closed-coil dynamo-electric machine, the armature core of which is drum-shaped. . MAC 398 MACHINE DYNAMO-ELECTEIC, CLOSED-COIL RING— A elosed-coil dynaino-eleclric machine, the armature core of which is ring-shaped. MACHINE, DYNAMO-ELECTRIC, COMPOUND-WOUND— Machines whose field mai^nets are excited by more than one circuit of coils, or by more than a single electric sonrco. MACHINE, DYNA]NrO-ELECTRIC, CONTINUOUS-CUR- RENT — A dynamo-electric machine, the current of which is commuted so as to flow in one and the sam'3 direction, as distinguished from an alternating dynamo. MACHINE, DYNAMO-ELECTRIC, EFFICIENCY OF— The ratio between the electric energj^ or the electrical horse-power produced by a dynamo, and the mechani- cal energy or horse-power expended in driving the dynamo. MACHINE, DYNAMO-ELECTRIC, FLASHING OF— A name given to long flashing sparks at the commutator, due to the short circuiting of the external circuit at the com- mutator, by arcing over the successive commutator in- sulating strips. IMACHINE, DYNAMO-ELECTRIC, MULTIPOLAR— A dyna- mo-electric machine, the armature of \vhieh revolves in a field formed by more than a single pair of poles. MACHINE, DYNAMO-ELECTRIC, OPEN-COIL— A dynamo- electric machine, the armature coils of which, though connected to the successive bars of the commutator, are not connected continuously in a closed circuit. MACHINE, DYNAMO-ELECTRIC, OPEN-COIL RING— An open-coil dynamo-electric machine, the armature core *»! which is ring-shaped. ' 399 MAC MACHINE, DYNAMO-ELECTRIC, REVERSIBILITY OF— The ability of a dynamo to act as a motor when trav- ersed by an electric current. MziCHINE, DYNAMO-ELECTRIC, SEPARATELY EXCIT- ED — ^A dynamo-electric machine in wliich the field mag'net coils have no connection with the armature coils, but receive their currerit from a separate machine or source. MACHINE, DYNAMO-ELECTRIC, SERIES-AVOUND— A dynamo-electric machine, in wfiich the field circuit and the external circuit are connected in series with the armature circuit, so that the entire armatuire current must pr'Ss through the field coils. MACHINE, DYNAMO-ELECTRIC, SHUNT- WOUND— A dynamo-electric machine in which the field mag-net coils are placed in a shunt to the armature circuit, so that only a portion of the current generated passes through the field magnet coils, but all the difference of potential of the armature acts at the terminals of the field circuit. MACHINE, DYNAMO-ELECTRIC, SINGLE-MACxNET— A djmamo-electric machine, in which the field magnet poles are obtained by means of a single coil of insulated wire, instead of by more than a single coil. MACHINE. DYNAMO-ELECTRIC, SPARKING OF— An ir- regular and injurious operation of a dynamo-electric machine, attended \vitli sparks at the collecting brushes, MACHINE, DYNAMO-ELECTRIC, TO SHORT CIRCUIT A — To put a dynamo-electric machine on a circuit of comparatively small electric resistance. MAC 400 MACHINF, ELECTROSTATIC INDUCTION— A machine in which a small initial charge produces a greatly increas- ed charge by its inductive action on a rapidly rotated disc of glass or other dielectric. Mx*. CHINE, ERICTIONAL ELECTRIC— A machine for the development of electricity by friction. MACHINE, HOLTZ— A particular form of electrostatic in- duction machine. MACHINE, INDUCTOR— An alternating current dynamo in vs^hich the field magnet projections are all of the same polarity. MACHINE, MAGNETO BLASTING— A magneto-electric machine employed for generating the current used in electric blasting. MACHINE, MAGNETO-ELECTRIC— A machine in \\'hich there are no field magnet coils, the magnetic field of the machine being due to the action of permanent steel magnets. MACHINE, RHEOSTATIC— A machine devised by Plante in which continuous static effects of considerable in- tensity are obtained by charging a number of condens- ers in multiple-arc and discharging them in series. MACHINE, TOPPLER-HOLTZ— A modified form of Holtz machine in which the initial charge of the armatures is obtained by the friction of metallic brushes against the armatures. MACHINE, WIMSHURST ELECTRICAL— A form of con- vection electric machine invented by Wimshurst. 401 MAG MAGNET — A body possessing the power of attracting' the unlike pole of another magnet or of repelling the like pole; or of attracting readily magnetizable bodies like iron filings to either pole. A body possessing a mag- netic field. MAGNET, AKTIFICrAI.— A mag-net produced by induction from another magnet, or from an electric current. MAGNET, COMPOUND— A number of single magnets^ placed parallel and with thcif" similar poles facing one" another. MAGNET, DAMPING— Any magnet employed for the pur- pose of checking the velocity of motion of a moving body or magnet. MAGNET, ELECTEO— A magnet produced by the passage of an electric current through a (Toil of insulated wire surrounding a core of magnetizable material. MAGNET, ETECTl^O, HOHSESHOE- An electro-magnet, the core of which is in the shape of a horseshoe or U. MAGNET, ELECTKO, HUGHES'— An elecfro-magnet in which a U-sha]:)ed permanent magnet is provided with pole pieces of soft iron, on which only are placed the magnetizing coils. A quick-acting electro-magnet, in which the magnet- izing coils are placed on soft iron pole pieces that are connected with and form, the prolongations of flie poles of a permanent horseshoe magnet. MAGNET, ELECTRO, IRON-CLAD— An electro-magnet whose magnetizing coil is almost entirely surrounded by iron. MAGNET, HORSESHOE— A magneiized bar of steel or iron bent in the form of a horseshoe or letter U. MAG 402 MAGNET, IROJS'-CLAD— A mag-net who^e mag-netic resist- ance is lowered by a casmg" of iron connected with the core and provided for the passage of the lines of mag-- netic force. MAGXET, KEEPER OF—A mass of soft iron applied to the poles of a magnet throngh which its lines of magnetic force pass. MAGXET, PEPtMAXENT— A magnet of hardened steel or other paramagnetic snbstance which retains its mag- netism for a long time after being magnetized. MAGXET, POPTATIVF POWER OF—The lifting power of a magnet. MAGXET, RELAY — ^An electro-magnet, whose coils axe connected to the main line of a telegraphic circuit, and the movements of whose armature is employed to bring a local battery into action at the receiving station, the current of which operates the register or sounder. MAGXET, FIELD, OF DYXA:M0-ELECTRIC :^L\CHIXE— One of the electro-magnets employed to produce the magnetic field of a dynamo-electric machine. MAGXETIC ATTRACTTOX- (See Attraction, Magnetic). MAGXETIC CIRCTTIJ— (See Circuit, Magnetic). MAGXETIC DEXSITY— (See Density, Magnetic). MAGXETIC FIELD— (See Field, Magnetic). MAGXETIC LEAKAGE— (See Leakage, Magnetic). MAGXETIC LIXES OF FORCE— (See Force, Magrnetic Lines of). MAGXETIC POLES— (See Poles, :\ragnetic). O' 403 MAG MAGNETIC "RELUCTANCE— (See Reluctance, MaGrnetic). MAGNETIC UESTSTANCE— (See Eesistance, Magnetic). MAGNETIC STOEM— (See Storm, Magnetic). MAGNETIC WKT"RL- (See Whirls, Magnetic). MAGNETISM— That branch of science \^4iich treats of the nature and properties of magnets and the magnetic field. MAGNETISM, AMPERE'S THEORY OF— A theory or hypo- thesis proposed by Ampere, to account for the cause of magnetism, by the presence of electric currents in the ultimate particles of matter. MAGNETISM, ELECTRO— Magnetism produced by means of electric currents. MAGNETISM, EWING'S THEORY OF— A theory of mag- netism proposed by Prof. Ewing, based on the assump- tion of originally magnetized particles. MAGNETISM, HUGHES' THEORY OF— A theory pro- pounded by Hughes to account for the phenomena oi magnetism apart from the presence of electric currents. MAGNETISM, RESIDUAL— The magnetism remaining in the core of an electro-magnet on the opening of the magnetizing circuit . The small amount of magnetism retained by soft iron when removed from any magnetizing field. MAGNETISM, STRENGTH OF— A term sometimes used in the sense of intensity of magnetization. MAGNETIZABLE— Capable of being magnetized after the manner of a paramagnetic substance like iron. MAI 404 MAGNETIZATION— The act of calling out or of eDdomiig with inagnetic properties. M:\GNETTZATION, INTENSITY OF— A quantity showing the intensity of the magnetization produced in a sub- stance. A quantity showing the intensity with which a magnetizable substance is magnetized. MAGNETIZATION, TME-LAG OF— A lag which appear*i to exist between the time of action of the macfnetizing force and the appearance of the magnetism. The time which must elapse in the case" of a given paramagnetic substance before a magnetizing force can produce mag- netization. ' , MAGNETIZE — To endow with magnetic properties. MAGNETO-ELECTEIC BELL— (See Bell, Magneto-Electric) MAGNETO-ELECTEIC BKAKE— (See Brake, Magneto- Electric). MAGNETOMETER— An apparatus for the measurement of magnetic force, MAGNETO-MOTIVE FOECE— (See Force, Magneto-Motive) MAIN, ELECTBIC— The principal conductor in any system of electric distribution. ^EAIN, HOUSE — A term employed in a system of multiple incandescent lamp distribution for the conductor con- necting the house service conductors with a center of distribution, or with a street main. MAIN, STREET — In a system of incandescent lamp distri- bution the conductors extending in a system of net- works through the streets 'from junction box to junc- tion box, through which the current is distributed from the feeder ends, through cut-outs, to the district to be lighted, and from which service ^vires are taken. 405 MET MAKE-AND-BREAK, AUTOMATIC— A term sometimes em- ployed for si]ch a combination of contact points with the armature of any electro-mag*net, that the circuit is automatically made and broken with great rapidity". MARrS"EK'S COMPASS— (See Compass. Azimuth). MATERIALS, INSULATING— Xon-conducting- substances which are placed around a conductor, in order that it may either retain an electric charge, or permit the pas- sage of an electric current through the conductor with- out sensible leakage. ^MATTING, INAn:SIBLE ELECTBIC FLOOR— A matting or other -floor covering, provided with a series of electric contacts, which are closed by the passage of a person walking over them. :\rEDIUM, ELECT'EO-MAGNETIC— Any medium in which electro-magnetic phenomena occur, MEG OR MEGA (as a prefix)— 1,000,000 times; as, megohm, 1,000,000 ohms; megavolt, 1,000,000 volts. MEGOHM— 1,000,000 ohms. METALLIC CIRCUIT— (See Circuit, Magnetic). METALLOID — A name formerly applied to a non-metallic body, or to a body having only some of the properties of a metal, as carbon, boron, oxygen, etc. METALLURGY, ELECTRO— That branch of applied science which relates to the electrical reduction or treatment of metals. Metallurgical processes effected by the agency of electricitj'. METER, A:\rPERE— (See Ampere-Meter. Ammeter). MIC 406 METER, CUEREXT— A term now applied to an electric meter or galvanometer which measures the current in amperes, as '^isting'uished from one which measures the energ-y in watts. METER. ELECTRIC— Any apparatus for measuring com- mercially the quantity of electricity that passes in a given time through any consumption circuit. METER, ELECTRO-CHEMICAL— An electric meter in which the current passing is measured by the electro- lytic decomposition it etJects. METER, ELECTRO-MA€XETIC— An electric meter In which the current passing is measured by the electro- magnetic effects it produces. METER, E>TERGY~A term sometim.es applied to a watt meter. METER, MTLLT- AMPERE— An ampere meter graduated to read milli-amperes. METER, WATT — An instrument generally consisting of a galvanometer constructed so as to measure directly the product of the (rarrent, and the diiference of potential. MHO — A term proposed by Sir Wm. Thomson for the prac- tical unit of cond^lctivit^ . Such a unit of conductivity as is equal to the reciprocal of 1 ohm. MICA — A maneral substance employed as an insulator, MICA, MOL'LDED — An insulating substance consisting of finelj^ divided mica made into a paste, with some fused insulating substance, and moulded into any desired shape. 407 MOR MICRO (os a prefx) — The one-millionth; as, a microfarad^ the millionth of a farad; a microvolt, the one-millionth of a volt. MICEO-FAEA.I)— (See Farad, Micro). MTCEOPHONE— An apparatus invented by Prof. Hnghei? for rendering- faint or distant sounds distinctly audible, MIL — A unit of length eqiial to the 1-1000 of an inch, or .001 inch, used in measuring- the diameter of wires. MIL, CIECLTLAR — A unit of area emijloj-ed in measuring^ the areas of cross-sections in wires, equal to ,78540 square mil. The area of a circle one mil in diameter. MIL, SQUARE — A unit of area employed in measuring- the areas of cross-sections of wires, equal to .000001 square- inch. One square mil equals 1.2732 circular mil. MILLI (as a prefix) — The one-thousandth part. MILLI-AMPERE — The thousandth of an ampere. ]^^^^E, ELECTRO-CONTACT— a submarine mine that is fired automatically on the completion of the current of a battery placed on the shore through the closing of floating contact points by passing vessels. MIRROR GALVANOMETER— (See Galvanometer, Mirror). MORSE ALPHABET— (See Alphabet, Telegraphic: Morse's) MORSE RECORDER— (See Recorder, Morse). MORSE SYSTEM OF TELEGRAPHY— (See Telegraphy, Morse System of). MORSE'S TELEGRAPHIC ALPHABET— (See Alphabet^ Telegraphic: Morse's). MOT 408 MOTIOX, SIMPLE-HAI^MOXIC— Motion which repeats it- self at reg-ular intervals, taking- place backwards or for^vards, and ^vhich may be studied by comparison with nniform motion round a circle of reference. MOTOGRAPH, ELECTRO— A land speaking telephone in- vented hj Edison whereby -the friction of -a platinum point against a rotating cylinder of moist chalk, is re- duced b3" the passage of an electric current. JMOTOR, COMPOUXD-WOUND— An electric motor whose field magnets are excited by a series and a shunt wire. :M0T0R, ELECTRIC— a device for transforming electric jjower into mechanical power. MOTOR, ELi:CTRIC, ALTERXATIXG-CURREXT— An elec- tric motor driven or operated by means of alternating currents. MOTOR, ELECTRIC, DIRECT-CURREXT— An electric m.o- tor driven or operated by means of direct or continuous electric currents, as distinguished from a motor driven or operated bj' alternating currents. MOTOR, ELECTRIC, SLOW-SPEED— An electric motor so constructed as to run with fair efficiency at slow speed. MOTOR, PYROIVIAGXETIC— A motor driven by the attrac- tion of magnet poles on a movable core of iron or nickel unequally heated, MOTOR, ROTATES G-CURREXT— An electric motor design- ed for use with a rotating electric current. MOTOR, SERIES-WOUXD— An electric motor in which the field and armature are connected in series with the external circuit as in a series dynamo. , 409 NEB MOTOE, SHUXT-WOUXD— An electric motor in which the field magnet coils are placed in a shunt to the armature circuit. MULTIPHASE CURKENT— (See Current, Multiphase). IMUITIPHASE DYyA]\TO~(See Dynamo, Multiphase). MULTIPHASE SYSTE]M— rSee System, Multiphase). MULTIPLE-SEEIES— A multiple connection of series groups. N N. — A contraction employed in mathematical writings for the whole number of lines of magnetic force in any magnetic circuit. N. — A contraction for Xorth Pole. KEEDLE, .^STATIC— A compound magnetic needle of great sensibility, possessing little or no directive power. An astatic needle consisting of two separate magnet- ic needles, rigidly connected together and placed par- allel and directly over each other, with opposite poles opposed. NEEDLE, MA.GNETIC— A straight bar-shaped needle of magnetized steel, poised near or above its center of gravit}^ and free to move either in a horizontal plane only, or in a vertical plane only, or in both. NEEDLE, MAGNETIC, DAMPED— A magnetic needle so placed as to quickly conie to rest after it has been set in motion. NEEDLE, MAG^'ETIC, DECLINATION OF— The angular deviation of the magnetic needle from the true 'geo- graphical north. The variation of the magnetic needle. 21 NIC xiO NEEBLE, ^sIAGXE'nC, DEFLECTIOX OF-The moTement of a needle out of a position of rest in the earth's mag- nelie field or in the field of another mag-net, bj' the action of an electric current or another Jiag'net. XEEDT.E, ^^FACyETIC, DIPPIXG— A raagneic needle sus- pended so as to be free to inove in a vertical plane, em- ployed to determine the angle of dip or the magnetic inclination. NEEDLE, Mx^GXETIC, DIRECTIVE TEXDEXCY OF— The tendency of a magDctic needle to mo^e so as to come to rest in the direction of the lines of the earth's mag- netic Held. NEEDLE, TELEGEAPinC— A needle employed in telegra- phy to represent by its movements to the left or right respectively the dots and dashes of the MorSe alphabet. XEGATIVE ELECTPODE— (See Electrode, Xegative). XEGATIVE ELE:SIFXT OF A VOLTAIC CELL— (See Ele- ment, Xegative, of a Voltaic Cell). X^EGATIVE FEEDEPS— (See Feeders, Xegative). XEGATIVE POLE— (See Pole. Xegative). XEUTRA]. FEEDER— The feeder that is connected with the nentral or intermediate terminal of the dynamos in a three-wire system of distribution. NEETRAL LINE OF CO:\nrrTATOP C^T.IXTDER— (See Line, Xentra], of Commntator Cylinder). XELTTRAL POTXT— (See Point, Xentral). NEUTRAL POIXTS OF DYX'A:NrO-ELECTRIC :NrACHIX&- (See Points, Xentral, of Dynamo-Electric Machine). NICKJ5L-PLATIXG-(See Plating, Xicl>-el). 411 OIL NOX-COXDUCTOES — Substances that olTer so o-reat resist- ance to the passage of an electric current through their mass as to practically exclude a discharge passing throuefh them. OHM — The unit of electrical resistance. Such a resistance as would limit the flow of electric- it^' under an electromotive force of one volt to a cur*^ rent of one ampere, or to one coulomb per second. OIIAr, B. A.- -A contraction for British Association ohm. OHM, BOAED OF TRADE— A unit of resistance as deter- mined by a committee of the English Board of Trade. Oinr, BP.ITISn ASSOCTATIOX— The British Association unit of resistance, adopted prior to 1884. OH^Nf, LEG AT.,— The resistance of a column of mercury 1 square millimetre in area of cross-section, and 106 centi- metres in length, at the temperature of degree C. or 22 degrees F, OHM, MEG— One million ohms. OHMTC RESISTAXCE— (See Resistance, Ohmic or True). OHMIMETER — A commercial galvanometer, devised by x\yr- ton. for directly measuring by the deflection of a mag- netic needle, the resistance of any part of a circuit through which a strong current of electricity isflo^Wng. OHM'S LAW— (^ee Law of Ohm). OILJLXSULATOR— (See Insulator, Oil). OIL TRANSFORMER— (See Transformer, Oil). PAR 412 OPE^^-CIRCUIT VOLTAIC CELT.-(See Cell, Voltaic, Open- Circuit). OPEN-CIRCUITED— Put on an open circuit. ^ OPEX-COIL DRT::\r dynamo-electric :\L\CITINE— (See Machine, Dynamo-Electric, Open-Coil Drum). OSCILLATIONS, ELECTRIC— The series of partial, inter- mittent di«^char5res of which the apparent instantane- ous discharge of a Leyden jar through a small resist- ance actually consists. OSMOSE, ELECTRIC— A differeuce of liquid level between two liquids on opposite sides of a diaphragm produced by the passage of a strong electric current through the liquid? between two electrodes placed therein. P. D. OR p. d. — A contraction frequently employed for dif- ference of potential. PACINOTTI RING- (See Ring, Pacinotti). PAIR, ASTATIC — A term sometimes applied to an astatic couple. PAPAEFINE — A name given to various solid hydrocarbons of the marsh gas series, that are derived from coal or petroleum by the action of nitric acid. PARAMAGNETIC — Possessing properties ordinarily recog- nized as magnetic. Possessing the power of concen- trating the lines of magnetic force. PARAMAGNETIS^NT — The magnetism of a paramagnetic substance. 413 PHA PETTIEK EFFECl — (See Effect, Peltier). PENDANT, ELECTRIC— A hangino- fixture provided with a sooV.et for the support of an incandescent lamp. PENDANT, FLEXIBLE ELECTPvIC LKiHT— V pendant for an incandescent lamp formed by the flexi15!e conductors which support the lamp. PENDULUM, ELECTKIC— A pendulum so arranged that its tto-ajid-fro moftdon send electric impulses over a line, either by makinof or breaking contacts. PFT^IODIC CUIiPENT, POWER OF— The rate of transform^ ation of the energy of a circuit traversed hy a simple periodic current. PERIODICITY- The rate of chamge in the alterations or pulsations of an electric current. PERMANENT MAGNET VOLTMETER-^ (See Voltmeter, Permanent Magnet). PERMEABILITY CURVE— (See Curve, PermeabiUty). PERMEABILITY, MAGNETIC— Conductibility for lines of magnetic force. The ratio existing between the magnetization pro- duced, and the magnetizing force producing such ma^*- netization. PERMEAMETER— An apparatus devised by S. P. Thomp- son for roughly measuring the magnetic permeability. PHASE, ANGLE OF DIFFFRENCE OF, BETWEEN AL- TERNATING CURRENTS OF SAME PERIOD- The angle which measures the shifting of phase of a simple periodic current with respect to another due to lag or other cause. PHO 414 PHASE, SHIFTING OF, OF ALTERXATING CURRENT— A chansre ir. pJiase of current due to magnetic lag or other causes. PHONE — A term frequently used for telephone. PHONOGRAM — A record produced by the phonograph. PHONOGRAPH — An apparatus for the reproduction of ar- ticulate speech, or of sounds of any character, at any indefinite time after their occurrence, and for any nnnjber of times. PHOSPHORESCENCE, ELECTRIC — Phosphorescence caused In a substance b}" the passage of an electric dis- charge. PHOSPHORESCENCE, PHYSICAL— Phosphorescence pro- duced in matter hy the actual impact of light wave? resulting in a vibratory motion of the molecules of suf- ficient rapidity to cause them to emit light. PHOSPHORUS— El^ECTRIC S:MELTING OF— An electric process for the direct pror'uction of phosphorus. PHOTO^IETER — An apparatus for measuring the Intensity of the light emitted by any luminous source. PHOTOMETER. ACTINIC— A photometer in which the in- tensity of any light is measured b^^ the amount of chemical decomposition it ellects. PHOTOMETER, DISPERSION— A photometer in w^hieh the light to^be measured is decreased in intensity a known amount so as to more readily permit it to be compared with a standard light of much smaller intensity. PHOTO^METER, SHADOW— A photometer in which the in- tensity of the light to be measured is estimated by a comparison of the distances ai which it cr.^i a standard light produce a shadow of ihe same intensity. 115 PIT PHOTOMETER, T"RANSLUCENT DISC— A photometer in which the light to be measured is placet! on one side of a partly translncent and partly opaqne disc, and a standard candle is placed on the opposite side, and the mtensit}' of the light estLmated by the distaiices of the light from the disc when an equal illumination of all parts of the disc is obtained. PHOTOPHONE— An instrument invented by Bell for the telephonic transmission of articulate speech along a ray of light instead of along a conducting wire. PIECES, POLE, OF DYNAMO-ELECTEIC MACHINE— Masses of iron connected with the poles of the Held magnet frames of dynamo-electric machines, and shap- ed to conform to the outline or contour of the armature. PILE, DRY — A voltaic pile or battery consisting of nu- merous cells, the voltaic coupl'e in each of w^hich con- sists of sheets of paper covered wdth zinc-foil on one disc and black oxide of manganese on the other. PILE, TIIEEMO, DIEFEPvEXTIAL— A thermopile in which the tw^o opposite faces are exposed to the action of two nearly equal sources of heat in order to deternnne accurately the differences in thermal in- iensities of such sources of heat. PILE, TriEHMO-ELECTPIC— A number of separate ther- mo-electric couples, united in series, so as to form a single thermo-electric source. PILOT LAMP— (See Lamp, Pilot.) PIN, INSULATOR— A bolt by means of which an insulator is attached to the telegraphic support or arm. PITH BALL- (See Balls, Pith.) ^LA 416 PLANE, PROOF — A sraall insulated conductor employed to take test charg-es from the surfaces of insulated, charged conductors. PLAT — ^A word sometimes used for installation, or for the npparntus required to carry on any manufacturing operation. PLANTS, ELECTETCITY OF— Electricity produced natur- ally by plants during their vigorous growth. PLATTE, NEGATIYF, OF STORAGE CELL— Tliat place of a storage cell which, by the action of the charging current, is converted iuto or partly covered with a coating of spongy lead. PLATE, NEGATIVE, OF VOLTAIC CELL— The electro- negative eleruent of a voltaic couple. That element of a voltaic couple \\'hich is negative in the electrolyte of the cell. PLATE, POSITIVE, 01' STORAGE BATTERY— That plate of a storage battery which is converted into, or covered by, a layer of lead peroxide, by the action of the charging current. That plate of storage battery which is connected with the positive terminal of the charging source and which is, therefore, the positive pole of the battery on discharging. PLATE, I'^OSITIVE. OF VOLTAIC CELL— The electro- positive in the electrolyte of the cell. PLATES OF SECONDARY^ OR STORAGE CELL, FORM- ING OF — Obtaining a thick coating of lead peroxide on the lead plates of a storage battery, by repeatedly sending the charging current through the cell alter- nately in opposite directions. 417 PLU PLATING, ELECTED— The process of coveriug- any elec- trically conducting- surface with a metal by the aid of the electric current. PLATING, NICKEL— Electro-plating- with nickel. PLATING, SILYEE— Electro-plating- A^ath silver. PLOW — The sliding- contacts connected to the motor of an electric street car, and placed within the slotted underground conduit, and provided for the purpose of taking- ofP the current from the electric mains placed therein, as the contacts are pushed forward over them by the motion of the ('ar. PLUG— A piece of metal in the shape of a plug-, provided for making- or breaking- a circuit by placing* in, or re- moving- from, a conical opening- formed in the ends of two closely approached pieces of metal which are connected with the circuits to be made or broken. PLUG, SAFETY— A wire, bar, plate or stripe of readily fus- ible metal, capable of conducting-, without fusing, the current ordinarily employed on the circuit, but which fuses, and thus breaks the circuit, on the passage of an abnormal current. PLUG, SHORT-CTECUITING— A plug by means of which one part of a circuit is cut out by being" short-cir- cuited. PLL^G, WALL — A plug pro\'ided for the insertion of a lamj) or other electro-receptive device in a wall soc- ket, and thus connecting it with a lead. PLUCKS, GEIB— Plugs of active material that fill the spaces or apertures in the lead grid or plate of a storage bat- tery. POL -^^^ PLUNGE BATTEEY— (See Battery, Plunge.) POINT, CAKBON— A term formerly applied to the car- bon electrodes used in the production of the voltajc arc. POTNTTS, NEUTEAI. OE DYNAINIO-T-'LECTEIC MACHINE —Two points of greatest difierence of potential, sit- L^ated on tLe commntator c^iinder, at the opposite ends of a diameter thereof, at which the collecting- brushes m.nst rest in order to carry off the current quietly. POLAPvlTY, :MAGNETIC— The polarity acquired by a mag-netizable • substance when brought into a mag- netic fjeld. POLARIZATION— A counter E. :NL F. produced by the pas- sage of a current, through an electric couple or battery. POIAEIZED AB:MATURE— See Armature, Polarized. POLE CHANGER— A switcli or ] portion al to the resistance when the current is con- stant. POTENTIAL, MAGNETIC— The amount of work required to bring- uj) a unit north -seeking magnetic pole from an inlinite distance to a given point ii^. a magnetic field. POTENTIAL, UxN^IT DIEFERENCE OF— Such a difference of potential between two points that requires the ex- penditure of one erg of work to bring a unit of posi- tive electricity^ from one of these points to another, against the electric force. (See Erg.) The practical unit of difference of potential is the volt. POTENTIOMETER— An apparatus for the galvanometer measurement of electromotive forces, or differences of potential, by a zero method. POWER— Eate of doing work. Mechanical power is generally measured in horse power, which is equal to w^ork done at the rate of 550 foot-pounds per second. POWER, CANDLE— An intensity of light emitted from a luminous body equal to the light produced by a stand- ard candle. POWER, CANDLE, NOAIINAL— A term sometimes applied to the candle-power taken in a certain favorable direc- tion. This term is generally used in arc lighting. In the ordinary arc lamp the greatest amount of. light is emitted at a particular point, viz: from the crater ii? the upper or positive carbon. PRI 4225 POWER, CANDLE, SPHERICAL— The average or mean value of candle pov^^er taken at a number of points around the source of lig-ht. POWER, CONDUCTING, FOR ELECTRICITY -The ability of a given length and area of cross-section of a sub- stance to conduct electricity, as compared with an equal length and area of cross-section of some other substance, such as pure silver or copper. POWER, ELECTRIC— Power developed by means of elec- tricity. POWER, ELECTRIC, DISTRIBUTION OF— The distribu- tion of electric power by means of any suitable system of generators, connecting circuits and electric motors. POWER, ELECTRIC TRANSMISSION OF— The transmis^ sion of mechanical energy by converting it into elec- tric energy at one point or end of a line, and recon- verting at some distant point from electrical to me- chanical energy. POWER, HORSE— A rate of doing work equal to 550 foot- pounds per second, or 33,000 foot-pounds per minute. POWER, HORSE, ELECTRIC— Such a rate of doing electric work as is equal to 746 watts per second. This rate is equivalent to 33,000 foot-pounds per min- ute, or 550 foot-pounds per second. POWER, PROJECTING, OF MAGNET— The power a mag- net possesses of throwing or projecting its lines of magnetic force across an intervening air space or gap. PRESSURE WIREvS— (See Wires, Pressure). PRIMARY COIL— (See Coil, Primary). ^ 423 QUA PRIMARY, THE— That conductor in an induction coil, or transformer, v.hich receives the impressed electromo- tive force, or which carries the inducing- current. PRIME CONDUCTOR— (See Conductor Prime). PROXY BRAKE— (See Brake, Prony). PLT^L, ELECTRIC BELT— A cir^.uit-closing- de\ice operated by a pull. PULSATUSTG CURRENT— (See Current, Pulsating). PUMP, AIR, MERCURIAL— A device for obtaining a high vacuum by the use of mercury. PUMP, AIR, SPRENGEL^S MERCURIAL— A mercurial air pump in which the vacuum is obtained by means of the fall of a stream of mercury. PUSH — A name sometimes applied to a push button, or to a floor push. PUSH BUTTON— (See Button, Push). PYRO-ELECTRICITY— (See Electricity, Pyro). PYROMETER, SIEMEN'S ELECTRIC— An apparatus for the determination of temperature by the measurement of the electric resistance of a platinum wire exposed to the heat whose temperature is to be measured. QUADRATURE, IN— A term employed to express the fact that one simple periodic quantity lags 90 degrees be- hind another. QUANTITY, UNIT OF ELECTRIC— A definite amount or quantity of electricity called the coulomb. BAI 424 R, — A contraction used for ohmic resistance. RADIATION, ELECTEO-MAGNETIC— The sending ot:-; in all directions from a conductor, through which an os- cillating discharge is passing, of electro-magnetic waves in all respects similar to those of light except that they are of mnch greater length, EAILKOAD, ELECTRIC— A railroad, or railway, the cars on which are driven or propelled by means of electric motors connected with the cars. RAILROADS, AUTOMATIC ELECTRIC SAFETY SYSTEM FOR — A system for automatically preventing the ap- proach of two trains at any speed beyond a predeter- ing safety from collisions of moving railroad trains by dividing the road into a number of blocks or sections of a given length, and so maintaining telegraphic com- munication between towers located at the ends of each of such blocks as to prevent, by the display of suitable signals, more than one train or engine from being on the same block at the same time, IcAILROADS, ELECTRIC, CONTINUOUS OVERHEAD SYSTEM OF MOTIVE POWER FOR— A variety of the dependent system of motive power for electric railroads in which a continuous bare conductor is connected with the terminals of a generating dynamo, and supported overhead by suitable means, and a traveling wheel or trolley is moved over the same by the motion of the car, in order to carry ofE the current from the line to the car motor. 425 RAl RAILrvOADS, ELECTKIC, CONTINUOUS SURFACE SYS- TEM OF MOTIVE POWEK FOR— A variety of the de- pendent system of mqtive power for electric railroads, in whicli the terminals of the generating- dynamo are connected to the continuous bare metallic conductor that extends along- the entire track on the s^irface of the roadway or street, and from which the current is taken off by means of a traveling* conductor connected with the moving- car. RAILROADS, ELECTRIC, CONTINUOUS UNDERGROUND SYSTEM OF MOnVE POWER FOR— A variety of the dependent system of motive power for electric raih ways, in which a continuous bare conductor is placed underg-round in an open slotted conduit, and the cur- rent taken off from the same by means of sliding or roiling contacts carried on the moving car. RAILROADS, ELECTRIC, DOUBLE-TROLLEY SYSTEM FOR — A. system of electric railroad propulsion, in which a double trolley is employed to take the driving cur- rent from two overhead trolley wires. RAILROADS, ELECTRIC, INDEPENDENT SYSTEM OF MOTIVE POWER FOR— A term for the electric pro- pulsion of railway cars by means of primary or storage batteries placed on the car and directly connected with the motor, KAILROADS, ELECTRIC, SINGLE-TROLLEY SYSTEM— A system of electric railroad propulsion in which a single trolley is employed to take the driving current from a single overhead trolley wire. 28 EEC 426 KAY, ELECTRIC— A species of fish named the ray, which, like the electric eel, possesses the power of producing electricity. EECETYEE, liATaiOXIC— A receiver, employed in systems of harmonic teleg-raphy, consisting of an electro-mag- netic reed; tnned to \ibrate to one note or rate only. EECEIVEK, PTIONOGEAPHIC— The apparatus employed m a telephone, phonograph, graphophone or gramo- phone for the reproduction of articulate speech. EECEIVER, TELEPHOXIC— The receiver employed in the telephone. EECOED, GEAMOPHONE— The irregular indentations, cut- lings or tracings marie by a point attached to the dia- Xohragm spoken against, and employed in connection with the receiving diaphragm for the reproduction of articulate speech. EECOEDEE, CHEMICAL, BAIX'S— An apparatus for re- cording the dots and dashes of a ^lorse telegraphic dis- patch, on a sheet of chemically prepared paper. EECOEDEE, MOESE— An apparatus for automatically re-, cording the dots and dashes of a Morse telegraphic dis- patch, on a fillet of paper drawn under an indenting or marking* point on a striking lever, connected ^\ath the armature of an electro-magnet. EECOEDEE, SIPHOX— An apparatus for recording in ink on a sheet of paper, by means of a fine glass siphon supported on a fine wire, the message received over a cable. EECTIFIED — Turned in one and ^* same direction. 427 EEL EEFLECTTNG GALVANOMETER— (See Ualvanometer, Re- !lectinf»") , REGISTER, TELEGRAPPITC— An apparatus employed at the receiving- end of a telegraphic line for the purpose of obtaining- a permanent record of the telegraphic dispatch. REGISTER, WATCHMAN'S ELECTRIC— A device for per- manently recording the time of a watchman's visit to each of the different localities he is required to visit at stated intervals. REGULATION, AUTOMATIC, OF DYNAMO-ELECTRJC [MACHINE — Such a regulation of a dynamo -electric machine as will automaticall\ present constant either the current or the potential difference. REGULATION, HAND- Such a regulation of a dynamo- electric machine as ^vill preserve constant, either the current or the potential, said regulation being etfected by hand as distinguished from automatic regulation. REGULATOR, AUTOMATIC— A device for securing auto- matic regulation as distinguished fromhand regulation. KELAY — An electro-magnet, employed in systems of tel- egrapliy, provided with contact points placed on a deli- cately supported armature, the movements of which throw a battery, called the local battery, into or out of the circuit of the receiving apparatus. RELAY, DIFFERENTIAL— A telegraphic relay containing two differentially wound coils of wire on its magnet cores. RELAY MAGNET — A name sometimes given to a relay. KES 428 RELAY, MICEOPHONE— A devnee for autoinatically repeat- ing- a telephonic message over another wire. RELAY, POLAKTZED-A teleoTaphle relay provided ^vith a permanently magnetized armature in piace of the soft iron armature of the ordinary instrument. RELUCTANCE, MAGNETIC—A term recently proposed in place of magnetic resistance to ex:press the resistance offered by a medium to the passage through its mass of lines of magnetic force. RELUCTANCE, MAGNETIC, UNIT OF- -Such a magnetic reluctance in a closed circuit that i)ermits unit mag- netic flux to traverse it under the action of unit mag- neto-motive force. REPEATERS, TELEGRAPHIC-Telegraphic devices v.here- hy the relay, sounder or regiotering apparatus, on the opening and closing of another circuit, ^^itli which it is .suitably connected, is caused to repeat the signals re- ceived. REPULSION, ELECTRO-DYNAMIC— The mutual repulsion between two electric circuits whose currents are flow- ing in opposite directions. REPULSION, ELECTRO-MAGNETIC-The mutual repul- sion produced by two similar electro-magnetic poles. REPULSION, ELECTROSTATIC— The mutual repulsion produced by two similar electric cliarges. REPULSION, MAGNT:TIC— The mutufil repulsion exerted between two similar magnetic poles. RESIDUAL MAGNETISM— (See Magnetism, Residual). ^29 REa EESIN — A g'eneial terni applied to a variety of dried juices of vegetable orififin. RESISTANCE — Something- placed in a oircr.it for the pur- jjose of opposing* the passag-e or fiow of the current in the circuit or branches of the circuit in which it is placed. The electrical resistance of a conductor is that quality of the conductor in virtue of which there is a fixed nu- merical ratio between the potential difference of the two opposing- faces of a cubic unit of such conductor, and the quality of electricity which traverses either face per second, assuming- a steady flow to take place normal to these faces, and to be uniformly distributed over them, such flow taking* place solely by an electro- motive force outside the volume considered. RESISTANCE, ABSOLUTE UNIT OF— The one thousand millionth of an ohm. RESISTANCE POX— (See Box, Resistance). RESISTANCE COIL— (See Coik Resistance). RESISTANCE, EFFECT OF HEAT ON ELECTRIC— Nearly all uietallie conductors have their electric resistance increased by an increase of temperature. The carbon conductor of an incandescent electric lamp, on the contrary, has its resistance decreased when raised to electric incandecsence. The decrease amounts to about three-eig-hths of its resistance when cold. RESISTANCE, ELECTRIC— The ratio between the electro- motive force of a circuit and the current that passes therein. The reciprocal of electrical conductivity. RES 430 EESISTAXCE, ELECTKIC, OF LIQUIDS— The resistance oft'eied by a liquic} mass to the passage of an electric ciirrent. As a rule the electric resistances of liquids, with the single exception of mercury, are enormously higher than tlxose of metallic bodies. r.ESISTAXCE, FALSE— A resistance arising from a coun- ter electromotive force and not directly from the di- mensions of the circuit, or from its specific resistance. RESISTANCE, IXDUCTIVE— A resistance which possesses self-induction. RESISTANCE, IXSULATIOX— The resistance of a line or conductor existing between the line or conductor and tlie earth through the insulators, or between the two wires of a cable through the insulating material sepa- rating them. RESISTANCE, MAGNETIC— The reciprocal of magnetic permeability or conductibility for lines of magnetic . force. Resistance offered by a medium to the passage of the lines of magnetic force through it. RESISTANCE, NON-INDItCTIYE— A resistance in which self-induction is practically absent. RESISTANCE, OPIMIC^-The true resistance of a conductor due to its dimensions and specific conducting power, as distinguished from the spurious resistance produced by a counter electromotive force. RESISTANCE, OR CELL, SELENIUM-^A mass of crystal- line selenium, the resistance of ^vhich is reduced by placing it in the form of narrow strips between the edges of broad conducting plates of brass. b 431 RHE RESIST AN^CE, SECONDARY-^A lerm sometimes used in place of external secondary resistance. RESISTxVA^CE, SPECIFIC— ^nie particular resistance wliich a substance offers to the passag-e of electricity throuf^rh it. RESISTANCE, UNIT OF— Snch a resistance tEat unit dif- ference of potential is required to cause a current of unit strength to pass. (See Ohm). RESOXAXCE, ELECTRIC— The setting up of electric pulses in open-circinted conductors, hj the action of pulses in neighboring conductors. RESONATOR, ELECTRIC— An apparatus employed by Hertz in his investigations on electric resonance. RESULTAXT--In mechanics, a single force that represents in direction and intensity the ei?ects of tv^o or more separate forces. RETARDATION- A decrease in the speed of telegraphic signaling' caused either by the induction of the line conductor on itself, or by mutual induction between it and neighboring conductors, or by condenser action, or by all. REVERSIP>ILITY OF DYNAMO— The ability of a dynamo to operate as a motor when traversed by an electric current. REVERSING IvEY—fSee I\ey, Reversing). RHEOSTAT— An adjustable resistance. A rheostat enables the current to be brought to a standard, i. e., to a fixed value, b3^ adjusting the resist- ance; hence the name. RUK 432 RHEOSTAT, WATEK— A rheostat the resistance of which is obtained by means of a mass of water of fixed di- mensions. KING PACINXOTTI— A kind of grame ring- containing- spaces or grooves for wire bobbins formed in the iron of the ring. ROCKEE, BRUSH — Tn a djnamo-electric machine or elec- tric motor, any device for shifting- the position of the brushes on the commutator cylinder. ROD, CLUTCH — A clutch or clamp provided in an arc lamp to seize the lamp ro'd and thus arrest its fall, during feeding, beyond a certain point. ROD, LAMP — A metallic rod provided in electric arc lamps for holding the carbon electrodes. ROD, LIGHTIS'IXG— A rod, or wire cable of good conduct- ing material, placed on the outside of a house or other structure, in order to protect it from the effects of a lightning discharge. ROD, LTGHTXTXG, POINTS ON— Points of inoxidizable material, placed on lightning rods, to effect the quiet discharcre of a cloud by convection streams. ROSETTE — An ornamental plate provided with contacts connected to the terminals of the service wires, and placed in a wall for the ready attachment of the in- candescent lamp. A word sometimes used in place of rose. ROTARY-PHASE CURRENT— (See Current, Rotating). ROTATING CURRENT— (See Current, Rotating). RUHMKORFF COIL— (See CoiL Rhumkorff). ■iHo SEO s S. — A contraction employed for second. SATE RATION, ]\rAGNETIC— The maximum mag-netization which can be imparted to a mag-hetic substance. The condition of iron, or other paramagnetic sub- stance, when its intensity of mag'netization is so great that it fails to be further sensibly magnetized by any magnetic force, however great. SCALE, THEElMO:\rETER, CEXTTGRADE— A thermometer scale, in which the length of the thermometric tube between the melting point of ice and the boiling point of water is divided into one hundred equal parts or degrees. SCALE, THE"R]^rOME7•ER, FAHEEXHEIT'S— A thermom- eter scale in which the length of the thermometer tube between the melting point of ice and the boiling point of water is divided into 180 equal parts called degrees. SCREEX, :>.rAGNETIC— A hollow box whose sides are made of thick iron, placed around a magnet or other body so as to cut it ofl- or screen it from any magnetic field external to the box. SCREENING, MAGNETIC— Preventing magnetic induction from taking place by interposing a metallic plate, or a closed circuit of insulated wire, between the body pro- ducing the magnetic field and the body to be mag- netically screened. SECOND, WATT— A unit of electrical work. SECONDARY BATTERY— (See Battery, Secondary). ^Kit 434 SECONDARY COIL— (See Coil, Secondary). SECOXDARY, MOVABLE— The secondary conductor of an induction coil, which, irstead of being- fixed as in most coils, is movable. SECTION, TROLLEY- A sing-le continuous length of trol- ley wire, with or without its branches. SEISMOGRAPH, MICRO— An electric apparatus for photo- graphically resfistering* the vibrations of the earth pro- duced by earthquakes or other causes. SELENIUM — A comparatively rare element generally found associated with sulphur. SELENIUM CELL— (See Cell, Selenium). SELE-INDUCTION— (See Induction, Self). SEMAPHORE — A variety of signal apparatus employed in railroad block systems. SEPARATOR — An insulating sheet of ebonite, or other similar substance, corrugated and perforated so as to conform to the outline of the plates of a storage bat- tery, and placed between them' at suitable intervals, in such a manner as to avoid short-circuiting, without impeding the free circulation of the liquid. SERIES, CONTACT— A series of metals arranged in such an order that each becomes positively electrified by \ contact with the one that follows it. SERIES DISTRIBUTION OF ELECTRICITY BY CON- STANT CURRENTS— (See Electricity, Series Distribu- tion of, by Constant Current Circuit), 435 SHU SEETES, THERMO-ELECTRIC— A list of metals so arrang- ed according to their thermo-electric powers, that each metal in the series is electro-positive to any metal lower in the list. SERIES TURNS OF DYNAMO-ELECTRIC MACHINE— (See Turns, Series, of Dynamo-Electric Machine). SERIES WINDING— (See Winding, Series). SERIES-WOUND DYNAMO- (See Dynamo, Series). SHELLAC — A resinous substance possessing valuable insu- lating properties, which is exuded from the roots and branches of certain tropical plants. SHOCK, ELECTRIC— The physiological shock produced in an animal bv an electric discharo-e. SHORT-CIRCUIT— To establish a short circuit. SHUNT — An additional path established for the passage of an electric current or discharge. SHUNT — To establish an additional path for the passage of an electric current or discharge. SHUNT CIRCUIT— (See Circuit, Shunt). SHUNT DYNAMO-ELECTRIC MACHINE— (See Machine, Dynamo-Electric, Shunt-Wound) . 5^HUNT, GALVAN01\[ETER— A shunt placed aroimd a sen- sitive galvanometer for the purpose of protecting it from the effects of a strong current, or for altering its sensisbility. SHUNT, MAGNETIC— An additional path of magnetic ma- terial provided in a magnetic circuit for the passage of the lines of force. SPA 436 SHUTTLE AKMATTJRE— (See Armature, Shuttle.) SILVER TLATTNG— (See Plating, Silver.) SIPHON, ELECTRIC-— A siphon in which the stoppage of flow, due to the gradual accunanlation of air, is pre- vented by electrical means. SMELTESG, ELECTRO— The separation or reduction of metallic substances from their ores by means of electric currents. SXAP SWITCH— (See Switch, Snap.) SOCKET, ELECTRIC LAMP— A support for the reception of an incandescent electric lamp. SOCKET, WALL — A socket placed in a w^all and provided with, openings for the insertion of a wall plug with w^hich the ends of a flexible twin-lead are connected. SOLENOID — A cyclindrical coil of wire the convolutions of which are circular. An electro-magnetic helix. SOLENOID CORE— The core, usually of soft Iron, placed within a solenoid and magnetized by the magnetic field of the current passing through the solenoid. SOLUTION, BATTERY— The exciting liquid for voltaic cells. (See Cell, Voltaic.) SOURCE, ELECTRIC — Any arrangement capable of main- taining a difl'erence of potential or an electromotive force. SPARK COIL— (See Coil, Spark.) SPARK, GAI»— (See Gap, Spark.) 437 STA SPARKI^G, LTXE OF LEAST— The line on a commutator cylinder of a dynamo connecting the points of contact of the collecting briishea where the sparking is a mini- mum. SPAEKIXG OF DYXA:M0-ELECTKIC MACHIXE— (See Ma^ chine, Dynamo-Electric, Sparking of.) SPECIFIC IXDITCTIVE CAPACITY— (See Capacity, Speci- fic. SPHEEICAL AE:NrATUKE— (See Armature, Spherical.) SPIDEE, AEMATITKE- A light framework or sketetou consisting of a central sleeve or hub keyed to the arma- ture shaft, and provided with a number of radial spokes or arms for fixing or holding the armature core to the d,yna mo-electric machine. SPKIXG-JxACK-— A device for readily inserting a loop in a main electric circuit. The spring-jack is generally used in connection with a multiple switch board. STAGGEEIXG — A term sometimes applied to the position of the brushes on a commutator cylinder, in which one brush is placed slightly in advance of the other brush so as to bridge over a break. STAXDAED, BYX A:\rO— The supports for the bearings of a dynamo-electric machine. STATIOX, CEXTEAL— A station, centrally located, from which electricity for light or power is distributed by a series of conductors radiating therefroni. STATIOX, TEAXSFOEMIXG— In a system of distribution by transformers or converters a station where a number of transformers are placed, in order to supply a group of houses in the neighborhood. SUS 438 STOOL, INSULATING— A support isolated from the ground usually by glass insulators. STORAGE BATTLKY— (See Battery, Storage.) STORAGE CELL— (See Cell, Storage.) STOEM, ELECTKIC— An unusual condition of the atmos- phere as regards the quantity of its free electricity. STOEM, M;\GNETTC— Irregularities occurring in the dis- tribution of the earth's magnetisin, affecting the mag- netic declination, dip, and intensity. STEEXGTH, FIELD— The intensity or total flux of magn- etism of a dynamo. STRIPPING — Dissolving the metal coating from a silver- plated or other metal-plated article. SUBMARINE CABLE— (See Cable, Submarine.) SUBWAY, ELECTPJC — An accessible underground way or passage provided for the reception of electric wires or cables. Sl'LPHATING- -A nam.e applied to one of the sources of loss in the operation of a storage battery, by means of the formation oi: a coating of inert sulphate of lead on the battery plates. SL^SCEPTIBILITY, MAGNETIC— The ratio existing be- tsveen the induced magnetization and the magnetic force producing such magnetism, or the intensity oi magnetism divided by the magnetic force. SUSPEX'SION, BI FILAR— The suspension of a needle by iwo parallel wires or fibres, as distinguished from a suspension by a single wire or fibre. 439 SWI SlTSPEXSTOiS", KXIFE-EDGE— The suspension of a needle on knife edges that are supported on steel or agate planes. SWITCH BOAKD- (See Board, Switch.) SWITCH, BREAIC-DOWX— A special switch, employed in small three-wire systems, for connecting the positive and negative bus-wires in such a manner as to prac- tically convert it into a two-wire system and permit the system to he supplied with current from a single dynamo. SWITCH, CHAXGTXG— A switch designed to throw a cir- cuit from one electric source to another. SWITCH, J)OUBI,]^-BREAK KXIFE— A knife switch pro- vided with double-break contacts. Sn^TTCH, DOUBLI'-POLE— a switch that makes or breaks contact with both poles of the circuit in which it is placed. A switch consisting of a combination of two separate switches, one connected to the positive lead and the other to the negative lead. SWITCH, FEEDFri— The switch employed for connecting or disconnecting each conductor of a feeder from the bus-bars in a central station. SVflTCH, KXIFE- -A switch^ which is opened or closed by the motion of a knife contact which moves between parallel contact plates. A knife-edge switch. SWITCH, BfiYETJSTNG— A switch for reversing the direc- tion of a circuit. TAG 440 SWITCH, SNAP— A switch in which the transfer of the contact points from one position to another is acccm- plished b}^ means of a quick motion obtained by the operation of a spring*. [^ SWITCH, TELEPHONE, AUTOMATIC— A device for auto^ matically transferring the connection of the main Jine from the call bell to the telephone circuit. SWITCH, THEEi:-POINT— A switch by means of which a circuit can be completed through three different con- tact points. SWITCH, TIME— An automatic switch in which a prede- termined time is required either to insert a resistance in or remove it from a circuit. SWITCH, TWO-POINl'— A switch by means of which a circuit can be completed through two different contact points. SYSTE:\r, THREE-WIRE— A system of electric distribution for lanjps or ether translating devices connected' in multiple, in which three wires are used instead of the two usually employed. In the three-w^ire system tw^o dynamos are generally employed, which are connected with one another in series. T T. — A symbol used for time. TACHOMETER — An apparatus for indicating at any mo- ment on a revolving dial the exact number of revolii- tions per minute of a shaft or machine. 441 TEL TALK, CEOSS — In telephony an indistinctness in the * speech transmitted over any circuit, due to this circuit receiving", either by accidental contacts or by induction, the speech transmitted over neighboring circuits. TANNING, ElrECTRIC— An application of electric currents to tanning leather. I^APE, INSULATING— A ribbon of flexible material im- pregnated with kerite, okonite, rubber or other suitable insulating material, employed for insulating wires or electri3 conductors at joints, or other exposed places. T \STE, GALVANIC — A sensation of taste produced when a voltaic current is passed through the tongue or in the neighborhood of the gustatory nerves, or nerves of c-aste. TEASER, ELECTRIC CURRENT— A coil of fine wire placed on the field magnets of a dynamo-electric machine, next to the series coil wound thereon, and connected as a shunt across the main circuit. This term is also used to designate the auxiliary winding us^ed for producing the polyphase current in a monocyclic dynamo. TECHNICS, ELECTRO— The science whicli treats of the physicol applications of electricity and the general princii)les applying thereto. TELEGRAPHIC— Pertaining to telegraphy. TELEGRAPHIC ALPHABET— (See Alphabet, Telegraphic.) TELEGRAPHIC CABLE— (See Table, Telegraphic.) TELEGRAPHIC CODE— (See Code. Telegraphic.) 29 TEL 442 TELEGEAPHIC KEY— (See Key, Teleg-raphic.) TELEGEAPHING — Sending- a communication by means of telegraphy. TELEGEAPHY, ACOUSTIC— A non-recording system of telegraphic communication,* in which the dots and dashes of the Morse system, or the deflections of the needle in the needle systems, are replaced by sounds that follow one another at intervals, that represent the dots and dashes, or the deflections of the needle, and thereby the letters of the alphabet. TELEGEAPHY AND TELEPHOXY, SIMULTANEOUS, OVEE A SINGLE WIEE— Any system for simultaneous transmission of telegraphic and telephonic messages over a single wire. TELEGEaPELY, AUTOMATIC— a system by means of which a telegraphic message is automatically trans- mitted by the motion of a previously perforated fillet of paper containing perforations of the shape and order required to form the message to be transmitted. TELEGEAPHY, CHEMICAL— A system by means of which the closings of the mainline-circuit, corresponding to the dots and dashes of the Morse alphabet, are recorded on a lillet of paper by the electrolytic action of the cur- rent on a chemical substance with which the paper fillet is impregnated. TELEGEAPHY, DIPLEX— A method of simultaneously sending- two messages in the same direction over a sin- gle wire. Diplex telegraphy is to be distinguished from duplex telegraphy, where two messages are simultaneously transmitted over a single wire in opposite directions, 443 TEL TELEGKAPHY, DLrPLEX, BRIDGE METHOD OF— A sys- tem whereby two telegraphic messages can be simul- • taneoiisly transmitted over a sing-ie wire in opposite directions. 'J ELEGFvAPHY, DUPLEX, DTFFEPEXTIAL METHOD OF — A system of duplex telegraphy in which the coils of the receiving" and transmitting- instruments are differ- entially wound. TELEGRAPHY, FAC-SIMILE— A system whereby a fac- simile or copy of a chart, diagram, picture or signature is telegraphically transmitted from one station to another. TELI:GRAPHY, fire ALARTT— a system of telegraphy by means of which alarms can be sent to a central sta- tion, or to the fire engine houses in the district, from call boxes placed on the line. TELEGRAPHY, GRAY'S H7^Ri>I0NIC MLTLTIPLE-A sys- tem for the simultaneous transmission of a number* of separate and distinct m.usical notes over a single wire, which separate tones are utilized for the simultaneous transnsissibn of an equal number of telegraphic mes- sages. TELEGRAPHY, LSDUCTION— A system of telegraphing by induction between moving trains and fixed stations on a railroad, bj^ means of impulses transmitted by in- duction between the car and a wire parallel with the track. l^ELEGRAPHY, INDUCTION, CURRENT SYSTEM OF— A system of induction telegraphy depending on current induction between a fixed circuit along the road, cind a parallel circuit on the moving train. TEL 444 Q'ELEGRAPHY, INDUCTIO]^*, STATIC SYSTElNf OP— A system of inductive telegraphy depending- on the static induction between the sending- and receiving* instru- ment. TELEGRAPHY, MORSE SYSTEM OF— A system of tele- graphy in which makes and breaks occurring* at inter- vals corresponding* to the dots and da:^hes of the Morse alphabet are received by an electro-magnetic sounder or receiver. TELEGRAPHY, MLT:.TIPLEX— A system of teleg*raphy for the simultaneous transmission of more than four sepa- rate messages over a sing*le wire. TELEGRAPHY, PRINTING— A system of telegi-aphy ip which the messag*es received are printed on a paper iih let. TELEGRAPHY, QUADRUPLEX— A system for the simul- taneous transmission of four messag-es over a single wire, two in one direction and the remaining two in the opposite direction. TELEGRAPHY, QUADRUPLEX, BRIDGE ]\rETHOD OF— A system of quadruplex telegraphy by means of a double bridge duplex system. TELEGRAPHY, QUADRUPLEX, DIFFERENTIAL ]NrETH- OD OF — A system of quadruplex telegraphy by means of a double dilTerential duplex system. TELEGRAPHY. SIMPLEX— A system of telegraphy in which in a single message only can be sent over the line. 445 THE TELEGRAFHY, STEP-BY-STEP— A system of telegraphy in which the signals are registered by the movements of a needle over a dial on which the letters of the al- phabet, etc., are marked. TELEGRAPHY, SUBMAEINE— A system of telegraphy in which the line wire consists of a submarine cable. TELEGRAPHY, SYNCHRONOUS-MULTIPLEX, DELANY'S SYSTEM!— A system devised bj^ Delany for the simul- taneous telegraphic transmission of a number of mes- sages either all in the same direction, or part in one direclion and the remainder in the opposite direction. TELEGRAPHY, WRITING— A species of fac-simile tele- graphy ^ by means of which the motions of a pen at- tached to a transmitting instrument so vary the resis- .% tance on two lines connected with a receiving instru- ment as to cause the current received thereby to re- produce the motions, on a pen or stylus, which trans- fers them to a sheet of paper. A sytem of writing telegraphy consists essentially of transmitting and receiving instrujnents connected by a double line wire. TELEPHONE — An apparatus for the electric transmission of articulate speech. TELEPHONIC EXCHANGE— (See Exchange, Telephonic, System of). TER3riNALS — A name sometimes ay>plied to the poles of a battery or other electric source, or to the ends of the conductors or wires connected thereto. THERAPEUTICS, ELECTRO, OR ELECTRO-THERAPY— The application of electricity to the curing' of disease. TOU 446 THEPvMO-ELECTKIC BATTERY— (See Battery, Thermo- Electric.) THEKMO-ELECTRTC COUPLE- (See Couple, Thermo-Elee- tric.) TIJERMO!\rETEE, ELECTRIC RESISTANCE— A thermo- meter the action of which is based on the change in the electric resistance of metallic substances with changes in temperature. TKEROMSTAT — An instrument for automatically miaintain- ing" a given temperature by the closing of an electric circuit through the expansion of a solid or liquid. THERMOSTAT, MERCURIAL- -A thermostat operating by the expansion of a mercury column. TITREE-WTRE SYSTEM— (See System, Three-Wire.) TICKER SERVICE, STOCK- -The simultaneous transmis- sion of stock quotations or other desired information to a number of subscribers. TIPS, POLAR — The free ends of the field magnet pole pieces of a dynamo-electric machine. TORQUE — That moment of the force applied to a dynamo or other machine which turns it or causes its rotation. The mechanical rotary or turning force which acts on the armature of a dynamo-electric machine or mo- tor and causes it to rotate. TOUCH, DOUBLE—A method of magnetization in which two closely approximated magnet poles are simultane- ously dra^vn from one end of the bar to be magnetized to the other and back again, and this repeated a num- ber of times. 447 TRA , TRACTION, MAGNETIC— The force w^ih which a magnet holds on to or retains its armature, when once attached thereto. TRAMWAY, EL7^:CTRIC— A railway over which cars are driven by means of electricity. An electric railroad. TRANSFORMER— An inverted Ruhmkorff induction coil employed in systems of distribution by means of al- ternating* currents. An apparatus for raising or lowering the voltage of an electric current used in /transmitting and distribut- ing power. A transformer is sometimes called a converter. The word transformer is, however, the one most employed. ^/TRANSFORMER, CLOSED IRON CIRCUIT— A transformer the core of which forms a complete magnetic circuit. These transformers are sometimes called ironclad transformers. TRANSFORMER, CONSTANT-CURRENT— A transformer in which a current of a constant potential in the pri- mary js converted into a current of constant strength in the secondary, despite changes in the load on the secondary. TRANSFORMER, CORE— A transformer in which the pri- mary and secondary wires are wrapped around the out- side of a core consisting of a bundle of soft iron wires or plates. TRANSFORMER, EFFICIENCY OF— The ratio between the whole energy supplied in any given time to the pri- mary circuit of a transformer and that which appears in the form of electric current in the secondary circuit. TRANSFORMER, HEDGEHOG— A name applied to a par- ticular form of open-iron circuit transformer. TEA 448 TKANSFOHMER, MULTIPLE— Any form of transformer which is connected in multiple to the primary circuit. TRANSFORMEK, OIL- -A transformer which is immersed in oil in order to insure a high insulation. TEAIN^SFORMER, EOTARY-CURRENT— A transformer operated by means of a rotary current. TANSFORMER, SHELIr— A transformer in which the pri- mary and secondary coils are laid on each other, and the iron core is then wound through and over them so as to enclose all the copper of the primary and sec- ond ai*y circuits within the iron. TRANSFORMER, STEP-DOWN— A transformer in which a small current of comparatively great difference of po- tential is converted into a large current of comparative- ly small difference of potential. TRANSFORMER, WELDING— A transformer suitable for changing a small electric current of comparatively high difference of potential, into the heavy currents of low difference of potential required for welding purposes. Welding transformers have in general a very low re- sistance in their secondary coils, and almost invariably consist of a single turn or at the. most of a few turns of very stout wire. TRANSLATING DEVICE— (See Device, Translating.) TRANSMITTER, CARBON, FOR TELEPHONES— A tele- phone transmitter consisting of a button of compressi- ble carbon. The sound waves impart to-and-fro movements to the transmitting diaphragm, and this to the carbon but- ton, thus varying its resistance by pressure. This but/- ton is placed in circuit with the battery and induction coil. 449 TUB TItANSMITTEK, ELECTRIC— A name applied to various electric apparatus employed in telegraphy or telephony to transmit or send the electric impulses over a line wire or conductor. TREATMENT, HYDRO-CARBON, OF CARBONS— Exposing carbons, while electrically heated to incandescence, to the action of a carbonizing gas, vapor or liquid, for the purpose of rendering them more uniformly electrically conducting throughout. TRIMMING — A term sometimes applied to the act of plac- ing the carbons in an electric arc lamp. TROLLEY — A rolling contact wheel that moves over the overhead lines proxided for a line of electric railway cars, and carries off the current required to drive the motor car. TROLLEY, DOUBLE— The traveling conductors, which move more over the lines of wire in any system of electric railways that employs two overhead conduc- tors. TROLLEY POLE— (See Pole, Trolley). TUBE, CROOKES'— A tube containing a high vacuum and adapted for showing any of the phenomena of the ultra-gaseous state of matter. TUBES, YACUUAf-Glass tubes, from which the air has been partially exhausted and through which electric discharges are passed for the production of luminous effects. TURN, AMPERE — A single turn or vdnding in a coil of wire through which one ampere passes. CJNI 450 TURNS, 3EKIES, OF DYNAMO-ELECTKTC MACHINES-- The ampere-turns in the series circuit of a compound- wound dynamo-electric machine. TURNS, SHUNT, OE DYNAINIO-ELECTRIC MACHINE— The ampere-turns in the shunt circuit of a couij>r.und- wound dynamo-electric machii^e. u UNITS, ABSOLUl^E— A system of units basi-d on the centi- metre for the unit of length, the gramme for the unit of mass, and the second for the unit of time. UNITS, CENTIMETRE-GRAMME-SECOND— A system oi units in which the centimetre is adopted for the unit of length, the gramme for the unit of mass, and the second for unit of time. UNITS, C. G. S. — The centimetre-gramme-seeond units. UxVITS, FUNDAMENTAL— The units of length, time and mass, to which all other quantities can be referred. UNITS, HEAT— Units based on the quantity of heat re- quired to raise a given weight or quantity' of a sub- stance, generally water, one degree. The principal heat units are ihe English heat unit, the greater and smaller calorie and the joule. (See Calorie. Joule.) UNITS, MAGNETIC— Units based on the force exerted be- tween two magnet poles. Unit strength of a magnetic pole is such a magnetic strength of pole that repels another magnetic pole of ^ equal strength placed at unit distance with unit force, or witJi the force of one dyne. 451 VIB UNITS. PKACTTCAL— Multiples or I'rnctions of the abso- lute or centiinetregramme-seeouci units. V — A contraction sometimes used for volt. V — A contraction sometimes used for velocity. VACUUM, HIGH — A space from which nearly all traces of air or residual gas have been removed. Such a vacuum that the length of the mean free path of the molecules of the residual atmosphere is equal to or exceeds the dimensions of the containing* vessel. VACUUM, TORKICELXIAN— The vacuum VN^hich exists above the surface of the mercury in a barometer tube or other vessel over thirty inches in vertical height. VARIATION, MAGNETIC— Variations in the value of the magnetic declination, or inclination, that occur simul- taneously^ over all the parts of the earth. VARNISH, ELECTRIC^An insulating material dissolved in a solvent. When the varnish is dry it should produce a layer or film of insulating material. VIBRATION OR WAVE, AlMPLITUDii] OP— The ratio that exists in a wave between the degree of condensation and rarefaction of the medium in which the wave is propagated. VIBRATION, PERIOD OF— The time occupied in execut- ing one complete vibration or motion to-and-fro. VIBRATIONS, ISOCmiONOUS— Vibrations which perform their to-and-fro motions on either side of the position of rest in equal times. VOL 452 VIBKATIONS, SYMPATHETIC— Vibrations set up in bodies by waves of exactly the same wave rate as these produced by the vibrating body. VIS-VIVA— The energy stored in a moving* body, and there- fore the measure of the amount of work that must be performed in order to bring* a moving body to rest. VOLT — The practical unit of electro-motive force. Such an electromotive force as would cause a current ductor which ciits lines of magnetic force at the rate of 100,000,000 per sec. Such a electromotive^ force as would cause a current of one ampere to flow against tlie resistance of one ohm, . VOLT-AMMETER— A wattmeter. A variety of galvanom.eter capable of directly meas- uring the product of the difference of potential and the amperes. VOLT AMPERE— A watt. VOLTAGE — This term is now very commonly used for either the electromotive force or difference of potential of any part of a circuit as determined by the reading of a voltmeter placed in that part of the circuit. VOLTAIC ARC— (See Arc, Voltaic.) VOLTAIC BATTERY— (See Battery, Voltaic.) VOLTAIC CELL— (See Cell, Voltaic.) VOLTAIC ELEMENT— (See Element, Voltaic.) VOLTAMETER— An electrolytic cell employed for meas- uring the quantity of the electric current passing through it by the amount of chemical decomposition effected in a given time. 453 VOL VOLTAMETER, COPPER— A voltameter Tn which the quantity of the current passin^^ is determined by the weig-ht of copper deposited. VOLTAMETER, VOLUME--A voltameter In which the quantity of the current passing- is determined by the volume of the g-ases evolved. VOLTMETER — An instrument used for measuring- differ- ence of potential. VOLTMETER, CARDEW'S— A form of voltmeter in which the potential difference is measured by the amount of expansion caused by the heat of a current passing through a fixed resistance. VOLTMETER, CLOSED-CIRCUIT— A voltmeter in which the points of the circuit, between which the potential difference is to be measured, are connected with a closed coil or circuit, and which gives indications by means of the current so produced in said circuit. VOLTMETER, GRAVITY— A form of voltmeter in which the potential difference is measured by the movement of a magnetic needle against the pull of a weight. VOLTMETER, MAGNETIC- VANE— A vol+meter in which the potential difference is measured by the repulsion exerted between a fixed and a moveable vane of soft iron placed within the field of the magnetizing coil. VOLTMETER, MULTI-CELLULAR ELECTROSTATIC— An electrostatic voltmeter in which a series of fixed and movable plates are used instead of the single pair em- ployed in the quadrant electrometer. WAT *±o4 VOLTMETER, OPEN-CIRCUIT—A voltmeter in which the points of the circuit where potential difference is to be measured are connected with an open circuit and give indications by means of the charges so produced. VOLTMETER, PERMANENT MAGNET— A form of volt- meter in which the difference of potential is measured by the movement of a magnetic needle under the com- bined action of a coil and a permanent magnet, against the ptill of a spring. VULCABESTON — An insulating substance composed of as- bestos and rubber. VULCANITE — A variety of vulcanized rubber extensively used in the construction of electric apparatus. Vulcanite is sometimes called ebonite from its black color. It is also sometimes called hard rubber. w W — A contraction sometimes used for watt. WALL SOCKET— (See Socket, Wall.) WATCHES, DEMAGNETIZATION OF— Processes for re- moving magnetism from watches. WATT — The unit of electric power. The volt-ampere. The power developed when 44.25 foot-pounds of work are done per minute, or 0.7375 foot-pounds per second. The 1-746 of a horse power. WATT-HOUR- A unit of electric work. A term employed to indicate the expenditure of an electrical power of one watt, for an hour. 455 WKB WATT-HOUR, KILO— The Board of Trade unit of v/ork equal to an output of one kilo-watt for one hour. WATT, KILO— One thousand watts. A unit of power sometimes used in stating- the out- put of a dynamo. WATT-METEK — A galvanometer by means of which the simultaneous measurement of the difference of poten- tial and the current passing* is rendered possible. The w^att-meter consists of tw^o coils of insulated wire, one coarse and the other jBue, placed at right angles to each other as in the ohm-meter, only, Instead of the currents acting on a suspended magnetic needle, they act on each other as in the electro-dynamometer. WAVE — A disturbance in an elastic medium that is periodic both in space and time. WAVE, ELECTRIC— An electric disturbance in an elastic medium that is periodic T)oth in space and time. WAVES, ELECTRO-MAGNETIC— AVaves in «ie ether that are given off from a. circuit through which an oscillat- ing discharge is passing, or from a magnetic circuit undergoing variations in magnetic intensity. WELDING, ELECTRIC— Effecting the welding union of metals by means of heat of electric origin. In the process of Elihu Thompson, the metals are heated to electric incandescence by currents obtained from transformers, and are subsequentify pressed ot Ijammered together. WHEEL, TROLLEY— A metallic w^heel connected with the trolley pole and moved over ^ the trolley wire on the motion of the car over the tracks, for the purpose of taking the curicent from the trolley wire by means of rolling contact therewitJx, WIE 456 WHIHL, ELECTRIC— A term employed to indicate the cir- cular direction of the lines of magnetic force snrronnd- ing a conductor convejdng an elastic current. WHIRL, MAGNETIC— The lines of magnetic force which surround the circuit of the conductor conreying an electric current. WIXDIXG, A^IPERE— A single winding or turn through which one ampere passes. Ampere-winding is used in the same signification as ampere-turn. WTLXDIXG, COMPOUXD, OF ]:)YXAMO-ELECTRIC MA- CHIXE — A method of winding in which shunt and ser- ies coils are placed on the field magnets. WIXDIXG, SERIES — A winding of a dynamo-electric ma- chine in which a single set of magnetizing coils are placed on the field magnets, and connected in series with the armature and the external circuit. WIRE, DEAD. OF ARMATURE— That part of the wire on the armature of a dynamo which produces no electro- motive force or resultant current. WIRE, DEPLEX — An insulated conductor containing two separate parallel wires. WIRE. FEEDIXG— A term sometimes applied to the wire or lead of a multiple circuit which feeds the main. In a system of electric railroads the feeding wires feed the trolley wires. WIRE, FL'SE — A readily fusible w^re employed in a safety catch to open the circuit when the current is excessive. 457 WIB WIRE, HOUSE— In a system of incandescent electric light- ing any conductor that is connected with a service con- ductor and leads to the meter in the honse. WIRE, INSUIiATED— Wire covered with any insulating ma-' terial. WIRE, IJNE— In telegraphy the wire that connects the different stations with one another. WIRE, NEGATIVE— A term sometimes applied to that wire of a parallel circuit which is connected to the negative pole of a source. WIRE, NEUTRAL— The middle wire of a three-wire system of electric distribution. WIRE, POSITIVE— The wire or conductor connected to the positive pole or terminal of any electric source. WIRE. SLIDE — A wire of uniform diameter employed in Wheatstone's electric bridge for the proportionate arms of the bridge. WIRE, SPAN — The wire employed in systems of electric railways for holding the trolley wire in place. WIRE, TROLLEY— The wire over which the trolley passes in a system of electric railways, and from which the current is taken to drive the motors on the cars. WIRES, DEAD — Disused and abandoned electric wires. WIRES, LEAI)ING-IN— The wires or conductors which lead the current through (into and out of) an electric lamj). WIRES, PILOT— In a system of incandescent lighting, where a comparatively low potential is employed on the mains, thin w^ires leading directly from the gener- ating station to different parts of the mains, in order to determine the differ^nQ^s of potential at such points. 30 ^ YOK 458 WIRES, PRESSURE— Tn a system of incandescent electric lig-htiDg-, wires or conductors, series-connected with the junction boxes, and employed in connection with suit- able voltmeters, to indicate the pressure at the junction boxes. The pressure ^vires are sometimes called the pilot wires. WIRING— Collectively the wires or conducting circuits used in any sj^stem of electric distribution. WORK — The product of the force by the distance through which the force acts. • A force whose intensity is equal to one pound acting through the distance of one foot, does an amonnt of work equal to one foot-pound. WORK, ELECTRIC— The joule. (See Joule). 1 joule equals 1 watt for 1 second. WORK, ELECTRIC, UNIT OF— The volt-coulomb or joule. The product of the volts by the coulombs. WORKING, PARALLEL, OF DYNAMO-ELECTRIC MA- CHINES — The operation of -working several dynamo- electric machines as a single source, by connecting them with one another in parallel or multiple arc. I YOKE FIELD— That part of the field magnet frame con- necting two magnet cores. YOKE, MULTIPLE-BRUSH— A term sometimes applied to multiple brush rocker of a dynamo or motor. 459 ZIN z ZINC, AMALGAMATION OF— The covering or amalgama- tion of zinc with a layer of mercury. ZINC, CP.OW-I'OOT— A crow-foot-shaped zinc used in the gravity voltaic cell. ^ INDEX TO TABLES. I. Properties of Copper Wire 13-14 II. Currents Allowed in Wires by Fire Underwriters... . 16 III. Electro-chemical Series of the Elements 26 IV. Data of Common Batteries 30 V. Properties of MetaiS 34 VI. Permeability Table 67 VII. Magnetic Traction or Pull 83 VIII. Magnetic Circuits of Dynamos 91 IX. Hysteresis in Soft Iron 131 X. Dynamo and Motor Windings 165-167 XI. Tensile Strength of Copper Wire 292 XII. Circumferences of Circles 293 XIII. Areas of Circles 294-295 XIV. Areas of Small Circles 296 XV. Price List Copper Magnet Wire 297 XVI. Specific Gravities of Metals 298 XVII. Decimal Equivalents of Parts of an Inch 299 XVin. Wire Gauges in Mils 300 XIX. Properties of Aluminum Wire 301-302 XX. Areas of different Wire Gauges 303 XXI. Current required by Motors 304 XXII. Type M. V. Chloride Battery 240 XXIII. Willard Standard Battery 241 XXIV. Willard Special Battery 241 XXV. Edison Battery. 243 INDEX. A Active material in storage batteries 239-242 Alternating currents 219 Alternating current, advantages of 222 Alternations 219 Aluminum wire, table of 301-362 Amalgamation of battery zincs 29 Ampere turns required in parts of magnetic circuit 64 Ampere turns, calculation of from table 67 Ampere turns, size of wire to produce certain 105 Analogy between water and electricity i Anode 31 Armature current, division of at brushes 137 Armature, drum 116 Armature, gramme ring 112 Armature, iron clad 66 Armature reaction 138 Armature reaction, magnetization of fields by 139 Armature, smooth core 65 Armature, tunnel wound 50 Arc lamps 203 Automatic rheostat 182 Automobile battery 238 Automobile controller 237 Automobile motor 232 Automobile, power required for 234 B Battery, automobile 238 Battery, charging of 243 464 Battery, Chloride . . 239 Battery, Edison 242 Battery for experimental purposes 29 Battery, storage .- 35 Battery, storage capacity of 36 Battery, storage uses of 36 Batteries, table of data of .' 30 Battery, troubles 247 Battery, Willard 240 Brakes, electric 86 Brush arc dynamo , 139 Brush arc motor 127 Brushes, inertia of 190 Brushes, position of in multipolar motors 112 Brushes, sparking affected by position of 146 c Calculation of ampere turns from table 72 Carbon brush 148 Carbon as positive element in battery ceil 28 Capacity of storage batteries 35 Cathode 31 Charging of automobile batteries 243 Chloride accumulator 239 Circuits, primary 227 Circuits, secondary 227 Commutation, conditions of perfect 146-149 Commutator, vibration of 190 Compass, mariner*s , 40 Compound winding 170 Compound winding, number of series turns 181 Connections of armature and field magnets 177 Constant potential system 20 465 Constant voltage, effect on life of lamps 202 Controller connections for automobiles 336 Copper wire, change of resistance with temperature .... 100 Counter E. M. F., identity with primary 123 Current required by motors 304 Current, three-phase 224 Current, two-phase 222 Cycle 219 Cycle, per second 221 D Density of electrolyte in batteries 246 Direction of flow of current 31 Drop allowed in street railway feeders 18 Drum armature 116 Drum armature, winding of 150 E Earth as magnet • 40 Eddy currents 133 Edison battery 241 Edison current meter . 31 Edison dynamo, leakage co-efificient of 90 Electric brakes 86 Electrolyte 247-247 Electro-magnet 43 Electropeon fluid for batteries 29 Electro-plating *. 32 E. M. F., counter 123 E. M. F., productior of in armatures Ii2 E. M. F., winding for different 117 Enclosed arc lamps 202 Energy formulae ,..,,,,,.,,...,..,,.?•??• ^ ,. » 95 466 Energy in electric circuits 95 F Feeders for street railway work 18 Field coil, improper connection of 196 Field coil, heating of 196 Field coil, open circuit in 194 Field coil, short circuit in 195 Field discharge 178 Field, distortion of by armature reaction 141 Field magnets , 175 Flow of current, direction of 31 Force, field of 41 Force, field of, strength in the U. S 41 Force, line of 41 Force, mechanical, exerted on wire carrying current in magnetic field 49 Friction between brush and commutator. 102 G Galvani, his discovery 25 Gramme ring armature 112 Gramme ring, practical advantage of 116 Grounds 192 Grounds, partial 193 Grounds, permanent 193 H Heating of commutator 192 Heating of field coils 196 Heating of magnet coils 108 Helix 14 High voltage, use in transmission of power 99 467 Horse power, electrical, equivalent of 95 Horse power required for automobiles 234 Horizontal winding 160 Hydrometer 246 Hysterisis 130 Hysterisis in four-pole field 132 I Incandescent lamps, life of 10 Iron clad armature — 66 L Lap winding 162 Leads, armature 160 Leakage of magnetic lines 89 Lentz law 119 Life of incandescent lamps 10 Lines of force 41 M Magnet electro 43 Magnet, field of 45 Magnet, best design for lifting purposes 84 IMagnet coils, calculation of 106 Magnet coils, heating of 124 Magnetic lines, bunching of 69 Magnetic lines, leakage of 89 Magnetic traction 82 Magnetic spectrum 42 Magnetic whirl 42 Magnetic vane voltmeter 214 Magnetism 40 Magnetism, residual 175-213 Magnetization of field by armature reaction 139 468 Mariner's compass 40 Mechanical force exerted on wire carrying current in magnetic field ; . . . . 49 Meter, Brush '. 213 Meter, Thompson's recording 215 Meter, Westinghouse 214 Meter, Western Electric 212 Meter, Weston 211 Motor, Baxter 127 Motor, Brush 127 Motors, compound wound 170 Motor, series and properti-es of 125-232 Motor, shunt wound, speed of 124 Motors 208-211 Multipolar fields, effect of an armature reaction 100 N Nitrate of soda as electrolyte 28 Number of bars in commutator 164 Number of slots in armature 164 Noise of machine in operation 197 o Ohms law 3 Open circuits 186 Open circuits in field coils 194 Over commutation 127 P Periodicity 221 Permeability 56 Plating, electro 32 Platinum sponge • • . • . 27 469 Platinum wire in incandescent lamps 202 Polarization 26 Porous cup 27 Polyphase currents from direct current commutators... 224 Position of brushes in multipolar machines 162 Power for automobiles 234 Power for primary batteries 28 Primary circuits 227 R Residual magnetism 175 Resistance of brush contact 147 Resistance of copper wire, change of with temperature 106 Resistance of copper wire, rule for 20 Revolving pole 224 Rheostat 177 Rhumkorf coil 228 S Saturation of magnetic circuit 56 Secondary circuits 227 Self induction 145 Series arc lamps 205 Series system of arc lighting 20 Series wound motor, properties of 125 Short circuits 187 Shunt motor proper, connection of 181 Shunt wound motor, constant speed of 124 Sine wave 221 Smee battery 27 Smooth core armature -. . . 65 Solenoid 45 Solenoid meter 216 470 Solid pole pieces, eddy currents in 134 Sparking 144-189 Spectrum magnetic 42 Starting box, automatic 182 Starting box, overload 183 Steel ingots handled by means of magnet 86 Storage batteries 35-238 Thompson recording meter 215 Three-phase current 226 Transformers ^ 227 Transmission of power by alternating currents 228 Traction magnetic 82 Transmission of power, connection with high voltage. . . 98-99 Transmission of power, weight of copper 99 Tungsten steel 210-240 Tunnel wound armature 50 Two phase current 224 V Vacuum 201 Vertical winding 160 Voltage constant, effect on life of incandescent lamps. . 202 Voltage of storage battery * 4-245 Volta's battery 25 Voltameter 31 Volt-meter, Weston 207 W Watts, mechanical equivalent of 25 Watts, radiated from armature 106 Watts, radiated from field coil 107 471 Watts required for incandescent lamps 263 Wave sine 221 Wave winding 161 Weston meters 207-208 Willard storage battery 250 Windings, armature 165 Winding lap 162 Wire winding, armature, arrangement of 158 Wire on dynamo, office of 157 Wiring for equal drop 17 Wood arc dynamo » o 139 Repair Work On the following page will be found our prices for rewinding armatures. For 14 years we have made a specialty of this branch of electrical repairing. We can rewind any kind of an armature, none too complicated for us to handle. Our long experience and responsi- bility, we feel, warrants your patronage. Cleveland Armature Works CLEVELAND, OHIO Price List for Winding Armatures RAILWAY GENERATOR ARMATURES Discount from these prices according to type. 15 Kilowatt, 500 volt 20 £0 45 60 90 100 150 175 200 . $ 50 00 . 66 00 . 77 00 . 94 00 . 105 00 . 115 00 . 132 00 . 148 00 . 154 00 . 19S 00 . 214 00 . 231 00 Larger sizes speciallj' quoted. RAILWAY MOTOR ARMATURES. Discount from these prices according to type, and whether drum or coil wound. 10 H. P., 500 volt $ 31 00 15 '• " 47 00 20 " " ... 50 00 25 " " 53 00 30 " " 58 00 50 " " 75 00 100 " " 121 00 Our prices for Railway Armature Coils will interest you. (We make them for every system.^ STATIONARY MOTOR ARMATURES Discount from these prices according to type and voltage. Commutators Armatures Refilled Rewound ^ H. P $ 4 25 $ 7 00 J/i " 4 50 10 00 Vi '' 5 00 14 00 1 " 5 70 16 00 \V2 '' 7 00 17 25 2 " 8 00 20 00 3 " 9 25 24 50 5 •• 11 00 28 00 6 " 13 00 29 00 IV2 '' 15 50 30 00 10 * ' IS 50 33 00 Stationary Motor Armatures- 15 H. P $20 25 20 25 30 40 50 24 50 30 75 35 00 43 00 52 00 -Con'd s^39 00 44 00 50 00 60 00 69 00 77 00 INCANDESCENT DYNAMO ARMATURES Discount from these prices according to type. Commutators Refilled lights $ 6 50 8 25 15 25 50 75 100 150 200 250 300 400 500 600 800 1000 10 50 14 00 16 75 19 25 21 25 25 00 30 75 37 00 45 00 52 00 63 00 75 00 Armatures Rewound $ 17 00 20 00 26 00 29 00 32 00 36 00 41 00 45 00 50 00 63 00 71 00 77 00 85 00 100 00 ALTERNATOR ARMATURES Discount from these prices according to type. 500 lights $40 00 650 800 1000 1200 1350 2000 42 00 49 00 59 00 65 00 68 00 S3 00 ARC ARMATURES Discount from these prices according to type, and whether drum or coil wound and voltage. 30 lights $150 00 35 50 60 80 100 158 00 195 00 215 00 235 00 255 00 Write for Discount, giving: make and capacity of Machine CLEVELAND ARMATURE WORKS, Cleveland, Ohio mxc c. A. ^v. Type A Dynamos and Motors Manufactured by Cleveland Armature nV orks CLEVELAND. OHIO A /IVCADC^^ experience in repairing most all I ^li I nAll J ^^^ diiferent makes of Dynamos and A j[ "Motors should be sufficient to enable a man of only ordinary intellect to detect the strong and weak points and to correct same in a machine of his own design. W^e ask permission to ship you one of our Dynamos 6r Motors subject to your approval and acceptance after 30 days' trial. Considering price alone, they are not cheap — but considering quality and price, they are the cheapest machines on the market. In writing for quotations, mention speed required. MOTORS DYNAMOS Shipping Weight in Box Pulley H. P. Speed liOand 220 volts Speed 500 volts K.W. 16 C.P. Lamp 9 Speed 110 to 115 volts c 5 1 14 1400 1700 .5 1550 180 3J/. 3 1 1800 2200 1.0 18 2000 180 3K2 3 1100 130i) 1.9 35 1300 250 4 3 3 1900 2100 2.75 50 2100 250 4 3 3 1050 1250 2.75 50 1250 425 4 iV2 4 1600 1850 3.50 60 1850 425 4 Wz 5 1050 1250 4.5 80 1250 625 5 5 7'A 1650 1(375 6.25 110 1675 625 5 5 T^-S 1000 1150 6.25 110 1150 775 6 5K> 10 1500 1650 8.50 155 1650 775 6 5'< 10 900 1050 8.50 155 1050 995 6 5!i r2K. 1200 1350 10.50 190 1350 995 6 hVi 1-2% 800 900 10.50 190 900 1300 7 6K' 15 1200 1350 12.50 230 1350 1300 6J/. 15 700 800 12.50 230 800 1G25 10 8 •20 1050 1200 16.75 310 1200 1625 10 8 XoS Cleveland Armature Works to Agents CLEVELAND, OHIO APB 1 "" >k. f One copy del. to Cat. Div. ^ APR U 1911 n