Iv] NATURE OF THE RADIATIONS oi 
When a=, i.e. when the rays are projected normally to the 
9 >) 
field, the particles describe circles of radius 
=f 
~ Jale *° 
The planes of these circles are normal to the field. Thus for 
a particular velocity V the value of R varies inversely as the 
strength of the field. In a uniform field the rays projected nor- 
mally to the field describe circles, and their direction of projection 
is a tangent at the origin. 
This has been verified experimentally by Becquerel for the 
B rays of radium, by an arrangement similar to that shown in 
Fig. 21. 
Se 
Ze, _A2 \Y 
eye N \ 
Sm eee. 
mamas \ 
/ a A4_ SN ¥ 1 
bv aN | 
VAN 7 Ne) 
vis 
Kg R 
whos 
\ SS6 554 Ay, \ =) 
\ SS oe ! ' 
WSS ) 1 
Ne Lop 
Fig. 21. 
A photographic plate P, with the film downwards, is enveloped 
in black paper and placed horizontally in the uniform horizontal 
magnetic field of an electromagnet. The magnetic field is sup- 
posed to be uniform and, in the figure, is at right angles to the 
plane of the paper. The plate was covered with a sheet of lead, 
and on the edge of the plate, in the centre of the magnetic field 
is placed a small lead vessel #& containing the radio-active matter. 
On exciting the magnet, so that the rays are bent to the left 
of the figure, it is observed that a photographic impression is pro- 
duced directly below the source of the rays, which have been bent 
round by the magnetic field. The active matter sends out rays 
equally in all directions. The rays perpendicular to the field 
describe circles, which strike the plate immediately under the 
source. A few of these rays, A,, A,, A;, are shown im the figure. 
The rays, normal to the plate, strike the plate almost normally, 
Be, poh. 7 
