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ROYAL SOCIETY OF CANADA 



Fig. 3, curve A, represents the logarithmic decay curve of the 

 active deposit of actinium, as measured by one of the standard vessels. 

 The ordinates represent time in minutes, and the abscissae the log. of 

 the voltages on the standard. The straight line, B, represents the 

 relative values of the ionization current at the different times, on the 

 assumption that the active matter decayed to half-value in 36 minutes. 

 If the current through the standard vessel were proportional to the 



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WO 



200 



2.50 



Fig. 3. 



potential difference between its plates, then curve A would coincide 

 with B. It is evident, from the figure, that the potential increases more 

 rapidly than the current; that is, the apparent resistance of the stand- 

 ard begins to increase when its voltage rises above about 5 volts. The 

 ratio of the abscissae of curves A and B at any time is a measure of the 

 resistance of the standard vessel for that voltage. If we thus compare 

 the resistances at 20, 40 and 60 volts, we find their ratio to be 1 :1.16: 



