202 



Dr. H. Geiger on the Transformation 



scale in the figure [curve II.]. It follows, therefore, that 

 the ranges 5* 7 and 6*5 are both due to the a particles from the 

 actinium emanation. 



Fig. 1. 



3 4-56 



ff/INGE //I/ CMS. OF////?. 



It may be added here that with the above arrangement 

 also a determination of the range of the a particles from 

 actinium X was carried out. This determination is somewhat 

 complicated by the fact that it is impossible to obtain 

 actinium X films free from emanation and active deposit, on 

 account of the rapid growth of these substances. The thin 

 actinium X film was placed inside the box described above, 

 and a strong current of air was allowed to pass through it 

 in order to reduce the effect from the emanation and the 

 active deposit as much as possible. By carrying out count- 

 ings in the same way as indicated above it was observed that 

 u particles of relatively short range [4*4 cm.] were present 

 in addition to the a rays from the emanation and the active 

 deposit [curve III.]. 



In investigating the range of the a particles from a film 

 of actinium X, 0, Hahn* found a maximum range of 

 6*55 cm. Since it was not known at the time that two 

 a particles are given off from the actinium emanation, this 

 long range was naturally, but incorrectly, ascribed to the 

 a particles from actinium X. The value found by Hahn for 



* 0. Hahn, Phys. Zeitschr. vii. p. 557 (1906). 



