386 Prof. W. H. Bragg on the Consequences of 



(8) The simple solution of at least two useful ionization 

 problems. The second of these leads to a ready 

 determination of the relative average ranges of ft rays 

 in various materials (the range being defined as the 

 total length of the track when straightened out). 

 These fit in very well with results obtained indirectly 

 by H. W. Schmidt, and so furnish a general expla- 

 nation of the form of the absorption curves of 

 ft rays. 



The idea that X and 7 radiations are both to be regarded 

 as consisting of streams of discrete entities has gained 

 ground steadily in the last year or two. Sir J. J. Thomson 

 looks upon the X ray as a kink in the one tube of force by 

 which he represents all the properties of the electron. Ac- 

 cording to present knowledge the 7 ray is of the same nature 

 as the X ray, so that an hypothesis regarding the nature of 

 the one must be taken to apply to the other also. J. Stark 

 has recently developed * the theory, based on the work of 

 Planck, that an X ray is a bundle of energy travelling 

 without alteration of form. This differs from Thomson's 

 theory in at least one important particular because the latter 

 involves a change of form f. I have my self found it con- 

 venient to regard the X ray as a negative electron to which 

 has been added a quantity of positive electricity which 

 neutralizes its charge, but adds little to its mass. 



Whatever view may be taken of the nature of the entity, 

 the acceptance of the corpuscle idea modifies our views of 

 the phenomena attending the passage of rays through matter, 

 and alters the language which we use in describing experi- 

 mental results. I think that it leads to a marked gain in 

 simplicity, and my object in writing this paper is to show, if 

 I can, that this is the case. 



It will be convenient to begin with a brief statement of 

 the main arguments for the entity hypothesis, though this 

 plan involves some little repetition of similar statements pre- 

 viously given. For this purpose it will be best to use the 

 results of recent investigations, since they are most fitted to 

 serve as a foundation for the case, although I would not 

 undervalue the older arguments which first suggested the 

 discrete form of the X ray. 



"When a pencil of 7 rays is directed normally upon a thin 

 plate, for example a plate of aluminium one or two milli- 

 metres in thickness, ft rays spring out from both sides of the 



* Phys. Zeit. x. p. 902 (1909) ; xi. p. 24 and p. 179 (1910). 



f Phil. Mag. Feb. 1910. 



