Bccquerel and Bontgen Rays in a Magnetic Field. 77 



Owing to the fact that the magnetic field was reversed instead of 

 being merely shut off, the experiment is really of double the sensitive- 

 ness indicated above. But, in order to be well on the safe side, it has 

 been thought best to leave this out of account. 



For the sake of comparison I have attempted a rough estimate of 

 the amount of the magnetic deflection of the Becquerel rays. The 

 method employed was as follows : — 



Fig. 1. 



A photographic plate, shown in section at ah, was laid on the top of 

 the square pole pieces of a magnet, the magnetic force being perpendi- 

 cular to the plane of the diagram. The plate was covered with thin 

 aluminium foil c is a metal capsule filled with the substance d, which 

 emitted the rays."^ 



When no magnetic force was acting, the rays were emitted from 

 the capsule as indicated in fig. 1, some of them striking obliquely on 

 the plate. On development after one hour's exposure, a shadow was 

 obtained beginning at the edge of the capsule c, and extending a short 

 distance. The effect gradually tailed off, and at a few cm. distance 

 away from r it was inappreciable. When the magnetic force was in 

 such a direction as to bend the rays down into the plate (fig. 2), the 



Fig. 2. 



a 



'b 



shadow extended further. When, on the other hand, the magnet was 

 reversed so as to bend the rays away from the plate (fig. 3), the 



Fig. 3. 



* The substance employed was a preparation from uranium residues, supplied 

 by de Haen, Hamburg. 



H 2 



