x] RADIO-ACTIVE PROCESSES 347 
208. Evolution of matter. Although the hypothesis that 
all matter is composed of some elementary unit of matter or pro- 
tyle has been advanced as a speculation at various times by many 
prominent physicists and chemists, the first definite experimental 
evidence showing that the chemical atom was not the smallest 
unit of matter was obtained in 1897 by J. J. Thomson in his classic 
research on the nature of the cathode rays produced by an electric 
discharge ina vacuum tube. Sir William Crookes, who was the first 
to demonstrate the remarkable properties of these rays, had sug- 
gested that they consisted of streams of projected charged matter 
and represented—as he termed it—a new or “fourth state of matter.” 
J. J. Thomson showed by two distinct methods that the cathode 
rays consisted of a stream of negatively charged particles projected 
with great velocity. The particles behaved as if their mass was 
only about 1/1000 of the mass of the atom of hydrogen, which is 
the lightest atom known. These corpuscles, as they were termed by 
Thomson, were found at a later date to be produced from a glowing 
carbon filament and from a zinc plate exposed to the action of 
ultra-violet light. They acted as isolated units of negative elec- 
tricity, and, as we have seen, may be identified with the electrons 
studied mathematically by Larmor and Lorentz. Not only were 
these electrons produced by the action of light, heat, and the 
electric discharge, but they were also found to be spontaneously 
emitted from the radio-elements with a velocity far greater than 
that observed for the electrons in a vacuum tube. 
The electrons produced in these different ways were all found to 
carry a negative charge and to be apparently identical; for the 
ratio e/m of the charge of the electron to its mass was in all cases 
the same within the limit of experimental errors. Since elec- 
trons, produced from different kinds of matter and under different 
conditions, were in all cases identical, it seemed probable that they 
were a constituent part of all matter. J. J. Thomson suggested 
that the atom is built up of a number of these negatively charged 
electrons combined in some way with corresponding positively 
charged bodies. 
On this view the atoms of the chemical elements differ from 
one another only in the number and arrangement of the component 
electrons, 
