} 
caused by the B and y Rays of Radium. 681 
The variation in the initial value of \ prevents an exact 
verification of the equation with the curve. 
Similar calculations for the curve in figure 4, when the 
secondary rays come from the surface which the primary 
rays first strike, lead us to expect a curve given by 
y=kp .rA/(XN+N) . A—eW tt”) 
where a is the thickness of the substance. The curve obtained 
has the general character required by the equation. 
Parr 11. 
Magnetic Effects. 
In order to determine the nature of the secondary radiation 
caused by y rays, a small electroscope was mounted on a lead 
platform (1-2 em. thick) on a lead cylinder 10 cm. high and 
10°7 cm, in diameter. 
Fig. 7. 
j CLL TG AAS, VY, 7 
“ay tip Ll es A/ 
Lb iy Cd ial yee OA 
yy ae yg 
A iy) wi: vi 
Mj) 16 Yes 7 
Vi ee 
Radium (25 mgs.) was placed at the bottom of a hole 
reaching to the centre of the cylinder. On applying a strong 
magnetic field, as at right angles to the plane of the paper 
(fig. 7), so as to bend the rays from the platform into the 
electroscope, it was found that the rate ot discharge was 
nearly doubled, rising from 9-2 to 18:2 scale-divisions per 
minute. It is therefore clear that either some of the y or of 
