Radiation f rem Substances of Low Atomic Weight. 143 



than the normal iron radiation. We must conclude, there- 

 fore, that if other homogeneous components coexist with the 

 normal in the radiation from iron, they form relatively un- 

 important parts of the whole. If, therefore, the softened 

 character of the radiation from carbon is to be explained in 

 terms of the soft residual component of the beams from iron, 

 copper, &c, we must assume that a substance like carbon is 

 a much more efficient scatterer for soft radiation than for 

 hard, especially as the softening effect becomes more pro- 

 nounced when the hard exciting beams are used. In order 

 to test this point, we used the secondary radiation from tin, 

 which is known to consist of a very penetrating radiation, 

 together with a component of appreciable intensity of a much 

 softer type. If this latter is scattered to a greater extent by 

 the carbon than the former, then since, if the secondary 

 beam from tin is cut down by plates of aluminium before 

 falling on the tertiary radiator, the soft radiation in the 

 secondary beam disappears first, we should get a correspond- 

 ingly rapid diminution in the intensity of the tertiary. Tho 

 results of such an experiment are given in Table II. 



Table II. 



-r, , ,. , , Intensity of tertiary radiation „ 



lielative value or ? tor 



„ „ secondary „ 



Tin radiation on Carbon. 



Substance in 



path of sec. 



beam. 



Deflexion 

 of primary 

 electroscope. 



Deflexion 



of tertiary 



electroscope. 



Deflexion | 

 of secondary 

 electroscope. 



Prim. 



Sec] 



Ter. 

 Prim. 



Ter. 



Sec. 





43-0 





10 









nil 



460 1 



44-8 J 



43-8 



10 



10 



4 34 



•220 



•956 





55-1 





10 









•01 cm. Al 



45-2 1 



44-7 j 



10 





5-43 



•222 



1-20 





53-5 





10 









•02 cm. Al 



58-0 



44-8 

 45-8 



58-7 



10 



10 



10 



513 i 221 



•03 cm. Al 



6P0 



47-01 



47-8 j 



60-4 



10 



10 



10 



6-07 



•211 



1-29 



1-26 



