Dr Barhla, Phenomena of X-Ray Transmission. 261 



Absorption. 



Experiments on absorption of X-rays have been made by a 

 number of experimenters, but owing to lack of knowledge of 

 secondary X-rays, and to heterogeneity in the beams experimented 

 upon, little regularity of behaviour could be observed from the 

 experimental results. 



/lasoRPTlON /r/ /ll (Jl\ 

 Fig. 2. 



The connection between the absorption of X-rays and the 

 secondary radiation emitted from the absorbing substance was 

 first shown by Barkla and Sadler in a paper on " Homogeneous 

 Secondary Rontgen Radiations." The laws governing the absorption 

 of X-rays have recently been more fully investigated*. The 



* " The Absorption of Bontgen Bays," Fhil. Mag., May 1909. 



