200 VOLTAIC ELECTRICITY. 



that the decomposition is produced by the abstraction of 

 electricity, rather than by any physical difference in the 

 fluid itself. By frictional electricity we may produce 

 curious molecular disturbances, and give rise to molecu- 

 lar re-arrangements^ which have been called " electrical 

 images," in glass, in stone, and in the apparently less 

 tractable metals : these images are rendered visible by 

 the manner in which, according to their electrical states, 

 some lines receive any particular powder, or vapour, 

 which is repelled from other spaces. Many of the great 

 natural phenomena, such as Lightning and Thunder, the 

 Aurora Borealis, and Meteors, may be imitated in a 

 curiously exact manner by the electrical machine and a 

 lew familiar arrangements.* 



Voltaic electricity, as the active force produced by 

 chemical change is commonly called, in honour of the 

 illustrious Volta, is now to be considered. It differs 

 from frictional electricity in this : the electricity deve- 

 loped by friction of the glass plate or cylinder of the 

 electrical machine is a discharge with a sort of explosion. 

 It is electricity suddenly liberated from the highest state 

 of tension, whereas that which is generated by chemical 

 action in the voltaic battery is a steady flowing current. 

 We may compare one to the ignition of a mass of gun- 

 powder at once, and the other to the slow burning of 

 the same quantity spread out into a very prolonged 

 train. 



There are numerous ways in which we may excite the 

 phenomena of Voltaism, but in all of them the decom- 

 position of one of the elements employed appears to be 

 necessary. This is the case in the arrangements of bat- 

 teries in which two dissimilar metals, zinc and copper, 

 silver and platinum, or the like, is immersed in fluids ; 

 the zinc or the silver are gradually converted into soluble 

 salts, which are dissolved, whilst the copper or platinum 



* Karsten ; PoggendorfFs Annalen, vol. Ivii. 



