300 ROUCH WAYS MADE SMOOTH. 



between these points a mobile chain, more or less conduc- 

 tive, and more or less heated, according to the intensity of 

 the current and the nature and separation of the electrodes ' 

 (that is, the quality and distance apart of the carbon or other 

 substances between which the arc is formed). 'These things 

 happen exactly as if the electrodes were united by a metallic 

 wire or carbon rod of small section ' (so as to make the 

 resistance to the current great), 'which is but saying that the 

 light produced by the voltaic arc and that obtained by in- 

 candescence arise from the same cause that is, the heating 

 of a resisting substance interposed in the circuit.' 



The intensity of the light from the voltaic arc and the 

 carbon points varies with circumstances, but depends chiefly 

 on the amount of electricity generated by the battery. A 

 fair idea of its brilliancy, as compared with all other lights, 

 will be gained from the following statements : If we re- 

 present the brightness of the sun at noon on a clear day as 

 1,000, the brightness of lime glowing under the intense heat 

 of the oxy-hydrogen flame is about 7 ; that of the electric 

 light obtained with a battery of 46 elements (Bunsen's), 235. 

 With a battery of 80 elements the brightness is only 238. 

 (These results were obtained in experiments by Fizeau and 

 Foucault.) The intensity does not therefore increase much 

 with the number of the component elements after a certain 

 number is passed. But it increases greatly with the suriace, 

 for the experimenters found that with a battery of 46 elements, 

 each composed of 3, with their zinc and copper respectively 

 united to form one element of triple surface, the brightness 

 became 385, or more than one-third of the midday bright- 

 ness of the sun (that is, the apparent intrinsic lustre of his 

 disc's surface), and 55 times the brightness of the oxy- 

 hydrogen lime-light. 



Another way of obtaining an intense heat and light from 

 the electric current generated by a strong battery is to in- 

 troduce into the electric circuit a substance of small con- 

 ducting power, and capable of sustaining an intense heat 

 without disintegration, combustion, or melting. Platinum 



