Iß Art. 10. — S. Kinoshita and H. Ikenti : 



11. Considerations on the ^photographie action of y rays. The 

 general feature of tlie photographic action of y rays may Ije inferred 

 from the facts liitherto accumulated. As is well known, X rays 

 do not directly ionise the molecules of a gas which the rays 

 traverse, but liberate from them corpuscular radiation which is 

 responsible for übe ionisation'^ The velocity of the emitted cor- 

 puscles is independent of the nature of the emitter and depends 

 only upon the wave-length of the exciting X rays, the smaller the 

 wave-length the greater the velocity. The excitation of the 

 "corpuscular radiation by X rays is not limited to gases 1)ut is also 

 true of solids and liquids. 



There is every reason to believe that this is the case with y 

 rays, which, as we know, differ from X rays only in wave-length. 

 It has already been shown that the corpuscular radiation set up by 

 X rays from a radium salt is nearly as swift as the primary ß rays 

 emitted by it^-*. Thus, the effect of exposing a photographic plate 

 to X or /' rays will be that corpuscular radiation is set up through- 

 out the exposed portion of the plate. Since individual ß particles 

 leave no detectable tracks of silver grains on a photographic plate, 

 it Avill be impossible to obtain a track of X or y rays on a photo- 

 graphic plate similar to that of X rays illustrated by the photo- 

 graphs obtained by C. T. E. Wilson in the condensation method. 

 It will be evident that the halide grains rendered capable of 

 development by a Hash of X or y rays are scattered very diffusely 

 throughout the volume of the emulsion film, but with no definite 

 arrangement. 



In an experiment we have exposed a plate to a flash of X rays 

 through an extremely narrow slit between two thick brass plates, 

 to see if any particular effects were produced in- and outside the 

 region upon which the X rays fell. Microscopic examination of 

 the plate gave negative results, as was naturally to be expected. 



1) C. G. Barkla and L. Simons, Phil. Mag. 23 (1912), p. 317; C. T. K. Wilson, Proc. Eoy. 

 Soc. A, 87 (1912), p. 277 ; C. G. Barkla and A. J. Philpot, Phil. Mag. 25 (1913), p. 832. 



2) A. S. Eve, Phil. Mag. 8 (1904), p. 669 ; S. J. Allen, Phys. Eev. 23 11906), p. 65. 



