Prof. Owens on Thorium Radiation. 



369 



that the radiations from uranium salts are also complex, 

 consisting mainly of two kinds, one much more penetrating 

 than the other. 



For investigating the nature of thorium radiations the 

 method employed by Rutherford was used. 



A layer of thorium salt was placed on the lower plate, 

 shown in fig. 1, charged to a potential of 95 volts, and the 

 conduction-current measured. 



Successive layers of foil were then placed over the salt 

 and the current measured for each additional layer. Table II. 

 gives the result for a thick layer of thorium oxide screened 

 by successive layers of aluminium foil, each approximately 

 "0008 centim. thick. The conduction-current with no foil 

 over the active material is taken as 100. 



Table II. 

 Thorium Oxide. Thick layer. 

 Screening effect of thin Aluminium foil. 

 Plates 5 cm. apart. Low T er plate 95 volts + 



Layers of foil. 

 



Time 



of 100 div. 



in sec. 



Current. 





100 





100-0 



1 





18-2 





58-0 



•> 





268 





400 



3 





300 





270 



4 





55-0 





19-3 



5 





74-8 





14-1 









1U40 





101 



7 





1256 





8-5 



8 

 '.1 





146-0 

 173-2 





73 



6-0 



10 





1830 





5-8 



11 





196-6 





5-4 



12 





1920 





5-5 



i 



The results are expressed graphically in fig. 3. 



Table III. gives the result for a thin layer uuder similar 

 conditions, the curve is shown in fig. 4. For convenience 

 of comparison the maximum current in the latter case is also 

 taken as 100 ; the actual current for the thin layer with no 



Phil Mag. S. 5. Vol. 48. No. 293. Oct. 1899. " 2 D 



