president's address — SECTION A. 45 



and " electrolytic " ; the definite proof that circuits, consisting entirely 

 of conductors of the first class, are not the seat of a current, while 

 mixed circuits in general carry currents ; above all, the great step 

 taken in theory by locating the seat of what we call " electromotive 

 force " in the common boundary of chemically dissimilar substances — 

 all these stamp Volta as an investigator of the first rank. Not one of 

 them has been upset ; on the contrary, they have been fully confirmed 

 by later study. It is true that the precise locality assigned by him 

 as the principal seat of electromotive force in the cell soon became a 

 matter of dispute ; but he had good experimental grounds for placing 

 it, as he did, at the metallic contacts of the circuit, and 80 years of 

 work were required to show that his experiments were open to a difEerent 

 interpretation from the one that he put upon them. 



Faraday's entrance into the arena preceded by man}" years the 

 development of the doctrine of energy, yet the whole tenor of his early 

 work seems to me to show that something of the kind was taking 

 shape in his masterful brain. Considerations not very easy to dis- 

 tinguish from our modern views about energy induced him to depart 

 from Volta's metallic contact hypothesis. The current, he contended, 

 was always the accompaniment of chemical action and exactly 

 measured its amount. It was, therefore, natural and logical to locate 

 the seat of the forces giving rise to the current at the places where 

 chemical action was going on. Thus was initiated the famous con- 

 flict between the " contact " and " chemical " theories of the cell : 

 one of the most valuable discussions, from the point of view of incite- 

 ment to research, that physicists have ever carried on. 



While the advocates of these two theories were fighting matters 

 out, without getting much nearer to a solution of their problem, a 

 gigantic revolution was silently going on in scientific thought. The 

 establislnnent of the non-material character of heat, and of the mutual 

 equivalence of heat and work, soon issued in the wider generalisations 

 which constitute the modern doctrine of energy. Helmholtz and Lord 

 Kelvin were quick to apply the new ideas to electrical theory. Of 

 the two workers, Kelvin (b) was earliest in the field as regards the 

 theory of the voltaic cell, and his calculation of the electromotive force 

 of the Daniell element from thermochemical data definitely annexed 

 the voltaic problem to the domain of thermodynamics. Unfortunately 

 his conclusions were misunderstood, his own express limitations to 

 the applicability of his method were disregarded, and, as a consequence, 

 investigators were soon face to face with a difficulty largely of their 

 own making ; the values of many electromotive forces computed 

 from Kelvin's formula- 



(c) E = 'E(J0e) 

 were found to conflict with experiment, consequently the applicability 

 of thermodynamics to the voltaic circuit incurred a degree of suspicion 

 which was quite unmerited. 



(b) Phil. Mag., 1851. Two papers. 



(c) The thermodynamic notation is that of my report — " On the Thermodynamics 



of the Voltaic Cell," A.A.A.S. Rep., 1898. 



