“it 2 
ey soi. 
Wy . 
< 
= . 
oe 
122 NATURE OF THE RADIATIONS [CH. 

If the particle, after passing through a uniform magnetic field for 
a distance l,, is deviated through a small distance d, from its 
original direction, 
Zed, — ly 
Le 
or d, = 9 an V slrofeyelelelsiors (eleistchoteletotctereteh=tekareta (1); 
If the rays pass through a uniform electric field of strength X and 
length /, with a deviation d., 
since = is the acceleration of the particle, at right angles to its 
2 
direction, and ;; is the time required to travel through the electric 
a 
field. 
From equations (1) and (2) 
_ dl? X 
Gb eal? 
Dies D0 RAVE 
and == le 
The values of V and e/m are thus completely determined from the 
combined results of the electric and magnetic deviation. It was 
found that 
V =2°5 x 10° cms. per sec. 
© =6 x 10%. 
m 
On account of the difficulty of obtaining a large electrostatic de- 
viation, these values are only approximate in character. 
The results on the magnetic and electric. deviation of the 
a rays of radium have been confirmed by Des Coudres}, by the 
photographic method. Some pure radium bromide was used as a 
source of radiation. The whole apparatus was enclosed in a vessel 
which was exhausted to a low vacuum. In this way, not only 
was he able to determine the photographic action of the rays at 
a much greater distance from the source, but he was also able 
1 Phys. Zeit. 4, No. 17, p. 483, 1903. 
