VI 



4G8 



Ri:roRT— 1 884. 



Quite detiiclicd from nny cotnicction with tlio controversy, because at 

 tliat tiiiio quite uiiintcUijijiblo to nil but one or two bero nnd there, two 

 papers ii|ijKiiretl in IH-M by the President of this Section, which were the 

 triumph and apotheosia of the chemicjil Ihcory of the source of the 

 current in the voltaic cell.' In one of these pap(TH (tliat on ' Klectro- 

 lysis') it is irrefutably established on the biisis of the conservation ol" 

 energy, that, makint? exception of such irreversible etfects as are not 

 readily brought into ealeulation, aiul allowit)g for certain jjossihle 

 reversible elfects to bo investigated thermo-electrieally, the K.M.F. of a 

 (;oll is not only dependent on the chemical action going on, but is 

 calculable numerically in absolute measure on {)urely chemical data 

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

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

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

 circuit.'"' 



In the other of the two papers (that on ' Thermo-electricity ') ifc 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 — inotherwords, 

 that the Peltier effect necessitated the previously discovered Scebeck 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- 

 iluccd by a battery was duo to, and was tho equivalent of, the chemical 



plays in tho production of a ciirrnit, Ji most clear-sighted tiling to do at tliat diito. 

 One more sontence may bo <|U()lL'd from tliis remarkable paper, though it is no! 

 <luito so striking as the preceding. I'aRC 4'.t :' These idoa.s are evidently directly in 

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

 the investiga'ion aflpeared extr(,'m('ly jirobable, viz., that chemical changes are tin' 

 /irimiiri/ cause f)f the phenomena of (ialvanism. Ucfori! the experiments of M. Vdlta 

 on the electricity excited by niere (M)ntact of metals wen; published, Iliad toa ceriiiiii 

 extent adopted this opinion ; l)ut the new fact immediately proved that another ikiwi r 

 must necessarily bo concerned, for it was not jiossilile to refer the electrieiiy e.x- 

 hibited by the; opjiosition of metallic surfaces to any chemical alterations, [larticularly 

 :is the ellcct is more distinct in a dry atmosphere, in which even the most oxiiii.sibic 

 mctala do not change;, than in a moist one, in which many metals uiulergn 

 oxidation.' 



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

 of the Principle of Mechanical Ellcct to the Mcasui-eiiunt of Electromotive iMUXcsin 

 Absolute Units.' — J'/iil.Mn;/. December, 18")!. J,'t://ri/if of Matltniiutlral and l'li;imcid 

 I'ltjicrSfVol. i. pp. 472 and 490. 2. ' On tlic Dynamical 'I'lieoiyof Heat, i)art vi. Tlicriiio- 

 I'lectric Currents.' — Proc. Jt.S., Edin., Dec. 1851 ; Trdiis. U.S. J.'diti., 1851 ; .Voih. ami 

 Phys. Papers, vol. i. p. 2IJ2 and p. 316. 



Hclmholtz also clearly applied the conservation of energy to voltaic circuits iiiliis 

 memoir. Die Hrhaltunii dir Kraft, xcaA before the I'liysical Society of Herlin, .Inly iM, 

 1847. In this ))owcrful memoir Prof, llelmholtz 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, a.s is 

 well known, that on this hypothesis central forces are the nece.-sary and suHicient 

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

 in the more sj ec^ial portions, among other things, he develops the mechanical theory 

 of the E.M.K. 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 thmugii 

 Ji translation, by J[ohn] Tfyndall], which appeared in Jlay, 1853, in the 'new .series 

 of Scientific Memoirs issued by Taylor & Francis. 



* Joule ; ' On the heat evolved by metallic conductors of electricity, and in tk' 

 cell.s of a battery during electrolysis,' Phil. Mag. [3] xix. 2G0, 1841 ; ' On the electric 

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

 gaged in chemical combinations, Phil. Mag. [4] iii. 481. See also Jieprint of Joulei 

 Papers by the Physical Society of London {Taylor & Francis). 



