140 



THE ROYAL SOCIETY OF CANADA 



like a pencil of a or /3 lays and that the main explanation of experi- 

 ments on secondary 7 rays is that when 7 rays are scattered, the 

 scattered rays are softer, the softeninjï being greater the greater the 

 angle of scattering. In support of this view it may be stated that 

 Sadler and Mesham* have found that when homogenous X rays are 

 scattered in carbon the scattered rays are less penetrating. Below 

 are given a description of the experiments and a discussion of the 

 results and their Ijearing on absorption experiments. 



Experimental arrangements and results. 



Figure 1 (which is drawn to scale) shows a horizontal section of the 

 apparatus used. For a source of 7 rays, 15 milligrams of radium 

 bromde was used. This was enclosed in a sealed glass tube, the latter 



-^lïas 



Figure 1 



being placed in a lead cylinder, the lead being 1 -7 mms. thick. Aj, Aj 

 represent different positions of the active material, Rj, R2 corresponding 

 positions of the radiators, Sj, 83 blocks of lead to screen the electroscope 

 E from direct radiation, L,, Lj lead plates to cut down the intensity of 

 the primary radiation and M a lead plate to test the penetrating power 

 of the scattered radiation from the radiator. The electroscope E was 

 a 14 cm. cube and all sides except the vertical sides BC and DF were 

 of iron 1 mm. thick covered by lead 2 mm. thick. The scattered rays 

 entered the electroscope through the side BC and this was closed by 

 aluminium l-60th mm. thick, and in front of the aluminium was placed 

 a carbon plate P, 2*7 cms. thick. The carbon cut off the /? rays from 

 the radiators and only a small percentage of 7 rays. The side DF 



*Sadler and Mesham, Phil. Mag., 24, p. 138, 1912. ~ 



