x] RADIO-ACTIVE PROCESSES 319 
active matter, which possess temporary activity and differ in 
chemical properties from the thorium. The constant radio-activity 
of thorium was shown to be the result of equilibrium between the 
processes of production of active matter and the change of that 
already produced. At the same time, the theory was advanced 
that the production of active matter was a consequence of the dis- 
integration of the atom. The work of the following year was 
devoted to an examination of the radio-activity of uranium and 
radium on similar lines, and it was found that the conclusions 
already advanced for thorium held equally for uranium and radium?. 
The discovery of a condensation of the radio-active emanations? 
gave additional support to the view that the emanations were 
gaseous 1n character. In the meantime, the writer* had found that 
the rays consisted of positively charged bodies atomic in size, 
projected with great velocity. The discovery of the material 
nature of these rays served to strengthen the theory of atomic 
disintegration, and at the same time to offer an explanation of 
the connection between the a rays and the changes occurring in 
the radio-elements. In a paper entitled “Radio-active Change,” 
Mr Soddy and the writer’ put forward in some detail the theory 
of atomic disintegration as an explanation of the phenomena of 
radio-activity, and at the same time some of the more important 
consequences which follow from the theory were discussed. 
In a paper announcing the discovery of the heat emission of 
radium, P. Curie and Laborde’ state that the heat energy may be 
equally well supposed to be derived from a breaking up of the 
radium atom or from energy absorbed by the radium from some 
external source. 
J. J. Thomson in an article on “ Radium,’ communicated to 
Nature’, put forward the view that the emission of energy from 
radium is probably due to some change within of the atom, and 
pointed out that a large store of energy would be released by a 
contraction of the atom. 
Sir William Crookes’, in 1899, proposed the theory that the 
1 Phil. Mag. April, 1903. 2 Phil. Mag. May, 1903. 
3 Phys. Zeit. 4, p. 235, 1902. Phil. Mag. Feb. 1903. 
4 Phil. Mag. May, 1903. > C. R. 136, p. 673, 1908. 
6 Nature, p. 601, 1908. 7 C. R. 128, p. 176, 1899. 
