Ions produced by ft and y Radiations from Radium. 321 



determination of the period by Boltwood is quite indepen- 

 dent of the correctness of the radium standard, since it merely 

 involves the comparison of two quantities of emanation. 



There is no radioactive method of checking the accuracy 

 of the value of n, the number of a particles expelled per 

 second per gram, except by comparison of the value of E, 

 which is deduced from the measurement of the total charge 

 rcE carried by a counted number of a particles with other 

 measurements of the unit charge. Taking the original 

 determination of Rutherford and Geiger, the electronic 

 charge comes out to be 4'65 x 10~ 10 e.s. units. If, however, 

 we substitute the recent value of e found by Millikan*, viz. 

 4*77 x 10- 10 , the value of n reduces to 3*48 x 10 10 instead of 

 3-57 x 10 10 . 



An accurate re-determination of the value of n and of 

 ?iE for radium is much to be desired ; for both of these 

 quantities are fundamental constants which should be known 

 with the greatest possible precision. 



University of Manchester, 

 June 1914. 



XXXIX. The Number of Ions produced by the ft and y Radia- 

 tions from Radium. By H. G. J. Moseley, M.A., and 

 H. Robinson, M.ScA 



RUTHERFORD aud Robinson J have shown that the 

 heat evolved in each of the first four transformations 

 of radium corresponds closely with the kinetic energy of the 

 a particles emitted. In the transformation of radium part 

 of the energy is carried by the ft and y radiations. The heat 

 evolved in the absorption of tin.' y radiation alone could be 

 deduced from the measurements, but the heating effects of 

 the a and the ft particles could not be separated. It was 

 therefore not possible to find the energy of the ft particles 

 by this direct method. An approximate knowledge, how- 

 ever, of the relative amounts of energy associated with the 

 three types of radiation may be gathered from a comparison 

 of the total numbers of ions which they produce in air. The 

 work described in this paper was done with this object in 

 view and at Professor Rutherford's suggestion. Our main 

 results were included in the paper by Rutherford and 

 Robinson, but no details have hitherto been published. 



* Millikan, Physical Review, ii. p. 109 (1913). 



{ Communicated bv Sir Ernest Rutherford. 



X Rutherford and Robinson, Phil. Mag. xxy. p. 312 (1913). 



