458 Prof. E. Rutherford on the Origin of 



probability most of the lines, Nos. 1 to 10, belong to radium B 

 and nor. to radium C. The energy of the ft particle for 

 group No. 21 is 8'63x 10 l3 e, while its velocity is *962 of the 

 velocity of light. Groups 22 and 23 are not included in 

 the calculation, for Danysz states that No. 22 includes 

 from 3 to 5 groups of ft rays, of which only the average 

 velocity is given ; similarly No. 23 is considered to be a 

 complex group. 



The values of the velocity of the ft particles will require 

 to be known with great accuracy before such a relation as is 

 indicated can be definitely established ; but it does not appear 

 likely that the connexion observed is accidental. It is of 

 interest to note that the value of E 2 = 1*556 x 10 13 e is in fair 

 accord with the calculated energy of the ft particle, viz., 

 1*5 x 10 13 £, which would be required to excite the charac- 

 teristic radiation from radium 0. The value of E x may in a 

 similar way be connected with the energy required to excite 

 the second type of characteristic X radiation which has been 

 observed in a number of elements by Barkla. 



It is possible that some of the groups from Nos. 10 to 1 

 may also belong to radium C. For example, No. 8 fits in 

 well with a difference 4E 1 + 3E 2 from No. 21. Hahn has 

 determined the velocity of the stronger groups of rays from 

 radium B and radium C separately. For radium B, the 

 values ft = '36, *41, "63, '69, *74 are given. The last three 

 no doubt correspond to groups Nos. J, 4, and 7 respectively 

 given by Danysz. A group for which ft = '80, which appears 

 to correspond to No. 10, is ascribed to radium C. Group 

 No. 10, however, does not fit in at all with the relation found 

 between Nos. 11 to 21. It would be of great value to deter- 

 mine definitely the division of the groups of ft rays observed 

 between radium B and radium C. 



If the groups Nos. 10 to 1 supposed to belong to radium B 

 be analysed in a similar way to the groups for radium C, the 

 differences may be approximately expressed by the relation 

 ^Ex + ^Ej, where E^'114 X 10 13 <> and E 2 = '144 x We. The 

 agreement, however, between calculation and theory is not 

 nearly so good as for the case previously considered, and it is 

 doubtful whether any weight can be attached to it. For the 

 slow velocity ft rays here considered, the reduction of velocity 

 in passing through the glass walls of the emanation tube is 

 quite appreciable, and the correction is different for each 

 group. Until this correction is made, it does not seem 

 possible to draw any definite conclusions. 



The simplest way of regarding this relation between the 

 groups of ft rays is to suppose that the same total energy is 



