1898.] on Some Neiv Studies in Cathode and Eontgen Badiations. 587 



Here, therefore, we have direct experimental evidence that in a focns 



tube, while the cathode stream of negatively electrified atoms proceeds 



at a great velocity through the centre of the bulb, the anode stream of 



positively electrified atoms returns to the cathode at a much lower 



velocity round the outside of the cathode stream. Fig. 6 shows 



approximately what probably occurs in 



a tube of the ordinary focus type, the 



direction of the two opposite streams 



of positively and negatively charged 



atoms being shown by the arrow-heads. 

 If the discharge within a focus tube 



be closely watched during the process 



of exhaustion, it will be found to alter 



as the vacuum increases. First of all, 



at a low vacuum, the cathode rays can 



be seen converging in the form of a 



cone from the concave cathode to a 



focus, and then immediately diverging 



again in another cone on the other side 



of the focus, as shown on the extreme 



left of Fig. 7. It can f ui ther be shown 



that the individual rays cross at the 



focus. As the exhaustion proceeds, 



both convergent and divergent cones, 



but especially the latter, become 



smaller and smaller, while the thread 



that joins them becomes longer and 



longer as shown in the succeeding 



sections of Fig. 7, till at last, at the 



highest vacuum at which the discharge 



will pass, the cathode rays, which are 



now very nearly invisible, appear to 



come off only from a small area at the 



centre of the cathode, and not very 



ajipreciably to diverge again after once having come together, as 



indicate! on the extreme right of the illustration. 



Now I have found that if the anti-cathode or anode upon which 

 the cathode rays impinge is made not of aluminium or of platinum as 

 usual, but of ordinary electric light carbon, the carbon becomes 

 luminescent where struck by the rays. Further, if the carbon anti- 

 cathode be so placed as to intersect either the convergent or divergent 

 cones of rays, these, instead of producing a uniform luminous patch 

 upon the carbon, produce a bright ring with a dark interior. This 

 ring becomes smaller as the vacuum is increased. It develops a 

 bright spot in the centre as exhaustion proceeds still further, and 

 finally with a still higher vacuum it closes round the spot until only 

 the spot itself is left. These effects are shown for each condition of 

 vacuum in the lower portion of Fig. 7, and I have here a tube that I 



Fig. 6. — Diiigram showing prob- 

 able circ ation of atoms in 

 a focus lube. 



