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 represent 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 surface, 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 brightness 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 introduce into the electric circuit a substance of small conducting power, and capable of sustaining an intense heat without disintegration, combustion, or melting. Platinum has been used for this purpose. If the conductive power of copper be represented by 100, that of platinum will be represented by 18 only. Thus the resistance experienced by a current in passing through platinum is relatively so great, that if the current is strong the platinum becomes intensely heated, and shines with a brilliant light. A difficulty arises in using this light practically, from the circumstance that when the strength of the current reaches a certain point, the platinum melts, and the circuit being thus broken, the light immediately goes out.