NO TES AND A PPEN DICES. 3 1 1 



has been clearly demonstrated by experiments both in Ame- 

 rica and in England, that the resistance of the arc varies as 

 the resistances in circuit vary. The following table will 

 show this : 



Current in Light in Resistance of Arc. 



Webers. Candles. Ohms. 



10 440 277 



16-5 705 1-25 



21-5 900 1-67 



30-12 1,230 -54 



" The light in the arc varies directly as the current, and not 

 as the square of the current, as generally assumed. 



" Now, in the case of light raised by incandescence, the 

 light will increase as the square of the current. It follows 

 that if in the one case viz., the arc the light increases as 

 the current only, and in the other case viz., incandescence 

 it increases as the square of the current, a point is reached 

 when the light produced by incandescence will equal that 

 produced by the arc. The difficulty in reaching that point 

 is the difficulty of obtaining a conductor with a sufficiently 

 high point of fusion to resist the effect of powerful currents. 

 Iridium is the only metal that is known to do this, and 

 iridium is too scarce and too dear to be used for the purpose. 



"The multiplication of the light by Gramme's machine 

 upon the Thames Embankment must not be taken as the solu- 

 tion of the problem of the subdivision of the light. Theory 

 shows unmistakably that to produce the greatest effect we must 

 have only one machine to produce one light. We know 

 from absolute measurements that such a machine can be 

 made to produce a light of 14,880 candles, and it is possible 

 to produce 1,254 candles per horse-power. But the moment 

 that we attempt to multiply the number of lights in circuit 

 this power diminishes, so that we have on the Embankment 

 lamps giving us a light of scarcely more than 100 candles. 

 The light of the Rapieff lamp in the Times office appears to 

 be about 600 candle-power, and the Wallace light is equal 



