10 Prof. Rutherford and Miss Brooks : Comparison of 



corresponded to two specimens of radium from P. de Haen, 

 •.-w-.n -^\t^a a nn-*^.m-k-i-»n-i-r\A }i ond " £kir>for»Vi }J respectively. JLhe 



marked " concentrated 



and " einfach 

 Kg. 3. 



Fig-. 4. 



curve for the specimen sent by Herrn Elster and Geiiel was 

 not very different from the two shown. Curves obtained 

 from specimens of the minerals " thorite " and " orangite " 

 gave practically the same curves as for thoria. 



The radiations may be arranged in the following order as 

 regards the power of penetration, beginning with the most 

 penetrating. 



Excited radiations due to Thorium and Radium : 



Thorium 

 Radium 

 Polonium 

 Uranium. 



The same order of penetration is observed for all the 



