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ROYAL SOCIETY OF CANADA 



ing. It would not, however, explain the change from negative to 

 positive of the tin combination after cleaning, unless, indeed, we are 

 to suppose that it was possible to select two pieces of tin from the same 

 sheet which differed in constitution and structure sufficient to exhibit 

 a contact difference of potential. It would also not explain the dif- 

 ferent sign of lead No. 2 in lead No. 4 (vide Table I, Nos. 17 and 18) 

 on two successive days, nor the chan,ge from negative to positive, when, 

 to the same combination of cylinders coated with aluminium paint, was 

 added two coats of bronze (vide Table I, Nos. 22 and 23). 



In the case of the tin combination coated with aluminium and with 

 bronze paints, at first a small positive charge was obser\'ed, which 

 slowly changed into a comparatively large negative one. This was 

 observed on two different days, and would seem to indicate the presence 

 of two opposing influences, one of which became insignificant as time 

 went on. 



TABLE III. 

 Lead No 1 in lead No. 2. 

 With radium. 



