144 



Miss E. W. Hobbs on the Change in the 



(a) or (h), of the full curves in fig. 3. The ordinates express* 

 the resistance of the film as a fraction of the first value in 

 each set of observations, which were always started about a 

 minute after the discharge was cut off. Though the results 



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20 40 60 80 100 120 140 



TIME IN MINUTES 



160 



of the first 90 minutes of ageing are alone shown, the readings 

 were in many cases extended over many hours; these confirm 

 the view that the film is settling down to a steady state, which, 

 however, may not be reached for days. 



On the question whether the rate of ageing of a film 

 depends on its thickness, there is no evidence one way or the 

 other. This is made apparent on reference to Table I., in 

 which all the results for platinum, including those plotted in 

 fig. 1, are given. R is the resistance of the film when the 

 pump is put on after the discharge has ceased, and R its 



resistance one hour afterwards. It will be seen that ^ 



