different Metals by Rontgen Rays. 



291 



Column I of the tables gives the thickness of aluminium in 

 millimeters ; columns II and II 7 give the intensity of the second- 

 ary rays after passing through the corresponding thickness of 

 aluminium for the two hardnesses respectively, the intensity of 

 the rays from the bare plate being always taken as unity. 



Copper. 



Hardness 



0= 0.68 



.001 .OOZ .003 .00 f 



008 



.0/2. 



171 m. of ALuminiu/n* 



.001 .OOZ .OOZ .OOf .008 



mtn. of Aluminium. 



