182 MecCieLttanp—On Secondary Radiation. 
The primary 6 rays were examined in the same way, so as to get a comparison 
of the velocities of the primary and secondary, the mass and the charge being 
no doubt the same in the two cases. The radium, with the accompanying 
lead screen, was placed so that the primary rays fell directly on the tube 7, 
passing between the poles of the magnet on the way. In this case a correc- 
tion had to be applied for the y rays which could not be deflected, and for 
the normal ionisation in 7’. 
The result is given in column 3 of the above table; the maximum, when 
no magnetic field is applied, is represented by 100 for both primary and 
secondary rays. The numbers show that, while the first small field removes more 
secondary than primary rays, it requires a stronger field to remove completely 
the secondary. The secondary pencil seems to include some rays which are 
travelling with a greater velocity than any of the primary rays. 
