Action of the a. Rays on Glass. 



195 



A reddish coloured area was seen to surround the whole 

 length of the capillary. The line of demarcation o£ the 

 coloured area from the almost colourless outside glass was 

 quite sharp. The distance from the edge of the capillary 

 bore to the edge of the altered area was equal in all parts of 

 the tube, notwithstanding wide variations in the bore of the 

 capillary along its length. The altered area was most marked 

 near the end of the capillary where the emanation had been 

 most concentrated, but was appreciable along the whole tube. 

 The effect observed will be clearly understood from the 

 accompanying photograph of the end part of the capillary 



1 



** I 



1 





• 



■ 

 ■ 



' 



; 



* 





E 



ACB 



F 



C, bore of capillary : A. B, edg-es of coloured are* 

 i], L\ external walls of capillary. 



tube. The magnification may be judged from the fact that 

 the external diameter of the capillary tube shown in the 

 photograph was at its middle point about '6 mm. This 

 micro-photograph was kindly taken for me by Dr. Stansfield 

 by immersing the end of the capillary tube in glycerine, 

 and using a point source of light. 



It will be seen that the depth of the darkening measured 

 Phil. Mag. S. 6. Vol. 19. No. 109. Jan. 1910. 



