ON A WANT OF SYMMETRY SHOWN BY SECONDARY X-RAYS 



By W. H. Bragg, M.A., F.R.S., Elder Professor of Mathe- 

 matics and Physics in the University of Adelaide. 



[Read September 8, 1908.] 



(Abstract.) 

 Experiments were described showing that the secondary 

 X radiation appearing on the emergence side of a plate 

 traversed normally by X-rays, was in general greater than 

 that appearing on the incidence side. Aluminium and cellu- 

 loid showed the effect well, but copper and iron did not show 

 it until all the softer portions of the secondary radiations 

 had been removed by screens. The results were favourable 

 to the theory that X-rays were of a material nature. See 

 the following paper, p. 301. 



