464 



Miss Slater on the Emission of Negative 



Time in minutes. 



Scale-readings. 



5 



70-6 



7 



70-0 



10 



68-8 



15 



68-4 



21 



67-5 



25 



67 -1 



30 



66 3 



35 



(55-8 



Leak per he 



ur, 9-6 cliv. 



From these observations it is evident that the greater part 

 of the leak observed was directly due to the presence of the 

 emanation, since for the first 5 or 10 minutes after breaking 

 the radium tube, the amount of excited activity in the bulb 

 must be very small, and the maximum amount would not be 

 produced for several hours. The change caused by cooling 

 the side-tube in liquid air would also occur much less rapidly 

 if the leak observed were mainly due to rays from the excited 

 activity on the walls of the vessel. That very little of the 

 initial leak was due to the presence of ionized gases in the 

 bulb, is shown by the very low value obtained when the gold- 

 leaf was charged negatively; so that the change caused by 

 the liquid air cannot be due merely to an improvement of the 

 vacuum, but must be owing to the condensation of a large 

 proportion of the emanation in the tube H. 



The effect was further investigated by sealing off the tube 

 B at the point C (fig. 2), and observing the rate at which the 

 leak subsequently decreased. This proved to be unexpectedly 

 high, as after two days the rate of leak had fallen to less than 

 half its original value. From this time onwards the rate of 

 decrease was less, having about the normal value for radium 

 emanation, viz. half in 4 days The rapid fall at first observed 

 may possibly have been due to absorption of the emanation 

 by the charcoal in the side-tube, after the radium was sealed 

 off ; moreover, the earlier readings were not very consistent 

 among themselves, so that it was thought desirable to repeat 

 the whole series of experiments under slightly different 

 conditions. 



The radium w r as sealed up in a little tube which was broken 

 as before, and the initial rapid rise in the leak to a maximum, 

 followed by a smaller fall, was confirmed. Then the side- 

 tube H, after being kept for some time in liquid air so as to 



