140 ELECTRIC LIGHTING. 



Light produced by means of conductors of in- 

 different conductivity. We have said at the commence- 

 ment of this chapter, that one of the means of producing the 

 electric light is the heating which takes place when a power- 

 ful current traverses a body of indifferent conductivity inter- 

 posed between two electrodes of good conductivity. We 

 have also seen that rods of carbon and of refractory sub- 

 stances constitute these bodies of indifferent conductivity, 

 and that Jablochkoff on one hand, and Lodyguine and 

 Kosloff on the other, had made some very interesting ex- 

 periments on this subject. It is this new .method of pro- 

 ducing the electric light that we are now about to consider, 

 and we shall begin by Jablochkoff's system, which is the 

 most curious. 



Jablochkoff ^ s System. In this new system the induction 

 currents from a Ruhmkoft's coil of moderate dimensions 

 are used, and a piece of slightly baked kaolin, two milli- 

 metres thick and one centimetre wide, which forms the semi- 

 conducting substance, is required to supply the incandescent 

 point, or rather the luminous source, for the whole appears 

 to be illuminated. With a single coil two sources of light 

 can easily be obtained in one circuit, but by increasing the 

 number of induction coils and the power of the generator, 

 the number of these luminous sources may be indefinitely 

 increased a circumstance which may in some degree solve 

 the difficult problem of the division of the electric light. We 

 shall, however, consider this question farther on. 



The arrangement of the system is very simple ; the small 

 piece of kaolin is introduced between two little iron nippers 

 which form the polar electrodes, and which are themselves 

 attached to two clips capable of moving horizontally by 

 means of a screw. These nippers seize the piece of kaolin 

 by its' upper slightly thinned edge, and even a little beyond 

 this edge, in order that the apparatus may be more easily 

 lighted ; for this apparatus must be lighted, and it will readily 

 be understood that the substance is not of itself sufficiently 



