32 TRANSIT OF ELECTRICITY. PART i. 



tional to the strength of the current, whatever may be 

 its direction, and that its power to overcome resistance 

 is as the square of the force of the current. The force 

 is exactly in proportion to the chemical action which 

 produces it, and that is measured by the quantity of 

 zinc consumed in the battery. Thus chemical action 

 produces electricity, and conversely electricity is a 

 powerful agent in the chemical composition and decom- 

 position of matter. 



The light and heat of the electric spark are intense 

 though instantaneous ; but a powerful induction appa- 

 ratus like Ruhmkorff's gives so rapid a succession of 

 sparks that the light and heat are sensibly continuous 

 and of great intensity. The light and heat, powerful 

 as lightning itself, are produced by the combined cur- 

 rents of two batteries, each consisting of fifty Bunsen 

 elements of moderate size. This formidable united 

 current passes through a circuit of thick copper wire 

 coated with silk thread, with an intensity of perpetually 

 renewed heat that no substance can resist. When the 

 copper conducting wires are fitted with charcoal termi- 

 nals and brought near to one another, the dazzling lights 

 emanating from, each pole combine in one blaze of in- 

 supportable brilliancy. The most refractory substances, 

 silica, alumina, iron and platinum, when placed between 

 the poles, immediately melt like wax, and volatilize. 

 Charcoal is so good a conductor of electricity that when 

 the terminals are in contact they complete the circuit, 

 and neither light nor heat appear. Air and glass are 

 non-conductors, yet the spark has passed through 

 several inches of air and perforated a mass of glass two 

 inches thick. A long electric spark combines or de- 

 composes a greater quantity of gas or vapour than a 

 short one, and for a given induction apparatus and 

 induction current, M. Perrot has shown that there 



