13 and 7 Rays from Radioactive Substances. 459 



emitted during the disintegration o£ each atom, but that the 

 energy is divided between /3 and 7 rays in varying pro- 

 portions for different atoms. For some atoms most, if not 

 all, of the energy is emitted in the form of a hi^h-speed 

 (3 particle; in others the energy of the /3 particle is reduced 

 by definite but different amounts by the conversion of part 

 of its energy into 7 rays. Suppose, for example, the total 

 energy liberated in the form of (3 and 7 rays during the 

 transformation of one atom is E . If the (3 particle before 

 it escapes from the atom passes through two regions where 

 the energy required to excite a 7 ray is E x and E 2 respectively, 

 the resulting energy of the (3 particle is E — (pEx + </E 2 ), 

 where p and q are whole numbers corresponding to the 

 number of 7 rays excited in each region. The energy emitted 

 in the form of y rays is pE x -f qE 2 , and p 7 rays of energy E x 

 and q of energy E 2 appear. 



According to this view, the transformation of one atom 

 gives rise to only one /3 ray, but to p 7 rays of one kind and 

 q of another. The groups of homogeneous (3 rays observed 

 are the statistical effect due to a large number of disinte- 

 grating atoms. The relative distribution of (3 particles 

 amongst the numerous groups of homogeneous rays will 

 depend on the probability that 0, 1, 2, &c. of the units of 

 energy E x and E 2 are abstracted from the /3 particle in 

 traversing the atom. 



This mode of regarding the connexion between /5 and 7 

 rays suggests that the number of 7 rays emitted from radium 

 is considerably greater than the number of /3 rays. Assuming 

 that each 7 ray from radium G was converted into one (3 ray, 

 Moseley (loc. cit.) found that at least two 7 rays appeared for 

 the transformation of one atom of radium 0. There is reason 

 to believe that this is a minimum estimate, and that the actual 

 number is two or three times greater. 



From the results already considered, it does not necessarily 

 follow that group No. 21 is to be regarded as the head of 

 the (3 ray series. Evidence on this point can be obtained by 

 calculating the energy E liberated per atom in the form 

 of 13 and 7 rays during the transformation of radium 0. In 

 same recent experiments the results of which have been 

 communicated to the Vienna Academy, the writer and 

 Mr. H. Robinson conclude that the heating effect of the/3 and 

 7 rajs from 1 gram of radium is 10"8 gram calories, of which 

 about 4*3 is due to the /3 rays and 6*5 to the 7 rays. An 

 uncertain part of this energy arises from the /3 and 7 rays 

 emitted by radium B ; but there will not be much error if it 

 be supposed that the energy of the /3 and 7 rays from 



