324 Sir E. Rutherford on Radium Constants 



In a similar way, the value of nE deduced from the 

 observed volume of the emanation is in close accord with 

 the experimental value. 



There is thus a satisfactory agreement between theory 

 and experiment in the above cases, but the agreement is not 

 nearly so good for the value wE deduced from the heating- 

 effect and the life of radium. These points will consequently 

 be considered in more detail. 



Heating Effect of Radium Emanation. 



In a recent paper, Mr. H. Robinson and myself* have re- 

 determined the velocity and value E/tw for the a, particles 

 expelled from radium. From these data we have compared 

 the calculated heating effect due to one curie of radium in 

 equilibrium due to a. rays alone, with the observed heating' 

 efiect due to these radiations. On the Internationa] Standard,, 

 the observed heating effect due to the a rays from one curie 

 of emanation is 99*2 gr. cals per hour, and the calculated is- 

 92*4, assuming nE = 11*1 x 10~ 10 e. m. units, and adding 2 

 per cent, for the energy of the recoil atoms. The calcu- 

 lated heating effect is thus 7 per cent, lower than the 

 observed. If all the heating effect of the a ray products is 

 due to the energy of the expelled a particles, it would follow 

 that the value of ??E is 7 per cent, too small. This seems- 

 improbable, so we must look for an explanation of this 

 apparent discrepancy in another direction. The general 

 radioactive evidence indicates that the loss of an a. particle 

 from an atom lowers the positive charge of the atomic nucleus- 

 by two units, and the expulsion of a /3 particle from the 

 nucleus raises it by one unit. Without entering into a dis- 

 cussion of the possible distribution and velocities of the 

 electrons external to the nucleus, it is to be anticipated on 

 general grounds that the kinetic energy of the total electronic 

 distribution external to the nucleus should increase with 

 increase of charge on the nucleus. The expulsion of an u 

 particle should thus result in a lowering of the total kinetic 

 energy of the electrons, and the expulsion of a fi particle to 

 an increase. Suppose, for simplicity, that this change of 

 energy is proportional to the variation of charge on the 

 nucleus, and is the same for each a ray transformation. 

 If A be the energy per atom liberated from the electrons 

 resulting from the ^expulsion of an a particle, then A/2 is 

 the energy absorbed in consequence of the expulsion of a 

 /3 particle. If E 1} E 2 , E 3 be the kinetic energies of the 



* Wien. Ber. exxii. Abt. II a, Not. 1913. 



