﻿the Mass of the a, particles from Thorium. 373 



rays from radium C under identical conditions serving as a 

 standard. 



For this purpose, the same wire was used as a source of 

 ra) r s in both the thorium and radium experiments. After the 

 wire had lost most of its activity, it was made the negative 

 electrode in a vessel containing a large quantity of the radium 

 emanation. The active wire, coated with a thin film of 

 radium 0, was then placed in the same position as before in 

 the deflexion apparatus and the experiment repeated. In 

 this case, an exposure of the plate for two hours was sufficient 

 to obtain well-marked photographs of the traces of the 

 deflected pencil of rays. 



In order to obtain a sufficiently intense source of rays for 

 the thorium experiment, a wire about 1*5 cm. long was made 

 the only negative electrode in a small closed vessel containing 

 the highly emanating preparation of radiothorium. After 

 two days' exposure, the activity of the wire had nearly reached 

 a maximum. In the preliminary experiments, the activity 

 produced on the wire was not very intense and the photo- 

 graphic impression produced in a ten hours' exposure was 

 very weak. By careful attention to the construction of the 

 vessel in which the wire was made active, and by further 

 chemical treatment of the radiothorium preparation in order 

 to make it highly emanating, it was found possible to obtain 

 wires sufficiently active to give a clear impression on the 

 photographic plate under the conditions of the experiment. 



Magnetic Deflexion of the ot rays from Thorium 

 B and C. 



We have seen that an examination of the ionization curves 

 of the active deposit of thorium had disclosed the existence 

 of two distinct a. ray products, thorium B and C, w T ith 

 different ranges in air. This conclusion w T as confirmed 

 by an examination of the magnetic deflexion of the pencil 

 of rays from the active wire. Two distinct sets of a rays 

 were found to be present which were unequally deflected 

 in a magnetic field. Each product emitted homogeneous 

 rays, but the a particles from thorium B had a lower 

 velocity than those from thorium C and were consequently 

 more deflected by the magnetic field than the latter. The 

 difference in the amount of deflexion of the two sets of rays 

 was not sufficient to obtain a complete separation of the 

 photographic bands due to them, but the amount of deflexion 

 of each pencil of rays could be deduced in the following 

 manner. 



