570 Sir E. Rutherford and Mr. H. Robinson on Mass and 



been shown to be in close accord with that deduced 

 from measurements of the rate of production of helium by- 

 radium *. Recently the value wE has been redetermined by 

 Duane and Danyszf, and found to be slightly less, viz. 

 10-09 x 10" 10 . 



Taking the value nE = 10*54 X 10~ 10 , the rate of emission 

 of energy in the form of a particles from one gram of radium 

 in equilibrium with its short-lived products, viz. the emana- 

 tion, radium A, and radium C, comes out to be 1*250 X 10 6 

 ergs per second. The corresponding value for one curie of 

 emanation in equilibrium with radium A and radium C is. 

 1*004 X 10 6 ergs per second. The respective rates of heat 

 emission correspond to 107*4 and 86*3 gram calories per hour. 

 This is in terms of the Rutherford-Boltwood old radium 

 standard. In terms of the International standard these 

 values become 112*8 and 90*6. Even adding two per cent, 

 to these figures so as to include the energy of the recoil 

 atoms, the numbers are about 7 per cent, lower than the 

 values 123*6 and 99*2 respectively, obtained by measurement 

 of the heating effect due to a rays in terms of the Inter- 

 national standard % . 



It does not seem probable that the value of nE is 7 per 

 cent, too small, and the values of the other quantities involved 

 in the comparison are probably known with a probable error 

 of less than 1 per cent. 



It thus seems reasonable to suppose that in a-ray changes 

 a small part of the heating effect observed is due to other 

 causes than the kinetic energy of the particle. No doubt, 

 some energy is liberated in the form of 7 rays, for Chadwick 

 and Russell have found that weak rays always accompany 

 the expulsion of a particles. 



It would thus appear probable that the rearrangement of 

 the constituents of the atom, consequent upon the expulsion 

 of an a particle, leads to a liberation of energy in other forms, 

 which manifests itself as heat. It is not to be expected that 

 the whole energy liberated by an atomic explosion should be 

 concentrated in the projectile, and in the recoil. The atom 

 itself must be set in violent vibration and adjust itself to a 

 new state of temporary equilibrium, and this may involve 

 the liberation of energy. 



* Boltwood and Rutherford, Wien. Ber. cxx. p. 313 (1911) ■• PhiL 

 Mag. xxii. p. 586 (1911). 



t Duane and Danysz, Le Radium, ix. p. 417 (1912). 



% Rutherford and Robinson, Wien. Ber. cxxi. p. 1491 (1912) ; PhiL 

 Mag. xxv. p. 312 (1913). 



