Electrical Discharge. 349 



be hence in some inverse ratio of this inductive action. Here is, 

 in a few words, the reason why we find the intensity of a given 

 quantity of electricity accumulated on thick glass so much greater 

 than that of the same quantity accumulated on thin glass ; the 

 coatings are, in fact, in the latter case nearer together, and con- 

 sequently the action in the direction of the glass in the latter 

 case gi-eater. The tendency of the accumulation is really to 

 break down the glass intermediate between the two coatings. 

 When, however, the opposite electrical forces operate almost 

 entirely through an external circuit joining the two coatings, all 

 the force in the direction of the intermediate glass vanishes, and 

 the whole accumulation being, as it were, thus set free, discharges 

 through the given circuit. The question of the electrometer 

 indication is purely a question of the development of force in 

 one direction rather than in another, and is certainly no sort of 

 measure of an assumed quality of " density " in the accumulated 

 electricity. 



14. That the heating eflFect of the discharge is less as we ex- 

 tend our battery by increasing the number of jars, the quantity 

 of electricity being the same, is also no doubt true; and if M. 

 De la Rive or M. Riess had met with my paper before quoted (1), 

 and other of my philosophical memoirs, he would have found this 

 question fully investigated, as well as several others of which he 

 has so ably treated. I have shown, for example, — 



(1.) That the heating effect of the discharge is proportional 

 to the square of the accumulation, all other things being the 

 same*. 



(3.) That the heating effect is diminished when we accumulate 

 and discharge a given quantity of electricity from a divided 



surfacet- 



(3.) That the heat excited in a metallic wire is reciprocally pro- 

 portional to the length of the circuit of discharge or resistance, 

 that is to say, to the retardation or duration of the discharge J. 



(4.) That by the introduction of imperfect conductors into the 

 circuit, such as water contained in tubes of glass, the heating 

 effect becomes extremely small §. 



The expression T= — , putting r = the retardation, and which 



is really nothing more than the expression T= — of M. Riess, 



has been therefore derived as well from my original investiga- 

 tions, as from the more recent researches of Professor Riess, 

 quoted by M. De la Rive. 



* Trims, of the Plvm. Inst. 1830, pp. (i8, 84. t Ibid. 



X Phil. Trans, for "1834. 



§ Ibid. p. 227, 228. See also Trans. Roy. Soc. Edinb. vol. xii. 



