468 report— 1884. 



Quite detached from any connection with the controversy, because at 

 that time quite unintelligible to all but one or two here and there, two 

 papers appeared in 1851 by the President of this Section, which were the 

 triumph and apotheosis of the chemical theory of the squrce of the 

 current in the voltaic cell. 1 In one of these papers (that on 'Electro- 

 lysis ') it is irrefutably established on the basis of the conservation of 

 energy, that, making exception of such irreversible effects as are not 

 readily brought into calculation, and allowing for certain possible 

 reversible effects to be investigated thermo-electrically, the E.M.F. of a 

 cell is not only dependent on the chemical action going on, but is 

 calculable numerically in absolute measure on purely chemical data 

 supplied provisionally by Dr. Andrews. It is proper to say, however, 

 that this brilliant theory is avowedly based on the laborious and acnte 

 experimental work of Joule on the conservation of energy in the voltaic 

 circuit. 2 



In the other of the two papers (that on ' Thermo-electricity ') it was 

 shown that, from the fact that a current absorbed or generated heat at a 

 metallic junction, an E.M.F. was necessarily situated there — in other words, 

 that the Peltier effect necessitated the previously discovered Seebeck one. 



The establishment of the conservation of energy, by Joule, for ever 

 placed beyond doubt the fact that the energy of the electric current pro- 

 duced by a battery was due to, and was the equivalent of, the chemical 



plays in the production of a current, a most clear-sighted thing to do at that date. 

 One more sentence may be quoted from this remarkable paper, though it is not 

 quite so striking as the preceding. Page 49 : ' These ideas are evidently directly in 

 contradiction to the opinion advanced by Fabroni, and which in the early stage of 

 the investigation appeared extremely probable, viz., that chemical changes are the 

 primary cause of the phenomena of Galvanism. Before the experiments of M. Volta 

 on the electricity excited by mere contact of metals were published, I had to a certain 

 extent adopted this opinion ; but the new fact immediately proved that another power 

 must necessarily be concerned, for it was not possible to refer the electricity ex- 

 hibited by the opposition of metallic surfaces to any chemical alterations, particularly 

 as the effect is more distinct in a dry atmosphere, in which even the most oxidisable 

 metals do not change, than in a moist one, in which many metals undergo 

 oxidation .' 



1 Sir W.Thomson: 1. ' On the Mechanical Theory of Electrolysis and the applications 

 of the Principle of Mechanical Effect to the Measurement of Electromotive Forces in 

 Absolute Units.' — Phil. May. December, 1851. Reprint of Mathematical and Physical 

 Papers, vol. i. pp. 472 and 490. 2. ' On the Dynamical Theory of Heat, part vi. Thermo- 

 electric Currents.' — Proc. R.S., Edin., Dec. 1851 ; Trans. U.S. Edin., 1854; Math, and 

 Phys. Papers, vol. i. p. 232 and p. 316. 



Helmholtz also clearly applied the conservation of energy to voltaic circuits in his 

 memoir, Die Erhaltuny der Kraft, read before the Physical Society of Berlin, July 23, 

 1847. In this powerful memoir Prof. Helmholtz sails placidly through a great part 

 of Physics, applying to various phenomena the then new principle of the conserva- 

 tion of energy. He regards all action as occurring at a distance, and shows, as is 

 well known, that on this hypothesis central forces are the necessary and sufficient 

 condition of conserved energy. This part may now be regarded as superseded ; but 

 in the more special portions, among other things, he develops the mechanical theory 

 of the E.M.F. of voltaic cells, of thermo-electric piles, and of magneto-machines ; 

 anticipating in many respects the somewhat later though independent work of Sir 

 \V. Thomson on these subjects. Prof. Helmholtz's memoir is easily accessible through 

 a translation, by J[ohn] T[yndall], which appeared in May, 1S53, in the 'new series ' 

 of Scientific Memoirs issued by Taylor & Francis. 



2 Joule : ■ On the heat evolved by metallic conductors of electricity, and in the 

 cells of a battery during electrolysis,' Phil. May. [3] xix. 260, 1841 ; ' On the electric 

 origin of the heat of combustion,' ibid., xx. 98, and xxii. 204 ; ' On the heat disen- 

 gaged in chemical combinations, Phil. May. [4] iii. 481. See also Reprint of Joule's 

 Pajyers by the Physical Society of London (Taylor & Francis). 



