198 insTonY OF ELECTRICITY. 



"1ms made electric by the electric attraction and repulsion of othei 

 bodies. Canton's experiments were communicated to the Royal 

 Society in 1753, and show that the electricity on each body acts 

 upon the electricity of another body, at a distance, with a repulsive 

 energy. TVilckc, in like manner, showed that parts of non-electrics, 

 plunged in electric atmospheres, acquire an electricity opposite to that 

 of such atmospheres. And ./Epinus devised a method of examining 

 the nature of the electricity at any part of U" e surface of a body, by 

 means of which he ascertained its distribution, and found that it, 

 agreed with such a law of self-repulsion. His attempt to give mathe- 

 matical precision to this induction was one of the most important 

 steps towards electrical theory, and must be spoken of shortly, in that 

 point of view. But in the mean time we may observe, that this 

 doctrine was applied to the explanation of the Leyden jar ; and the 

 explanation Avas confirmed by charging a plate of air, and obtaining a 

 shock from it, in a manner which the theory pointed out. 



Before we proceed to the history of the theory, we must mention 

 some other of the laws of phenomena which were noticed, and which 

 theory was expected to explain. Among the most celebrated of 

 these, were the effect of sharp points in conductors, and the phe- 

 nomena of electricity in the atmosphere. The former of these 

 circumstances was one of the first which Franklin observed as remark- 

 able. It was found that the points of needles and the like throw off 

 and draw off the electric virtue ; thus a bodkin, directed towards an 

 electrized ball, at six or eight inches' distance, destroyed its electric 

 action. The latter subject, involving the consideration of thunder and 

 lightning, and of many other meteorological phenomena, excited great 

 interest. The comparison of the electric spark to lightning had very 

 early been made ; but it was only when the discharge had been 

 rendered more powerful in the Leyden jar, that the comparison of the 

 effects became very plausible. Franklin, about 1750, had offered a 

 few somewhat vague conjectures 13 respecting the existence of elec 

 tricity in the clouds ; but it was not till Wilcke and yEpinus had ob- 

 tained clear notions of the effect of electric matter at a distance, that 

 the real condition of the clouds could be well understood. In 17-52, 

 however, 14 D'Alibard, and other French philosophers, were desirous of 

 verifying Franklin's conjecture of the analogy of thunder and elec- 

 tricity. This they did by erecting a pointed iron rod, forty feet high, 



13 Letter v. H Franklin, p. 107 



