452 Mr. J. Crosby Chapman on Homogeneous 



same. By continuing the curve before mentioned, it will be 

 seen that this value lies approximately on it. 



Although it has only been proved in these two cases that 

 elements in the solid and vapour state emit the same type 

 of radiation, yet it is safe to conclude that what applies here 

 holds generally ; especially considering that the atomic 

 weights of bromine and iodine are well separated. It is 

 evident that this similarity of character in the radiations is 

 what would follow from the fact that the phenomena of 

 secondary X-rays are atomic in their nature. 



Bombardment of Atoms by Ejected Corpuscles. 

 In a previous paper * facts have been brought forward 

 indicating that the characteristic secondary radiation does 

 not result from the subsequent bombardment of atoms by 

 ejected corpuscles. A slight adaptation of the above experi- 

 ment shows this. For if carbon dioxide and hydrogen are 

 used separately under the same conditions as the gas in which 

 the vapour of ethyl bromide is passed into the chamber, in 

 the former case it is the carbon dioxide gas which is chiefly 

 bombarded by ejected electrons, while with hydrogen it is the 

 ethyl bromide itself which has for the most part to stop the 

 expelled corpuscles. Therefore, if subsequent bombardment 

 causes the characteristic radiation, we should expect greater 

 intensity with the hydrogen than with the carbon dioxide as 

 the gas. This point can be investigated experimentally. 



The apparatus used was practically identical with that 

 previously described. The tin box was moved farther back 

 and the primary rays were cut dowm by a lead tunnel in 

 place of the slits then used. At the same time, the electro- 

 scope S was moved into a position to receive radiations from 

 a thin stick of selenium so placed in this tunnel that a small 

 part of the exciting radiation from the X-ray bulb fell on 

 it. The electroscope M was brought nearer to the box, this 

 was possible owing to the alteration in breadth of the 

 primary beam. 



Since the atomic weight of selenium is 79 while that of 

 bromine is 80, the intensity of secondary radiation from the 

 stick of selenium in the tunnel standardizes the power of 

 the incident rays in exciting the homogeneous bromine 

 radiation. In the first part of the experiment, the carbon 

 dioxide gas obtained from a cylinder was saturated with 

 ethyl bromide at 3°*5 C, and was passed through the chamber 

 till a steady state was reached. The deflexion in the electro- 

 scope receiving radiations from the chamber, while the other 

 * Chapman & riper, Phil. Mag. June 1910. 



