108 NATURE OF THE RADIATIONS [CH. 
Thus these rays had a velocity more than half the velocity of light, 
and an apparent mass about the same as the cathode ray particles, 
z.e. about 1/1000 of the mass of the hydrogen atom. The 8 ray is 
therefore analogous in all respects to the cathode ray, except that 
it differs in velocity. In a vacuum tube the cathode rays generally 
have a velocity of about 2 x 10° cms. per sec. In special tubes 
with strong fields the velocity may be increased to about 10” cms. 
per sec. These charged particles behave lke isolated units of 
negative electricity. The conception of such disembodied charges, 
known as electrons, has been examined mathematically among 
others by Larmor, who sees in this conception the ultimate basis 
of a theory of matter. The @ rays from radium may also be 
considered as electrons, but when obtained from this source have 
velocities varying from about 1/3V to at least ‘96V, where V is the 
velocity of light, and thus have an average velocity considerably 
greater than that of the electrons produced in a vacuum tube. 
These moving electrons are, it seems, able to pass through much 
greater thicknesses of matter before they are absorbed than the 
slower electrons produced in a vacuum tube, but the difference 
is one merely of degree and not of kind. Electrons are thus con- 
tinuously and spontaneously expelled from radium with enormous 
velocities. It is difficult to avoid the conclusion, that this velocity 
has not been suddenly impressed on the electron. Such a sudden 
gain of velocity would mean an immense and sudden concentration 
of energy on a small particle, and it is more probable that the 
electron has been in rapid orbital or oscillatory motion in the atom, 
and, by some means or other, suddenly escapes from its orbit. 
According to this view, the energy of the electron is not suddenly 
created, but is only made obvious by its escape from the system to 
which it belongs. 
76. Variation of with the velocity of the electron. 
The fact that radium throws off electrons with rates of speed 
varying from 1/8 to 9/10 the velocity of light has been utilised by 
Kaufmann?! to examine whether the ratio e/m of the electrons 
varies with the speed. It has been shown by J. J. Thomson’, 
1 Phys. Zeit. 4, No. 1b, p. 54, 1902. 2 Phil. Mag. April, 1881. 
