230 



Mr. D. C. H. Florance on 



1. The Quality of the Secondary Radiation, 

 The radiator was so placed that its centre approximately 

 coincided with the centre of rotation of the electroscope. 

 The side of the electroscope through which the rays entered 

 was an aluminium plate '202 cm. thick. The quality or 

 penetrating power of the secondary radiation was measured 

 by placing a lead screen -084 cm. against the aluminium side 

 of the electroscope and also by adding a second lead plate 

 '303 cm. thick. In Table I. are given these absorption 

 coefficients in lead for the four positions of the electroscope. 

 The emanation was screened with lead *084 cm. thick, so 

 that the primary rays consisted of a mixture of 7 rays from 

 radium B and from radium C. 



Table I. 



Radiator. 



Absorption coefficients in lead. 



Angle 43°. 



E 2 . 



Angle 70°. 



E 3 - 



Angle 103°. 



Ei- 

 Angle 127°. 



1-06 cm. zinc . 

 0'63 cm. lead . 



■084 

 cm. 



•303 

 cm. 



•084 

 cm. 



•303 

 cm. 



•084 

 cm. 



•303 

 cm. 



•084 

 cm. 



•303 

 cm. 



! 



2-70 



T75 



4-20 



2-5 



2-6 

 1-7 



! 65 



9-2 



4-8 

 3-0 



10-6 

 11-4 



5-2 

 3-6 



The emanation was then screened with lead 1 cm. thick so 

 that the 7 rays from radium B were no longer present. The 

 absorption coefficients are measured in *084 cm. of lead and 

 the results are tabulated in Table II. 



Table II. 



Radiator. 



Absorption coefficients measured in '084 cm. lead. 



B,. 



E 2 . 



E 3 - 



E 4 - 





1-5 



•96 



34 



55 



7 5 



9-9 



0"63 cm. lead 



2-2 



5-5 



These values confirm and extend the results already 

 obtained by the writer, that the penetrating power of the 



