604 



Mr. S. Oba on the 



figs. 2, 3, 4, and 5. Table I. refers to aluminium as absorber 

 and Table II. to iron. The aluminium used was of density 2*70 

 and was practically pure ; and for iron, sheets of mild steel 

 of density 7*7 were used. In the first column of either table 



Fiff. 2. 



Fig. 3. 



cms orM. 



the material and thickness of the hardener are given. The 

 thicknesses of 2*4 cm. copper, 2*5 cm. tin, 1*1 cm. lead were 

 chosen, because they have about the same total absorption. 



The remaining columns give the values of ^ x 100, where D 



is the density of the absorber and p is the absorption co- 

 efficient calculated by the equation 



ii/i. = • 



M(*2-*i) 



