Iv | NATURE OF THE RADIATIONS 125 
charge and are difficult to deflect by a magnetic field. The experi- 
ments of Wien have shown that the velocity of projection of the 
Canal rays varies with the gas in the tube and the intensity of the 
electric field applied, but it 1s generally about 1/10 of the velocity 
of the a particle from radium. The value of e/m is also variable, 
depending upon the gas in the tube. 
It has been shown that for the a rays of radium 
Vi= 25 < 10 "and =e) — Gee 10? 
Now the value of e/m for the hydrogen atom, liberated in the 
electrolysis of water, is 107: Assuming the charge carried by the 
a particle to be the same as that carried by the hydrogen atom, the 
mass of the @ particle is about twice that of the hydrogen atom. If 
the a particle consists of any known kind of matter, this result 
indicates that it consists either of projected helium or hydrogen. 
Further evidence on this important question is given in section 202. 
The a rays from all the radio-active substances and their 
products, such as the radio-active emanations and the matter 
causing excited activity, possess the same general properties and 
do not vary very much in penetrating power. It is thus probable 
that im all cases the a rays from the different radio-active sub- 
stances consist of positively charged bodies projected with great 
velocity. Since the rays from radium are made up in part of a 
rays from the emanation stored in the radium, and from the 
excited activity which it produces, the a rays from each of these 
products must consist of positively charged bodies; for it has been 
shown that all the a rays from radium are deviated in a strong 
magnetic field. 
The kinetic energy of each projected particle is enormous, com- 
pared with its mass. The kinetic energy of each a particle 
= 3 me 5 eo xm eres! 
Taking the velocity of a rifle bullet as 10° cms. per second, it is 
seen that, mass for mass, the energy of motion of the @ rays is 
6 x 10° times as great as that of the rifle bullet. In this projection 
of bodies atomic in size with. great velocity probably les the 
principal cause of the heating effects produced by radium (section 
106). 
