- 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE, 



[SIXTH SERIES.] 



AUGUST 1912. 



XIX, Further Experiments on Positive Bay k 

 By Sir J. J. Thomson, OJl, FM,S* 



[Plate IX.] 



FTYHE experience gained in the Gourse of the investigations 

 JL of these rays has led to some modifications in the 

 apparatus which increase the brightness of the positive rays 

 and thereby facilitate their investigation, The following are 

 the most important changes made since the publication of my 

 paper " On a New Method of Chemical Analysis," Proc. Roy. 

 Inst, 1911. 



Shape of the front of the Cathode and its position in the 

 Twfo\---Cathodes of various shapes have been tried- — flat, 

 concave, and convex ; the best results have been obtained 

 with a cathode shaped so that its section has the form 

 represented by C in fig. 1 (p. 210). 



The tubes we use for the discharge are spherical flasks 

 about 30 Gin, in diameter, the cathode being in the neck 

 of the flask. The brightness of the rays is very much 

 affected by the extent to which the cathode projects into 

 the flask ; if the cathode either extends far into the flask 

 or is far back in the neck, the rays are comparatively 

 feeble: the best position is when the front of the cathode 

 comes nearly flush with the opening into the flask. The 



* Communicated by the Author. 

 Phil Mag. S, 6, Vol 24, No, 110, Aug, 1912. V 



