{ROBERTSON] INSULATED METALLIC CONDUCTORS 



TABLE II. 



117 



In all cases where the inner and outer cylinder were known to be 

 of the same composition, namely, tin No. 1, tin No. 2, and tin No. 1. 

 with its various coats of paint, with the single exception of the cleaned 

 tin, the sign was negative. Whenever the outer and inner cylinders were 

 not of exactly the same material, there would be a contact potential 

 difference, and in all such cases this would be an important factor in 

 determining the nature of the charge acquired. Assuming that there 

 was a negative effect due to another cause, this Volta effect would explain 

 the variations in the sign for many other combinations, and also for 

 the change from positive to negative of the lead combination after clean- 



