430 ANALOGIES OF 



while metals and other dense bodies that evolve 

 much less caloric, are good conductors, and 

 that other things being equal, the conducting 

 power of metals is augmented in proportion as 

 they are deprived of caloric. 



It is also known that the lightest solids, cateris 

 paribus, afford the largest amount of electricity 

 by friction, and that they are bad conductors of 

 electricity. It was further ascertained by Sir 

 H. Davy, that the conducting power of metals 

 for voltaic electricity is diminished in proportion 

 to their temperature; (Phil. Trans. 1821 :) (and I 

 have shewn that their cohesion is diminished in 

 the same ratio.) It is therefore evident, that the 

 conducting power of bodies for both caloric and 

 electricity is modified by every alteration in the 

 relative proportions of aethereal and ponderable 

 matter of which they are composed ; and that as 

 a general rule, with few exceptions, the same 

 bodies are conductors and non-conductors of 

 both.* (See Theory of Conduction.) 



It was before observed, that no two series of 



* It may be objected, that some bodies which are non-con- 

 ductors of electricity when solid, become conductors in the liquid 

 state. But it is doubted by Dr. Faraday whether such bodies 

 ever do conduct electricity without undergoing decomposition, 

 as he found that, whenever they act chemically on the plates of 

 a battery, electricity is disengaged. Query. Is it not more pro- 

 bable that the non-conducting power of such bodies in the solid 

 state is owing to the crystalline arrangement of their particles, as 

 in the form of ice or snow ? (See p. 190.) 



