46 ROYAL SOCIETY OF CANADA 



Uranium, y Rays, 

 Emergent Secondary Radiation. 



Pb 100 



Sn 76 



Cu 70 



Zn '.. 70 



Fe 72 



Al 77 



C 90 



The curve is given in figure 5, and it shows that the ;- rays from 

 uranium X resemble those of Ra C more nearly than they resemble 

 the secondary y rays due to Ra C. It would be interesting to obtain 

 the curve more correctly with uranium X concentrated in the manner 

 recently described by Soddy.^ 



The five curves seen in figs. 3 and 5 show the gradual changes 

 in the emergent secondary radiation from very soft to very hard 

 y rays. 



Reversals with Four Plates. 



It is now possible to explain the results obtained by reversing 

 the'^order of plates at the front and back of the electroscope. Let 

 the plates A, B, C, D consist two of aluminium, two of lead, then 

 the ionization currents in the electroscopes for the arrangements 

 stated have the following relative values, when the y rays have 

 passed through a screen of lead 0.6 cm. thick. 



The results obtained by Bragg' were found with an arrangement 

 different from mine, for he placed the radium close to the electro- 

 scope. 



1 " Nature," 28 Jan. 1909. 



2 Trans. Roy. Soc. S. Aust., 32, 1908. 



