318 Sir E. Rutherford on the 



plates but was not recorded in the list of lines published 

 by Rutherford and Andrade. The corresponding lines 

 involved in the radium JB spectrum are at 3° 18', 2° 28 f , 

 and 2° 20'. 



It is of interest to note that the soft 7 rays of radium B 

 which give two strong spectral lines reflected at 10° or 12° 

 from rocksalt and have values hv, '125, *104xl0 13 e, re- 

 spectively, do not appear to be responsible for any of the 

 observed /3-ray lines in radium B. The fact that the energy 

 of the slowest group of (3 rays *376 is about 3X'125 is 

 probably merely a coincidence. 



Some recent measurements of Miss Szmidt in this 

 Laboratory have brought out the surprisingly small amount 

 of energy emitted in the form of these soft 7 rays, the 

 amount being only about 2 per cent, of the energy of the 

 more penetrating 7 rays from radium B and only about 

 '014 per cent, of the total energy of the 7 radiation from 

 radium B and radium C together. Although the energy of 

 these soft rays is only about 1/1000 of the total 7-ray energy 

 emitted from an emanation tube, they yet give the most 

 intense spectrum lines under the experimental conditions. 



The small relative amount of energy from the soft 7 rays 

 shows that either these rays are emitted from only a small 

 fraction of the disintegrating atoms, or, what is more probable, 

 that they do not consist of trains of waves but mostly of single 

 waves. 



The general comparison of the soft j3 and 7 ray spectra of 

 radium B with radium C indicates that the higher the 

 frequency of the radiation, the greater the tendency to excite 

 long trains of waves. It does not seem possible at this stage 

 to decide whether this is a definite property of the vibrating 

 systems, or whether it is due to the violence of the disturbance 

 in the case of the higher frequencies of vibration. 



Excitation of fi-ray spectra by characteristic X rays. 



It is known that when a comparatively light element like 

 nickel is bombarded by cathode rajs, the X rays initially 

 emitted consist mainly of the "K" characteristic radiation 

 of that element. Rawlinson* has found that with increasing 

 voltage, more and more penetrating types of radiation appear 

 in addition, but no certain evidence has been found that 

 these penetrating rays give a line spectrum on reflexion from 

 crystals. Moseley showed that the characteristic radiation 

 of nickel consists mainly of two strong lines reflected from 



* Phil. Mag. August 1914. 



