Sig. Quirino Majorana on the Contact Theory. 245 



region of hypothesis ; there is no experimental fact which 

 confirms them *. 



Lodge would have us assume that the thermoelectric 

 electromotive force, as measured by the Peltier effect, really 

 exists at the contact of two metals, and maintains that the 

 difference between this and the electrostatic measurements is 

 due to the tendency to chemical combination of the melals with 

 the surrounding oxygen. The views of Lodge have, however, 

 been opposed by Lord Kelvin f . In his criticism the latter 

 asks how oxygen can be effective in the case in which the 

 condenser plates are completely varnished ; or, again, in the 

 experiments of Erskine-Murray J, in which the disks of zinc 

 and copper are cleansed and polished in molten paraffin in 

 order to remove from them every trace of atmospheric film ; 

 and, finally, in the experiments of Bottomley and others, in 

 which the plates of copper and zinc are placed in the best 

 vacuum that can be obtained. Lodge's views are therefore 

 not generally accepted, but everything points to the fact that 

 there is no general agreement concerning the interpretation 

 of the Volta phenomenon. 



In connexion with the researches about to be described 

 reference must be made to the work of Exner§. The ideas 

 of this physicist, who is the author of a chemical theory of 

 contact electricity, have not found supporters, just as in the 

 case of De la Rive, probably because he was too zealous in 

 refuting the researches of Volta by asserting the existence 



* I do not wish to leave this argument without referring to the 

 important statement of Lord Kelvin (Phil. Mag. July 1898, p. 102) :— 



" Many recent writers (perhaps following Maxwell, or perhaps 

 independently) . . . have assumed that the Peltier evolution of heat is the 

 thermal equivalent of electromotive force at the junction. In conse- 

 quence much confusion in respect to Volta's contact electricity and its 

 relation to thermoelectric currents, has largely clouded the views of 

 teachers and students. We find over and over again the statement that 

 thermoelectric electromotive force is very much smaller than the Volta- 

 contact electromotive force of dry metals. The truth is, Volta-electro- 

 motive force is found between metals all of one temperature, and is 

 reckoned in volts, or fractions of a volt, without reference to tempera- 

 ture. If it varies with temperature its variations may he stated in 

 fractions of a volt per degree. On the other hand, thermoelectric electro- 

 motive force depends essentially on difference of temperature, and is 

 essentially to be reckoned per degree; as for example in fraction of a 

 volt per degree." 



t Loc. cit. 



X Erskine-Murray, " On Volta Electricity of Metals/' Phil. Mag. xlv. 

 p. 898 (1898). 



§ All the papers of Exner are in the Sitzb. der Wien. Akad. der 

 Wissensch. and are reprinted in Carl's Repertorium and in Wiedemann's 

 Annalen between the years 1877 and 1887. 



