Rontgen Radiation from Vapours. 447 



chromium onwards emit almost wholly the characteristic 

 radiation which, on account o£ its homogeneity, suffers equal 

 percentage absorptions when transmitted through equal 

 thicknesses of aluminium. By determining these percentage 



absorptions the values of — (where I = I 0< ?~ A;r and p = density 



of aluminium) have been obtained for the different elements 

 giving characteristic radiations. Previously, in experiments 



performed for determining the coefficient - , the elements 



used have been, for purposes o£ convenience, in the solid 

 state, either pure or in the form of compounds. The following 



Fig. 1. 



experiments were undertaken at the suggestion of Prof. Barkla 

 with a view to showing that the same type of homogeneous 

 radiation is emitted by the elements, whether they are in tho 

 solid state or in the form of vapour. 



