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mains 163 per cent. ; utilized as light, erator of five ohms, making the total 413 per cent. To bring the utilization resistance twenty-six ohms, there is utilup to between 49 and 50 per cent., the izable as light the ten-thirteenth part of mains must weigh 32 pounds per foot, the current generated, or about 77 per and will therefore cost $101,376. The cent. Applied to lamps of low resistance, respective resistances will then be: as (ne ohm each, the arrangement would Generator, .2; mains, .01; lamps, .2 of have to be materially changed ; for, unan ohm.
less changed, the external resistance of In corresponding ratio the size of one the lamp circuit would be but one-tenth mile mains for 10,000 lamps must be in
10x1 creased, if we desire to approach a reali- of an ohm
and the total
100 zation in light of even 50 per cent. of the current generated, and the internal re- whence it follows that we would only be
resistance of the system 6.1 ohms; sistance of the generator must be reduced able to utilize in the production of light to two one-hundredths of an ohm. We 1.64 per cent of the current generated. shall not pause to consider the character of a generator of the required power and viding 10 branches, each containing 100
Reversing this arrangement and proof so low an internal resistance, for we have no practical data upon which to lamps
, we have a circuit resistance of 10 base an opinion. The production of a ohms
and with a gengenerator of the resistance given, com
10 bined with the capacity indicated, is at erator resistance of 2.5 ohms, and a all events possible. Concerning the re- resistance in the mains of .25 ohm, mak
Fig. 69. Multiple-Series Circuit.
quirements of any multiple-circuit gen- in the mains of one ohm, and in the generator, however, we are enabled to see ing the total resistance of 12.75 ohms, that it must be one of multiple induction, we are enabled to utilize as light 78 per the coils of which shall be automatically cent. of the current generated; but we joined together to form á multiple-inter- must light substantially the entire hunnal circuit, which shall both increase the dred lamps in each branch at once and quantity of the current generated and extinguish them all at once, or else we reduce the internal resistance of the gen- must waste the current which would go erator, in proportion as the number of to the lamps in equivalent artificial relamps in the external circuit is increased sistances when we extinguish a part of and the external resistance reduced. In the lamps; for, as the current is to be the mechanical construction of such a equally divided among all the branches, generator there is a wide field for study a branch must in practice either be enand experiment.
tirely cut off from, or its entire resistance. Referring now to the multiple-series interposed in, the circuit. system (Fig. 69), it is evident that, in In the fourth or series-multiple sysoperating 1,000 lamps of 200 ohms re- tem of subdivision (Fig. 70), as in the sistance each, there may be one hundred multiple-series system, the resistance of branches across from main to main, and the external circuit may be anything dein each branch ten lamps, which would sired, and there may be operated in the make the external resistance of the cir- same circuit very many different combicuit, not including that of the mains, 20 nations of lamps. The main conductor, (10 x 200
which is single as in the series system, ohms
(10X2200 = 20). With a resistance is cut at the points at which light is
Fig. 70. Series-Multiple Circuit.
With 10,000 lamps there may be 500 points of divergence, each containing 20
lamps, by which arrangement the resistance of the lamp circuit becomes 25 ohms (500+1
=25); and with a generator re20 sistance of 5 ohms, and a resistance in the connecting conductors of 1 ohm, the proportion of current available for light
is 80 per cent. of the total production. SK
We might continue these calculations indefinitely, but to no further purpose. The flexibility of the system is obviously such as to permit of any regular combi. nation of lamps whatever, and thus to obtain any external resistance whatever ; and it will be found to permit equally well of all irregular combinations, so that in one division, where the volume of light required is great, there may be, say, five lamps in multiple, and in the next division, where the volume of light required is ordinary, there may be ten lamps in multiple, each of the latter ieceiving but one-fourth as much current as each of the former, because the joint resistance of the ten lamps is .1 ohm,
while the joint resistance of the five * EX
lamps is .2 ohm; and the ten lamps receive but half as much current as the five lamps, while the number of lamps is doubled. The closing-up, short-circuiting, or reducing the resistance of any division acts simply to reduce the resistance of the whole circuit, in the same manner as removing a portion of the lamps in a simple-series system. The relative advantages of the multipleseries and the series-multiple systems can only be determined by the number of lamps operated from a single source and the practical operation of both systems, although there are considerations
of simplicity which would seem to fadesired, and from the two disconnected vor the series-multiple arrangement of ends a number of small conductors are lamps, whose connection with a line of run each to a lamp or series of lamps. dwellings is illustrated in Fig. 71. In the operation of 1,000 lamps by this system there may be, say, one hundred REGULATORS AND SWITCHES.-Although points of divergence, and at each of these it is matter of common knowledge that points ten lines of wire containing one a carbon loop or pencil, intensely heated lamp each. Thus the resistance of the by the passage of the electric current,
(100+1 lamp circuit is made 10 ohms =10) becomes luminous, it is not generally and with a generator resistance of 2.5 luminosity bears to the strength of the ohms, and a resistance in the connecting current. The precise relations of the conductors of .25 ohm, we utilize as current supplied and the light produced light 78 per cent. of the whole current. have never been determined; but results
Vol XXIV.—No. 3–16.
which, it is believed, closely approximate portion to its length and cross section, the truth were first obtained in August, the percentages observed in one lamp 1878.
are the percentages of all lamps in which A Sawyer-Man lamp of high resistance wastage of the carbon by chemical
Fig. 71, House-Connections with Main Conductor. a, b, Points of Divergence.
(.6 of an ohm) was employed in the tests action is obviated. Disintegration at then made ; but it should be borne in the points of contact when these are immind that, without reference to the perfect, mechanical disengagement of length or cross section of the carbon, so particles of the carbon, and rupture due long as the current supplied is in pro- to imperfections in the constitution of
the carbon are occurrences common to resistances is 4.2 ohms, thus sending all incandescent lamps.
through the lamp six-sevenths of the A dynamo-electric machine wound ex- current, while maintaining the resistpressly for the purpose, and driven at ance from the+ to the-point the same. an unvarying speed, was used ; and as It was found that when the volume of there was abundance of power, and as current supplied to the lamp was threethe speed remained constant under almost sevenths of the whole current, the conany circumstances, it was deemed neces- tact-piece B bearing upon the studs 4, 4, sary, in order to obtain a satisfactory the carbon was brought to a low red result, that the resistance external to the heat. With four-sevenths of the curmachine should be kept constant. rent supplied to the lamp, the carbon Therefore the internal resistance of the gave a light of about one candle ; fivelamp to be experimented upon was meas- sevenths of the current, the light, measured, and it was found to be as stated. ured by a sugg photometer, was three A new form of current regulator, after- candles; with six-sevenths of the curwards known as the Sawyer-Man switch rent, nine candles ; with the whole cur(Fig. 72), was employed in the tests. rent, twenty-seven candles. When the
The poles of the generator had connec- contact piece B was bearing upon the tions at the+and-points, A being a studs 1, 1, the whole current passed sliding-bar, and the cross piece B being through the artificial resistance of .60 a spring contact-piece brought to a bear- ohm. The gradations of light by this ing upon the two rows of studs 1, 2, 3, means being too sudden (from less than 4, 5, 6, 7, 8, accordingly as it is moved one candle light to three candle light, backward or forward. Whatever posi- from three to nine, and from nine to tion the cross piece assumes, it will be twenty-seven candle light), the resistnoted that the resistance of the circuit ances were subsequently changed so as from the+ to, the-point is the same. to admit to the lamp first one-half of In the position shown, all the current the current, then five-eighths, three traverses the lamp. With the contact- quarters, seven-eighths, fifteen-sixpiece B bearing upon the studs, 7, 7, teenths, thirty-one-thirty seconds, and two paths for the current are afforded, finally the whole current. one by way of a resistance of .10 ohm arrangement the gradations were gradand the lamp outward, making a total ual and pleasing. resistance of .70 ohm in that circuit, and The disparity between the volume of the other by way of resistance of 2.10, current supplied and the intensity of .70, .35, 21, .14, 10, and .60 ohms, out- the light obtained is very clearly indicaward, the sum total of which series of tive of the requirements of an incandes
cent lamp. Since five-sevenths of the not lessened, but the entire current that total current for a single lamp produces served to operate the lamp is wasted in but three candle-light, while the whole heating an artifical resistance. It was current produces twenty-seven candle- this consideration that led to the designlight, or nine times as much, it follows ing of the graduating switch (Fig. 73), that in order to secure the maximum economy the carbon must be raised to a high temperature. For if we have a supply of current equal only to the maximum requirements of fifty lamps, from which we may obtain a sum total of 1,350 candles, we cannot divide this current among seventy lamps without sustaining enormous loss, as the sum total of light given by the seventy lamps will
Fig. 73. Small Sawyer Switch. be but 210 candles, while the expenditure of power will be the same. There which is fixed to the wall of a room or is a compensating influence in the case in any other convenient place, or atof lamps in series driven by a dynamo- tached to the lamp fixture. In this generator, consisting in the increase per- switch, which is illustrated apart in Fig. centage of current exterior to the gene- 74, there is an insulating disc, upon rator when the resistance of the external circuit is increased.
To sustain the high temperatures necessary to the economical operation of an incandescent-lighting system the carbon must be hard, dense, and substantial; and in the absence of these qualities is found the explanation for the inefficiency of fine, filamentary carbons, which can never be safely brought above the temperature of a gas flame. Carbon incandescence (that of white light), unlike the incandescence of an iron or platinum conductor, is of two grades
Fig. 74. Switch apart. and various intensities. In the first the carbon is intensely white, and its form which are fixed four brass segments, of optically broadened and lost in a sur a circle. Over this disc is placed the rounding haze of light. In the second brass enclosing cap, through which and more intense incandescence its form passes loosely a slotted iron pin carry, stands out sharply defined, and it ap- ing a brass contact bar, which is forced pears no longer opaque but limpid, seem- to a bearing upon the brass segments, by ingly translucent, like the body of the means of a steel spring coiled in the sun. It is to this degree of intensity head of the cap. Upon the end of the that economical lighting by incandes- iron pin the finger piece is finally cence is confined.
screwed. By turning the finger piece The Sawyer-Man switch affords a in one direction or the other the light is ready means of dividing the current in turned on or off, or regulated to intermeany desired manner, while maintaining diate points of intensity. In Fig. 75 the resistance of a circuit constant. the switch, as attached to the arm of a Thus any number of lamps provided chandelier or bracket, is illustrated, the with it may be operated by a single gen- circular case at the end of the arm being erator, and any portion of them may be shown partly in section. The lamp is regulated to any desired degree of in- fixed to the nipple above the switch tensity without affecting other lamps in case, and the insulated conducting wires circuit. The objection to its use con- pass through the hollow arm. The consists in the fact that when a lamp is ex. nections of the switch are shown in tinguished the work of the generator is Fig. 76.