186 Magnetic and Electric Deviation of Radium Rays. 



the gas below a certain velocity, which is very great com- 

 pared with the velocity of translation of the molecules. 



It is of interest to consider the probable part that the a 

 rays play in the radioactive bodies on the general view of 

 radioactivitv that has been put forward by Mr. Soddy and 

 myself in the Phil. Mag. Sept. and Nov. 1902. It is there 

 shown that radioactivity is due to a succession of chemical 

 changes in which new types of radioactive matter are being 

 continuously formed, and that the constant radioactivity of 

 the well known active bodies is an equilibrium process, where 

 the rate of production of fresh active matter is balanced by 

 the decay of activity of that already produced. Some very 

 interesting points arose in the course of these investigations. 

 It was found that the residual activity of uranium and thorium 

 when freed from UrX and ThX by chemical processes con- 

 sisted entirely of a rays. On the other hand, the radiation of 

 UrX* consisted almost entirely of ft rays, while that of ThX f 

 consisted of both a and /3 rays. Similar results probably hold 

 also for radium, for the Curies have shown that radium 

 dissolved in water and then evaporated to dryness temporarily 

 loses to a large extent its power of emitting ft rays. 



It thus appears probable that the emission of a rays goes 

 on quite independently of the emission of ft rays. There 

 seems to be no doubt that the emission of ft rays by active 

 substances is a secondary phenomenon, and that the a rays 

 play the most prominent part in the changes occurring in 

 radioactive matter. The results obtained so far point to the 

 conclusion that the beginning of the succession of chemical 

 changes taking place in radioactive bodies is due to the 

 emission of the a rays, i. e. the projection of a heavy charged 

 mass from the atom. The portion left behind is unstable, 

 undergoing further chemical changes which are again accom- 

 panied by the emission of a rays, and in some cases also of 

 frays'. " 



The power possessed by the radioactive bodies of apparently 

 spontaneously projecting large masses with enormous veloci- 

 ties supports the view that the atoms of these substances are 

 made up, in part at least, of rapidly rotating or oscillating 

 systems of heavy charged bodies large compared with the 

 electron. The sudden escape of these masses from their 

 orbit may be due either to the action of internal forces or 

 external forces of which we have at present no knowledge. 



It also follows from the projection nature, of the a rays 

 that the radioactive bodies, when inclos.d in sealed vessels 



* Soddv, Proc. Chem. Soc. 1902. 



t Rutherford arid Grier, Phil. Mag, Sept. 1902. 



