THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAG AZI NE 



AND 



JOURNAL OF SCIENCE, 



[FIFTH SERIES.] i 







* 



SEPTEMBER 189i>\» 



XXY. On the Contact Theory. • ?' 



By Sign or Quirlno Majorana. Parts I. and IL^s-<».- " 



THE fundamental experiment of Volta, which shows that 

 two unlike metals when brought into metallic contact 

 are charged to different potentials, is usually described as 

 follows : — Let a condenser be formed of two insulated flat 

 disks, one of zinc and the other of copper; let the two disks 

 be put in metallic communication with each other, and the 

 capacity of the system made as great as possible by bringing 

 the disks together ; if the metallic communication be now 

 broken and the zinc separated from the copper, the former is 

 found to be charged positively and the latter negatively. 

 The interpretation of the phenomenon is based on the 

 assumption that at the point of contact of the two metals 

 there exists an electromotive force of contact, which has the 

 effect of keeping the two disks always at the same difference 

 of electrical potentials independently of their capacity ; in the 

 above experiment this capacity is made first to increase with 

 the approach, and then to decrease with the separation, of the 

 two metals. 



All metals may be arranged in a definite series, such that 

 any member of the series is positive to those which follow it. 



* From the Rendiconti delta R. Accademia dei Lincei, viii. i. (1899), 

 pp. 188-195, 255-259 : translated by Dr. J. L. Howard, University 

 College, Liverpool, from a separate impression communicated by Lord 

 Kelvin. 



Phil. Mag. S. 5. Vol. 48. No. 292. Sept. 1899. T 



