304 ROUGH WAYS MADE SMOOTH. 



carbon rods would allow the passage of the electric current 

 at the place of nearest approach, and therefore of least 

 resistance to its passage. A variable and imperfect illumi- 

 nation would result. M. Jablochkoff, however, interposes 

 between the separate carbon rods a slip of plaster of Paris, 

 which is a non-conducting material. The upper points of 

 the carbon rods are thus the only parts at which the current 

 can cross. They are connected by a little bridge of carbon, 

 which is necessary for the starting of the light just as in 

 the case of the ordinary electric light, the two carbons must, 

 in order to start the light, be brought into contact When 

 the current flows, the small bridge of carbon connecting the 

 two points is presently consumed, but the arc between 

 the points is still maintained : for the plaster becomes 

 vitrified by the intense heat of the two carbon points on 

 each side, and me'ts down as the carbons are consumed. 

 If the light is in any way put out, however, a small piece of 

 carbon must be set again, to form a bridge between the 

 carbon points. Throughout the burning of the Jablochkolt 

 candle the fused portion of the insulating layer forms a 

 conducting bridge between the carbon points ; and hence 

 there is a considerable loss of electric force (probably about 

 thirty per cent.), which in the ordinary arrangement would 

 increase the intensity of the light. The great advantage of 

 the candle consists in the circumstance that throughout its 

 consumption the carbon ends are at a constant distance 

 from each other without any mechanical or other arrange- 

 ment being necessary to maintain them in due position. 



One point should be noticed here. In the ordinary 

 arrangement of carbon points, the positive carbon, as we 

 have already said, is much more intensely heated, and con- 

 sumes twice as fast as the negative carbon. Now, if one 

 carbon of the Jablochkoff candle were connected with the 

 positive, and the other with the negative pole of the battery 

 or of a machine, the former side would consume twice as 

 fast as the latter, and the two points would no longer remain 

 at th? same horizontal level, which is essential to the proper 



