Homogeneous fi-P articles of Different Velocities. 867 



made of soft iron in order to protect the rays passing through 

 it from the magnetic field, and thus prevent their deflexion 

 to the sides. The ionization vessel rested on a plate P of 



Eur. 1. 



the substance used for reflexion, which had a hole cut in it 

 corresponding to the hole in S. The plate P could be turned 

 about the end D by means of an arrangement not shown in 

 the figure, so that any desired angle with the horizontal could 

 be obtained. A change in the inclination necessarily in- 

 volved also a change of the tube S. A plate of the substance 

 used as reflector could be placed so as to cover the upper 

 side of the ionization vessel as shown by Q. To determine 

 the ionization by the 7 rays alone, a sheet of lead of sufficient 

 thickness to absorb all the /3-particIes was placed between 

 the pole-pieces of the magnet so as to cover the hole P. In 

 the experiments with different reflecting substances the plates 

 P and Q were of the same substance. It was found necessary 

 to keep the plate P always in position in order to reduce the 

 effect of scattered radiation from various parts of the apparatus. 

 During an experiment on the reflexion of the /3-particles 

 of any velocity the following readings were taken in the 

 order given, and in the reverse order, repeating many times 

 and using the mean values : 



(1) 7-ray effect, Q in position ; 



(2) /8 + 7-ray effect, Q in position ; 



(3) /3 + 7-ray effect, Q taken off ; 



(4) 7-ray effect, Q taken off. 



