Delta Bays produced by Beta Bays. 783 



(h) The ratio T lo ° was low and T 40 was hio-h for the hard 

 ' I90 I90 ° 



portions o£ the secondary beam. 



(c) The amount of the forward radiation was always con- 

 siderably greater than the radiation sent in a direction 

 opposite to that of the beam. 



(2) The results, though apparently contradictory, are very 

 simply explained ; as 



(a) When the primary beam is soft the secondary beam 

 consists of scattered radiation and an " extra " radiation 

 which is softer than, the primary. The proportion of extra 

 radiation on the forward direction is very much greater than 

 in the other direction. 



(/>) When the primary beam is hard the secondary beam 

 consists of scattered radiation, a larger proportion of '* extra" 

 radiation than when the beam was soft, and hard fluorescent 

 carbon radiation. 



(3) Confirmation of these views has been obtained by a 

 study of the relative absorbabilities of the primary and 

 secondary beams. 



George Holt Physics Laboratory, 

 July 31,1912. 



LXXiX. Delta Bays produced by Beta Bays. 

 By Norman Campbell, Sc.D* 



1. TN several previous papers experiments! have been 

 J_ described which appear to prove conclusively that 

 the Quality of the § rays emitted from solids under the action 

 of « rays is independent of the velocity of the a rays and the 

 nature of the solid. Accordingly this quality must be deter- 

 mined either by some structure which is common to ail 

 a rays (that is, by the nature of the helium atom of which 

 all ol rays consist) or by some structure common to all atoms 

 which is concerned in the process of ionization of those 

 atoms. The alternatives may be distinguished by discovering 

 whether the action of ionizing agents other than a. rays 

 results in the production of similar £ rays. 



2. When the literature of the subject was examined it 

 appeared immediately that it was exceedingly probable that 

 £ rays of a quality very similar to those produced by a. rays 

 were produced by the action of /S or cathode rays. It was 



* Communicated bv the Author. 



1911, p. 276 j Jan. 1912, p. 46 ; Oct. 1912, p. 527. 



