Homogeneous Corpuscular Radiation. 345 



fig. 6, which show the corpuscular radiation from iron excited 

 by Sr, Mo, and Ag respectively. 



The horizontal portion represents the space in which no 

 further ionization is produced by the corpuscular radiation. 

 It is easily seen from the curves that the corpuscular radia- 

 tions from iron excited by the various homogeneous Rontgen 

 radiations penetrate to different distances in air. 



Homogeneity of the Corpuscular Radiation. 



In an account of some experiments upon the corpuscular 

 radiation from metals Cooksey showed that in some special 

 cases the corpuscular radiation was absorbed by thin sheets 

 of Al according to an exponential law*. 



In these experiments, using an ordinary primary beam, 

 he found that the values of the absorption coefficients deduced 

 from his readings depended upon the degree of " hardness " 

 of his bulb. The corpuscular radiation excited by a " soft " 

 primary beam was in some cases very heterogeneous, while 

 that excited by a " hard " beam was more homogeneous, and 

 also of a more penetrating type. But since a heterogeneous 

 primary beam was used to excite these corpuscular radiations 

 no definite values of their absorption coefficients in aluminium 

 were available. 



It was desirable to obtain detailed knowledge of the cor- 

 puscular radiations excited by the various homogeneous 

 beams, and if possible determinations of their absorbability. 

 For this purpose air at atmospheric pressure was used as the 

 medium in which the absorptions were measured. The method 

 of obtaining the absorption coefficients was similar to that 

 described above. 



As an example, the following observations were made to 

 determine the character of the corpuscular radiation from 

 iron excited by the secondary homogeneous radiation from 

 silver. The inner sliding tube of the ionization-chamber I 

 was adjusted until the distance between the aluminium 

 window B and the radiator R 2 was 1 mm. (the radiator R 2 

 had been ground plane and adjusted as accurately as possible 

 in a plane perpendicular to the axis of the sliding tube, so 

 that the plate was parallel to the plane of the aluminium 

 window); the adjustment being made by means of the scale 

 on the sliding tube and the vernier on the outer case. The 

 deflexion on the electroscope E 2 corresponding to a deflexion 

 of 20 divisions upon the electroscope E 3 was noted. The 

 sliding tube was now withdrawn through 0*5 mm. and a 



* Cooksey, American Journal of Science, October 1907, pp. 285-304. 



