weight. At a later date Rutherford and Soddy showed that the radium and thorium emanations behaved like chemically inert gases, since they were unaffected by the most drastic physical and chemical treatment.
On the other hand, P. Curie, who, in conjunction with Debierne, had made a series of researches on the radium emanation, expressed dissent from this view. P. Curie5 did not consider that there was sufficient evidence that the emanation was material in nature, and pointed out that no spectroscopic evidence of its presence had yet been obtained, and also that the emanation disappeared when contained in a sealed vessel. It was pointed out by the writer6 that the failure to detect spectroscopic lines was probably a consequence of the minute quantity of the emanation present, under ordinary conditions, although the electrical and phosphorescent actions produced by this small quantity are very marked. This contention is borne out by later work. P. Curie at first took the view that the emanation was not material, but consisted of centres of condensation of energy attached to the gas molecules and moving with them.
M. and Mme Curie have throughout taken a very general view of the phenomena of radio-activity, and have not put forward any definite theory. In Jan. 1902, they gave an account of the general working theory7 which had guided them in their researches. Radio-activity is an atomic property, and the recognition of this fact had created their methods of research. Each atom acts as a constant source of emission of energy. This energy may either be derived from the potential energy of the atom itself, or each atom may act as a mechanism which instantly regains the energy which is lost. They suggested that this energy may be borrowed from the surrounding air in some way not accounted for by the principle of Carnot.
In the course of a detailed study of the radio-activity of thorium, Rutherford and Soddy8 found that it was necessary to suppose that thorium was continuously producing from itself new kinds of active matter, which possess temporary activity and differ in chemical properties from the thorium itself. 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 disintegration 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 radium9. The discovery of a condensation of the radio-active emanations10 gave additional support to the view that the emanations were gaseous in character. In the meantime, the writer11 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 α rays and the changes occurring in the radio-elements. In a paper entitled “Radio-active Change,” Rutherford and Soddy12 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 Laborde13 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