LAWS OF ELECTRIC PHENOMENA. 197 



The essential circumstances of the electric shock were gr&lnallv 

 unravelled. Watson found that it did not increase in proportion 

 either to the contents of the phial or the size of the globe by which 

 the electricity was excited ; that the outside coating of the glass 

 (which, in the first form of the experiment, was only a film of water), 

 and its contents, might be varied in different ways. To Franklin is 

 due the merit of clearly pointing out most of the circumstances on 

 which the efficacy of the Leyden phial depends. He showed, in 

 1 74V, U that the inside of the bottle is electrized positively, the outside 

 negatively ; and that the shock is produced by the restoration of the 

 equilibrium, when the outside and inside are brought into communi- 

 cation suddenly. But in order to complete this discovery, it remained 

 to be shown that the electric matter was collected entirely at the sur- 

 face of the glass, and that the opposite electricities on the two oppo- 

 site sides of the glass were accumulated by their mutual attraction. 

 Monnier the younger discovered that the electricity which bodies can 

 receive, depends upon their surface rather than their mass, and Frank- 

 lin 12 soon found that "the whole force of the bottle, and power of 

 giving a shock, is in the glass itself." This they proved by decanting 

 the water out of an electrized into another bottle, when it appeared 

 that the second bottle did not become electric, but the first remained 

 so. Thus it was found " that the non-electrics, in contact with the 

 glass, served only to unite the force of the several parts." 



So far as the effect of the coating of the Leyden phial is concerned, 

 this was satisfactory and complete : but Franklin was not equally suc- 

 cessful in tracing the action of the electric matter upon itself, in 

 virtue of which it is accumulated in the phial ; indeed, he appears to 

 have ascribed the effect to some property of the glass. The mode of 

 describing this action varied, accordingly as two electric -fluids were 

 supposed (with Dufay,) or one, which was the view taken by Franklin. 

 On this latter supposition the parts of the electric fluid repel each 

 other, and the excess in one surface of the glass expels the fluid from 

 the other surface. This kind of action, however, came into much 

 clearer view in the experiments of Canton, Wilcke, and ^Epinus. It 

 was principally manifested in the attractions and repulsions which 

 objects exert when they are in the neighborhood of electrized bodie- ; 

 or in the electrical atmosphere, using the phraseology of the time. At 

 present we say that bodies are electrized by induction, when they are 



n Letters, p. 13. l - Letters, iv. Sect. 16. 



