358 



On the Production of Helium from Radium. [Apr. 14, 



the a-particle, as calculated from its mass and its velocity. By making 

 certain assumptions about to be considered, he deduced that Q M must 

 lie between 0*6 and 0'06 cub. mm. The maximum estimate, which is 

 almost exactly one-half the experimental value found by us, was based 

 on the assumption that the whole, and the minimum estimate on the 

 assumption that only one-tenth, of the energy of disintegration is mani- 

 fested in the kinetic energy of the a-particle expelled. It was further 

 assumed that only one a-particle was expelled from each atom, at each 

 disintegration accompanied by a-radiation that is known to occur. If 

 more than one a-particle is expelled at each disintegration, the theo- 

 retical estimate must be correspondingly reduced. Since the experi- 

 mental value exceeds the maximum theoretical estimate, it follows that 

 there are now direct experimental reasons for believing that — 



(1) Only one a-particle is expelled from the atom at each dis- 

 integration. 



(2) The greater part of the energy of disintegration appears in the 

 form of kinetic energy of a-radiation. 



(3) The emanation is a monatomic gas. 



It must be remembered that the experimental value is necessarily a 

 maximum value ; for if any impurity were present with the emanatic*, 

 it would increase the volume measured. 



