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LV. — ON AN ANALOGY BETWEEN ELECTKIC AND 

 THEEMAL PHENOMENA. By GEOEGE FEANCIS 

 FITZGEEALD, F. T. C. D. 



[Eead, November 17, 1884.] 



The object of the following communication is to sliow how little 

 we know of the nature of what are called electric currents, by 

 pointing out that electric quantities may be described in terms of 

 temperature and entropy just as satisfactorily as in terms of pres- 

 sures and volumes, which are the terms analogous to electric poten- 

 tial and quantity of electricity in consonance with the usually 

 drawn analogy between an electric current and a current of an 

 incompressible fluid, upon which is founded such terms as electric 

 current and electric displacement. The thermal analogy usually 

 drawn is between quantity of electricity and quantity of heat ; but 

 I think the analogy I am pointing out in every way preferable, for 

 energy is of the nature of temperature by entropy, just as it is of 

 the nature of pressure by volume or potential by quantity of elec- 

 tricity. The work done in bringing a quantity of entropy, (j>, from 

 temperature Ti to T^is, W =- (Ti - Ts)^; and if the transference be 

 effected in a reversible manner the entropy taken from one source 

 is equal to that given to the other. Indeed we can easily conceive 

 of systems in which all transference of entropy is effected without 

 loss, and in that case the quantity of entropy would be constant. 

 It is to be observed that the temperature and entropy of a body 

 are quite independent of one another, so that we can suppose either 

 to be altered while the other remains constant. If we apply this 

 conception to electrostatic phenomena, we must call potential the 

 temperature of the ether and quantity of electricity its entropy. 

 As the same relations connect these pairs of analogues with energy 

 they will obey similar laws, and what is further required is to show 

 how it may be supposed that bodies at different temperatures can 

 throw the intervening medium into the sort of stress that Maxwell 

 has shown is required to explain electrostatic forces. I premise 

 that Maxwell has not made any attempt in his electricity and 



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