Manchester Meuioirs, Vol. liv. (1909), No. %. 



V. The Action of the a Rays on Glass. 



By Professor E. RUTHERFORD, F.R.S. 



Received and read November joth, rgog. 



It has been shown by Joly that the pleochroic halos 

 observed in mica are to be ascribed to the action on the 

 mica of the a rays emitted by small inclusions of radio- 

 active material. The radius of the halo (about '04 mm.) 

 indicates that the effect is due in large part to the rays 

 from radium. I have recently reproduced the conditions 

 under which such halos would be formed by enclosing a 

 large quantity of radium emanation in a fine capillary 

 tube of soda glass. After the emanation had decayed, 

 the inner wall of the capillary was seen under the micro- 

 scope to be surrounded by an area of distinct colouration 

 extending about 04 millimetre from the walls. The 

 outer boundary of the coloured region was sharply 

 defined, and the depth of the colouration was equivalent 

 to the maximum distance of the most penetrating a par- 

 ticle from the active matter. This result strongly 

 confirms the correctness of the explanation of halos 

 given by Joly. 



December 24th, igog. 



