HELMHOLTZ ON THE CONSERVATION OF FORCE. 151 



the principle of the conservation of force, from the fact that the 

 intensities of these circuits are not to be calculated from the law 

 of Ohm, as the chemical processes remain the same. In 

 support of the view that in circuits where the polarization has 

 ceased, the numerator of the formula of Ohm is dependent on 

 the nature of the negative metal, 1 have been unable to find any 

 certain observations. In order to set the cun-ent of polarization 

 quickly aside, it is necessary to increase as much as possible the 

 density of the current on the polarized plate, partly through the 

 introduction of cells with a constant intensity, and partly by di- 

 minishing the surface of the plate. In the experiments of Lenz 

 and Saweljev*, which bear upon this point, the constancy of the 

 current was, according to their own statement, not attained ; the 

 electromotive forces calculated from their observations contain 

 therefore those of the currents of polarization also. They found 

 for zinc and copper in sulphuric acid 0*51, for zinc and iron 0'76, 

 for zinc and mercury 0*90. 



I may remark, in conclusion, that to prove the equality of the 

 heat developed chemically and electrically, an experiment has 

 been made by Joule f. His method of experiment is however 

 open to many objections J. He assumes, for example, for the 

 tangent compass, the law of tangents as correct up to the highest 

 degrees ; he did not work with constant currents, but calculated 

 the intensity from the mean of the first and last deflections ; he 

 also assumes the constancy of the electromotive force, the re- 

 sistance of the cells and the gas development. Hess has already 

 drawn attention to the divergence of his quantitative determina- 

 tions of heat from numbers found by others. In a notice in the 

 Comptes RenduSy 1843, Mo. 16, E. Becquerel is said to have cor- 

 roborated the same law empirically. 



We have above seen ourselves necessitated to refer the idea of 

 a contact-force to simple forces of attraction and repulsion, in 

 order to bring it into coincidence with our principle. Let us 

 now endeavour to refer the electric motions between metal and 

 fluid to the same cause. Let us imagine the particles of the 



* Bull, de la Classe Phys. Math, de TAcad. d. Scienc. de St. Petersburg, 

 t. V. p. 1 ; and Pogg. Anv, Ivii. 497. 



t Pliil. Mag. 1811, vol. xix. p. 275 ; and 1843, vol. xx. p. 204. 

 X See note to page 131. — Ed. 



M 2 



