424 Prof. E. M. Wellisch : Experiments on 



being again closed by the rubber stopper. It was demon- 

 strated repeatedly during the course of the investigation that 

 less than 1 per cent, of the amount of emanation escaped 

 during the process of introducing and withdrawing the 

 central electrode ; the decay of the emanation was examined 

 from day to day, and in this way the loss could be estimated. 

 It was found that the most convenient method of comparing 

 the activities of rods which were introduced under different 

 conditions was to measure the activity at any convenient 

 period after removal, and then to calculate the activity 

 corresponding to the lapse of a definite period from the time 

 when the rod was originally withdrawn. The definite period 

 chosen was 4 hours 40 minutes. The measurements of the 

 activity were made at a sufficiently long time after removal, 

 so that thenceforth the activity decayed with the period of 

 KaB. 



These experiments were designed to furnish information 

 with regard to the activity accumulating in the gas ; by 

 repeating them from day to day we could ascertain how this 

 gas activity varied as the amount of emanation decreased 

 through disintegration. In addition to these experiments 

 electrodes were often introduced with various potentials 

 applied to the case and allowed to remain for several hours 

 before removal ; their activity was estimated in the same 

 manner as before. Moreover, advantage was taken of these 

 long exposure experiments to determine the relative amount 

 of emanation in the vessel. This was accomplished by 

 measuring the ionization current by means of a sensitive 

 Siemens Halske galvanometer (4*5 x 10~ 9 ampere per cm. 

 when unshunted) ; in measuring the current a potential of 

 1000 volts was applied, because with potentials of only a few 

 hundred volts there was evidence of abundant recombination, 

 so that with these small potentials the currents would not be 

 proportional to the amount of emanation. 



Two distinct series of experiments were made in this con- 

 nexion ; in each instance about 2\ millicuries of emanation 

 were introduced, and each series occupied a little over one 

 month. Several hundred measurements of the activity were 

 made under various conditions, but for the sake of brevity 

 only a few results which are most typical are here given 

 (Table II.). These, however, are sufficient to illustrate the 

 interpretation which is given later. 



The column headed u accumulation " gives the time during 

 which the deposit particles were allowed to accumulate in 

 the gas before the insertion of a central electrode. This 

 time is reckoned from the time of withdrawal of the electrode 



