[ROBERTSON] 



INSULATED METALLIC CONDUCTORS 



127 



TABLE XI. 



Table XI gives the results of some measurements made by using 

 different upper plates. The metals are arranged in the order in which 

 they occur in the Volta series, and it will be seen from the values of 

 the maximum potentials recorded that other influences besides the Volta 

 effect must have contributed to the result. The values obtained are 

 very much lower than the contact potential differences usually recorded. 

 Further, although aluminium and zinc come higher in the contact series 

 than lead, yet, when the plates were 2 nun. apart, lead gave a higher 

 positive potential, to the copper plate than either of them. Indeed, 

 aluminium and the thicker zinc plate, as will be seen, gave a slightly 

 negative value to it. With both the zinc and copper plates, an increase 

 in the thickness resulted in an increased negative charge on the free 

 plate. 



Upper plate zinc. 



TABLE XII. 



