/)r Bar Ida, Fhenomena of X-Ray Transmission. 265 



These results must be connected with the results of experi- 

 ments on secondary radiation and absorption. Carbon, Nitrogen, 

 Oxygen and Sulphur, elements in the group in which an appreciable 

 homogeneous radiation within this range of penetrating power 

 has not been detected, and in which there is proportionality of 

 absorption within this range of penetrating power, here exhibit 

 proportionality of ionization also. 



Ethyl bromide and Tin bichloride exhibit a like proportionality 

 in ionization until the radiation becomes more penetrating than 

 the radiations characteristic of Br and Sn respectively. For more 

 penetrating radiations the relative ionization increased just as the 

 secondary radiation in Br and Sn began to be excited and as the 

 absorption began to increase. 



/Ibiorpl.nii of .jic Radii 



biorption of Primary in Al. 



Fig. 4. 



Methyl Iodide, which was not subjected to a radiation of more 

 penetrating type than that characteristic of Iodine, also exhibited 

 approximately the same proportionality of ionization. 



We are thus led to the conclusion that as in the case of the 

 secondary radiation and absorption, the turning point in the 

 curves showing the relation between ionization and the pene- 

 trating power of the primary radiation is just where the primary 

 radiation becomes more penetrating than the homogeneous 

 radiation characteristic of the substance traversed, or of one of the 

 elementary constituents of the substance traversed. 



18—2 



