Decay of the Active Deposit from Radium. 407 



are shown in fig. 2, where the ordinates represent differences 

 between the ionizations in A and B, and the abscissae times 

 reckoned from the moment at which the wire is removed from 

 the emanation. The iclwle ionization in each vessel was 1600 

 scale-divisions, 48 minutes after removal from the emanation, 



Fi« 



40 

 . 30 



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 O 



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 -10 



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r c 



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^D= 7-0 cms 









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+ T/MF IN MINS 



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1 



so that the deviations of the points from the curves (fig. 2) 

 in no case amounted to as much as one per cent, of this 

 quantity. The activity decreased with time according to the 

 usual laws *. It will be noticed that for small distances of 

 the wire from the vessel A the difference in the observed 

 rates of decay of the deposit on the two wires is small, but 

 for large distances (7 cms.) it is considerable. 



Now it is known that the range of the a particle from 

 radium C is just over 7 cms.f; consequently when the wire 

 is at this distance from the vessel A the a rays contribute but 

 little to the ionization in this vessel, which is for the most 

 part due to the rays emitted by radium B. If the observed 

 effect is due to the slowly moving /3 rays emitted by radium B, 

 the difference in the rate of decay of the activity as measured 

 in the two vessels A and B should therefore be greater in 

 these circumstances than when measurements are made with 

 the active wire near to A. Moreover, the ionization in the 

 vessel A should decay more rapidly than that in the vessel B. 

 This is, in fact, found to be the case, so that we may conclude 



* Miss Brooks, Phil. Mag-. Sept. 1904. 



t Bragg & Kleeman, Phil. Mag. Sept. 1905. 



