588 



Mr. Alan A. Campbell Sivinton 



[Feb. 4, 



will put into action and show the effect for one degree of vacuum. 

 As you observe, the luminescence on the carbon is very bright, in fact 

 the surface appears white hot. It, however, takes the shape of a well 

 defined hollow ring with a dark interior and a bright spot at tlie 

 centre, and as I deflect the stream of cathode rays with a magnet, the 

 ring also moves with no perceptible lag, being at the same time 

 somewhat deformed, but still retaining its hollow character. 



By means of a tube in which the carbon anti-cathode is connected 

 to the positive terminal by sliding connections, and can be caused to 

 move along the tube so as to intersect either the convergent or di- 



f 



t 



,v^^^ 



@ 



-Appearance and efiect of the cathode rays in a focus tube at four 

 diffennt degrees of exhaustion. 



vergent cones at any desired point, it can be shown that with cathodes 

 of considerable concavity, both the convergent and divergent cones 

 of cathode rays are never solid but always more or less hollow in 

 section. 



Now, how can this remarkable effect be explained ? Perhaj^s the 

 most satisfiictory explanation is that suggested by Professor G. F. 

 Fitzgerald, which accords with the Crookes theory of cathode rays, 

 and also with what I have already mentioned as to the anode stream 

 of positively charged atoms returning to the cathode outside of the 

 cathode stream 2)assing in the opj^osite direction. If we return to 

 Fig. G, it is evident that the supply of atoms to the active cathode 



