CALORIC AND ELECTRICITY. 437 



experiments, hitherto instituted for the purpose 

 of ascertaining the relative degrees of cohesion 

 and conducting power of the different metals, 

 have presented the same results. (See p. 180.) 

 It is however certain, that copper, gold, silver, 

 platina, iron, and zinc, are the best conductors 

 of electricity, and it has been shown by M. 

 Becquerel, that potassium is of all others the 

 worst conductor. (Ann. de Chim. et de Phys. 

 xxxii. 420.) 



In opposition to the simple and rational theory 

 of Franklin, that electricity repels its own par- 

 ticles, and is attracted with various degrees of 

 force by different species of ponderable matter, it 

 has been maintained by Coulomb, Poisson, and 

 other philosophers, that there is no affinity between 

 electricity and ponderable matter, and that it is 

 confined to the surface of bodies by the pressure of 

 the atmosphere. 



Nothing could more clearly illustrate the ten- 

 dency of mankind to take things upon trust, and 

 without examination, than the general adoption 

 of this partial and erroneous doctrine, by nume- 

 rous modern writers on physical science. It 

 seems to have been founded chiefly on the fact ? 

 that electricity escapes from the surface of 

 bodies more readily in vacua than under the pres- 

 sure of the atmosphere. But it has been de- 

 monstrated by Morgan, Cavallo, Ampere, and 

 Sir Humphrey Davy, that electrical attractions 



