252 



Dr. E. S. Willows on the Effect of a 



equivalent to 1 mm. ; the ordinates measured upwards show 

 the percentage decrease in current produced by the action of 

 the field. 



In a tube in which the electrodes were a disk and a point 

 it was found that the results obtained were slightly different 

 according to which was the cathode. This was the case only 

 when the field was produced at some distance from the 

 cathode, and provided the magnet did not produce marked dif- 

 ferences in the appearance of the discharge in the two cases,, 

 as sometimes happened, when further differences were noted. 



No matter what the shape of the electrode, if the current 

 through the tube was feeble (less than about 15 gal. divisions, 

 one division representing 2*5 x 10~ 5 amperes) then the mag- 

 net stopped the discharge altogether at pressures below 

 •1 mm 



With currents so strong that the discharge was not stopped, 

 then at low pressures the magnetic field caused a large 

 increase in current when the cathode was a point. With a 

 disk-cathode two cases appeared according to the appearance 

 of the discharge. 



Fi<r. 2. 



*N 



+ <5*<f 



D-e-ii 



[Bright part of B going 

 to back of cathode.] 



'I'lll'lr 



•i' " 



m 



Small + ve glo\ 



A. Faint violet glow gradually 

 merging into B. 



B. Reddish violet stronger than A. 



0. Dark space, 14 mm., hazy 

 violet. 



The appearance of the tube at about '2 mm. was as shown 

 in fig. 2, when no magnetic field was on. Going round the 

 cathode from the reddish violet light B was a small band of 

 stronger and redder light D, otherwise the tube was nearly 

 filled with negative glow, shading away from reddish violet at 

 B to a very faint violet at A. 



When the magnet was put on there was a large increase 

 in current if D did not disappear, and the whole tube was 

 filled with a brilliant light, most of which came from the 

 positive column which the field caused to appear, while the 

 remainder appeared to come from the reddish violet light B 



