LAWS OF ELECTEIC PHENOMENA. 193 



at that period was unavoidable, do liiin no discredit when compared 

 with the doctrines of his successors a century and a half afterwards. 

 But such speculations belong to a succeeding part of this history. 



In treating of these Sciences, I will speak of Electricity in the first 

 place ; although it is thus separated by the interposition of Magnetism 

 from the succeeding subjects (Galvanism, &c.) with which its alliance 

 seems, at first sight, the closest, and although some general notions of 

 the laws of magnets were obtained at an earlier period than a know- 

 ledge of the corresponding relations of electric phenomena : for the 

 theory of electric attraction and repulsion is somewhat more simple 

 than of magnetic ; was, in fact, the first obtained ; and was of use in 

 suggesting and confirming the generalization of magnetic laws. 



CHAPTER I. 



DISCOVERY OF LAWS OF ELECTRIC PHENOMENA. 



WE have already seen what was the state of this branch of know- 

 ledge at the beginning of the seventeenth century, and the advan- 

 ces made by Gilbert. We must now notice the additions which it 

 subsequently received, and especially those which led to the discovery 

 of general laws, and the establishment of the theory ; events of this 

 kind being those of which we have more peculiarly to trace the con- 

 ditions and causes. Among the facts which we have thus especially to 

 attend to, are the electric attractions of small bodies by amber and 

 other substances when rubbed. Boyle, who repeated and extended the 

 experiments of Gilbert, does not appear to have arrived at any new 

 general notions ; but Otto Guericke of Magdeburg, about the same 

 time, made a very material step, by discovering that there was an 

 electric force of repulsion as well as of attraction. He found that 

 when a globe of sulphur had attracted a feather, it afterwards repelled 

 it, till the feather had been in contact with some other body. This, 

 when verified under a due generality of circumstances, forms a capital 

 fact in our present subject, Hawkesbee, who wrote in 1709 (Physico- 

 Mechanical Experiments,) also observed various of the effects of at- 

 traction and repulsion upon threads hanging loosely. But the person 

 who appears to have first fully seized the general law of these facts, is 

 VOL. II. 13. 



