602 



Mr. S. Oba on the 



concluded that in the scattering of 7 rays, the rays undergo 

 a change in quality, becoming softer on scattering. The 

 object of the present experiments was to try to investigate 

 whether or not 7 rays are changed in their quality by passing- 

 through matter. For this purpose the absorption by alu- 

 minium and iron was determined both for the primary 7 rays 

 of radium and for the rays after passage through different 

 thicknesses of hardening materials such as copper, tin, and 

 lead, since it is known that these metals apparently decrease 

 the absorption coefficient in aluminium of 7 rays which have 

 passed through them. 



The experimental arrangement is shown in fig. 1. The 



-Fig. 1. 

 /?/i. Em. 



Hardener. 



Absorber. 



7 rays from the source of radium emanation in equilibrium 

 with its products passed through the hardener and the 

 absorber, aluminium or iron, and into the electroscope below. 

 The radium emanation was enclosed in a small glass tube, 

 and was suspended by strings 50 cm. above the middle of 

 the electroscope. It could therefore be considered as a 

 point source, and practically no correction was necessary 

 for the oblique passage of the rays through the absorption- 

 sheets. The absorbers and hardeners consisted of plates of 

 equal size, 20 cm. square, projecting 4 cm. beyond the side 

 walls of the electroscope. The hardeners were placed so as 

 to rest on the absorber. The top of the electroscope was 



