ON ELECTRICITY IN EQUILIBRIUM. 507 



Science, xi. 309. Ph. Tr. 1830, p. 257. Guyton de Morveau's Pyrometer, Ann. 

 de Ch. xlvi. 276. 



On the Expansion of Gases. Priestley, Experiments and Observations on Air, 

 3 vols. 1774-7. Gay Lussac, Ann. de Ch. cxxviii (xliii.) 137. Dalton, Manch. 

 Mem. v. 595. Gilbert, in Gilb. Ann. xiv. 266. Rudberg, Pogg. Ann. xli. 271 ; 

 xliv. 119. 



Expansion of Liquids. Hallstrb'm, Pogg. Ann. i. 129, xix. 135. De Luc, 

 Recherches sur les Modifications de 1'Atmosphere. Gay Lussac, Ann. de Ch. ii. 

 130. 



Solids. Smeaton, Ph. Tr. 1754, p. 598. Errata. Roy, Ph. Tr. 1777, p. 653. 

 De Luc on Pyrometry and Areometry, ibid. 1778, p. 419. Lavoisier and Laplace, 

 Ann. de Ch. i. 101. Dulong and Petit, ibid. ii. 240, vii. 113, 225. Daniell, Ph. Tr. 

 1831, p. 443. 



Freezing, Sfc. Braun, De Frigore Artificial!, 4to, Petersb. 1760 ; on the Freez- 

 ing of Mercury, Nov. Com. Petr. ii. 268, 302. Hutchins on do. Ph. Tr. 1776, 

 p. 174 ; 1783, p. 303. Cavendish on Hutchins's Exper. ibid. 1783, p. 303 ; on 

 M'Nabs, ibid. 1786, p. 241 ; 1788, p. 166. Blagden's Hist, of the Congelation of 

 Mercury, ibid. 1783, p. 329. Guthrie on do. 4to, Petersb. 1785. Walker on 

 Freezing Mixtures, Ph. Tr. 1788, p. 395 ; 1795, p. 270 ; 1801, p. 120. 



Specific Heat. Meyer, Ann. de Ch. xxx. 46. De la Roche and Berard, ibid. 

 Ixxxv. 72. Dulong and Petit, ibid, (new series), vii. 113, 142, x. 395. Ure, Ph. Tr. 

 1818, p. 378. Haycraft, Ed. Tr. x. 195. Avogadro, Mem. di Torino, xxviii. 1, 

 xxix. 79. Neumann, Pogg. Ann. xxiii. 1. Thomson's Heat (1840) is very copious. 



LECTURE LIII. 



ON ELECTRICITY IN EQUILIBRIUM. 



THE phenomena of electricity are as amusing and popular in their 

 external form as they are intricate and abstruse in their intimate nature. 

 In examining these phenomena a philosophical observer will not he content 

 with such exhibitions as dazzle the eye for a moment, without leaving 

 any impression that can be instructive to the mind, hut he will be anxious 

 to trace the connexion of the facts with their general causes, and to com- 

 pare them with the theories which have been proposed concerning them : 

 and although the doctrine of electricity is in many respects yet in its 

 infancy, we shall find that some hypotheses may be assumed which are 

 capable of explaining the principal circumstances in a simple and satisfac- 

 tory manner, and which are extremely useful in connecting a multitude of 

 detached facts into an intelligible system. These hypotheses, founded on 

 the discoveries of Franklin, have been gradually formed into a theory, by 

 the investigations of Aepinus and Mr. Cavendish, combined with the 

 experiments and inferences of Lord Stanhope, Coulomb, and Robison. 



We shall first consider the fundamental hypotheses on which this system 

 depends, and secondly the conditions of equilibrium of the substances 

 concerned in it ; determining the mode of distribution of the electric fluid, 

 and the forces or pressures derived from its action when at rest ; all which 

 will be found to be deduced from the theory precisely as they are experi- 

 mentally observable. The motions of the electric fluid will next be noticed, 



