S40 



SCIENCE. 



by the current from the bobbin, which also traverses the 

 voltaic arc. 



This is the mounting adopted to-day in most of the 

 monophote regulators. 



On examining this system a little closer, we see that it 

 presents a serious inconvenience. When the arc is 

 lengthened, the intensity of the current diminishes, for 

 two reasons, first, in consequence of the increase of re- 

 sistance of the current ; second, because this enfeeble- 

 ment corresponds to an enfeeblement in the same way 

 of the power of the inductors, and, as a result, of the 

 electro-motive force of the machine, since this electro- 

 motive force is itself a function of the power of the induc- 

 tors. If the arc is made shorter, the reverse phenom- 

 enon results. This is a poor condition of regulation, 

 since the increase of power of the machine corresponds 

 to a shortening of the arc, and inversely, the diminution 

 of the electro-motive force, corresponds to the lengthen- 

 ing of the arc. The production of the machine is, then 

 in a contrary direction to the needs of the arc, and it is 

 certainly one of the great reasons for which this mounting 

 demands, in order to work well, sufficiently sensible reg- 

 ulators. They avoid this inconvenience by several 

 methods. 



The first consists of arranging the inductors by deri- 

 vation; this arrangement, conceived by Wheatstone in 

 1866, has not yet received many practical applications. 

 M. Siemens, of London, is studying it at the present time 

 and we shall find, by and by, an application of it in 

 Edison's machine. 



The second method, universally employed in the ma- 

 chines with alternative currents and which is commencing 

 to spread in somewhat important applications where the 

 lights have continuous currents, consists of charging 

 the inductors of a series of machines by a special machine. 

 Diagram 2 represents this arrangement. The arcs 1, 2, 



Fig. 2. — Machines charged by a special machine. Four machines with 

 continuous currents supplying four regulators with a voltaic arc. The 

 inductors are supplied by a separate generator. 



3, 4 are bound to the brooms of the inducted bobbins Ai, 

 Aa, As, &c, of the respective machines. 



By this means a constant magnetic field is assured, 

 whose power depends only on the velocity of the genera- 

 tor ; as a result, the electro-motive force is then absolutely 

 independent of the variations of resistance of the voltaic 

 arc which it sustains. Thus is found the advantage of 

 the magneto-electric machines whose magnetic field is 

 constant, but we gain the additional advantage of having 

 the most powerful machines, and of being able to vary 

 the production of these machines by regulating at will 

 the rapidity of the generator. There is in the French 

 section a series of machines, arranged according to this 

 principle. 



Such are the arrangements employed with the mono- 

 phote apparatus. 



When a single machine is to supply several lights 

 the arrangements change, and the lamps can be grouped 

 in different ways. 



When they are all branched over two general conduc- 

 tors starting from the limits of the machine, the lights 

 are said to be established in derivation, in multiple or in 

 quantity (fig. 3). When the lights are arranged, one 



B 1 s 5 



Fig. 3. — Mounting in derivation, in multiple arc, or in quantity. 



following the other, on one and the same conductor, they 

 are said to be mounted in tension, in series, or in circuit 

 (fig. 4). 



The mounting in multiple arc requires volume, that 

 in circuit requires especially pressure or tension. The 

 one or the other is applied according to the case. 



Sometimes even several derivations are established, 

 each carrying two, three, ten, etc., lamps in circuit. It 

 is the case, for example, of the lamps of the Swan system 

 of incandescence, fed by Brush machines. 



The reasons of these multiple combinations are easy 

 to comprehend. If the electric source of'the machine we 

 are arranging has more electro-motive force than that 

 exacted by a single light, it would be an advantage to 

 group several lights on the same circuit ; when, on the 

 contrary, the volume of current which the machine can 

 produce is greater than that which is necessitated by a 

 single light, we arrange them in quantity or in deriva- 

 tion. The Edison and Maxim systems of incandescence 

 are monted in quantity over the source. They differ only, 

 leaving on one side for a moment the lamp itself, in the 

 manner of regulating the current. 



In the Maxim system, the mounting of which is repre- 

 sented in figure 5, a separate generator supplies a series 



Fig. 5. — Mounting of the Maxim machines. 



of machines, whose brooms are set between them in 

 quantity, that is to say, by poles of the same name. All 

 the lamps are branched over the conductors in derivation. 

 The regulating obtains, by charging automatically the 

 setting of the brooms of the generator, which reacts on 

 the power of the current of the generator, and, conse- 

 quently, on that of the inductor. 



In the Edison system, the lamps are also mounted in 

 derivation, but the inductors ll 1 (rig. 6) are placed on a 

 derived circuit led to the brooms of the machine in Band 

 B 1 . The power of the inductors is regu'ated, and con- 

 sequently that of the machine, by manoeuvring by hand a 

 rheostat which serves to increase or diminish the resist- 

 ance of the generating current, and consequently the 

 electro-motive force of the machine. It is the Wheat- 

 stone mounting. 



Machines with slltcrnativc Currents.— The employ- 

 ment of alternative currents steps in with electric candles, 

 because the two carbons must beequally consumed. Cer- 

 tain regulators also act with the alternative currents. The 

 equal consuming of the carbon limits the displacement 

 of the luminous point, which is often an advantage. All 



