Actinium and Thorium Emanati 



415 



the gradient of active deposit on their surfaces. One of the 

 plates was placed on a small platform which could be moved 

 along so that small portions (*4 cm. lengths) of it came beneath 

 a slit in a lead sheet, just above which was an ionization 

 vessel. The saturation current produced in this vessel by 

 the a. rays emitted from the active deposit on the plate was 

 measured by means of an electrometer, and readings were 

 usually taken for about 4 cms. length of the plate. Cor- 

 rections were applied for the decay of the active deposit with 

 time, for change in sensitiveness of the electrometer during 

 the measurements, and for the natural leak of the ionization 

 vessel. 



/ z 



A selection of the results for the different gases will be 

 found in Table I. and seen graphically in fig. 1, where the 



2F2 



