ELEMENTAKY ELECTRO-TECHNICAL SEEIES ELECTRIC ARC LIGHTING- EDWIN J. HOUSTON, PH. D. AND A. E. KENNELLY, Sc. D. SECOND EDITION, ENLARGED NEW YORK ELECTRICAL WORLD AND ENGINEER .... COPYRIGHT, 1902, BY ELECTRICAL WORLD AND ENGINEER VK 4-31 1 PREFACE. THIS little volume, like the others in the Electro-Technical Series, is written in lan- guage such as will enable the general public readily to understand the leading principles underlying the art of electric arc lighting, without any special training in electro- technics. The rapid growth of out-door illumina- tion by means of the arc light has rendered it a matter of necessity that the public should be able to possess a more extended knowledge of the principles underlying the production of the voltaic arc than can be obtained from the daily newspapers. IV PEEFACE. It is with the view of placing this knowledge in an accessible form, that the authors present this little book to the general reader. A brief account is given of the early history of arc lighting, of the manufacture of arc-light carbons, and the mechanisms both for single and double-carbon lamps. Especial attention has been devoted to the physics of the carbon voltaic arc, the re- sults of the most recent researches in this important branch of electric science having been carefully considered. Not only has the detailed structure of the lamp mechanism been treated of, but also the various accessories connected with the commercial installation of the lamps in circuit have been fully considered. The difficult subject of the amount of light emitted by the arc lamp, and the most satisfactory methods of estimating PEEFACE. V the same have been considered on account of the importance they possess in the com- mercial sale of light. The authors trust that this little book will prove of benefit to the general public. PKEFACE TO THE SECOND EDITION. IN preparing the second edition of this little volume, the authors have added four chapters which cover the main develop- ments of the last five years in this branch of electro-technics. It is believed that this will practically bring the work up to date. CONTENTS. CHAPTER PAOB I. EARLY HISTORY OF ARC LIGHTING, . 1 II. THE VOLTAIC ARC, . . . .16 III. ELEMENTARY ELECTRICAL PRIN- CIPLES, 37 IV. ARC LAMP MECHANISMS, ... 56 V. SERIES-CONNECTED ALL-NIGHT LAMPS, . . . . .117 VI. CONSTANT-POTENTIAL LAMPS, . . 137 VII. APPURTENANCES AND MECHANICAL DETAILS OF ARC LAMPS, . . 163 VIII. ALTERNATING-CURRENT ARC LAMPS, 209 IX. LIGHT AND ILLUMINATION, . . 237 X. PROJECTOR ARC LAMPS, . . . 268 XI. ARC LIGHT CARBONS, . . . 307 XII. DYNAMOS, 323 vii v'ii CONTENTS. CHAPTER PAGK XIII. ENCLOSED ARC LAMPS, . . . 356 XIV. SERIES ALTERNATING ARC-LIGHT- ING FROM CONSTANT- CURRENT TRANSFORMERS, . . . 375 XV. MULTI-CIRCUIT ARC-LIGHT GENER- ATORS, 393 XVI. PHOTOGRAPHY BY THE ARC-LIGHT, 397 INDEX, ...... 407 ELECTRIC ARC LIGHTING, CHAPTER I. EARLY HISTORY OF ARC LIGHTING. UNFORTUNATELY for our planet, so far as its illumination at night is concerned, it has but a single moon, and this, on an aver- age, is with us, on our hemisphere, but half of the nights throughout the year, so that half of our nights are necessarily devoid of moonlight. During full moon, when the sky is clear, the amount of light our earth receives from the moon is sufficient for all ordinary purposes of outdoor light- ing, although, as we shall hereafter see, its 2 ELECTRIC ARC LIGHTING. light is only about the l-500,000th part of full sunlight. Were we as favored as some of our sister planets as regards the number of moons, the problem of artificial outdoor lighting, during clear weather, would never have arisen. Had we, for example, the five moons of Jupiter, and did each of these afford as much light as our own moon, the intervals of no moonlight in fine weather would only occur about once a year. But even under these favorable cir- cumstances, we would be dependent for our outdoor lighting on fair weather, so that the problem of outdoor lighting would still present itself. Until the introduction of gas there were practically no means devised for out- door lighting over extended areas, such, EARLY HISTORY OF ARC LIGHTING. 3 for example, as the streets of a large city. It is true that candles and oil lamps afforded a meagre lighting in mediaeval times, but the necessity for the night watchman to carry a lantern with him in his rounds always existed. In recent times, the electric arc lamp has almost completely supplanted gas for the outdoor illumination in our large cities. The reason for this is to be found in its great power; i. e., the large quantity of light which a single lamp is capable of producing as compared w r ith a single gas burner, even when of large dimensions. Artificial illumination by means of arc lamps is by no means an invention of the last decade. The brilliant light emitted by the carbon voltaic arc was known shortly after the invention by Volta of the 4 ELECTRIC ARC LIGHTING. voltaic pile in 1796. The credit of this discovery h'as been erroneously assigned to Sir Humphrey Davy, and its date fixed by some at 1813. Before this date; i. e. t in 1809, Davy, by means of a powerful voltaic pile, first exhibited, on an extended scale, at the Koyal Institution in London, the splendors of the voltaic arc; but, as he himself acknowledged, the credit of its discovery did not lie with him. Indeed, a little reflection will show that this must necessarily have been the case, since large voltaic batteries were employed before this date, and the mere opening of the circuit of one of these batteries must necessarily have been attended by the production of an arc. The intense brilliancy of the voltaic arc must have convinced many of those who first saw it, that in this agency the world possessed an admirable means for artificial illumination, and it is EARLY HISTORY OF ARC LIGHTING. 5 not surprising, therefore, that many and various devices were produced, at an early date, for its employment. As is well known, when carbon elec- trodes, placed in a circuit carrying a powerful electric current, are slightly separated, a carbon voltaic arc is formed between them. During the maintenance of this arc the carbons are gradually consumed so that the space which separates them gradually increases, and a necessity thus arises for occasionally bringing the carbons nearer together. The early arc-light regu- lators employed for this purpose effected this regulation by hand ; that is, when the operator deemed that the distance was ex- cessive, he approached one of the carbons towards the other by some suitable hand adjustment Subsequently, automatic arc- liglit regulators were introduced. These 6 ELECTRIC ARC LIGHTING. early attempts at practical arc lighting were continued for many years after the first demonstration of the possibility of the carbon arc light, but it gradually became evident, that in the only source of elec- tricity the world then possessed ; namely, the voltaic battery, arc lighting was im- practicable, except on an experimental scale, owing to the expense. The invention by Bunsen about the year 1840 of his modification of Grove's voltaic cell marks another era in the history of arc lighting. Bunsen's type of voltaic cell employed two fluids, or was a double-fluid cell, and was a marked improvement on the voltaic cells previously existing, since it was not only able to furnish powerful cur- rents, but could also furnish them steadily, a respect in which earlier voltaic cells had signally failed. EARLY HISTORY OF ARC LIGHTING. 7 Two distinct improvements in the lamp mechanism characterize this era in the his- tory of arc lighting ; namely, improvements in the character of the carbon electrodes employed, and improvements in the nature of the regulating devices. Bunsen em- ployed for the negative element of his voltaic cell, rods or plates of artificial car- bon, which he formed from pastes made of mixtures of carbonaceous powders with some carbonizable liquid and subsequently carbonized the mixture, while out of con- tact with the air. Inventors were not slow to recognize the applicability of this invention to the production of the carbon rods or pencils required for arc lamps, and many improvements were made on Bun- sen's process, as we shall describe in the chapter on arc-light carbons. But the improvements made during this epoch in the regulators were not of less importance 8 ELECTRIC ARC LIGHTING. than those in the nature of the arc-light carbons, and many forms of lamp mechan- isms appeared, capable of automatically maintaining a fairly steady light for several consecutive hours. Some of the pioneer inventors in arc-lamp mechanisms belonging to this period, are, Wright, Staite, Le Molt, Foucault, Serrin and Harrison, whose inven- tions were recorded between 1845 and 1857. Times, however, were not yet ripe for the commercial introduction of arc lighting. Although the Bun sen batteiy was a great improvement over other forms of batteries, yet it was not capable of producing electric current with sufficient readiness and cheap- ness. It was troublesome to manage, and expensive to maintain. In the face of these difficulties all improvements in the lamp and its mechanism proved futile, and another period of inaction supervened. EARLY HISTORY OF ARC LIGHTING. 9 The essential requirement for the pro- duction of a practical arc lamp was a cheap and effective generator. Like other great inventions, this was the product of several independent workers. The germ of the invention had its birth in Faraday's discovery of a means for pro- ducing electricity by the aid of magnetism. Many early forms of magneto-electric gen- erators were invented. Van Malderen's modification of Nollet's generator, which was employed as early as 1863 for the illumination of the light houses at Havre and Odessa, was, perhaps, the best fairly commercial machine then produced. Even this machine did not fully meet the require- ments of every-day practice, and it was not until the invention by Gramme of what may, perhaps, be regarded as the first thoroughly commercial form of mag- 10 ELECTRIC ARC LIGHTING. netogenerator, that the next marked era in electric arc lighting began. The world was thus given a means for the ready, reliable and cheap production of electric current, from a generator driven by a steam engine, or other source of mechanical power, and there again began a revival of arc lighting invention. This third period or epoch, has extended uninterruptedly to the present day, receiving, however, a great stimulus about 1876, when Jablochkoff produced his simple and then fairly effi- cient form of arc-light caudle. The necessity for more or less elaborate feeding mechanism in arc lamps, for the purpose of maintaining approximately constant the distance between the elec- trodes, despite their consumption in use, formed in the opinion of some, an insuper- able obstacle to the extensive commercial EARLY HISTORY OF ARC LIGItTING. 11 use of the arc light. As we well know actual practice has shown this fear to be groundless. In JablochkofFs simple form of arc lamp, the carbons were main- tained at a constant distance apart by a device which dispensed with regulating mechanism. Jablochkoffs arc lamp or candle, as it was generally called, was based on the method of maintaining the carbons at a constant distance apart by placing them parallel to each other, and insulating them from each other by a block of kaolin, or some other non-con- ducting material. As the arc was formed, this material was volatilized and the arc was maintained between the carbons. It was believed that this simple device solved the much desired problem of a cheap and reliable regulating mechanism fbr the arc lamp. 12 ELECTRIC AEG LIGHTING. When Jablochkoff s candle was put to the test of actual commercial use, it failed in a number of respects. At first the sys- tem employed continuous currents. Under these circumstances it is evident that, since the rate of consumption of the positive carbon is practically twice that of the negative, although at the start, when the arc was formed at their extremities, the two carbons would be in the same hori- zontal plane, yet, after burning for some time, the positive carbon would have been consumed to a distance much lower down than the negative carbon, thus leaving a greater separation between the two carbons than the thickness of the separat- ing material and thus finally resulting in the extinguishment of the arc. Fig. 1, shows a form of Jabloclikoff candle. It consists of two carbons A and EARLY HISTORY OF ARC LIGHTING. 13 FIG. 1. JABLOCHKOFF CANDLE. , cemented together by a mass of kaolin, which not only insulates them from each other but separates them the required dis- 14 ELECTRIC ARC LIGHTING. tance. Inasmuch as the separated carbons cannot, as in the case of the ordinary lamp mechanism, be brought together and after- ward separated for the purpose of estab- lishing the arc between them, a device called an igniter was employed. This consisted of a mass of carbonaceous mate- rial which bridged over and separated the arc. After extinction of the candle, it would, of course, be- impossible to relight it without a new bridge, and for this reason a number of candles were placed on the same lamp support inside a common globe. With a view to avoiding some of the above difficulties, Jablochkoft* employed alternating currents for his candles, thus en- suring a uniform consumption. Although this greatly improved the operation of the apparatus, and this method of illumination was employed commercially, yet on account EARLY HISTORY OF ARC LIGHTING. 15 of its expense and for other reasons, it was soon replaced by improved devices. Since the inventions of this epoch prac- tically embrace the balance of the subject of arc lighting, they will be considered in detail throughout the book. CHAPTER II. THE VOLTAIC ARC. As already mentioned, some doubt ex- ists as to when the voltaic arc was first observed, but it would seem that this phenomenon must have been noticed coin- cidentally with the use of the first power- ful voltaic battery. When wires or other conductors con- nected with a powerful voltaic battery, or other electric source, are brought together and then slowly separated, the electric cur- rent does not immediately cease to flow; that is to say, provided the wires are not separated too widely, the circuit is not THE VOLTAIC ARC. 17 FIG. 2. JABLOCHKOFF CANDLE HOLDER. broken, but the space between them is traversed by a cloud of highly heated metallic vapor which carries the current. This incandescent cloud of vapor assumes 18 ELECTRIC ARC LIGHTING. a bow or arc shaped form, which has received the name of the electric or voltaic arc, after Volta, the inventor of the pile or battery, by the use of which the arc was first obtained. Such an arc, when formed between metallic substances, is called a metallic arc. The color of the light of metallic arcs varies with the metals form- ing the wires. In the case of copper the light is of a greenish hue. Nearly all metallic arcs possess a characteristic flam- ing. When the arc is produced between two carbon wires or rods, the carbon arc is formed, the color of which has a dazzling whiteness approaching that of sunlight. It is assumed, for convenience, that in the electric circuit the current flows in a definite direction ; namely, from the posi- tive pole of the source through the circuit to the negative pole. When the circuit is THE VOLTAIC ARC. 19 interrupted and an arc is formed at the gap, the current is assumed to flow from the positive carbon rod or electrode, across the intervening space, and to- enter the negative rod or electrode, on its way to the negative pole of the source. If, for example, the two carbon elec- trodes shown in Fig. 3, are connected with FIG. 3. CARBON ELECTRODES. the terminals of a sufficiently powerful electric course, and, after being brought into contact, are gradually separated to a distance of about l/8th of an inch, the direction of the current being such that 20 ELECTRIC ARC LIGHTING. the electric stream leaves the upper elec-. trode, passes through the arc and enters the lower electrode, then the upper elec- trode will be the positive, and the lower, the negative, electrode. The positive elec- trode is generally indicated, as shown in the figure, by a + sign, and the negative electrode by a sign. The carbon voltaic arc is too brilliant to be observed directly by the eye, but if it be examined through smoked or densely colored glass, the following characteristics may be observed : In the space or gap between the opposed carbons an arc or bow-shaped bluish flame appears, much less brilliant than the ends of the carbon electrodes. If the arc has been maintained for a little while, the ends of the carbons will be observed, as shown in Fig. 4, to differ markedly in THE VOLTAIC ARC. FIG. 4. CARBON VOLTAIC ARC. shape, the end of the positive electrode being hollowed out in a small crater or cup- shaped form ; while the opposed surface of the negative electrode will be seen to have 22 ELECTRIC ARC LIGHTING. a minute projection or nipple formed on that part of its surface directly opposite the crater. It will be evident too, that while the ends of the carbon electrodes are brighter than the mass of the arc proper ; i. e., of the arc-shaped flame between them, that they are by no means of equal brilliancy, the positive carbon being much brighter than the negative. Moreover, it will be seen that all parts of the end of the positive carbon are by no means equally bright, but that most of the light issues from the crater. Since the light giving power of a heated body increases rapidly with its temperature, a mere in- spection of the arc will show that the crater in the positive carbon is the hottest part of the arc. When the current is powerful, a duller incandescence can be observed, acconi- THE VOLTAIC ARC. 23 parried by a bluish, lambent flame, over the ends of the carbon electrodes, for dis- tances varying from 1/2 to 3/4ths of an inch. This flame is of similar origin to that which may be observed over the surface of a hard coal fire when insuffi- ciently supplied with air, and is due to the burning of the carbon vapor in the oxygen of the surrounding air. It is well known, that carbon may undergo chemically two distinct forms of oxidation ; namely, first, incomplete oxidation, producing what is called carbon monoxide, characterized by the blue flame of the coal fire already referred to, and second, a more complete oxidation producing what is called carbon dioxide or carbonic acid. It is believed that in the interior of the arc no oxidation' of carbon vapor occurs, not only because the vapor fills this interior space, and, therefore, displaces the air, but also be- 24 ELECTRIC ARC LIGHTING. cause the temperature of the disengaged vapor is so high that it is above that at which carbon monoxide, can exist without dissociation, or separation into carbon and oxygen. Even a casual inspection of the ends of the electrodes will show that, with the current strength ordinarily employed, the incandescence extends to a compara- tively short distance from the tips. This is the region in which the burning or oxidation of the carbon is most marked, and after the arc has been maintained for a while under the double influence of volatilization and oxidation, the ends of the electrodes assume a more or less irregu- lar shape as represented in Fig. 4. Confining our attention to the conical shaped ends of the carbons, minute globules of molten matter will be seen scattered here and there over their sur- THE VOLTAIC ARC. 25 faces. These globules are probably mol- ten drops of various mineral impurities in the carbon, and the more nearly pure the carbons, the fewer they will be. It will soon become evident, on continuing an examination of the arc, that the crater does not maintain its position, but shifts, at irregular intervals, from point to point on the surface of the positive electrode. The cause of this shifting is to be found in the fact that as the carbon is consumed by volatilization and oxidation, the edge of the crater becomes unequally worn at different parts, and the arc tends to be established at the point where the distance is the least, thus temporarily determining the new position of the crater. So, too, should slight impurities or irregularities in the quality of the positive carbon exist, they will determine a different rate of vol- atilization, the portions which volatilize 26 ELECTRIC ARC LIGHTING. most readily at any given time, tending to become the centre of the crater. This ' shifting of the position of the crater, and consequently of the arc, is objectionable from the fact that it leads to an unsteadiness or flickering of the light and a consequent variation in the distribu- tion of the light over the surrounding space. When, therefore, the flickering is frequent and marked, the effectiveness of the illumination suffers. Various expedi- ents have been adopted in order to reduce this shifting of the arc to a minimum. Among the most important of these are the reduction of the diameter of the car- bon, so as to afford a smaller area over which the arc can shift, and providing the centres of the electrodes with a softer carbon, so as to insure the greatest libera- tion of carbon vapor from the central por- THE VOLTAIC ARC. 27 tions and the consequent formation of the arc at these parts. Such carbons are called cored carbons. If a vessel of water is placed on a fire, or other source of heat, and heated under circumstances in which its vapor is per- mitted readily to escape into the air, the temperature of the water can never, at ordinary atmospheric pressures at the level of the sea, be raised above that of its boil- ing point; namely, 212 F. or 100 C. Under these conditions the temperature of the boiling point of water is the tem- perature of its volatilization. This is a general law for the volatilization of all substances ; namely, if the vapor which is formed during volatilization is free to escape, the temperature of the liquid will remain constant during its ebullition or volatilization. An increase in the tempera- 28 ELECTRIC ARC LIGHTING. ture of the source, has the effect only of accelerating the volatilization and increas- ing the rate of the formation of vapor. In the same way it is believed that the tem- perature of the positive carbon or crater in the arc lamp is thus limited to the tem- perature of the boiling or volatilization of carbon under atmospheric pressures. An increase in the current strength; i. hm - The resistance of a wire or circuit is a very important quantity and constantly enters into electrical determinations. As examples of a few resistances of well-known apparatus we may take the following : The ordinary Bell telephone has a resist- ance of about 75 ohms. An ordinary 16-candle-power incan- descent lamp has a resistance of about 250 ohms, when hot. The resistance of a mile of ordinary iron telegraph wire is about 13 ohms. Electromotive forces are measured in units of electromotive force called volts. ELEMENTARY ELECTRICAL PRINCIPLES. 45 All electric sources produce electromotive forces, and it is these E. M. Fs., acting on a conducting circuit, which cause electricity to flow through the circuit. A well-known electric source, called the blue-stone voltaic cell, produces an E. M. F. of approximately one volt. When it is desired to obtain a higher E. M. F. from blue-stone cells, it is necessary to connect a number of separate cells in series, so as to permit them to act as a single source. Such a combination is called a voltaic battery. A dynamo-electric machine is another source employed for pro- ducing E. M.Fs., the value of which depends, in any given machine, among other things, upon the rate of rotation of the armature. Dynamo-electric machines for the proper operation of incandescent lamps, produce E. M. Fs. of about 120 volts; those for operating arc lamps, may produce E. M. Fs. varying from 50 to 10,000 volts, according 46 ELECTRIC ARC LIGHTING. to the number of lamps placed in the same circuit, each ordinary arc lamp requiring, approximately, 50 volts to maintain it. Railway generators, required to operate railway systems, are designed to supply an E. M. F. of about 500 volts, between the trolley and the track wire. The most important consideration re- specting an electric circuit, is the quantity of electricity per second, or the current, which passes through it ; or, in other words, the rate at which electricity is caused to flow through the circuit. The quantity of elec- tricity which flows through any circuit is measured in units of electric current called amperes. In the case of the electric cir- cuit, as in the case of the hydraulic circuit, the rate of the flow is conveniently meas- ured as the quantity per second ; thus we may speak of a gallon per second. So ELEMENTARY ELECTRICAL PRINCIPLES. 47 in the electric circuit, the rate of flow or current is conveniently referred to a certain quantity per second. The unit of electric quantity is the coulomb, and is such a quan- tity as will produce, when passing in one second, a unit current or rate of flow, or, one ampere. Or, in other words, if one coulomb of electricity passes through an electric circuit in a second of time, it will produce a rate of flow which can be cor- rectly expressed as one ampere. An ordi- nary 16-candle-power incandescent lamp requires, usually, a current of about half an ampere to maintain it. A 2,000 candle- power arc lamp of the ordinary outdoor type requires nearly 10 amperes. A street car motor when in operation, requires on an average about 1 2 1/2 amperes. A tele- graphic relay requires about th of an ampere, or about 10 milliamperes. 48 ELECTRIC ARC LIGHTING. In order to determine the value of the current which will pass in any gi\ 7 en cir- cuit under given conditions of E. M. F. and resistance, reference is had to a law, called Ohm's law, after the name of its discoverer. Ohm's law may be briefly stated as follows : The current strength in any circuit is equal to the E. M. F. acting on that cir- cuit, divided by the resistance of the cir- cuit ; or, briefly, the current which will flow in amperes, is equal to the E. M. F. ex- pressed in volts, divided by the resistance expressed in ohms. Suppose, for example, that an E. M. F. of 100 volts, acts on a circuit, the resist- ance of which is 50 ohms; then the cur- rent strength which will flow through the circuit under these conditions will be ELEMENTARY ELECTRICAL PRINCIPLES. 49 100 -T- 50 = 2 amperes, and this current will be maintained so long as the E. M. F. and resistance bear this ratio to each other. When an electric current passes through a circuit, certain characteristic effects are produced in various apparatus, such as lamps or motors, placed in the circuit. In producing these effects, energy is expended or work is done, which energy is derived from the electric current, which in its turn derives it from the electric source. For example, when an electric motor is ob- served to raise a number of passengers in an elevator, the work which it has to do in order to lift them against gravitational force, is derived from the electric circuit which supplies the motor, and the circuit in its turn receives this power from the generator supplying the E. M. F., while the generator receives the same from the 50 ELECTEIC ARC LIGHTING. engine, which drives it. The amount of work done in raising the elevator may be measured by the number of pounds weight in the loaded elevator, and the distance in feet through which the elevator is raised. For example, if the elevator with three passengers weighs 2,000 pounds, and if the distance through which it was lifted by the motor was 200 feet, the work done by the motor in raising the elevator would be 200 X 2,000 = 400,000 foot-pounds. A unit frequently employed for the unit of work, is called the foot-pound, and is the amount of work done in lifting one pound, through a vertical distance of one foot, against the earth's gravitational pull. The foot-pound is not, however, the unit of work that is generally employed in electrical measure- ments. For several reasons it is more con- venient to employ a unit of work called the joule, which is, approximately, 0.738 ELEMENTARY ELECTRICAL PRINCIPLES. 51 foot-pound. One one-foot pound is, there- fore, greater than a joule, being approxi- mately 1.355 joules. Consequently, the amount of work expended by the motor on the elevator, in the case jnst alluded to, might be expressed as 400,000 X 1.355 = 542,000 joules. When an E. M. F. acts upon a current in a circuit it always expends energy, on the current, or does work on it. In other words, an E. M. F. cannot drive a current through a circuit without the expenditure of energy, or without doing work. In ordinary mechanical work, the amount of energy expended may be expressed, as we have seen, by the foot-pound, as being equal to a number of pounds raised through a certain number of feet. So in electric work, the amount of energy expended may 52 ELECTRIC ARC LIGHTING. be expressed by the volt-coulomb, that is, by a certain number of coulombs passing through a circuit under a pressure of a cer- tain number of volts. For example, if a circuit has acting in it an E. M. F. of 120 volts, and 100 coulombs of electricity pass through the circuit, either in a second, an hour, or a day, the total amount of work expended in this flow will be 120 x 100 = 12,000 volt-coulombs. The electrical units have been so chosen that a volt-coulomb is equal to the joule ; so that in the preced- ing case the work done would be 12,000 joules = 12,000 x 0.738 = 8,856 foot-pounds. The rate-of-doing-work or of expending energy is called activity. The unit of ac- tivity generally employed in ordinaiy me- chanical applications is the foot-pound-per- second, or, in larger units, the horse-power, which is 550 foot-pounds per second. ELEMENTARY ELECTRICAL PRINCIPLES. 63 Thus, if the elevator previously mentioned was lifted through a total distance of 200 feet, in 40 seconds, the average rate of do- ing work in this time would have been r~ = 10,000 foot-pounds-per-second. It is evident that, no matter how long the motor took to raise the elevator, the total amount of work done would be the same, whether the elevator were lifted in one second or in one minute, but the rate at which the work was done would vary very greatly, since, in the former case, the energy would have to be expended sixty times more rapidly than in the latter. The electrical unit of activity is the joule- per-second, or the volt-coulomb-per-second. Since a coulomb-per-second is, as already stated, equal to one ampere, the electrical unit of activity is the volt-ampere; or, as 54 ELECTRIC ARC LIGHTING^. it is more frequently called, the watt. If then, we multiply the number of volts, which are acting on a circuit, by the num- ber of amperes passing through it, the product will be the number of watts, representing the activity, or the rate-of- working in the circuit. For example, an ordinary outdoor arc lamp usually requires an E. M. F. of about 45 volts to be main- tained at its terminals, and a current strength flowing through the lamp of 10 amperes. Under this pressure of 45 volts, the activity, or rate-of -doing-work, in the lamp is usually about 45 X 10 = 450 volt- amperes = 450 watts, and since 746 watts are equal to one horse-power, the average rate of working in an ordinary arc lamp is about 450 HTT^-ths horse-power; or, approximately, 3/5ths horse-power. Similarly, an ordinary incandescent lamp, operated from a 110-volt ELEMENTARY ELECTRICAL PRINCIPLES. 55 circuit, usually requires a current of about half an ampere. The activity in such a lamp is, therefore, 110 X 1/2 = 55 watts, or about 55/746ths horse-power, or about 1/1 3th horse-power. CHAPTER IV. AEC LAMP MECHANISMS. SINCE, during the establishment of the voltaic arc, the carbons are consumed at unequal rates, and the maintenance of the arc depends upon their preserving a proper distance from each other, it is evi- dent that some form of mechanism is necessary, which shall automatically main- tain this distance between them under all circumstances. In the early history of the arc, such mechanisms were controlled by hand, but it is needless to say that hand regulators have now been entirely re- placed by automatic regulators. AKC LAMP MECHANISMS. 57 There are two distinct classes of mechanism employed in arc - lamps; namely, those which maintain constant the distance between the electrodes, but do not keep the position of the arc fixed, and those which not only keep the dis- tance between the carbons fixed, but which also maintain fixed the position of the arc. In the first class of mechanisms but one carbon, usually the upper or posi- tive carbon, is fed or moved ; in the other class, both carbons are moved, and in this case, since the positive is consumed more rapidly than the negative, the relative mo- tions of the two carbons must be different. To the first class of mechanism belongs the ordinary type of arc lamps employed for street lighting. To the second class belong various projectors, search lights or other apparatus employing reflectors or lenses. Here it is necessary that the arc 58 ELECTRIC ARC LIGHTING. shall be maintained at the focus of the reflector or lens. In any form of arc lamp, three condi- tions must be complied with, by the feeding mechanism, in order to insure con- tinuous operation : (1) It must bring the carbons initially into contact. (2) It must then separate the carbons to a suitable distance and maintain this distance. (3) It must cause or permit the carbons to approach when consumption has ren- dered their separating distance too great. The carbon electrodes of arc lamps are placed in the lamp in various positions. Lamps have been employed in which the carbons are inclined, or placed horizontally or vertically as shown in Fig. 6 ? at A, j5, ARC LAMP MECHANISMS. 69 and C. The vertical position, however, is now almost invariably adopted, since it not only places the positive crater in the most effective position for throwing light down- wards, but it also permits the approach of the positive towards the negative carbon m. PIG. 6. ARRANGEMENT OF ARC LIGHT CARBONS. to be effected by the influence of grav- ity. As we shall see, however, in many forms of projectors, where it is desired that the most powerful beams shall be pro- jected in a nearly horizontal direction, the carbons are inclined in the same straight line from the vertical as shown in Fig. V. 60 ELECTRIC ARC LIGHTING. Before proceeding to a description of the different forms of arc-lamp mechan- isms, it will be necessary to describe in de- tail the various methods by which the lamps are connected with their generators. \ FIG. 7. ARRANGEMENT OF CARBONS FOR USE IN A PROJECTOR. Although many forms of circuits for this purpose are in use, yet they can all be arranged in two classes ; namely, the (1) Series circuit. (2) Parallel circuit. In the series circuit of arc lamps, the current passes through each lamp in sue- ARC LAMP MECHANISMS. 61 cession. A series connection of arc lamps is shown in Fig. 8, where six arc lamps are connected to the line in series. Here as will be seen, the current entering at the left hand or positive terminal of the lamp, passes through the lamp mechanism, FIG. 8. SERIES CONNECTION OF ARC LAMPS. issues from the upper carbon, which is here the positive carbon, and leaves the lamp after having passed through the negative carbon, at its negative terminal. The negative carbon of the first lamp, is thus connected to the positive terminal of the second lamp, and its negative terminal 62 ELECTRIC ARC LIGHTING. to the positive terminal of the third, and so on throughout the series. In other words, the current entering at the positive end of the line passes through each lamp in succession, leaving each lamp at its negative terminal. In the drawing, the lamps, for convenience, are shown as placed close together, although, of course, in practice, they may be separated by con- siderable distances. The generator or dynamo-electric ma- chine is not shown in the figure, but it will be understood that the two wires, A and B, are connected to the terminals of the dynamo which generates the current, so that the electric current leaving the dynamo and entering the circuit at the point A, passes successively through each of the lamps shown, again entering the dynamo at, say, the point .Z?. ARC LAMP MECHANISMS. 63 In the parallel or multiple connection of arc lamps, as shown in Fig. 9, all the posi- tive terminals of the separate lamps are connected to a single positive lead or con- ductor, and all the negative terminals, to a single negative lead or conductor. Here it B B FIG. 9. PARALLEL OK MULTIPLE CONNECTION OF ARC LAMPS. will be seen that all the six lamps shown have the current entering at their positive terminals and passing out at their negative terminals. The current, as before, leaves the machine, enters the positive lead near the point marked A, and returns to the 64 ELECTRIC ARC LIGHTING. machine after having passed through all the lamps in the circuit, at the point marked J9. The properties and peculiarities of the series and multiple circuit, will be better understood when a fuller knowledge has been obtained of the lamp mechanism, and will, therefore, be reserved for a subse- quent chapter. Commercial arc lighting, as employed at the present day, invariably employs considerably more than a single lamp in a dynamo circuit. In the early histoiy of the arc, where but a single lamp was employed in connection with a single circuit, a much simpler form of feeding mechanism was compatible with fairly satisfactory uni- formity in the intensity of the light fur- nished, and some of the earlier forms of ARC LAMP MECHANISMS. 65 arc lamp mechanism consisted essentially of a single electromagnet placed in the main circuit. One of such simple forms of early sin- gle-light lamps was the arc lamp of Archereau, shown in Fig. 10. This lamp possessed the merit of extreme simplicity and gave fairly good results. It will be seen that the upper carbon was fixed, while the lower carbon was suitably sup- ported on a rod of iron placed inside a helix or coil of insulated wire called a solenoid, being balanced therein by a counterpoise or weight passing over a pulley, as shown. When no current was passing through the lamp, the weight raised the carbon and its supporting rod, and brought the end of the lower car- bon into contact with the upper carbon. As soon as the current passed through the 66 ELECTRIC ARC LIGHTING. circuit, the attraction of the solenoid on its iron core caused the solenoid to be FIG. 10. AUCHEREAU'S REGULATOR. sucked into the core, with a consequent separation of the lower movable carbon from the upper carbon and the formation ARC LAMP MECHANISMS. 67 of an arc between the two. When, during the maintenance of the arc, the carbons were gradually consumed and the distance between their free ends thus increased, the smaller current strength passing through the circuit, on account of the increase in its resistance, caused the solenoid to attract its core less powerfully, and per- mitted the weight to move the lower car- bon toward the upper carbon. On the other hand, when this distance became too small, the increased current strength pass- ing through the solenoid again caused the separation of the lower carbon from the upper. This lamp, despite its simplicity, gave fairly good results. Other early forms of arc lamps were operated on a somewhat similar principle, and consisted of devices whereby an elec- tromagnet, placed in the main circuit, 68 ELECTRIC ARC LIGHTING. caused the separation of the carbons, which were always in contact when the current was not passing through the lamp. Most of these forms fed the upper carbon, the mechanism being such that the weakening of the current, consequent upon the forma- tion of too long an arc, permitted the upper carbon to descend by gravity to- wards the lower carbon, while the strength- ening of the current, following a de- creased distance between the carbons, again insured a lifting of the upper carbon. Lamps of a description somewhat similar to the preceding are still in use on multiple circuits, and some of these will be subse- quently shown. A little consideration will show that a lamp with a single electro- magnetic feeding device is not suitable for use in series-connected circuits, especially when, as is usually the case, a very great ARC LAMP MECHANISMS. 69 number of lamps are placed in the same circuit. Series-connected arc light circuits in- variably employ two electromagnets, in the feeding and controlling mechanisms, princi- pally for the reason that such a system permits the feeding of each lamp to depend entirely on its own requirements, and pre- vents it from being affected by every other lamp in the circuit. Suppose, for example, that one of the carbons of a single lamp should temporarily stick, or be iinable to move towards the other carbon, thereby unduly increasing the size of its arc. This increase in the resistance of the circuit, will, of course, diminish the current strength in all the other lamps, and they will, in consequence, all regulate so as to feed their carbons too close, in an endeavor to restore the current strength. If, then, 70 ELECTRIC ARC LIGHTING. the temporarily arrested lamp feeds sud- denly, the current in the circuit will be much too strong, and there will be a rapid regulation in all the lamps, tending to separate the carbons. In this way, the lamps become unstable in their adjust- ments, and rapidly oscillate, or see-saw, pulling alternately long and short arcs, at the same time causing a marked travelling of the arc around the carbon, and a conse- quent flickering of the light. It is evi- dently necessary, therefore, to adopt some other expedient. The great discovery, which rendered series arc lighting a possibility, was made as early as 1855, by Lacassagne and Thiers, who introduced into the arc lamp mechanism, an electric device known as a derived circuit or shunt. If more than a single path is open to an electric circuit, ARC LAMP MECHANISMS. 71 when, for example, as in Fig. 11, a circuit branches through the two paths AGB and ADJ3, the proportion in which the current will divide through these two circuits will depend upon their relative conducting powers, and will be, therefore, inversely as FIG. 11. DERIVED OB SHUNT CIRCUIT. their relative resistances. If the circuit AOJB, originally existed alone, and the additional circuit ADB, were provided by connecting the conductor Z>, at the points A and D, then the latter would be called a derived or shunt circuit, and this portion of the conductor would be said to be placed " in shunt " with the conductor A OB. 72 ELECTRIC ARC LIGHTING. If, in the case shown in Fig. 11, the re- sistance of the two circuits be equal, then half of the current would pass through each branch, or the current would divide equally, the current strength being the same in each branch. If, however, the branch ADS, have, say 100 times the re- sistance of the branch AGB, then the amount which will flow through ADB, will be the th part of that which will 100 flow through A OB / or, in other words, the greater the resistance of the path ADB, relative to the resistance of the path A CB, the smaller will be the proportion of the current which passes through it. If, in Fig. 11, the resistance ABD, is fixed in amount, and A CD, is variable, then these variations will automatically vary the cur- rent strength in ADB, as well as in ACS. ARC LAMP MECHANISMS. 73 We have already pointed out the fact that series-connected arc lamps cannot be made to operate with the steadiness re- quired for commercial purposes, when their mechanism contains but a single electro- magnet, since, under these circumstances, the operation of the feeding mechanism is not only dependent on the requirements of the lamp itself, but is liable to be affected by the action of any other lamp in the cir- cuit. A single faulty lamp thus possesses the power of producing unsteadiness in all the other lamps in the circuit. It is evi- dent, therefore, that for commercial pur- poses, a successful lamp mechanism must be able to effect the regulation indepen- dently of the other lamps in the circuit. To give the arc lamp this power, a shunt or derived circuit is required. Since its in- troduction into the art by Lacassagne and Thiers, many modifications of the principle 74 ELECTRIC ARC LIGHTING. have been made, but all the series arc lamps of to-day employ essentially this principle. It is, therefore, important to FIG. 12. DIAGRAM OF SHUNTS AND SERIES MAGNETS. describe in detail the general plan of operation of such arc-lamp mechanism. Fig. 12 represents, diagramrnatically, the essential relations of a shunt magnet as utilized in an arc lamp mechanism. Here A, represents the voltaic arc established between the carbons, M, a magnet placed ARC LAMP MECHANISMS. 75 in the direct circuit of the arc, and /SJ a shunt magnet, of fine wire and having a high resistance, placed in the derived or shunt circuit around the arc as shown. In accordance with the principles already explained in connection with shunt circuits and Fig. 11, it is evident, since the resist- ance of the magnet S, is large, that practi- cally all the current passing through the lamp will traverse the arc. The pressure existing between the main terminals T^ and T 2 , expressed in volts, will depend upon two circumstances ; namely, (1) The counter E. M. F. of the arc (C. E. M. F.) ; i. e., an E. M. F. opposed or acting in the opposite direction to that which causes the current to pass through the arc. (2) The drop of pressure or apparent C. E. M. F., due to the combined resistance of the carbons; the resistance of the arc 76 ELECTRIC ARC LIGHTING. itself between carbons, and the resistance of the coils of the magnet M. When a current is passed through a resistance under the action of an E. M. F., then in accordance with Ohm's law, the pressure at the terminals of the resistance, in volts, will be the product of the resist- ance in ohms and the current strength in amperes. If a pressure of 10 volts be maintained at the terminals of a resistance of 5 ohms, the current strength passing through the resistance will, by Ohm's law, be, 10 volts -5- 5 ohms = 2 amperes; or, we may regard the product of 5 ohms X 2 amperes =10 volts, as being the drop of pressure, which necessarily attends the pas- sage of the current through the resistance. Of the resistance in the main arc cir- cuit ; namely, the carbons, direct magnet, AEC LAMP MECHANISMS. 77 and arc proper, the values of the two former, assuming a fixed temperature and length of carbons, are fixed, while the resistance of the arc itself varies with its length, and area of cross-section, the longer the arc and the smaller the area of cross-section, the greater its resistance. The resistance of the arc carbons may be 3 about ths of an ohm, so that a current of 10 amperes, passing through the car- bons, would produce a drop of 10 x o ths or 3 volts ; i. , provided that these latter are in contact. The excitation of the coil Mj will cause the cut-out e7, to be broken, and the upper carbon to be lifted, thus establishing the arc. If the pressure across the arc becomes excessive, the shunt winding S t neutralizes the main winding J/, sufficiently far to permit the clutch to 112 ELECTRIC ARC LIGHTING. FIG. 23. INTERIOR MECHANISM OF ARC LAJCP. ARC LAMP MECHANISMS. 113 relax and the carbon to feed. If the cur- rent through S t becomes excessive the cut- out magnet K, short circuits the lamp. An exceedingly great number of arc lamp mechanisms have been devised, many of which are in extended use. Though all of these forms differ in minor de- tails and in the arrangement of interior circuits, yet practically all lamps suitable for series connection in arc-light circuits are designed on essentially the same general principle ; that is to say, an elec- tromagnet in the main circuit operates on mechanism which effects the separation of the carbons, while another electromagnet, placed in the shunt circuit, effects an approach of the carbons. Moreover, all of these lamps are provided with some form of automatic cut-out device, which pre- vents the failure of any one lamp to 114 ELECTRIC ARC LIGHTING. FIG. 24. MECHANISM OP ABC LAMP. ARC LAMP MECHANISMS. 115 M- Fio. 25. SINGLE CABBON AKC LAMP. 116 ELECTRIC ARC LIGHTING. operate, from extinguishing the entire cir- cuit. In addition a hand switch is em- ployed for convenience in cutting out the lamp when not required for use, as well as for safety in re-carboning the lamp. A few other forms of lamp mechanisms are illustrated in figures 22, 23, 24 and 25. CHAPTER V. SERIES-CONNECTED ALL-NIGHT LAMPS. DURING the continuance of the arc, on account both of the volatilization and com- bustion of the carbon with the oxygen of the air, a wasting or consumption of the electrodes takes place. In the case of the positive carbon this wasting is due both to volatilization and to oxidation; the nega- tive carbon having, as we have seen, a lower temperature, only wastes through oxidation. Moreover, the rate of consump- tion of the negative carbon is prolonged by the fact that it receives a deposition of cooled carbon vapor from the positive crater. The positive carbon, therefore, 118 ELECTRIC AKC LIGHTING. consumes or wastes away more rapidly than the negative carbon. This rate of consumption will necessarily vary with the character of the carbons, with their size and with the strength of current em- ployed, but with the carbons ordinarily employed, the consumption of a 1/2" posi- tive rod, in a 2,000 candle-power lamp, takes place at a rate somewhat greater than one inch per hour. The rate of con- sumption of the negative carbon is about half as much, or about 1/2" per hour. Since, during the winter nights in high latitudes, the hours of darkness greatly exceed the life of the 12" x 1/2" carbon, which is approximately nine hours, a necessity arises for re-carboning the lamp, during its use. In order to avoid this necessity, and produce what is called an all-night arc lamp, various devices have SERIES CONNECTED ALL-NIGHT LAMPS. 119 been employed. An early method of obtaining this result was that devised by De Mersanne. It might be supposed that the problem of producing an all-night lamp could readily be solved by increas- ing the length of the carbons, but a little reflection will show, that since the positive carbon in nearly all forms of lamp mechan- isms is connected to the lamp rod, whose length, in order to permit of continuous feeding, is approximately the same as the positive carbon, too great an increase in the length of the positive carbon would make the lamp unwieldy and would limit its use to rooms with high ceilings. More- over, the necessity existing in all arc lamp mechanisms in which the carbons are vertical, of obtaining truly straight carbons free from curvature, would be greatly increased with the increase in length. 120 ELECTRIC AP.C LIGHTING. De Mersanne in endeavoring to solve the problem of all-night lamps, devised a mechanism in which this objection arising from the excessive length of the carbons is avoided. In his regulator, the carbons were placed horizontally, both in the same horizontal line. By employing carbons a metre or more in length, he was able to obtain a duration of light exceeding that of the longest night in winter. The De Mersanne regulator can scarcely be re- garded as having possessed commercial merit, since the expense of the carbons and their liability to fracture, were greater than in the ordinary lamp. Moreover such lamps necessarily produced an irreg- ular distribution of light, from the fact that the positive crater, being horizontal, threw more light in one direction than iu another. SERIES-CONNECTED ALL-NIGHT LAMPS. 121 It might be supposed that the problem of all-night lighting would find a ready solution in increasing the diameter of the carbons, and many inventors have pro- duced lights of this type. From what has been said concerning the liability of the arc to travel, where carbons of fairly large diameter are employed, and the conse- quent unsteadiness of the light so pro- duced, it is evident that such forms of all-night lamp are objectionable from the flickering of the light they produce. An early form of large carbon, all-night lamp devised by Wallace, is represented in Fig. 26. Here the carbon electrodes are formed of plates instead of rods, the arc being formed at some point between them. In this form of lamp, like the arc lamp mechanisms already described, when no current is passing, the carbons are in con- tact. On the passage of the current the ELECTRIC ARC LIGHTING. FIG. 26. THE WALLACE ALL-NIGHT LAMP. carbon plates are separated, and the arc is established at the nearest points between their opposed surfaces. In practice, how- ever, the light produced by this form of SERIES-CONNECTED ALL-NIGHT LAMPS. lamp proved so unsteady from the ten- dency of the arc to travel, that it never attained extensive use. FIG. 27. PILSEN LAMP. A similar type of lamp is shown in Fig. 27, named the Pilsen lamp. It is practi- cally identical with the Wallace lamp, ex- 124 ELECTRIC ARC LIGHTING. cept that the plates are narrower. Like the Wallace lamp this never gave a satis- factory steady light. Notwithstanding the unsatisfactory ser- vice of the above type of lamp, many invent- ors have endeavored to solve the problem of all-night lighting in a similar manner, by the employment of carbons of fairly con- siderable diameter. In some forms of such lamps, both carbons are made large ; in others, only one, generally the positive carbon is increased in dimensions. Proba- bly the most practical form of lamp of this general type was one employed at a very early era in arc lighting (1845), by an English inventor, named Wright. This lamp more nearly solved the problem in that, although large masses of electrodes were employed, yet the position of the arc was maintained fairly constant and the SERIES-CONNECTED ALL-NIGHT LAMPS. 125 consumption rendered fairly uniform. In Wright's all-night lamp, one or both of the carbons had the form of a disc, the FIG. 28. HARRISON'S LAMP. arc being established either between two discs, rotating in planes at right angles to each other, or, as in a modified form of Wright's lamp invented by Harrison in 126 ELECTRIC ARC LIGHTING. 1857. Harrison's regulator is shown in Fig. 28. Here the arc is established between a vertical carbon rod, and a disc revolving beneath it. The operating mechanism is placed in the lower part of the lamp. An evidence of the tendency at a later date to attempt to obtain an all- night lamp by increasing the size of the carbons, is seen in the form of lamp repre- sented in Fig. 29. Here elliptical carbons are employed, both of which are made of fairly large area of cross-section. Another endeavor in the same direction is shown in Fig. 30. Here the upper carbon is of markedly large dimensions, and, in order to render the consumption of its surface more nearly uniform, the upper carbon in being fed is given a lateral SERIES CONNECTED ALL-NIGHT LAMPS. 127 FIG. 29. ALL-NIGHT ELLIPTICAL CARBON LAMP. 128 ELECTEIC ARC LIGHTING. FIG. 30. RECIPROCATING CARBON ALL-NIGHT LAMP. slow reciprocating motion, so as to bring fresh portions of its surface into action. This lateral motion is obtained with the aid of a rack shown on the right hand side of the frame. SERIES-CONNECTED ALL-NIGHT LAMPS. 12d Perhaps, the best solution for all-night series arc lamps has been found in what are called double-carlan lamps, or twin- carbon lamps. This type of lamp, as the name indicates, consists essentially of a lamp provided with a mechanism which controls a double set of positive and negative carbons, of the same size as those used in ordinary lamps. The mechanism is such that on the passage of the current through the lamp only one pair of carbons is so separated that the arc can be formed between them, the other pair being separated too far to permit the arc to be maintained between them. In most forms of double-carbon lamps, the same feeding mechanism is employed for each set of carbons, the arrangement being such that it brings one pair of carbons into action, and when this pair is con- sumed the second pair automatically receives the current. The means by 130 ELECTRIC ARC LIGHTING. which one of the earliest forms of these lamps effected this result is shown in Fig. 31. In this form, the clamp or lifting device is represented as a ring-clutch or FIG. 31. BRUSH WASHER OR RING CLAMP. clutch-washer. It is evident that when such a ring is maintained in a horizontal position, the lamp rod can slip through it, but wheu tilted, it grips the lamp rod at diagonally opposite corners. SERIES-CONNECTED ALL-NIGHT LAMPS. 131 In order to ensure the formation of the arc between one pair of carbons only, the FIG. 32. BRUSH DOUBLE LAMP. lifting device K, that acts on the washer- clutch by the jaws which embrace them, has one pair of jaws wider than the other 132 ELECTRIC ARC LIGHTING. J. MECHANISM OF A SERIES DOUBLE-CARBON ARC LAMP. SEUIKS-CONttECTED ALL-NlGIIT LAMPS. 133 pair, so that when the frame is lifted, the washer connected with the wider jaws takes a grip before the other, and, conse- quently, lifts its carbon higher than the other. In this case the arc is permanently established across the shorter distance, and the subsequent feeding of the lamp mechanism affects this pair of carbons alone, and not the other pair, because though these are raised and lowered with the first, yet the distance between them is too great for the arc to be established. When, however, the consumption of the carbons has reached the point when they can no longer come into contact, and the frame drops, the arc is established be- tween the other pair of carbons and con- tinues there until they are consumed. The appearance presented by this form of double lamp is shown in Fig. 32. An inspection of this will show that the same 134 ELECTRIC ARC LIGHTING:. FIG. 34. MECHANISM OP A SERIES DOUBLE-CARBON ARC LAMP. SERIES-CONNECTED ALL-NIGHT LAMPS. 135 FIG. 35. FORM OF DOUBLE-CARBON ARC LAMP. 136 ELECTRIC ARC LIGHTING. electromagnets are employed to operate both pairs of carbons. Fig. 33 represents the mechanism of another form of double- carbon lamp, pro- vided with gear feed. Here the apparatus is essentially the same as that already described in connection with Fig. 15, a simple device being provided, whereby, when one pair of carbons is consumed, the current is automatically sent to the other. Fig. 34 represents the clutch feed mechanism in a double-carbon arc lamp. Here the mechanism is of the same type as that shown in Fig. 17. Fig. 35 represents still another form of double-carbon arc lamp. CHAPTER VI. CONSTANT-POTENTIAL LAMPS. ARC lamps, as we have already seen, may be connected either in series or in parallel. If we assume that each lamp takes a cur- rent of 10 amperes, when supplied with a constant pressure of 45 volts at its ter- minals, then the activity developed in the lamp will be 450 watts. If now, 100 of these lamps have to be lighted together, it is possible to connect them either in series or in parallel. If they are connected in series, the current strength in the circuit must everywhere be 10 amperes, but the pressure at the dynamo terminals, if we 187 138 ELECTRIC ARC LIGHTING. neglect the drop of pressure in the line wires, will be 100 X 45 = 4,500 volts. On the other hand, if we connect the lamps in parallel, each lamp will take 10 amperes, and the total current supplied by the dynamo will, therefore, be 10 X 100 = 1,000 amperes, at a pressure, neglecting drop in the line wires, of 45 volts. It is evident, therefore, that a series circuit is essentially a high-tension but low-current circuit, and that a multiple or parallel circuit is essentially a low-tension but high- current circuit ; but, neglecting the drop of pressure, or power expended, in the line wires, the amount of energy delivered to the circuit will, in each case, be the same. Thus, the series circuit would take from the dynamo 4,500 volts X 10 amperes = 45,000 watts = 45 KW. The multiple circuit would take 45 volts x 1,000 am- peres = 45,000 watts = 45 KW. CONSTANT-POTENTIAL LAMPS. 13D When, however, we come to study the effects of adopting one or other of these two systems of distribution upon the nature and amount of line wire employed, we are met with a very marked contrast. In the case of the series circuit, it is evi- dent that the line wire has to carry a cur- rent of but 10 amperes, and, consequently, its dimensions will always be compara- tively small. The size of wire commonly adopted for arc lighting in such circuits, is No. 6 B. & S. (Brown & Sharpe) or A. W. G. (American Wire Gauge). This wire has a diameter of 0.162", and a resist- ance per mile of a little more than 2 ohms. Suppose now that these 100 arc lamps have to be distributed uniformly around a circle of 10 miles circumference, as shown iu Fig. 36, adjacent lamps being, there- fore, 528 feet apart. On the series system 140 ELECTRIC ARC LIGHTING. the length of No. 6 wire required would be 10 miles, offering a total resistance, of say 20 ohms. The total drop of pressure in FIG. 36. SERIES ARC LIGHT DISTRIBUTION. the wire, would, therefore, be 10 amperes X 20 = 200 volts, making the pressure at the dynamo terminals 4,700 volts, repre- CONSTANT-POTENTIAL LAMPS. 141 senting a total activity of 47 KW, or 2 KW, expended uselessly in the line wire. If, however, 100 arc lamps be supplied in parallel, from two wires carried around the circle from a single point of supply, as shown in Fig. 37, then, in order to have 2 KW, expended in the wires as before, or in other words, to maintain the same economy in distribution, it would be neces- sary to employ two wires, each having, approximately, 2,500 times the weight and cross-section of the No. 6 wire in the pre- ceding case, so that the total weight of copper will be increased about 5,000 times. It is evident, therefore, that parallel dis- tribution is far more expensive for conduct- ors, at a given efficiency of transmission, than series distribution, and the amount of copper which has to be employed increases 142 ELECTRIC ARC LIGHTING. inversely as the square of the pressure. Thus, if we raise the pressure 10 times at the dynamo brushes, we employ 100 times FIG. 37. PARALLEL ABC LIGHT DISTRIBUTION. less copper in the distributing system, other things remaining the same. In other words, in the series circuit, the economy increases with the number of CONSTANT-POTENTIAL LAMPS. 143 lamps connected in the circuit, while in the parallel circuit, the economy decreases with the number of lamps in the circuit. On the other hand, however, when the distance to which the lighting has to be extended is comparatively small, as fre- quently occurs, for example, in large build- ings, or -in streets of large cities, the difference between the economy of dis- tribution by series and by parallel systems greatly diminishes. Large cities are generally supplied with incandescent lighting by systems of under- ground mains. When these mains form part of & low-pressure system; i. ?., of a system employing a pressure not in excess of 250 volts, it will generally be found more convenient to light a certain number of arc lamps from such circuits, rather than install a special series circuit and system. 144 ELECTRIC ARC LIGHTING. This convenience is evidenced by the fact that in a single city, Brooklyn, there are at the present time no less than 3,750 FIG. 38. INCANDESCENT CIRCUIT, WITH SHOBT LAMPS. arc lamps operated in parallel from the low-tension system of 230 volts. Since the pressure in the low-tension in- candescent system is never less than 110 volts, in order to utilize such a system, to as great advantage as possible, in arc light- ing, it is necessary to place two arc lamps in series across such mains. If only one CONSTANT-POTENTIAL LAMPS. 145 lamp requires to be installed, additional resistance is inserted with the single lamp. Fig. 38 represents two arc lamps, of the short, stumpy character, suitable for low ceilings, connected in series with a rheostat and controlled by a double-pole snap switch, from a safety block, connected with the 110-volt circuit. Fig. 39, represents the same arrange- ment in the case of two lamps, in which case no additional resistance outside the lamps is required. Such, lamps, however, usually insert a resistance in their interior, capable of maintaining a drop of say 10 volts, when in operation. Four arc lamps are sometimes joined in series across 250 volts pressure, and eight or nine across a 500-volt railway circuit. Fig. 40, illustrates the connections of a 146 ELECTRIC ARC LIGHTING. lamp of the same type as that shown in Figs. 15, 17, and 33, but arranged for low- tension circuits. The only essential differ- FIG. 39. INCANDESCENT CIRCUIT WITH Two ARC LAMPS. ence between this arrangement and that of Fig. 15, lies in the fact that the hand switch represented at the negative terminal does not short circuit the lamp, but merely breaks its circuit, also that a safety fuse is placed between the lamp and the line, CONSTANT-POTENTIAL LAMPS. RESIST 147 FIG. 40. CONNECTIONS OF CONSTANT-POTENTIAL ABC LAMP. on one side, and a fixed resistance, between the lamp and the line on the other side. The fuse is intended to cut the lamp out 148 ELECTRIC ARC LIGHTING. FIG. 41. INTERIOR MECHANISM OF A FORM OF CONSTANT- POTENTIAJU ARC LAMP. CONSTANT-POTENTIAL LAMPS. 149 of circuit, in the manner of an automatic switch, should the current become ex- cessive. Fig. 41, represents a form of arc lamp mechanism suitable for use on constant- potential circuits, and corresponding to the type of mechanism for series circuits represented in Fig. 18. In this form of lamp the carbons are not in contact when no current is passing through the apparatus. The main-circuit magnet is horizontal and is marked M. The shunt-circuit magnets are marked , and the clutch c. A long resistance coil 7?, is designed to be cov- ered by a suitable tube, not shown in the figure. Fig. 42, is a diagram showing the con- nections of the preceding lamp mech- anism. On the completion of the circuit 150 ELECTRIC ARC LIGHTIHGL FIG. 42. CONNECTIONS OF ARC LAMP MECHANISM SHOWN IN FIG. 39. CONSTANT-POTENTIAL LAMPS. 151 through the tipper resistance, the current passes through the fine wire vertical coils alone, since the carbons are not in contact ; the armature A, is raised and the clutch is thereby depressed, carrying with it the lamp rod and upper carbon until contact is made beneath, with the lower carbon. The current then immediately passes through the carbons, and the main-circuit magnet, which, being more powerful than the shunt magnet, opposes and overcomes its pull, by raising the armature 7?, thus lifting the upper carbon to the proper distance and establishing an arc. The position of the armature lever is de- termined by the relative powers of the op- posing main and shunt magnets. As soon as the arc becomes too long, the main magnet weakens, while the shunt magnet strengthens, thus depressing the lamp rod and clutch, until the clutch stop strikes the 152 ELECTRIC ARC LIGHTING. plate C. When this happens, the clutch releases slightly and enables the lamp rod to make a small descent, shortening the arc. Another form of gear-feed, constant-po- tential, arc-lamp mechanism, is shown in Fig. 43, where J^J/J-are the main circuit magnets and 88, the shunt magnets. The lamp rod is rectangular in cross-section and is provided with rack teeth on one face. The pinion mounted on an arbor carrying the wheel W, engages with this rack. The wheel W t also engages with a pinion on a second arbor carrying a second or trawl w r heel with fine teeth cut in its periphery. Before the current passes through the lamps the carbons are in contact. As soon as the current passes through the main-cir- cuit magnets, which are hollow spools, the cores A A, which constitute the armature, CONSTANT-POTENTIAL LAMPS. 153 the lever frame k Jc by the jaw J. The frame K K', is pivoted at V, and on the FIG. 43. INTERIOR. MECHANISM OF A FORM OF CONSTANT- POTENTIAL ARC LAMP. 154 ELECTRIC ARC LIGHTING. elevation of the end 1C, the pinion forces up the lamp rod thus separating the car- bons and establishing the arc. The shunt magnets attract the armature a, which is held in position by the spring G. The tension of this spring is capable of being adjusted by the screw head H. As soon as the length of the arc is excessive, the at- traction of this armature releases the pawlj?, from the periphery of the trawl wheel, and thus permits the upper carbon slowly to descend. Another form of arc lamp, suitable for use on constant-potential circuits, is shown in Fig. 44. This form of lamp is intended to produce light without any attention for re-carboniug for 50 hours at a time ; when, by merely pushing" up the lower carbon, it will furnish light for another period of 50 hours. Although half inch carbons are CONSTANT-POTENTIAL LAMPS. 155 FIG. 44. FORM OP ARC LAMP FOR CONSTANT-POTEN- TIAL CIRCUITS. 156 ELECTRIC ARC LIGHTING. used, and although the length of the posi- tive carbon is only 12", yet by the method employed, the carbons last, as al- ready stated, for at least 100 hours. The means whereby this increased duration is obtained are very simple. A semi-opale- scent shade D, Fig. 45, surrounds the arc. This chamber is closed, but not air tight. As soon as the lamp is lighted, the air sur- rounding the arc is rapidly deprived of its oxygen, so that the residual atmosphere consists of carbon monoxide and nitrogen in a heated, and, therefore, rarefied condi- tion. The outer chamber contains a store of these inert gases, which are practically prevented from escaping owing to the fact that the top of the outer globe is air-tight, so that the external air can only enter at the base of the external globe by diffusion. Consequently, the carbons are soon sur- rounded by an inert atmosphere which CONSTANT-POTENTIAL LAMPS. 157 FIG. 45 Auc LAMP, WITH OUTSIDE GLOBE REMOVED. 158 ELECTRIC AKC LIGHTING. greatly prolongs their life. The positive carbon consumes at the rate of about l/20th inch an hour, and the .negative carbon at the rate of about l/50th inch. In fact almost the entire consumption is due to volatilization, in contradistinction to combustion. Fig. 46 partly shows the mechanism in this form of lamp. A hollow spool or solenoid M, in an iron frame F F, is pro- vided with a soft iron armature core A, which holds, in its interior, the upper car- bon. When no current passes through the lamp, the upper carbon falls by gravitation on to the lower, establishing a circuit through the lamp. When the current is allowed to pass through the lamp, the solenoid M is energized, and the armature A, is lifted, thus gripping the carbon and establishing the arc. CONSTANT-POTENTIAL LAMPS. 159 . 46. FORM OF ARC LAMP FOR CONSTANT-POTENTIAL CIRCUITS, SHELL AND OUTSIDE GLOBE REMOVED. 160 ELECTKIC ARC LIGHTING. Fig. 47 is a section of the mechanism just described, MM is the magnetizing coil in the iron frame t> b b b b b. The arma- ture core a a a a a a, is provided at its upper extremity with a conical extension suitably conformed to a similar cone on the field-magnet frame. Within the armature is the upper or positive carbon c c, and its brass tube holder t t. At the lower ex- tremity of the armature are ring clamps, j9, p, which separate and release the carbon when the armature falls on to the tube u it, but which grip the carbon when the arma- ture rises clear of this tube. In the lower cylinder B, are rings r, r, which do not interfere with the free movement of the carbon, but which maintain electrical con- nection with its surface, and supply it with the current. As soon as the armature lifts, under the action of the solenoid, the car- bon c c, is gripped and raised to a distance CONSTANT-POTENTIAL LAMPS. 161 A b FIG. 47. SECTION OP MECHANISM SHOWN IN FIGS. 44, 45 AND 46. 162 ELECTRIC ARC LIGHTING. of about 3/8ths of an inch, this being the length of the arc usually employed. When the arc becomes too long, the arma- ture falls, allowing the carbon to slip for a short distance through its clamps, p, p. As in the case of all constant-potential lamps, an additional resistance is inserted in the circuit of each lamp. In Fig. 45, this resistance is placed in the crown of the lamp, and the switch handle If, in con- nection with the same, serves to turn the light on and off. The lamp is usually operated from a 110- volt circuit, with a current of 5.5 amperes, thus representing an expenditure of activ- ity amounting to about 600 watts. The pressure across the lamp terminals, beyond the resistance, is usually about 80 volts, representing a drop of about 30 volts in the additional resistance. CHAPTER VII. APPURTENANCES AND MECHANICAL DETAILS OF AEC LAMPS. WE have heretofore described the elec- trical regulating mechanism of arc lamps, whereby the carbons are maintained at a constant distance apart, despite their consumption by combustion and volatili- zation. The mechanical details of con- struction of the arc lamp, together with poles, hoods, hangers and other appurten- ances connected with their commercial use, will now claim our attention. An arc lamp proper may be regarded as being composed essentially of the fol- lowing parts ; namely, of the feeding and 163 164 ELECTRIC ARC LIGHTING. regulating mechanism which we have already described, the lamp, frame and coyer, the carbon holders, the globe holder and the globe. Besides these, lamps are frequently provided with a hood for the double purpose of protecting them from the weather and also for throwing the light downwards. The separate lights are mounted on the tops of poles or suspended from cords or outriggers. We have already pointed out the fact that the lamp rod which supports the pos- itive carbon is, necessarily, of practically the same length as this carbon. The proper working of the lamp requires that the lamp rod be kept from dirt and oxida- tion. To ensure this, when the lamp is re-carloned or trimmed, this rod should be occasionally cleaned and is always pro- tected from the weather by a prolongation APPURTENANCES. 165 of the cover on the lamp mechanism. When crocus cloth is used, the rod should always be wiped with a piece of clean cot- ton waste, before the rod is pushed up into the lamp. The feeding mechanism is usually sup- ported on the upper part of the lamp frame. In the case of most lamps the frame is pro- vided with two suspension hooks which are generally in electrical connection with the positive and negative terminals of the circuit, but insulated from the main body of the frame. The suspension hooks are generally furnished with binding post at- tachments, in order to ensure a more inti- mate contact with the circuit wires than could be secured by mere hanging. One of the commonest forms of arc lamp suspension is that in which the weight of 166 ELECTRIC ARC LIGHTING. FIG. 48. FORM OP ARC LAMP SUSPENSION. APPUETENAtfCES. 167 FIG. 49. OUTRIGGER SUSPENSION. the lamp is not permitted to be sustained by the hooks, but is borne by a line con- nected to an eye-piece, at the top of the 168 ELECTRIC ARC LIGHTING. lamp. Such a form of lamp is shown in Fig. 48, where H If, are the hooks, and B, FIG. 50. OUTRIGGER AND HOOD. is the supporting eye-bolt. Fig. 49, shows a lamp suspended in this way from an APPURTENANCES. 169 FIG. 51. HOOD SUSPENSION. 170 ELECTRIC ARC LIGHTING. outrigger attached to a wall. Here the conductors G C, C C, keep the lamp from spinning around the supporting rope. If, however, the lamp is suspended by its upper ring from a fixed hook this rota- tion becomes impossible. Fig. 50, shows a different form of out- rigger support, in which an iron frame is substituted for the rope. The lamp can be lowered by the rope H H for trimming. The conductors G C, enter the hood by the frame. Fig. 51, shows a form of lamp where the suspension hooks are attached to the hood. Fig. 52, represents a form of suspension in which the lamp is held from a hanger board by two rods connected directly with the suspension hooks. APPURTENANCES. 171 Fig. 53, represents a form of adjustable lamp hanger in which the lamp is sup- FIG. 52. LAMP AND HANGER BOARD. ported by rope attached to the suspension hooks. The form of attachment shown is 172 ELECTRIC ARC LIGHTING. FIG. 53. ADJUSTABLE LAMP HANGER, WITH AUTO- MATIC SWITCH. APPURTENANCES. 173 also provided with an automatic switch so arranged that when the lamp is lowered for purposes of trimming or re-carboning, it is automatically removed from the circuit, FIG. 54. CROSS- WIRE SUSPENSION. thus preventing the possibility of danger to the trimmer. Fig. 54, shows a form of cross-wire sus- pension for arc-lamps. By means of a twin- pulley and cord, attached as shown, the lamp is raised and lowered at will. (7(7, 174 ELECTRIC ARC LIGHTING. FIG. 55. SIDE FRAME LAMP. APPURTENANCES. 175 CO, are the conducting wires. An in- spection of the. figure will show that when the weight on the left is raised, the lamp is lowered. A form of lamp suitable for cross- wire suspension, commonly called a side-frame lamp, is shown in Fig. 55. Such a lamp can throw a shadow of its frame only on one 'side. Fig. 56, represents an ornamental form of lamp suitable for indoor use. This lamp is secured to the ceiling of a hall or room. The connecting wires are shown at the top. The simplest method of hanging a lamp from a cross wire, is to support it from the wire, connecting the wire to the lamp ter- minals on each side. The span wire is then 176 ELECTRIC ARC LIGHTING. FIG. 56. INDOOR LAMP FOB CEILING SUSPENSION. APPURTENANCES. 177 cut and the ends connected through an in- sulator, called a circuit-loop breakinsulator. Several forms of these insulators are shown in Figs. 5f and 58. The circuit would FIG. 57. CIRCUIT-LOOP INSULATORS. evidently be open entirely at the insulator if the lamp, connected as a shunt, did not permit the current to pass from one side to the other. 178 ELECTRIC ARC LIGHTING. A very common form of support for arc lamps in street lighting is the pole support. Many forms of pole supports have been FIG. 58. CIRCUIT-LOOP INSULATORS. devised. One of the simplest forms of single-lamp pole support is shown in Fig. 59. A cross-arm bearing two insulators, II, carries the conducting wires C C\ through the vertical frame supported on APPURTENANCES. 179 FIG. 59. POLE SUPPORT. a cast-iron bracket, placed at the top of the poles. The hood and the lamp are supported on the top of this frame as shown. 180 ELECTRIC ARC LIGHTING. FIG. 60. IRON POLE SUPPORT. APPURTENANCES. 181 A similar form of pole support is shown in Fig. 60, where the hood is seen in sec- tion, and the lamp is supported from a device called a hanger board, placed inside the hood. Pole lamps of the character represented in Figs. 59 and 60, being provided with no means for lowering, require the trimmer to climb the pole for re-carboning. The poles are, therefore, usually provided with fixed steps shown on the right hand side of Fig. 61, whereas the pole seen on the left hand side of the same figure has to be reached by means of a ladder. Other forms of ornamental, cast-iron poles, for use iii cities, are shown in Fig. 62. ; In order to avoid the necessity of climb- ing the pole or of carrying a ladder in trimming lamps, pole lamps are frequently 182 ELECTRIC ARC LIGHTING. FIG. 61. ORNAMENTAL POLES. APPURTENANCES. 183 FIG. 62. ORNAMENTAL POLES. 184 ELECTRIC ARC LIGHTING. provided with, means whereby the lamp may be lowered. In the device shown in FIG. 63. MAST-AKM SUPPORT. LAMP RAISED. Fig. 63, a mast arm A A, is rigidly sup- ported at the top of the pole P P. A flexible rope, wound on the wheel W, APPUKTENANCES. 185 passes through the pulleys p 1 p z . An eye- bolt, on the top of the lamp hood, is FIG. 64. MAST-ABM SUPPORT. LAMP LOWERED. fastened to the rnast arm at the point t. The conductors r\ parallel beam, then 12,566 x ^ lumens would be thrown into a parallel beam which would be lost by absorption only after traversing long distances of atmosphere. Consequently, at a distance of 100 or 1,000 metres, the quantity of light would be 7,540 lumens. Practically no reflector can be made which will not itself absorb some light or which will render the PROJECTOR ARC LAMPS. 275 FIG. 110. SIMPLE FORM OF SEARCH LAMP. 276 ELECTRIC ARC LIGHTING. beam perfectly parallel. It is impossible, therefore, to obtain a uniform illumination at all distances. The light invariably be- comes scattered and the illumination dimin- ishes independently of absorption by the atmosphere, but the distance to which pow- erful lights can be visibly thrown, under favorable conditions, is very great, being more than 100 miles. Fig. 110, represents a simple form of search lamp. It consists, as seen, of a cylindrical box containing the arc lamp, and capable of being moved about the vertical axis on which it stands, and also about a horizontal axis, passing through the box. This motion can be effected by the lever L. In this way the beam can be directed all around the horizon, or in any direction upwards or downwards. A clamp C y prevents motion about the hori- PROJECTOR ARC LAMPS. 277 FIG. 111. SEARCH LAMP WITH SLOW MOTION SCREW. 278 ELECTRIC ARC LIGHTING. FIG. 112. THIRTY-INCH PROJECTOR. PROJECTOR ARC LAMPS. 279 zontal axis when so desired, and another clamp c } prevents motion about the verti- cal axis. The window W, is provided with slats of thin glass in order to protect the arc from wind and weather. When a projector exceeds a certain size, it is sometimes difficult to obtain the re- quisite accuracy of adjustment of the beam by hand, and slow motions, in both alti- tude and azimuth, are obtained by means of screws. Thus, in Fig. Ill, the handle If, permits of a slow motion around the horizontal axis, or in azimuth, while the handle 7i t secures a slow motion in altitude. Fig. 112, represents a still larger and more powerful projector of 30" diameter, where the slow motions in azimuth and altitude are arranged either for control at the side of the projector, or by gear, from 280 ELECTRIC ARC LIGHTING. FIG. 113. THIRTY-INCH PROJECTOR ON MOUNT WASHINGTON. PROJECTOR ARC. LAMPS. 281 FIG. 114 ILLUMINATION OF THE LIZZIE BOURNE MONUMENT. 282 ELECTRIC ARC LIGHTING. a distance. Fig. 113, shows this projector in operation. Some idea of the power of the projector shown in Figs. 112 and 113, in concentrating light at a distance, may be gathered from an inspection of Fig. 114, which shows the illumination produced at a distance of 1,200 feet, upon a monument, at night time. Fig. 115 shows a form of search-light projector for use on vessels at sea, with gear control for projecting the beam from the pilot house. Fig. 116, represents the handles and part of the mechanism in the gear control for azimuth and altitude, while Fig. 117, represents the action of the mechanism. Another form of pilot-lwuse controlling gear is shown in Fig. 118. In order to be able to utilize, for the opera- tion of a search-light, the regular pressure of 110 or 80 volts, which may be employed PROJECTOR ARC LAMPS. FIG. 115. MARINE SEARCH-LIGHT PROJECTOR, WITH GEAR CONTROL. 284 ELECTRIC ARC LIGHTING. on board ship, a rheostat, or regulable re- sistance, is inserted in the circuit of the arc lamp. The rheostat is arranged in FIG. 116. HANDLES FOR CONTROLLING BEAM OF PRO- JECTOR, LOCATED IN PILOT HOUSE. such a manner that the turning of a handle enables resistance to be inserted in, or removed from, the circuit. Such a form of rheostat is shown in Fig. 119. PROJECTOR ARC LAMPS. 285 FIG. 117. PILOT HOUSE OP YACHT "VARUNA" WITH SEARCH-LIGHT. 286 ELECTRIC ARC LIGHTING. FIG. 118, PILOT HOUSE CONTROLLING GEAK. PROJECTOR ARC LAMPS. 287 Perhaps the largest search-light pro- jector ever constructed, was that 'exhibited at the Chicago Columbian Exhibition in FIG. 119. PROJECTOR RHEOSTAT. 1893. This projector is represented in Fig. 120. Its total weight is 6,000 pounds, and its reflector is five feet in diameter. It is operated by a current of 288 ELECTRIC ARC LIGHTING. FIG. 120. SIXTY-INCH PROJECTOR. PROJECTOR ARC LAMPS. 280 FIG. 121. MANGIN'S PROJECTOR. 200 amperes, and, therefore, takes an ac- tivity of about 10 KW. or 13 1/3 HP. Both carbons are cored ; the upper carbon being 1 1/2" in diameter, and the lower car- 290 ELECTRIC ARC LIGHTING. bon 1 1/4" in diameter. The dioptric re- flector is a glass mirror of special form, called a Mangin reflector. It consists of a spher- ical mirror, whose inner and outer surfaces are of different radii. The outer surface is silvered, so that the rays coming from the lamp pass outward through the sub- stance of the glass before being projected outward as parallel rays. Some idea of this form of projector can be obtained from an inspection of Fig. 121. It will be seen from this figure, and from Fig. 120, that the light is not allowed to pass directly from the arc into the beam, but is thrown from the arc, back to the Man- gin reflector, partly with the aid of a small mirror placed in front of the arc, and then from the Mangin reflector outward. The voltaic arc has long been employed for illumination from lighthouses. In PEOJECTOR ARC LAMPS. 291 FIG. 122. FIRE ISLAND LIGHTHOUSE LENS. 292 ELECTRIC ARC LIGHTING. such cases the light is collected by a large lens and transmitted in a parallel beam. PIG. 123. LOCOMOTIVE Anc HEADLIGHT. The problem of lighthouse illumination differs markedly from that of the marine PROJECTOR ARC LAMPS. 293 search -light, since, in the latter case, the object is to illumine a distant object, while that of the lighthouse is to mark the posi- tion of a certain point to vessels approach- ing in any direction. Lighthouse illumination is of two dis- tinct types; namely, the fixed light and the flashing light. In the illumination of the coasts or islands of a continent, it does not suffice to simply mark the position of the coast by a light. Means must be devised whereby one light can be readily distinguished from another. For this pur- pose various devices have been employed, such as colored lights, but the device most frequently employed is that of the flash- ing light. Flashing lights, as the name indicates, are lights visible to a distant ship during periodic intervals of time only, which vary with different lighthouses, so 204 ELECTRIC ARC LIGHTING. i Fio. 124. LANTERN PROJECTION ARC LAMP. PROJECTOR ARC LAMPS. 295 that it becomes possible for the ship to readily distinguish between a number of lights along a coast, comparatively near FIG. 125. ELECTRIC STEREOPTICON. together. Fig. 122, shows a form of light- house lens employed in the lighthouse on Fire Island, N. Y. This lens is nine feet 296 ELECTRIC ARC LIGHTING, FIG. 126. OPEN REFLECTOR STAGE LAMP. PROJECTOR ARC LAMPS. 297 FIG. 127. STAGE LAMP. 298 ELECTRIC ARC LIGHTING. in diameter and weighs half a ton. A focusing arc lamp is placed with its arc at the focus of the lens. The light after passing through the circular prisms emerges in a sensibly parallel beam. It is arranged to revolve once every five seconds, so that the light is of the flashing type. The arc used with this apparatus is about 1/6 inch long, and the carbons are about one inch in diameter. The pressure is about 48 volts and the current about 100 amperes. Arc-lamp projectors have been em- ployed as electric headlights on locomotive engines. Fig. 123, shows a form of such attached immediately in front of the smoke stack. A focusing arc lamp is employed to a great extent for the purposes of lantern PROJECTOR ARC LAMPS. 299 projection. A suitable form of focusing lamp is placed before the focusing lenses FIG. 128. OLIVETTE Box. of the lantern, as shown in Fig. 124. A pair of such lamps, arranged for dissolving views, is shown in Fig. 125. 302 ELECTRIC ARC LIGHTING. An electric arc lamp is frequently used in theatrical representations, and portable lamps are made to reflect the light in any required direction. Two forms of such lamps are shown in Figs. 126 and 127. The mechanism calls for no special con- sideration. Fig. 128, is an olivette box; namely, a box employed in front of the lamp for obtaining a uniform field of color over a large surface, such as a stage scene. A ground glass face ensures a thorough dispersion of the light and in front of this is placed a color frame to produce the requisite tint. The search-light is frequently employed in order to produce striking scenic effects. Such effects were finely produced at the World's Columbian Exhibition, where the powerful search-light striking on the w r hite " staff " covering the buildings PROJECTOR ARC LAMPS. 305 illumined them to great advantage. Fig. 129 represents the effect produced by the FIG. 133. PHOTO-ENGRAVING ARC LAMP. arc lamps situated on the roof of the Manufacturers' Building at the World's 306 ELECTRIC ABC LIGHTING. Fair. Figs. 130 and 131 show search-light effects produced at the San Francisco Mid- Winter Fair of 1895. Fig. 132 shows the effect produced by search-lights in a naval review in New York harbor. The preponderance of blue rays in the arc lamp, as well as its great candle- power, render it particularly useful for photographic purposes, thus making the operator independent of sunlight. Such lamps are frequently employed in photoen- graving. A form of lamp suitable for this purpose is shown in Fig. 133. CHAPTER XI. AEC LIGHT CARBONS. FOR his early exhibitions of the voltaic arc, Davy employed rods or electrodes of willow charcoal. These gave an admir- able light but possessed the disadvantage of too rapid consumption. The first practical improvement in arc- light carbons was made by Foucault, who made use of the very hard carbon de- posited on the inside of the retorts em- ployed in the manufacture of illuminating gas, by the destructive distillation of coal. These deposits were cut and fashioned into the required shape by means of a saw, 807 308 ELECTRIC ARC LIGHTING. They were a marked improvement, so far as duration was concerned, but pos- sessed the disadvantage of not only being quite expensive, owing to the difficulty of working this extremely hard carbon, but especially from the fact that the carbon contained impurities and varied markedly in its hardness, thus giving rise to irregu- larities or flickeriugs of the light. Besides this, while such a source of carbon elec- trodes might have answered at the time of Foucault, yet, at the present day, when the daily consumption of carbon rods amounts to many hundreds of miles, this source of supply would be entirely inade- quate, even were it satisfactory in other respects. "We have already referred to the dis- covery of the Grove voltaic cell, and its modification by Bunsen, as marking an era ARC LIGHT CAEBONS. 309 in the history of electric lighting, not only on account of the more reliable source of electricity which his battery afforded, but also from the fact that the method he employed in the production of artificial carbons for the negative plates of his cells, disclosed a means whereby carbon rods could be manufactured for arc lights. Inventors were not slow to avail them- selves of the means thus pointed out, and many processes were devised for the pro- duction of artificial carbons. The method employed by Bunsen consisted substan- tially in making mixtures of finely divided carbonaceous materials with tar and glue, and subjecting the same to a carbonizing or baking process, while out of contact with air. Unfortunately, during this proc- ess the material employed to bind the mixture of carbonaceous materials together, 310 ELECTRIC ARC LIGHTING. resulted in the production of a semi-porous mass of carbon. Bunsen increased the density of his carbons by soaking them in sugar solution and re-carbonizing. By re- peating this process he obtained very dense, fairly uniform carbons. Although many improvements have been made in the practical production of arc light carbons, yet the processes are essentially developments of this early method of Bunsen, and consist, substan- tially, like the Bunsen process, of thor- oughly incorporating some carbonizable liquids with various mixtures of pure car- bon, and passing the same, under hydrau- lic pressure through suitably shaped dies. The carbon rods so obtained, are then carefully dried and subjected to various processes of carbonization, generally as in the Bunsen process, and are subsequently ARC LIGHT CARBONS. 311 subjected to rebaldngs after immersion in syrup or other carbonaceous liquid. Before, however, proceeding to the fuller description of the modern process em- ployed in the manufacture of arc light carbons, a brief history of early carbon manufacture may not prove uninterest- ing. As early as 1846, Staite and Edwards, who were among the pioneer inventors in arc-lamp mechanism, took out a patent for the manufacture of arc light carbons, on essentially the same lines as employed by Bunsen in 1849. A Frenchman by the name of Le Molt, patented a substantially similar process for the manufacture of carbon electrodes, observing, however, great care in the prior purification of the carbons. In 1857, Lacassagne and Thiers, the inventors of the shunt-circuit arc lamp, 312 ELECTRIC ARC LIGHTING. endeavored to employ gas-retort carbons, purified in various processes, by the re- moval of its silicon and other materials. Probably the most successful endeavor, in this direction, however, was that made by Jacquelaiu, who prepared pure artificial gas-retort carbons by distillation of puri- fied tar. In 1876, Carre took out a patent for the manufacture of carbons, which, however, did not differ markedly from the preced- ing. Carre employed a mixture of pow- dered coke, lampblack, and a specially prepared syrup formed of cane sugar and gum. As before, the materials, mixed into paste and passed through a die under hydraulic pressure, were dried and subse- quently carbonized. The pencils were then re-treated in sugar solution and then re-carbonized. AKC LIGHT CARBONS. 313 The prime essential of a good electric light carbon is purity of material. The effect of impurity on any carbon must necessarily be to lower the temperature of the arc, and thus very materially diminish the amount of light emitted; for, as we have seen, the temperature of the positive crater is that of the volatilization of the materials, and the presence of substances whose points of volatilization are much lower than that of carbon, must result in a considerable diminution of temperature and, consequently, in a decrease of the intensity of the light. The purity of the carbon being assured, the next most im- portant point is the homogeneity of the material. Carbons vary very considerably in their compactness or hardness. Con- sequently, if the carbons are made from a mixture of various carbonaceous powders, unless all of these ingredients possess 314 ELECTRIC ABC LIGHTING. nearly the same hardness, irregularities both in the consumption and temperature will cause unsteadiness of the light. Thoroughness of mixture, and uniformity as near as possible in the hardness of the different carbon ingredients must, there- fore, be ensured. The processes employed at the present day for the manufacture on a commercial scale, of arc light carbons, may be di- vided into two general processes ; namely, moulding and squirting. In the moulding process, as the name in- dicates, the carbonaceous material, in the form of a paste, is moulded, in suitable forms by hydraulic pressure. Different carbonaceous materials are employed by the different makers, but refined petro- leum coke, ordinary gas coke, and lamp- ARC LIGHT CARBONS. 315 black are among the commonest. A high degree of uniformity and purity is neces- sary, and whatever means are employed for mixing, it is essential that this mix- ing shall be thorough. The solid ma- terials are thoroughly ground and mixed into a stiff paste. The moulded material is then thoroughly dried, the drying being gradually accomplished by passing the ma- terial through ovens at successively increas. ing temperatures. Finally, the carbons are fired, or subjected to a carbonizing proc- ess, while wholly out of contact with air, by prolonged exposure to intense heat. If properly prepared, the carbons should have, when struck, a metallic ring, indicative of great hardness. In some processes, as we have seen, the carbons are subjected to a rebaking, after dipping in saccharine solu- tions, for the purpose of increasing their density. In order to ensure the ready and 316 ELECTRIC ARC LIGHTING. thorough penetration of the liquid into the interior of the carbons, they are sometimes treated with the saccharine liquid while in a vacuum. We have already referred to the un- steadiness of the arc light, due to the travelling of tlie arc, and have alluded to the fact that this travelling may be de- creased by the use of cored carbons. In cored carbons, as the name indicates, the core or central part of the carbon is formed of a different material from the main body of the carbon. These carbons are prepared by squirting the material through a proper die, so as to leave a cylindrical cavity at the centre of the car- bons. This cavity is subsequently filled with a softer variety of carbon. Electric light carbons are either bare or coppered. Coppered carbons are coated ARC LIGHT CARBONS. 317 with a thin adherent conducting layer of metallic copper, deposited electrolytically. FIG. 134. SOLID COPPEKED CARBON ROD. The carbon electrodes are immersed in a bath of copper sulphate, while connected with the negative terminals of an electric 318 ELECTRIC AKC LIGHTING. source, and placed opposite plates of copper connected with the positive ter- Fio. 135. CORED CARBON ROD. minal. The effect of the copper coating is to increase_the life of the carbons, and to ARC LIGHT CARBONS. 319 ensure a more nearly uniform consumption with a reduced expenditure of energy in the resistance of the carbon rods. More- over, the thin coating of copper largely - ~ ^^^ FIG. 136. CROSS SECTIONS OF CABBONS. prevents the disintegration of the carbons, except within the arc. Carbons are of various shapes, although the cylindrical form is generally employed. They are of various diameters, from 1/4", up to an inch or more. The lengths are generally either one foot, or seven inches. A form of coppered cylindrical solid carbon , i. e.j a careless carbon is shown in Fig. 134. 320 ELECTKIC ARC LIGHTING. A longitudinal section through the axis of a cored carbon is shown in Fig. 135. Fig. 136, shows various cross-sections em- ployed for special or long-lived carbons. The cross-section of the carbons employed varies with the current and voltage, but the commonest size for street lighting is 1/2" in diameter. The length of life of an arc light carbon depends upon the current strength and upon the diameter of the carbon, as well as on its hardness and character. The usual duration of a pair of half inch car- bons is about nine hours, and a pair of 7/16* about seven hours. Various forms of carbon holders are em- ployed both to attach the upper carbon to the lamp rod, as well as to hold the lower carbon in position. Frequently the lower ARC LIGHT CAfcfeONS. 32l carbon is provided with an ash pan, a device for preventing it from dropping through the holder, and so possibly caus- FIG. 137. CARBON HOLDERS. ing damage or fire. A few forms of carbon holders are shown in Fig. 137. When a lamp maintains its arc at too short a distance, a disagreeable hissing noise is apt to be produced. If burnt at too long an arc, a flaming of the arc, often 322 ELECTRIC ARC LIGHTING. accompanied by noise, is produced. The voltages required to bring about the hissing and flaming of an arc will vary considerably with the character of the carbons. CHAPTER XII. DYNAMOS. THE source of E. M. F. employed -for the commercial operation of arc lights is invariably some form of dynamo-electric machine. In these machines, the electric current is produced not by friction, but by the rotary movement, through magnetic fluXj or magnetism, supplied by the field coils, of coils of wire secured to the arma- ture. When a coil of wire passes one of the poles in the field frame, the E. M. F. makes one reversal ; i. e., an impulse of E. M. F. in one direction is produced, and the next pole it passes will develop in the wire an impulse of E. M. F. in the oppo- 324 ELECTRIC ABC LIGHTING. site direction, so that, if, as is often the case, the field frame has two poles, or the machine is a bipolar machine, the coil will receive two impulses of E. M. F. during one revolution, one impulse, being say pos- itive, and the next impulse, negative. The coils are arranged in such a manner that the E. M. Fs. which are induced in them by their rotation past the poles are united, and if the machine is provided with a com- mutator, the alternate impulses of E. M. F. are so timed in reference to the passage of the commutator beneath the brushes rest- ing upon it, that the current in the ex- ternal circuit does not alternate but remains uniform in direction. Such a machine is called a continuous-current machine. Sometimes, however, no attempt is made to commute the direction of E. M. F., the ends of the coils being directly con- DYNAMOS. 325 nected with the external circuit. In this case, the E. M. F. and current generated will be alternating, not only in the arma- ture, but also in the external circuit. It is generally easy to determine from a casual inspection of a dynamo, whether it has been designed to furnish continuous or alternating currents. In the former case it will always be provided with a commu- tator. In the latter case no commutator will be seen, although alternating-current generators ; i. e., alternators, are sometimes self -exciting, or are provided with a com- mutator, the function of which is to com- mute a small portion of the alternating current supplied by the machine, which commuted current is used to energize its field coils. Fig. 138, represents a particular form of bi-polar continuous-current arc-light gen- 326 ELECTRIC ARC LIGHTING. Y FIG. 138. BIPOLAR CONTINUOUS-CURRENT GENERATOR. DYNAMOS. 327 erator, intended to produce a current of 9.6 amperes, at a maximum pressure of 6,250 volts, and, therefore, to deliver an out- put of 9.6 x 6,250 = 60,000 watts, or 60 KW approximately 80 HP when run- ning at a speed of 500 revolutions per minute. Such a machine is intended to supply 125 arc lamps in series. The machine rests upon a cast iron base B J3, which is capable of being advanced along the surface of the base frame SS t by means of a ratchet worked by the handle JT, thus enabling the driving belt, not shown in the figure, but which rests over the driv- ing pulley Y y to be tightened. The field frame B M P M Y M, has four magnetiz- ing coils M) M, M, M, and magnetizes two pole-pieces, one of which JP, is seen in the figure. Between these two poles rests the armature A A, in two main journal bearings G, G. The commutator (7, con- 328 ELECTRIC ARC LIGHTING. sists of a number of insulated conducting segments, each symmetrically connected to some point of the armature winding. Commuted currents are carried off from the commutator by the brushes J2, B, of which there are two pairs, one pair for each terminal. The position of these brushes relatively to the commutator, is adjusted automatically, by imparting a rotary movement, when necessary, to the brush holder frame F, through the rod It, under the influences of the regulator m, which is placed in the main circuit of the machine. When the current exceeds a certain strength, the regulator magnet m, attracts its armature more powerfully against the opposing forces of a spring, moving the brushes- in one direction over the commutator, and when the current unduly weakens, the brushes are moved in the opposite direction. The power for DYNAMOS. 329 H FIG. 139. SERIES ARC DYNAMO. moving the brush holder frame in obedi- ence to the action of the regulator magnet, is obtained from the armature shaft, through the belt and the pulleys y y, Ick, 330 ELECTRIC ABC LIGHTING. are draw-oft' cocks for the oil in the self- oiling bearings, which are filled through the aperture O. When, during the rota- tion of the machine, the coils on the arma- ture are moved forward through the mag- netic flux produced by the field magnets, E. M. Fs. are generated in the former, and are carried to the arc light circuit after they have been commuted. Fig. 139, represents another form of bi- polar continuous-current arc-light generator. Here the pulley is not visible but the armature A A, revolves with its conductors and commutator C, in the magnetic flux produced between the poles P, P, under the excitation of the magnetizing coils M, M. Here the regulator 7?, actuated through the pulleys y y, adjusts the positions of the brushes B, of the commutator. The switch W, opens and closes a short cir- DYNAMOS. FIG. 140. BIPOLAR GRAMME-RING ARC-LIGHT GENERATOR. cuit around the field magnets. In order to tighten the belt, the handle IT, is used. Fig. 140, shows another form of bipolar Gramme-ring arc-light generator, intended 332 ELECTRIC ARC LIGHTING. for the supply of eighty 2,000 candle-power arc lamps, and, therefore, capable of pro- ducing, at its terminals, a pressure of 4,000 volts at a speed of 875 revolutions per minute, and with a current of 9.6 amperes. This represents a maximum external ac- tivity of 38.4 KW or about 51.2 HP. Here the armature A, driven by the belt on the pulley Y, rotates between the poles Pj P, which are produced by the magnetiz- ing coils J/J M, M. Two pairs of brushes, one of which only is seen in the figure, rest upon the commutator. A regulating magnet J?, controls the position of these brushes so that the current strength in the circuit remains constant. Fig. 141, is a diagram representing the connections of this machine, and may be taken as typical of the connections of a series-connected continuous-current arc generator. By trac- ing the connections, it will be seen that 334 ELECTRIC ARC LIGHTING. the current issues from the armature through the commutator to the pair of brushes which is partly hidden from view, then around the coils of the regulating magnet R, to the upper pair of field magnetizing coils m l m 2 , then through the lower pair of the field magnetizing coils m 3 w 4 , and finally through the external cir- cuit to the arc lamps COCO, returning to the armature through the second pair of brushes, thus completing the circuit. Wj represents the switchboard connections which will be alluded to later. L, repre- sents lightning protectors, or lightning arresters, designed to protect the generator from accidental discharges due to lightning arriving from the line, these discharges being led harmlessly to earth by the wire shown. It is thus evident that the regu- lator magnet is situated in the main cir- cuit, and through its action the strength of DYNAMOS. 335 the current supplied in the machine is maintained constant. FIG. 142. BIPOLAR CONTINUOUS- CURRENT ARC-LIGHT GENERATOR. Fig. 142, represents another form of bi- polar continuous-current arc-light generator. Here the armature A, part of which is just visible in the centre of the machine, is 336 ELECTRIC ABC LIGHTING. rotated between the poles produced by the large niagnet coils M, M, by a pulley at the back of the machine. The commutator O, revolves with this armature, but outside the bearing G, and contains only three segments on its commutator, corresponding to the three coils which are wound on its armature. These three segments are con- nected with the armature coils by three wires which pass through the centre of the hollow shaft. The brushes B, B, B, of which there are two pairs, rest upon the surface of this commutator, their position upon the surface being regulated by the action of the regulator magnet J, which is connected in the main circuit. 7J T, are the main terminals of the machine. M, is a dash-pot filled with glycerine for preventing sudden movements of the regulator. W } is a field short-circuiting switch, DYNAMOS. 337 Fig. 143, represents in detail tlie various parts of the preceding generator. (1), is the armature, which is nearly spherical in FIG. 143. PARTS OF GENERATOR SHOWN IN FIG. 142. shape, the coils being connected so as to form three windings, the ends of which appear at the end of the shaft. (2), is the left hand field coil and frame ; (3), the 338 ELECTRIC ARC LIGHTING. right hand field coil and frame ; (4), is the pulley journal bearing ; (5), the commu- tator journal bearing ; (6), are the field rods which are bars of soft iron rigidly connec- ing the field magnet; (7), and (8), the regulator magnet; (9), is the air blast or small air-pump mechanically operated by the armature in order to blow out the spark at the commutator segments ; (10), is the commutator ; (11), the brushes; (12), the brush holders; (13) and (15), caps of the bearings. Fig. 144 represents another form of arc- light generator intended to supply 60 lamps of 2,000 candle-power, and, there- fore, capable of furnishing 3,000 volts at its terminals. The armature A A, is driven by a belt on the pulley Y, between the poles P, Pj produced by the four mag- netizing coils 'Mj M, Mj M. The three 340 ELECTRIC ARC LIGHTING. pairs of brushes, 13, 12, J3, take off the cur- rent from the commutator.. T, T, are the main terminals. FIG. 145. ARC-LIGHT GENERATOR. A somewhat different style of machine intended to supply one hundred and twenty-five 2,000 candle-power arc lamps, DYNAMOS. 341 and, therefore, developing a maximum of about 6,250 volts at its terminals, is shown in Fig. 145. Here the armature A A, re- FIG. 146. ARMATURE OF GENERATOR SHOWN IN FIG. 145. volves between the four poles P, P, two only of which are seen. There are four magnetizing coils M, M, and three pairs of brushes /?, B, B, as before. The gen- eral arrangement of the armature, its shaft ELECTRIC AKC LIGHTING. FIG. 147. ARC-LIGHT GENERATOB. DYNAMOS. 343 and the commutator, can be best seen from an inspection of Fig. 146. Fig. 147, shows another form of arc-light generator capable of supplying one hundred and twenty-five 2,000 candle-power lamps. A, A, is the armature driven by the pulley Y y between the poles P, P. The pole faces Q, Q, are unhinged, and thrown aside, ready to permit the armature to be inspected or withdrawn. M, M, are the magnetizing coils, and B, B, the brushes. Fig. 148, shows a larger machine of this type with the pole faces in place. This machine is intended to supply two hundred 2,000 candle-power arc lamps in a single circuit, and, therefore, is capable of furnish- ing about 10,000 volts and 10 amperes at its terminals. Such a machine has a capacity of 100 KW, or about 134 HP, at 625 revolutions per minute. 344 ELECTRIC ARC LIGHTING. FIG. 148. ARC-LIGHT GENERATOR. The generators we have heretofore described in this chapter, have all been designed to furnish continuous currents. DYNAMOS. 345, It has already been mentioned that arc lamps can be satisfactorily operated by FIG. 149. 30 KILOWATT ALTERNATOR. means of alternating currents. We will, therefore, describe a form of alternating- current generator, or alternator, employed 346 ELECTRIC ARC LIGHTING. for this purpose. This is seen in Fig. 149. Its capacity is 30 KW. Here the arma- ture A, revolves within a circle of ten poles produced by the magnetizing coils FIG. 150. ABMATUKE OF TYPE OF ALTERNATOR SHOWN IN FIG. 149. M, M, M. There are two sets of brushes on this machine. One set rests on plain collector rings -??, J%, and carries off the alternating currents from the armature to the external circuit, while the others rest on a double commutator (7, for the pur- pose of commuting a portion of these cur- DYNAMOS. 347 rents to be used in exciting the field mag- nets with a continuous current. Fig. 150 shows the armature of such a machine in greater detail. A, A, is the armature frame, I, I, laminated iron discs or sheet stampings associated together on the shaft and forming the iron core. C, (7, the double commutator. 6r, G, the oil rings for keeping the oil in the bearings in motion over the shaft. Fig. 151, indicates the method by which the armature coils are set in position on such an armature. Here the iron core discs /, f, are seen rigidly attached to the shaft $, $, $. The coils Z/, I/, are wound on suitable frames and then slipped into their position on the iron teeth I, J, by the aid of a handvise V, shown in position at the top of the armature. 348 ELECTRIC ARC LIGHTING. FIG. 151. ARRANGEMENT OF ARMATURE COILS. We have hitherto described belt-driven arc-light generators, that is, arc generators in which the power of the engine is com- municated Jo .the generator by means of a belt. In some cases, however, the belt DYNAMOS. 349 is omitted, and the generator shaft is coupled directly to the main shaft of the driving engine. Such a direct-coupled machine is represented in Fig. 152. Here the arc-light generator 6r, of 50 KW capac- ity, is coupled directly to the 90 HP com- pound engine through the coupling C. The common shaft of the engine and generator makes 460 revolutions per minute. Such a connection is economical of floor space and is finding favor in large central sta- tions where large units of power are employed. It necessitates the use of com- paratively high-speed engines and of com- paratively low-speed generators. The arc-light generators here described are either installed directly in the build- ing to be lighted ; or, as is more gener- ally the case, in a central station. The latter arrangement possesses a marked ad- DYNAMOS. 351 vantage over the former in economy of operation over a large district. In central station practice, where a number of dynamos are employed, the necessity fre- quently arises to transfer the current and load from one dynamo to another, or at times to connect two or more dynamos in series. This operation is performed through the agency of a switchboard. Such a switchboard will contain, besides devices for effecting the ready transfer of circuits, or for the coupling together of dynamos, various instruments for measur- ing the current on each circuit. Moreover, since arc light circuits extend over consid- erable areas, and danger would result from an accidental flash of lightning entering the station, lightning protectors are usually provided. Fig. 153, represents such a switchboard situated on the wall of a cen- tral station dynamo room. DYNAMOS. 353 Here carefully insulated conducting cords connect the various machines with FIG. 154. ARC SWITCHBOARD. the different circuits, each circuit and each generator having their respective numbers. An ammeter is permanently placed in each 354 ELECTRIC ARC LIGHTING. FIG. 155. SWITCHBOARD WITH FACE REMOVED. circuit to show the current strength pass- ing in the same. DYNAMOS. 355 Fig. 154, shows another form of switch- board. Here the generators are brought to the lower row of terminals marked +1, +2 etc., while the circuits are brought to the upper row, marked +1, H-2 etc. By suitably connecting the dynamos and their circuits, with pin plugs, the current delivered from the station can be controlled. The cut shows each dynamo at work upon its own circuit, although it is evident that any one dynamo could be applied to operate any other circuit. Fig. 155 shows the same switchboard with the front panel removed in order to exhibit the lightning arresters in place with their lower jaws connected directly to the ground. CHAPTER XIII. ENCLOSED AKC-LAMPS. WHEN a direct-current arc-lamp is oper- ated in free air, as in the ordinary open arc- lamp, the principal consumption of carbon takes place at the positive electrode. Here the carbon is partly volatilized, and partly consumed by combination with oxygen in the surrounding air. With the exception of such portions as become disintegrated and drop from the arc, nearly all of the carbon eventually becomes consumed by combustion. If, however, the arc be placed in a closed chamber from which nearly all the air has been ex- hausted, i. e., in what is practically a ENCLOSED ARC LAMPS. 357 vacuum, the arc can still be maintained between the carbons, but the consumption of carbon by combustion will have prac- tically ceased. The volatilization of car- bon will, of course, continue from the positive electrode, and a large portion of this volatilized carbon will be deposited upon the extremity of the negative elec- trode, while a smaller portion will be deposited as a thin layer upon the walls of the containing vessel. Under these conditions, the life of the carbons will be very greatly increased. It is impracticable to operate arc- lamps in vacua / but it is practicable to prevent oxygen from obtaining free access to the arc. This is accomplished by placing a small thin glass bulb, or inner globe, around the carbons, so that only a small free space is left 358 ELECTRIC ARC LIGHTING. between the positive carbon and the edge of the inner globe. When the arc is first established within this globe, the oxygen of the air it contains is rapidly removed by combustion. The chamber, neglecting the vapor of carbon, and oxides of carbon, then contains nitrogen, an inert element. The contained gases are heated to a relatively high temperature by the arc within the globe, and the entrance of fresh oxygen, through the narrow annular aperture surrounding the positive carbon, is necessarily very slow. Under these conditions the consumption of carbon by combustion is greatly diminished, being mainly reduced to that by volatilization. Consequently, the consumption of positive carbon, instead of being roughly about an inch per hour, is reduced to about 1/14" per hour, while the consumption of the negative carbon, instead of being ENCLOSED ARC-LAMPS. 359 about 1/2" per hour, is only about 1/40" per hour; or, about l/3rd of the consump- tion of the positive carbon. These con- sumptions refer to a current strength of 5 amperes. A 1/2" X 12" positive carbon, at this rate, would last 168 hours, if it could be entirely consumed. In practice, the life of carbons, in ordinary enclosed arcs, is from 100 to 150 hours. The life-time depends in some degree upon the number of hours of consecutive ope-ration, since at each intermission, and cooling of the lamp, some oxygen finds access to the inner globe. Enclosed arc-lamps have now largely superseded open arc-lamps, mainly owing to the fact that the expense" of recarboning is thereby reduced. The amount of light yielded by an enclosed arc-lamp is really less than the amount of light which would 360 ELECTRIC ARC LIGHTING. be yielded by the same electric power in the open arc, by reason of the absorption of light within the walls of the inner globe. On the other hand, the light from the enclosed arc is much more uni- formly distributed than the light of an open arc, since the inner globe diffuses the light. Enclosed arc-lamps are oper- ated from both direct-current and alter- nating-current circuits, either in series or in parallel, the lamps being constructed and adjusted to meet these different con- ditions. The interior mechanism of a Man- hattan, direct-current, constant-potential enclosed arc-lamp is shown in Fig. 156. A resistance coil, wound on a porcelain grooved cylinder, is placed in series with the arc, to prevent overloading the lamp by a short circuit through the carbons, ENCLOSED ARC-LAMPS. 361 FIG. 156. MECHANISM OF A MANHATTAN DIRECT-CUR- KENT CONSTANT-POTENTIAL ENCLOSED ARC LAMP. which are initially in contact. It also keeps the required pressure at the car- 362 ELECTRIC ARC LIGHTING. bons when the normal current is flowing through the apparatus. An electroinag- FIG. 157. INDOOR LAMP WITH COVER AND GLOBE. net, also in series with the arc, controls the feeding mechanism. The inner globe may be either of clear or opalescent ENCLOSED ARC-LAMPS. 363 glass. A general view of the indoor lamp, with the glass cover and outer globe in FIG. 158. INDOOR LAMP WITH REFLECTOR. place, is seen in Fig. 157. These lamps are constructed for 110-volt, direct-current circuits, and are intended to take either 364 ELECTRIC AUC LIGHTING. 4.5 amperes, or 3 amperes, with from 75 to 80 volts between the carbons. Both Fia. 159. OUTDOOR LAMP. electrodes are solid 1/2" carbons, the upper or positive, being 12", and the ENCLOSED ARC-LAMPS. 365 lower or negative, 5" in length. The nor- mal life of the carbons is 150 hours. Fig. 158, shows the same lamp with reflector, and Fig. 159, illustrates the out- door type. In the alternating-current, constant-potential, enclosed arc-lamp, the resistance coil of the direct-current lamp is replaced by a choking coil, or reactance coil. Fig. 160, shows several parts of en- closed arc-lamp mechanism, including a resistance, a reactance coil, and a top plate. These lamps are designed for operation from alternating-current, constant-potential mains, at from 100 to 120 volts pressure, with frequencies from 60 to 133 cycles per second, the arc voltage being auto- matically reduced to 70 volts with a 306 ELECTRIC ARC LIGHTING. normal current of 6 amperes. At 105 volts terminal pressure, the power-factor is about 71.5 per cent. The carbons FJG. 160. DETAILS OF LAMP. are 1/2* in diameter, one being cored and the other solid, the upper carbon being 10" long and the lower 5". The normal life is from 80 to 100 hours. An outer globe not only protects the inner globe from the weather, but also aids in preventing the oxygen of the air from obtaining access to the arc. The outer globe is often omitted and replaced by a reflector. This lamp affords a very ENCLOSED ARC-LAMPS. 367 efficient way of lighting interiors of stores and windows. Particular attention has to be paid to the quality of the carbons em- ployed with enclosed arc-lamps ; otherwise, the inner globes will become rapidly blackened. Even with the best carbons, the inner globes require cleansing at inter- vals, and in some cases it is the custom to replace the inner globe by a clean one every time the lamp is recarboned. The shielding of the arc from the move- ments of the outer air enables a much greater length of arc to be employed than would otherwise be practicable. The ordinary pressure at carbons employed in direct-current enclosed-arcs is from 80 to 85 volts, instead of about 45 volts in open arcs. Moreover, on 220-volt direct-current 368 ELECTRIC ARC LIGHTING. circuits, enclosed arc-lamps are frequently operated with a potential difference be- tween the carbons, of 150 volts, and a distance between the carbons of about 1 1/8". In some special cases arcs are carried with 200 volts between carbons. An approximate rule for finding the length, in hundred ths of an inch, of direct- current enclosed-arcs for a given voltage between the carbons, is to subtract 45 from this voltage, so that a 145- volt arc would roughly have a length of 100 hun- dredths of an inch, or one inch. The length of an arc, either enclosed, or open, depends, however, not only upon the voltage between the carbons, but also upon the strength of current, and upon the quality of the carbons. The 220-volt-circuit arc, with 150 volts between the carbons, is usually designed ENCLOSED ARC-LAMPS. 369 to take a current of 2.5 to 3 amperes. At 2.5 amperes it consumes 550 watts at terminals, of which 375 are consumed in the arc. In many cases, however, two en- closed arc-lamps are operated in series from 220-volt mains, or five in series from 500-volt mains. In these cases an auto- matically operated cut-out is employed which, in case of accident to any lamp, substitutes in the series circuit a corre- sponding resistance of ware. These lamps ordinarily receive 5 amperes, and burn for 130 to 150 hours at one carboning. The connections of a General Electric alternating-current, constant-potential, en- closed arc-lamp are seen in Fig. 161. A O, is the reactance coil, or choking coil, connected in series with the controlling magnets in, m, and the arc a. The react- ance coil is tapped at six points marked 370 ELECTRIC ARC LIGHTING. FIG. 161. DIAGRAM FOR ADJUSTMENT OF ALTERNATING- CURRENT, CONSTANT- POTENTIAL ARC LAMP. ENCLOSED ABC-LAMPS. 371 Q K, L, and M, for main voltages, increasing from 100 to 125 volts, while the lower carbon is connected either to the point A, or the point B, of the reactance coil, according as the frequency of the cir- cuit is 60 or 125 cycles per second. T, T', are the main terminals. Fig. 162, shows the connections of such lamps with the mains, p, p, are the primary mains, at either 1,040 or 2,080 volts pressure ; T, is the step-down transformer ; s, s, the second- ary mains, to which incandescent or arc lamps may be individually connected. A double-pole switch and a double-pole fuse box are inserted between the mains and each enclosed arc-lamp. Additional advantages incidental to the use of enclosed arc-lamps are reduced risk of fire from sparks., or incandescent por- tions of carbon, dropping from the arc- 372 ELECTRIC ARC LIGHTING. Primary Ct'iwff: P FIG. 163. DIAGRAM OF CONNECTIONS. ENCLOSED ARC-LAMPS. 373 lamp, greater steadiness of burning, so far as concerns the action of air currents, and the reduced brightness of the arc as a O source of light, which by diffusion over a comparatively large surface of the outer globe, virtually divides the total emitted light over the enlarged surface of the outer globe, with a corresponding reduc- tion of surface brightness. Consequently, the eye can rest without discomfort upon the outer globe, whereas it is pained by watching the naked arc in the ordinary ox>en arc-lamp. If we call the total quantity of light emitted in all directions from a point- source of a He'fner-Alteneck standard lamp, 12.566 Hefner-lumens, then the efficiency of constant-potential enclosed arc-lamps is usually about 4 Hefner-lumens per watt, at lamp terminals, with opalescent 374 ELECTRIC ARC LIGHTING. outer globe ; about 5 Hefner-lumens per watt with clear outer globe; and 6 Hefner- lumens per watt with no outer globe, the inner globes being slightly opalescent. Incandescent lamps at a consumption of 3 watts per candle have an efficiency of about 3.5 Hefner-lumens per watt, or not far below the efficiency of the doubly enclosed arc-lamp with opalescent globes, and with a steadying resistance coil in the circuit. On the other hand, the series open-arc- lamp may frequently have an efficiency of 17 Hefner-lumens per watt. In general, the efficiency of a direct-current enclosed arc is somewhat greater than that of an alternating-current enclosed arc of the same input, apparently owing to the dif- ference between cyclic heating and steady heating of the carbon electrodes. CHAPTER XIV. SERIES ALTERNATING ARC-LIGHTING FROM CONSTANT-CURRENT TRANSFORMERS. THE essential feature of the series arc- lighting system is necessarily the mainte- nance of a constant-current strength in the circuit; so that no matter how the number of lamps in the circuit may be varied, within the limits of the apparatus, the current and pressure at the terminals of any single lamp will remain constant. Consequently, in such a circuit the current is constant at all loads, or for all numbers of lamps operated ; while the E. M. F. in the circuit varies proportionally to the number of lamps inserted in the circuit. 375 376 ELECTRIC ARC LIGHTING. In Chapter XII., various dynamos have been described which are constructed in such a manner as to maintain approxi- mately constant current under all vari- ations of load, within the limits of their capacity. These dynamos supply either direct currents or alternating currents. It sometimes happens, however, that a large central station may be equipped with' con- stant-potential alternating-current genera- tors for its principal service. The intro- duction of series arc-lighting into the service of such a station necessitates either the introduction of a special class of constant-current generators, to supply the new demand, or some interme- diate apparatus which shall transform from constant potential to constant current. Such an apparatus is fur- nished by the Thomson constant-current transformer. SERIES ALTERNATING ARC-LIGHTING. 377 The mechanism of one of these trans- formers is shown at Fig. 163. FIG. 163. MECHANISM OF CONSTANT-CURRENT, ARC- LIGHTING TRANSFORMER. The primary coil P, lies at the base, and receives the constant alternating primary 378 ELECTRIC ARC LIGHTING. pressure, which is ordinarily either 1,100 or 2,200 volts. The secondary coil 8, instead of being rigidly secured close to the primary coil, as in the ordinary trans- former, is movable in a vertical direction, sliding freely up and down the central core, from or towards the primary coil. It is supported by a chain from one end of the beam BB, pivoted on a horizontal axis at X. The weights suspended from the other end of the beam are intended to balance the secondary coil, so that the secondary coil is supported freely at the end of a balance beam. The electric cur- rents in the primary and secondary coils set up a mutual electromagnetic repulsion, tending to lift the secondary coil, or aid the gravitational pull of the weights. Conse- quently, if the induced secondary current is too strong, the electromagnetic force will raise the secondary coil. If, on the other SEIIIES ALTERNATING ARC-LIGHTING. 379 Land, the secondary current is too weals; the weight of the secondary coil will over- come the electromagnetic force, and the coi] will descend until the secondary current strength regains its normal value. The E. M. F. induced in the secondary coil increases with its proximity to the primary coil, since, when the two coils are close together, nearly all the magnetic flux established by the primary coil will be linked with the secondary; whereas, when the secondary coil is lifted far above the primary, the magnetic leakage through the intervening air space will rob the sec- ondary coil of a considerable amount of magnetic flux, and, therefore, of a corre- spondingly considerable amount of induced E. M. F. Under these conditions, the secondary coil, aided by the adjustment of the curves on the ends of the balance beam, always tends to assume such an 380 ELECTRIC ARC LIGHTING. elevation and distance from the primary coil, that the current strength in the secondary coil shall be constantly that required for the operation of the arc- lamps in the series circuit. This current strength is usually 6.6 amperes. The whole apparatus is placed inside the tank represented in Fig. 164, which is filled with oil, so that the secondary coil rises and falls in oil. This oil not only maintains good insulation, but also tends to damp out mechanical oscillations which might other- wise be set up. The walls of the tank are sometimes corrugated, so as to expose a greater convective surface for the liberation of the heat unavoidably wasted in the ap- paratus. A constant-current transformer of this type can be readily constructed to maintain a closer automatic adjustment to constant current under varying loads, SERIES ALTERNATING ARC-LIGHTING. 381 than can the ordinary constant-potential transformer maintain constant potential. Fia. 164. EXTERNAL VIEW OF CONSTANT-CURRENT ARC-LIGHTING TRANSFORMER. These constant-current transformers are usually constructed in sizes of 25-light, 50-light, 75-light, and 100-light capacity, 382 ELECTRIC ARC LIGHTING. about 80 volts being allowed on the aver- age per lamp at tlie secondary terminals with 6.6 amperes, or about 528 volt- amperes in the secondary circuit per lamp, at a mean power-factor of, approximately, 0.8, or 422 watts per lamp. The current supplied on the primary side is practically constant at all loads. Since the primary pressure is also constant, the apparent power, or volt-amperes, supplied from the primary circuit, is also nearly constant, the real power varying with the load in the secondary circuit by the automatic adjustment of the phase-difference be- tween the primary pressure and current ; i. e. y the automatic adjustment of the primary power-factor. In the larger sizes of these transformers, there are two fixed primary coils, one at the top and the other at the bottom of the SERIES ALTERNATING ARC-LIGHTING. 383 FIG. 165. MECHANISM OP CONSTANT-CURRENT ABC- LIGHTING TRANSFORMER. 384 ELECTRIC ARC LIGHTING. transformer, and also two movable second- ary coils, as shown in Fig. 165. At full load the two secondary coils, which are interconnected by chains, are brought to their furthest distance from each other and close to their respective primary coils. At no load in the secondary circuit, i. e., at short circuit in the secondary, the two secondary coils are brought together, half- way up the core, so as to be placed at the maximum distance from their respective primaries. The external appearance of one of these larger transformers is shown in Fig. 166. The two secondary circuits may be operated either in series, or in parallel, as desired. Fig. 167, shows the connections of one of these transformers, having two separate secondary circuits. Owing to the fact that the primary power factor necessarily becomes about 33 SERIES ALTERNATIN3 ARC-LIGHTING. 385 Fia. 166. CONSTANT-CURRENT ARC-LIGHTING TRANSFORMER COMPLETE. ELECTRIC ARC LIGHTING. Primary Circuit Tubular Plu Switch Tube Fuse Short Circuiting Switch (Open ciciHrxg operation) FIG. 167. CONNECTIONS OF CONSTANT-CURRENT ARC- LIGHTING TRANSFORMER. per cent, at 40 per cent, of full load, it is desirable to operate these trnnsformers under nearly full load, when their power SERIES ALTERNATING ARC-LIGHTING. 387 factor may be V5 per cent., and their efficiency over 90 per cent. The appa- ratus is usually designed so as slightly to increase the secondary volts per lamp at light loads, owing to variations necessarily produced, under variations of load, in the shape of the alternating-current waves. In this manner the watts per lamp in the secondary circuit may be kept very nearly constant under all loads. The frequency of the currents supplied in such a system is usually 60 cycles per second. The practical advantage of such trans- formers, when operating under satisfactory conditions of distribution, lies in the fact that the apparatus requires very little attention, and may be placed in a sub- station at a considerable distance from the main power-house. If a motor- dynamo were substituted for a constant- 388 ELECTRIC AfcC LIGHTING. current transformer under such conditions, it would usually be necessary to provide the services of an attendant in the sub- station. The power-factor of- an alternating-cur- rent arc-lamp, as measured at its terminals, is always less than unity, or 100 per cent., if only on account of the fact that the regulating magnet coils of the lamp, as well as the ehoking coil, in series with the arc, possess inductance, and bring about a lag in the current, or a wattless component of current. Moreover, even if we consider the power delivered to an alternating-current arc at the carbons, and thus eliminate the effect of inductance in the regulating coils, it is found that the power-factor is less than unity, or the watts in the arc at carbons are less than the volt-amperes. The power-factor of the SERIES ALTKllNATHSTG AftC-LlGHTING. 389 arc itself may, in fact, be as low as eighty pel 1 cent, under certain conditions. The arc has neither inductance nor capacity, and, consequently, the current through the arc neither leads nor is led by the pressure at carbons. The alternating-current waves cross the zero line, or vanish cyclically, at the same instants as the waves of P. D. between carbons. The waves of current have, however, a different shape to the waves of potential dif- ference, which would not be the case if the arc acted like a simple resistance of metal wire. The resistance of the arc varies in fact with the current that passes through it, being relatively small with strong currents and great with weak currents. Consequently, if we force a 'simple sinusoidal wave of current through the arc, the P. D. will become magnified during the intervals of feeble current, 390 ELECTRIC ARC LIGHTING. and the wave of alternating P. D. at the carbons will be double-peaked, or will have a depression at the place where the crest should appear. Conversely, if the conditions of the circuit are such as to im- pose a simple sinusoidal wave of E. M. F. at the carbons, then the current which will flow through the arc at the crests of the waves, will be relatively more power- ful than the currents which flow through the periods of ascent and descent, so that the current wave will be sharply peaked. A sinusoidal wave is the simplest type of alternating wave. It is so called be- cause, when depicted graphically, the ele- vation at each point of the wave is pro- portional to the sine of the distance along the axis measured from the zero-point or point of mean level. It corresponds in contour to an ocean wave in deep water. SERIES ALTERNATING ARC-LIGHTING. 891 When a series of alternating-current lamps is supplied from a constant-current transformer at full-load, or with all the lamps in circuit, the inductance of the secondary coils of the transformer, which are close to the primary winding, is com- paratively small, and the secondary waves of E. M. F. are nearly faithful copies of the waves of primary E. M. F. supplied by the generator. Assuming that the gener- ator gives a nearly sinusoidal wave, then the E. M. F. at lamp terminals will be nearly sinusoidal, but the currents in the lamps will tend to differ considerably from sine waves, or will be centrally ele- vated into peaked waves. On the other hand, at very light loads, or with a small number of lamps in the circuit, the second- ary coils will develop a considerable inductance, and this inductance will tend to smooth out the current-waves, and force 392 ELECTRIC ARC LIGHTING. a more nearly sinusoidal type of current- wave upon the circuit. Under these con- ditions the E. M. F. developed in the secondary coil will flatten or tend to become double-humped. Consequently, the shapes of the waves of current and potential in such an arc-light circuit tend to undergo variation with change of load. CHAPTER XV. MULTI-CIRCUIT ARC-LIGHT GENERATORS. THE modern tendency of development in the electric generation of power is towards larger sizes and powers of machinery ; i. e., larger generating units. Whereas, only a few years ago, in constant- potential systems a 50-KW. generator was regarded as a large unit, and a central station was an aggregation of a number of such units, at the present time a 500 KW. machine is regarded as a compara- tively small unit. The same tendency has manifested itself in arc-lighting gener- ators, but here progress has been retarded by reason of the fact that, with constant- 393 394 ELECTRIC ARC LIGHTING. current machines, any increase in capacity is necessarily accompanied by a further increase in the terminal voltage. This terminal voltage is limited not merely by structural difficulties, but also by difficul- ties of circuit insulation. Thus a 10- arnpere constant-current generator of 10- KW. capacity would have a full-load terminal pressure of 1 kilovolt, while a 70-KW. generator of the same type would have a full-load pressure of 7 kilovolts. In order to keep the terminal pressure within convenient limits, the expedient has of recent years been adopted of divid- ing the armature coils of a generator into several groups, each of which forms electric- ally a separate armature, and is connected to a separate commutator and external circuit. Such a machine is called a multi- circuit machine, and the total voltage is MULTI-CIRCUIT ARC-LIGHT GENERATORS. 395 FIG. 168. MULTI-CIRCUIT, 4 CIRCUITS, SHOWING TU.A GENERATOR, SWITCHBOARD, AND THE DIFFERENT LAMP CIRCUITS. 396 ELECTRIC ARC LIGHTING. divided among the separate circuits. A 4-circuit Brush arc generator is repre- sented in Fig. 168. Here the head board of the machine carries five single-pole switches. One of these switches short- circuits the field magnets, and, therefore, acts as the main switch for the machine. Each of the four remaining switches short- circuits a group of armature coils and an external circuit. Consequently, any num- ber of circuits, up to four inclusive, can be operated simultaneously through the inter- mediate switch-board, diagramatically in- dicated at & These machines are either belt-driven or direct-driven, and are at present constructed in sizes up to 76 KW. in two-circuit, three-circuit, or four- circuit types. These machines are de- velopments of the type of single-circuit generator already shown in Figs. 145 and 146. CHAPTER XVI. PHOTOGEAPHY BY THE ARC-LIGHT. IN the ordinary operation of blue-print- ing, the paper is placed below the tracing and exposed to ordinary sunlight. Not only is this process dependent upon fine weather for its maintenance, but it is also dependent upon securing a proper expos- ure. In large office buildings a suitable exposure to sunshine is sometimes difficult to obtain, and in some localities the local conditions may preclude the possibility of the exposure ever being obtained. The electric arc-lamp permits blue-printing to be carried on independently of weather and exposure to sunshine, arc-light being 397 398 ELECTRIC ARC LIGHTING. capable of replacing sunlight for photo- graphic work. Although the time of exposure to arc-light is considerably in excess of the time of exposure to bright sunlight, yet the uniformity with which conditions can be reproduced in the case of arc-lighting, enables prints to be of ob- tained with a greater degree of certainty and precision than is possible with sun- light, under the ordinary varying condi- tions of cloud and atmospheric absorption. A more sensitive and rapid blue-print paper is also employed with arc-lamps, in order to lessen the time necessary for exposure. A general view of a standard equip- ment for electric blue-printing is shown in Fig. 169, and Fig. 170 shows the same equipment dismantled. A pair of arc- lamps, of the enclosed arc type, are sup- PHOTOGRAPHY BY THE ARC-LIGHT. FIG. 169. EQUIPMENT FOU ELECTUIC 400 ELECTRIC ARC LIGHTING. ported from a wooden beam, which is car- ried on rollers movable on an overhead rail. A large hood reflector, usually 4' x 3', is supported from the arc lamp covers, and is lined on the interior with white enamel. Where the printing is invariably carried on by arc-light, this travelling pair of lamps and reflector can be brought over a suitable fixed flat printing table, but where resort may be made occasion- ally to sun printing, a movable table is used, which is shown in Fig. 169. Here the printing frame may be supported at any desired angle to face the sun at an open window, when the arc-light appa- ratus is not in use. It is customary to employ a more sensitive and rapid blue- print paper in such a printing frame for arc-light printing, and the ordinary less rapid paper for sun printing. The time required for exposure in arc printing PHOTOGRAPHY BY THE ARC-LIGHT. 401 FIG. 170. ARC LAMPS AND HOOD SHOWING USUAL METHOD OF SUPPORT. 402 ELECTRIC ARC LIGHTING. under such conditions is usually about three minutes. In order conveniently to develop the maximum actinic power of the arc, a long and high-pressure arc is employed; other- wise, the time of exposure will be greatly prolonged. With direct-current arcs, the pressure of the arc as ordinarily used, is 80 volts with a current of 5 amperes per lamp on 110-volts circuit, making an ex- penditure of energy of 550 watts per lamp, or 1.1 KW. for a double-lamp frame. With alternating-current supply, the pres- sure of the arc is ordinarily 73 volts effect- ive, with a current of 7.5 amperes per lamp and 104 volts at terminals, representing 15 amperes for a double-lamp equipment. In some cases a vertical cylindrical printing frame is employed with a glass PHOTOGRAPHY BY THE ARC-LIGHT. 403 surface inside, and an arc-lamp is auto- matically lowered at a steady rate down the axis of the cylinder. FIG. 171. STANDARD HAND- FEED LAMP. For photographic reductions or enlarge- ments, a type of arc lamp is sometimes em- ployed which is either hand-fed, as shown 404 ELECTRIC ARC LIGHTING. FIG. 172. STANDARD AUTOMATIC LAMP WITH HOOD AM> REPLECTOB. PHOTOGRAPHY BY THE ARC-LIGHT. 405 in Fig. 171, or automatically fed, as shown in Fig. 172. Such an arrangement, with 20 amperes, will enable a single arc-lamp to make an ordinary blue-print 2' x 3' in area, at a distance of 4 feet from the arc in about 12 minutes with rapid paper. INDEX. Absorption of Light by Globes, 205. Activity, Definition of, 52. , Electrical Unit of, 53. , Unit of, 52. Adjustable Arc Lamp Hanger, 172. All-Night Arc Lamp, 118. Arc Lamp, Wallace, 121, 122."! Elliptical Carbon Lamp, 126, 127. Lamps, Series-Connected, 117 to 136. Reciprocating Carbon Lamp, 128. Alternating Carbon Arc, Electromotive Force Required for, 212 to 218. Current Arc Lamps, 209 to 236. Current Arc Lamps, Circuit Connections for, 219. 220. 407 408 INDEX. Alternating-Current Arc Lamps, Influence of Fre- quency on, 209, 236. Current Arc Lamps, Mechanism for,. 212 to 218. Current Arc Lamps, Methods for Con- necting, 221, 222. Current Arc Light, Distribution of, 258. Current Arcs, 34. Current Constant-Potential Enclosed Arc- Lamp, 365, 366. Current Constant- Potential Lamp, Forms of, 230, 231. Current Generator, 345. Current Lamp-Mechanism, Circuit Con- nections of, 216. Current Transformer, 217. Electric Currents, 34. Alternator, 217. Alternators, 325. , Self-Excited, 325. Amount of Work, How Measured, 50. Ampere, Definition of, 46. Analogy of Electric Current and Water Current, 38, 39. Apparent C. E. M. F. of Arc, 75. INDEX. 409 Arc Circuit, Total Resistance of, 77, 78. , Carbon, 18. , Carbon, Probable Temperature of, 30. , Carbon Voltaic, Physical Characteristics of, 23, 24. Carbons, Equal Consumption of, with Alternating Currents, 35. Carbons, Unequal Consumption of, with Continuous Currents, 35. , Causes of Unsteadiness of Light from, 26. , Effect of Distance between Carbons on, Lamp, Ash Pan for, 321. Lamp, Candle Power of, 259. Lamp Carbons, 307 to 322. Lamp Circuit, Series, Diagram of Connec- tions of, 108, 109. Lamp, Cross-Wire Suspension, 173. Lamp, Dash -Pot for, 105. Lamp, Derived-Circuit, 89. Lamp, Diffusing Reflector for, 264. Lamp, Double-Carbon, 129. Lamp for Diffused Lighting, 263. Lamp for Lantern Projection, 294. Lamp for Photo-Engraving, 305. 410 INDEX. Arc Lamp Hanger-Board, 181. Lamp Hangers, 189, 190. Lamp, Inner Globe of, 357. Lamp Mechanism, 55 to 125. Lamp Mechanism, Series Magnet for, 86. Lamp Mechanism, Shunt Magnet for, 86. Lamp Mechanism, Forms of, 89 to 103. Lamp, Pole Support for, 179. Lamp Poles, Forms' of, 182, 183. Lamp Projectors, 57. Lamp, Projectors for, 268 to 306. Lamp, Ring Clutch for, 106. Lamp, Shunt and Series Magnets of, 74. Lamp, Siemens' Later Form of, 93. Lamps, Alternating-Current, 209, 236. Lamps, Constant-Potential, 137 to 162. Lamps, Constant-Potential, Connections of, 147, 148, 150. = Lamps, Enclosed, 356 to 374. Lamps, Focusing, 267. Lamps, Mast-Arm Support for, 184, 185. Lamps, Multiple Connection of, 63. Lamps, Series Connection of, 61. Light Carbons, 7. Light Carbons, Cross Sections of, 319. INDEX 411 Arc Light Carbons, Various Dispositions of, 59. Light Circuit, Lightning Arrester for, 208. Light Circuits, Parallel, 60. Light Circuits, Series, 60. Light Dynamos, Series, 329. Light Generator, Multi-Circuit, 393 to 396. Light Generators, 339 to 341. Light Globes, Forms of, 204. Light Main-Circuit Magnet, 86. Light Photography, 397 to 405. Light Regulator, Siemens' Early Form of, 88. Light Regulators, 5. Light Regulators, Automatic, 5, 6. . Light Transformers, Connections of Pri- mary Circuits of, 23, 232. Lighting Central Station, 350, 351. Lighting, Early History of, 1 to 15. Lights on Incandescent Circuits, 142 to 146. , Metallic, 18. , Ohmic Resistance of, 84. Resistance, Circumstances Affecting, 79 to 81. 412 INDEX. Arc, Resistance of, 78. , Travelling of, 316. , Voltaic, 16 to 36. , Voltaic, Causes of Flickering of, 26. , Voltaic, Counter-Electromotive Force of, 75. Voltaic, Temperature of Positive Crater, 28. , Alternating, 34. , Continuous-Current, 34. Archereau's Regulators, 66. Armature of Alternator, 346, 347. Artificial Carbons, Bunsen's Process for, 310. Graphite, 34. Ash-Pan for Arc Lamp, 321. Atoms, 239. Automatic Arc-Lamp Regulators, 54. Arc-Light Regulators, 5, 6. B Bare Carbons, 316. Battery, Voltaic, 45. Beam of Light, 242. Belt-Driven Generators, 348. INDEX. 413 Bipolar Type, Continuous-Current Arc-Light Gen- erator, 330. Continuous-Current Generator, 326, 327. Dynamo-Electric Machine, 324. Gramme-Ring Arc-Light Generator, 331, 332. Blue-Printing, Electric, 398 to 400. Board-Hanger for Arc Lamp, 171. Bougie-Decimale, 252. Bougie-Metre, 253. Box, Olivette, 302. British Standard Sperm Candle, 248. Brush Double-Carbon Lamp, 131. Brush Washer or Ring Clamp, 130. Bunsen, 6. Process, 310. c C. E. M. F., Apparent, of Arc, 75. of Arc, 75. Candle, British Standard Sperm, 248. Candle, Jablochkoff, 10 to 15. Candle-Foot, 253. Candle-Power of Arc Lamp, 259, 414 INDEX. Carbon Arc, 18. Arc, Causes of Shifting of, 25. : , Ebullition of, in Voltaic Arc, 27. Electrodes, Various Positions of, 59. Holders, 320, 321. Vapor, Condensation of, on Negative Car- bon, 31. Voltaic Arc, 5. Voltaic Arc, Characteristics of, 20, 21. : Voltaic Arc, Nipple of, 20, 22. Voltaic Arc, Principal Source of Light of, 23. , Volatilization of, in Voltaic Arc, 27. Carbonizing Process, 308, 309. Carbons, Arc-Light, 7. , Arc-Light, Cross Sections of, 319. , Bare, 316. 1 Circumstances Affecting Density of, 315, 316. , Coppered, 316. , Cored, 316. , Cored, for Arc Lights, 27. ? Coreless, 319, 320. , Effect of Impurity of, on Light of Arc, 313. -, for Enclosed Arc-Lamps, 367. INDEX. 415 Carbons, Firing Process for, 315, 316. for Arc Lamps, 307 to 322. , Influence of Nature of, on Quietness of Arc, 322. , Life of, 320. , Long-Lived, 320. , Moulding Process for, 314. , Rate of Consumption of, in Enclosed Arc- Lamps, 358, 359. , Solid, 316. , Squirting Process for Incandescing, 314. Carcel Colza Oil Lamp, 249. Carre, 312. Ceiling Suspension for Arc Lamp, 176. Cells, Voltaic, Double-Fluid, 6. Central Station, Switchboard for, 352, 353. Characteristic Bow-Shape of Arc, Cause of, 32. Characteristics of Carbon Voltaic Arc, 20, 21. Choking Coil, 218. Circuit Arrester for Arc Lights, 208. , Break, Insulators, 177, 178. Connections of Alternating-Current Arc Lamp, 219, 220. Connections of Alternating-Current, Arc- Lamp Mechanism, 216. 416 INDEX. Circuit, Electric, 37. , Hydraulic, 40. , Primary, of Transformer, 218. , Secondary, of Transformer, 218. Circuit, Shunt or Derived, 70, 71. , Shunt, Principle of, 72. Circuits, Parallel Arc-Light,, 60. , Series Arc-Light, 60. Circular Hangers for Arc Lamps, 191, 192, 193. Circumstances Affecting Resistance of Arc,79 to 81. Coil, Choking, 218. , Economy, for Alternating-Current Arc- Lamp, 222 to 225. , Economy, for Alternating-Current Arc- Lamp, Connections for, 224. , Resistance, 218. Color, Cause of, 243. of Light, 241. Value of Sunlight, 244. Condensation of Carbon Vapor on Negative Car- bon, 31. Constant-Current Arc-Lighting Transformer, Thomson's, 376 to 387. Current Transformers, Series- Alternat- ing Arc-Lighting, 375 to 392, INDEX. 417 Constant-Potential Arc-Lamps, Connections of, 147, 148, 150. Lamps, 137, 162. Continuous-Current Arc-Lamp, Distribution of Luminous Intensity of, 256. Dynamo Electric Machine, 325. Current Arcs, 34. Electric-Current, 34. Controlling Gear for Arc-Light Projector, 282. Coppered Carbons, 316. Core, Laminated, of Transformer, 227. Cored Carbons, 316. Carbons for Arc Lights, 27. Coreless Carbons, 319, 320. Coulomb, Definition of, 47. Counter-Electromotive Force of Voltaic Arc, 75. Crater of Carbon Voltaic Arc, 21. of Voltaic Arc, Temperature of, 28. Cross- Wire Suspension for Arc Lamp, 173. Crucibles, Electric, 33. Current, Continuous Electric, 34. , Electric, Definition of, 46. Strength, Definition of, 28. Currents, Alternating Electric, 34. 418 INDEX. Cut-Out Switches for Arc-Light Circuits, 194 to 198. Cylinder, Damping, for Arc Lamps, 105. D Damping Cylinder for Arc Lamps, 105. Dash-Pot for Arc Lamp, 105. Davy, 307. , Alleged Discovery of Voltaic Arc by, 4. Daylight, Colors of, 244. De Mersanne, 119, 120. Density of Carbons, Circumstances Affecting, 315, 316. Derived-Circuit Arc Lamp, 89. or Shunt Circuit, 70, 71. Device, Gripping, for Arc Lamp, 88. Diagram of Connections of Arc-Light Generator, 333. of Connections of Series Arc- Light Cir- cuit, 108, 109. Differential Lamp, 89. Diffused Lighting, Arc Lamp for, 263. Reflector for Arc Lamp, 264. INDEX. 419 Diffusing Globe for Arc Lamp, 266. Direct-Coupled Generator, 350. Direct- Driven Generators, 349. Double-Carbon Arc Lamp, 129. Arc-Lamp Mechanism, 132, 133. Double-Fluid Voltaic Cells, 6. Drop of Pressure of Arc, 75. Dynamo Electric-Machine, 45. Machine, Continuous-Current, 324. Machines, 62. Dynamos, 355. E. M. ^., Meaning of, 38. Early History of Arc Lighting, 1 to 15. Ebullition of Carbon in Voltaic Arc, 27. Economy Coil for Alternating-Current Arc-Lamp, 222 to 225. Coil-for Alternating-Current Arc-Lamps, Connections for, 223. Edwards, 311. Efficiency, Luminous, 246. Electric Arc-Light Tower, 188. 420 INDEX. Electric Blue-Printing, 398 to 400. Circuit, 37. Crucibles, 33. Current, Definition of, 46. Furnaces, 33. Light Photographic Reductions or En- largements, 403, 404. Light Tower, 188. Quantity, Unit of, 47. Resistance, 41. . Sources, 37. Stereopticon, 295. Electrical Unit of Activity, 53. Electricity, Quantity of, 41. Electrode, Positive, Crater in, 21, 22. Electrodes, Carbon, Various Positions of, 59. Electromotive Force, 37. Force, Unit of, 44. Elliptical All-Night Carbon Lamp, 126, 127. Enclosed Arc-Lamp, Rate of Consumption of Carbons in, 358 to 359. Arc-Lamps, 356 to 374. Arc-Lamps, Advantages of, 360. Arc-Lamps, Automatic Cut- Outs for, 369, 370. INDEX. 451 Enclosed Arc-Lamps, Carbons for, 367. Arc-Lamps, Length of Arc in, 367, 368. Arc-Lamps, Luminous Efficiency of, 373, 374. Equal Consumption of Arc Carbons with Alter- nating Currents, 35. Ether Vibrations, Range of Frequency of, 240. F Faraday, 9. Feeding Mechanism, Requisites for Proper Opera- tion of, 58. Flickering of Voltaic Arc Light, Causes of, 26. Fire-Fly, Light of, 247. Fire Island Lighthouse Lens, 291. Flashing Light for Lighthouses, 293. Flux, Magnetic, 323. of Light, Unit of, 251. Focusing Arc Lamps, 267. Lamp, Automatic, 270. Lamp, Automatic, Vertical, 272. Lamp for Lighthouse, 293. Lamp, Necessity for, 269. Lamps, Varieties of, 273. 42 INDEX. Foot-Pound, Definition of, 50. per-Second, 52. Force, Electromotive, 37. Forms of Arc-Lamp Mechanism, 95 to 103. Foucault, 8, 307. Frame, Side, of Arc Lamp, 174. Frequency, Influence of, on Alternating-Current Ai'c-Lamps, 209 to 236. Furnaces, Electric, 33. G Generator, Alternating-Current, 345. , Belt-Driven, 348. , Bipolar, Continuous-Current, 326, 327. , Direct-Coupled, 350. , Direct-Driven, 349. , Multi-Circuit Arc, 393 to 396. Generators, 62. , Magneto-Electric, 9. , Railway, 46. Globe, Influence of, on Intensity of Arc Light, 262. Globes, Absorption of Light by, 205. INDEX. 423 Globes for Arc Lights, Forms of, 204. Gramme, 9. Graphite, Artificial, 34. Gripping Device for Arc Lamp, 88. Grove, 6. H Hanger Board for Arc Lamp, 171, 181. Board Hood, 199. Boards, 191, 192, 193. Hangers for Arc Lamps, 189, 190. Harrison, 8. Harrison's Arc Lamps, 125, 126. Head-Light for Locomotives, 292. Ilefner-Alteneck Amyl-Acetate Lamp, 249. Holder, Jablochkoff's Candle, 17, 18. Holders for Carbons, 320, 321. Hood and Hanger Board, 199. for Arc-Lamp Suspension, 200, 203. Hoods for Arc Lamps, 199 to 203. Horse-Power, Definition of, 52. Hydraulic Circuit, 40. 424 INDEX. I Igniter of Jabloclikoff's Candle, 14. Illumination and Light, 237 to 267. by Moonlight, 1, 2. , Liglithouse, 293. , Practical Unit of, 252. , Unit of, 250. Incandescent-Circuit Arc Lights, 142 to 146. Infra-Red Light, 240. Inner Globe of Enclosed Arc-Lamp, 357. Insulators, Circuit Break, 177, 178. , Circuit Loop, 177, 178. Intensity, Maximum, of Light, 255, 256, 257. of Horizontal Light, 255, 256, 257. of Light, 259. Iron Wire Arc-Light Globe Netting, 206. Jablochkoff's Candle, 10 to 15. Candle Holder, 17, 18. Candle, Igniter of, 14. Candle, Use of Alternating Currents for, 14. INDEX. 425 Jacquelain, 312. Joule, Definition of , 50, 51. per-Second, 53. Lacassagne and Thiers, 70, 311. Laminated Core of Transformer, 227. Lamp, Aro, 450- Watt, 45-Volt, 261. , Carcel Colza Oil, 249. , Derived Circuit, 89. , Differential, 89. , Focusing, Varieties of, 273. Frame with Inside Globe, 207. Frame with Outside Globe, 207. , Hefner-Alteneck Amy 1- Acetate, 249. Rod, 87. , Twin-Carbon, 129. , Violle Platinum Standard, 249. Lamps, All-Night Series-Connected, 117 to 136. , Arc, Hoods for, 189 to 203. , Search Light, 274 to 279. , Search, Simple Form of, 275, 276. Lantern Projector, Arc Lamp, 294. 426 INDEX. Law, Ohm's, 48. Leads, Negative, 63. , Positive, 63. Length of Arc in Enclosed Arc-Lamps, 367, 368. Le Molt, 8, 311. Life of Carbons, 320. Light, Actinic Power of, 241. and Illumination, 237 to 267. , Beam of, 242. , Color of, 241. , " Dark," 240. , Diffusing Arc Lamp Globe, 266. , Flux, Unit of, 251. , Focusing for Lighthouses, 293. , Frequency of Vibration of, 240. , Infra-Red, 240. , Intensity of, 259. , Mean Spherical Intensity of s 256. , Objective Cause of, 237, 238. of Fire-Fly, 247. , Spectrum, 242. , Standard Source of, 248. , Two-Fold Use of Word, 237. , Ultra- Violet, 240. } Unit of, 249. INDEX. 427 Light, Velocity of, 242. Lighthouse Illumination, 293. Lens, Fire Island, 291. Lighthouses, Flashing Light for, 293. Locomotive, Electric Headlight for, 292. Long-Lived Carbons, 320. Lumen, 251. Luminous Efficiencies; Table of, 246. Efficiency. 246. Efficiency of Enclosed Arc-Lamps, 373, 374. Lux, 253. M Machine, Bipolar Dynamo-Electric, 324. , Dynamo-Electric, 45, 62. Magnet, Main-Circuit Arc Light, 86. Magnetic Cause of Bow-Shape of Voltaic Arc, 32. Flux, 323. Magneto-Electric Generators, 9. Main-Circuit Arc-Light Magnet, 86. Mangin's Projector for Search Light, 289. Reflector, 290. Marine Search Light Projector, 283. Mast- Arm Support for Arc Lamps, 184, 185, 186. 428 INDEX. Maximum Intensity of Light, 255, 256, 257. Mean Spherical Intensity of Light, 255, 257. Mechanism, Arc-Lamp, 55 to 115. for Alternating-Current Arc Lamps, 212 to 218. of Double-Carbon Arc Lamps, 132, 133, 134. Melting Points of Refractory Metals, 29. Metals, Refractory, Melting Points of, 29. Metallic Arc, 18. Microhm, Definition of, 43. Molecules, 239. Moonlight, Illumination by, 1, 2. Moulding Process for Carbons, 314. Multi-Circuit Arc-Light Generators, 393 to 396. Multi-Circuit Generator Switchboard and Lamp Circuit of, 394 to 396. Multiple Connection of Arc Lamps, 63. and Series Distribution, Influence of, on Weight of Conducting Circuit, 139 to 142. jsr Negative Arc-Light Carbons, Rate of Consump- tion of, 118. INDEX. 429 Negative Carbon of Voltaic Arc, Lower Tempera- ture of, 31. Leads, 63. Pole of Electric Source, 38. Nipple on Carbon Voltaic Arc, 20, 22. Nollet, 9. o Ohm, Definition of, 42. Ohm's Law, 48. Ohmic Resistance of Arc, 84. Oil-Insulated Transformer, 228, 229. Olivette Box, 302. Outrigger and Hood for Arc Lamps, 169. Parallel Arc-Light Circuits, 60. Connection of Arc Lamps, 63. Pencils, Arc-Light Carbon, 7. Photo-Engi-aving, Arc Lamp for, 305, 306. Photographic Reductions or Enlargements, Elec- tric Light, 403, 404. Photography, Electric-Light, 397 to 405. 430 -INDEX. Physical Characteristics of Carbon Voltaic Arc, 23, 24. Pilot-House Controlling Gear for Projector, 282. Pilsen Arc Light, 123, 124. Pole, Negative, of Electric Source, 37. , Positive, of Electric Source,. 37. Support for Arc Lamp, 179. Support for Arc-Lamp Hoods, 202, 203. Poles of Electric Source, 37. Positive Arc-Light Carbons, Rate of Consumption of, 118. Electrode, Crater of, 20. Leads, 63. Practical Unit of Illumination, 252. Primary Circuit of Transformer, 218. Process, Carbonizing, 308, 309. Projectors, Arc-Lamp, 57 and 268 to 306. , Mangin's, 289. , Search Light, 278 to 289. Q Quantity of Electricity, 41. of Electricity, Unit of, per Second, 46. Quietness of Arc, Influence of Carbons on, 322. INDEX. 431 R Railway Generators, 46. Rate of Consumption of Negative Arc-Light Carbon, 118. of Consumption of Positive Arc-Light Carbon, 118. of Doing Work, 52. Range of Frequency of Pother Vibrations, 240. Reactance Coil of Enclosed, Alternating-Current Arc-Lamp, 365. Reciprocating Carbon Ail-Night Lamp, 128. Reflector, Mangin's, 290. , Stage, for Theatres, 296, 297. Refractory Metals, Melting Points of, 29. Regulators, Archereau's, 66. , Arc-Light, 5. , Automatic Arc-Lamp, 54. , Automatic Arc-Light, 5, 6. Reichsanstalt Standard, 249. Resistance Coil, 218. , Electric, 41. , Ohmic, of Arc, 84. of Arc, Circumstances Affecting, 79 to 81. 432 INDEX. Resistance of Arc, Effect of Counter Electromo- tive Force on, 84, 85. of Arc, Effect of Current Strength on, 83. , Unit of Electric, 42. Resistivity, Definition of, 43. Rheostat for Projector, 287. Ring Clutch for Arc Lamps, 106. or Washer Clamp, 130. Rod Lamp, 87. Rods, Arc-Light Carbon, 7. S Search Light Lamps, 274 to 279. Lights, 57. Secondary Circuit of Transformer, 218. Self -Excited Alternators, 325. Series and Multiple Distribution, Influence of, on Weight of Conducting Circuit, 139 to 142. Alternating-Current Arc-Lighting from Constant-Current Transformers, 375 to 392. Grouping of Alternating-Current,Constant- Potential Enclosed Arc-Lamps, 370, 371. . INDKX. 4'63 Series Arc-rLamp Circuit, Diagram of Connec- tions of, 108, 109. Arc Lamp, Interior Mechanism of, 110 to 114. Arc-Light Circuits, 60. Arc-Light Dynamo, 329. Connected All Night Lamps, 117 to 136. Connection of Arc Lights, 61. Distribution, 139 to 142. Magnet for Arc-Lamp Mechanism, 86. Serrin, 8. Shifting of Carbon Arc, Causes of, Voltaic, 25. Shunt and Series Magnets of Arc Lamp, 74. Circuit, Principle of, 70, 71. Magnet for Arc-Lamp Mechanism, 86. or Derived Circuit, 70, 71. Side Frame of Arc Lamp, 174. Siemens' Arc Lamp, Later Form of, 93. Regulator, Early Form of, 38. Solenoid, 65. Solid Carbons, 316. Sounds, Characteristic, of Voltaic Arcs, 35, 36. Source, Standard, of Light, 248. Sources, Electric, 37. Squirting Process for Incandescing Carbons, 314. 434 INDEX. Stage Reflector Lamp for Theatres, 296, 297. Staite, 8, 311. Standard, Reichsanstalt, 249. Sources of Light, 248. , Vernon-Harcourt Pentane, 249. Station, Central, for Arc Lights, 250, 251. Step-Down Transformer, 223. Transformer, Details of Construction of, 226, 227. Stereopticon, Electric, 295. Sunlight Color Values, 244. Suspension, Cross- Wire, of Arc Lamp, 173. Hood for Arc Lamps, 169. , In-Door, for Arc Lamps, 176. Outrigger for Arc Lamps, 167, 168. and Lamp Circuit of Multi-Circuit Gen- erator, 394 to 396. Switchboard, 351, 352. for Arc Lighting, 351 to 355. for Central Station, 352, 353. Switches, Cut-Out, for Arc-Light Circuits, 194 to 198. T Table of Luminous Efficiencies, 246. INDEX. 435 Temperature at which Bodies Become Luminous, 30. Temperature of Crater of Voltaic Arc, 28. Theatre, Stage Reflector, Lamps for, 296, 297. Thomson's Constant-Current Arc-Lighting Trans- former, 376 to 387. Tower, Electric Light, 188. Transformer, Alternating-Current, 217. , Laminated Core of, 227. , Oil-Insulated, 228, 229. , Primary Circuit of, 218. , Secondary Circuit of, 218. , Step-down, 223. Travelling of Arc, 316. Twin-Carbon Arc Lamps, 129. u Ultra-Violet Light, 240. Unequal Consumption of Arc Carbons with Alter- nating Currents, 35. Unit of Activity, 52. of Electric Current, 46. of Electric Quantity, 47. of Electric Resistance, 42. 436 INDEX. Unit of Electrical Activity, 53. of Electromotive Force, 44. of Flux of Light, 251. of Illumination, 250. of Illumination, Practical, 252. of Light, 249. of Quantity of Electricity per Second, 46. of Work, 50. Use of Alternating Currents for Jablochkoff's Candle, 14. Van Malderen, 9. Velocity of Light, 242. Vernon-Harcourt Pentane Standard, 249. Vertical Automatic Focusing Lamp, 272. Vibration, Frequency of Light, 240. Violle Standard Platinum Lamp, 249. Volt, Definition of, 45. Volta, 18. Voltaic Arc, 16 to 36. Arc, Alleged Discovery of, by Davy, 4. Arc, Bow Shape of, 20. Arc, Carbon, 5. INDEX. 437 Voltaic Arcs, Characteristic Sounds of, 35, 36. Battery, 45. Volatilization, Constant Temperature of, 27. of Carbon in Voltaic Arc, 27. Volt-Coulomb, 52, 53. w Wallace All-Night Lamp, 121, 122. Washer or Ring Clamp, 130. Water-Motive Force, its Analogy to Electromo- tive Force, 38, 39. Watt, 53, 54. Wire Netting for Arc-Light Globes, 206. Work, Unit of, 50. Wright, 8, 124. 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