Radio-active Products of Short Life. 



035 



and of the product obtained by recoil from the active deposit, 

 which were consistent with the existence of a product subse- 

 quent to actinium C, with a period of a few seconds. 



The smallness of the observed effect would be explained 

 by the fact that no measurements were taken until a minute 

 after the decay had started. 



The existence of this product was therefore tested by the 

 method described in this paper. 



A plate rendered active by exposure to actinium emanation 

 was placed in front of the rotating disk. Opposite the disk 

 was an electroscope with an opening large enough to receive 

 a fourth part of any radiation coming from the disk. The 

 electroscope was fixed to a bracket projecting from a wall, 

 in order to avoid the vibration set up by the rotation of 

 the disk. 



When the plate was uncharged, no activity was transferred 

 to the disk. On charging the plate positively, those atoms 

 which by the expulsion of an a particle had been projected 

 into the air, were carried to the disk. Such atoms consisted 

 of actinium D and of the hypothetical new product. Since 

 actinium D does not emit a particles, the ionization in the 

 electroscope would be mainly due to the new product, unless 

 this product either had decayed before reaching the electro- 

 scope, or belonged to some side branch from the main dis- 

 integration series. The rise of activity on the disk, on 



charging the active plate, is shown in fig. 2, the time 

 interval before reaching the electroscope being *15 second. 



