12 ROYAL SOCIETY OF CANADA 



dary rays, whilst 6 cms. of brick do not give full value. Slate gives 

 secondary kathode and y rays, both somewhat less intense than 

 brick gives. 



5. When the radium was in a glass test tube, without steel or 

 lead around it, the ft and y rays gave from a secondary radiator of 

 lead a current measuring 250 scale divisions a minute in the electro- 

 scope, the y rays gave 7.5 per cent of that amount. The latter could 

 be divided into two parts, kathode and y in type, The y type was 

 the following percentages of the total (kathode and ;/), for lead 

 radiator 6.2, for iron 25, for brick 28. 



6. The values of the coefficients of absorption by a sheet of 

 aluminium, 0.41 mm. thick, are as follows: — 



Primary' y rays 21 



Secondary kathode due to ft and ;/ rays striking 



(a) lead 24 



(b) iron 35 



Secondary kathode due to y rays striking 



(a) lead 31 



(b) iron 34 



Thus the ft rays cause secondary kathode rays slower than the 

 primary rays which cause them, and the y rays cause secondary 

 kathode mys, yet slower. But all these rays have velocities of the same 

 general order, and faster than the secondary kathode rays due to the 

 X rays. This has already been proved by Dorn, Allen, Kleeman and 

 others. 



7. The values of the coefficients of absorption of the secondary y 



rays, due to primary y rays, were also determined for lead screens, 



changing the thickness from 2 to 4 mms. 



A 



(a) Radium in lead (1 cm) Lead radiator 2 .46 



Iron radiator 3 .70 

 Brick radiator 3 .68 



(b) Radium in steel (2.2 cms.) Lead radiator 4 .35 



Iron radiator 4 .65 

 Brick radiator 4.60 



These may be compared with the coefficients of absorption of the 

 primary y rays passing through lead.' 



Radium 0.57-0.45 



Uranium 1 .4 



Actinium 4.7-2.7 



' Phil. Mag., April 1906. 



