Contact Electricity of Metals. 101 



sj 22. Peltier's admirable discovery (1834) of cold produced 

 where an electric current crosses from bismuth to antimony, 

 and heat where it crosses from antimony to bismuth, in a 

 circuit of the two metals, with a current maintained through 

 it by an independent electromotive force, is highly important 

 in theory, or in attempts for theory, of the contact electricity 

 of metals. 



From an unsatisfactory * hypothetical application of Car- 

 net's principle to the thermodynamics of thermoelectric 

 currents I long ago inferred f that probably electricity cross- 

 ing a contact between copper and iron in the direction from 

 copper to iron would produce cold, and in the contrary 

 direction heat when the temperature is below 280° C. (the 

 thermoelectric neutral temperature of copper and iron J), and 

 I verified this conclusion by experiment §. Hence we see, 

 looking to fig. 10, if the movable copper plate CD is allowed 

 to move inwards (in the position shown in the diagram it is 

 pulled inwards by the Volta-eleetrifications of the opposed 

 surfaces of iron and copper), cold will be produced at the 

 junction J, all the metal being at one temperature to begin 

 with ; and if we draw out the copper plate CD, heat will be 

 produced at J. The thermodynamics of this action ||, because it 

 does not involve unequal temperatures in different parts of the 

 metals concerned, is a proper subject for unqualified applica- 

 tion of Carnot's law, and has nothing of the unsatisfactoriness 

 of the thermodynamics of thermoelectric currents, which 

 essentially involves dissipation of energy by conduction of 

 heat through metals at different temperatures in different 

 parts. At present we cannot enter further into thermody- 

 namics than to remark that when the plate CD is drawn out, 

 the heat produced at J is not the thermal equivalent of the 

 work done by the drawing out of the copper plate, but in all 

 probability is very much less than the thermal equivalent. 

 Probably by far the greater part of the work spent in draw- 



* • Mathematical and Physical Papers,' vol. i. art. xlviii. §10(3, re- 

 printed from ' Transactions of the Roval Society of Edinburgh,' May 

 1854. 



t Ibid. § 116 (19). 



J In a thermoelectric circuit of copper and iron the current is from 

 copper to iron through hot when both junctions are below 280° C. It is 

 from iron to copper through hot when both junctions are above 280° O. 



§ ' Experimental Researches in Thermoelectricity,' Proc. P. S. May 

 1854 ; republished as art. li. in ' Mathematical and Physical Papers/' 

 vol. i. (see pp. 4G4-465). 



|| [March, 1898.] It has been given in a communication to the Poyal 

 Society of Edinburgh entitled ' The Thermodynamics of Volta-contact 

 Electricity : Feb. 21, 1898. 



