208 PKOFKSSOR E. RUTHKKI'OIM) < >N THE 



the disintegration of radium have been very closely investigated, and it has been 

 found that, with the exception of the rayless change, all the changes are accompanied 

 by the emission of a particles with great velocity. The ft and y rays appear only in 

 the fifth change. In the case of thorium, it has not been found possible to completely 

 free the product ThX from ft rays, on account of the difficulty of entirely removing 

 from it the products of the subsequent change. The proportion of ft rays is, however, 

 greatly reduced if the emanation produced by the ThX is removed by passing a rapid 

 current of air through a solution of ThX. The emanation itself gives out only 

 a rays, but the second product, thorium B, arising from it gives out all three types of 

 rays. A removal of part of the emanation thus decreases the amount of ft rays from 

 the ThX. I think there is little doubt that, if the emanation could be removed from 

 the ThX as fast as it was formed, it would be found that the ThX itself gives out 

 only a rays, and that the ft and y rays, as in the case of radium, appear only in the 

 fifth change. 



It is remarkable that the ft and y rays of uranium, thorium, and radium appeal- 

 only in the last of the rapid succession of changes occurring in those bodies. It has 

 already been pointed out that the ft and y rays always appear together and in the 

 same proportion. There is now little doubt that the y rays are electromagnetic 

 pulses, similar to X rays, generated at the moment of the sudden expulsion of the 

 ft particle from the radio-atom. 



In the three radio-elements, the expulsion of the ft particle results in the appearance 

 of a product either permanently stable, or, in the case of radium, of a product far 

 more stable than the preceding one. It would appear that the initial changes are 

 accompanied only by the expulsion of an a particle, and that once the ft particle is 

 expelled, the components of the residual atom fall into an arrangement of fairly 

 stable equilibrium, when the rate of disintegration is very slow. I think that it is 

 more than a coincidence that the ft and y rays appear only in the last of the rapid 

 changes in the three radio-elements. 



It appears probable that the ft particle, which is finally expelled, may be regarded 

 as the active agent in promoting the disintegration of the radio-atom in successive 

 stages. According to the modern point of view of regarding atomic structure, the 

 atoms of the radio-element may be supposed to be made up of electrons (ft particles) 

 and groups of electrons (a particles) in rapid motion, and held in equilibrium by their 

 mutual forces. If the atom is to remain permanently stable, it is necessary that there 

 should be no loss of energy as a whole from the moving charged parts of which the 

 atom is built up. LARMOR has shown that this condition is fulfilled if the vector 

 sum of the accelerations of the moving particles is permanently null. If this is not 

 the case, there must be a continuous drain of energy from the atom in the form of 

 electromagnetic radiation. This, in the course of time, must disturb the equilibrium 

 of the atom, and result either in a re-arrangement of its component parts or to its 

 final disintegration. It may, perhaps, be supposed that occasionally one of the 



