1891.] 



liquid electrodes in vacuum tubes. 



231 



constant. For one of the vertical tubes, say AE, the distance 

 of D above the electrode was 170 mm. of which the lowest 

 100 mm. was of uniform diameter, 13"5 mm. externally. Above 

 this the tube narrowed for some 12 mm. and then continued of 



uniform external diameter 8 mm. up to E at 250 mm. above 

 the electrode. The horizontal tube DF had an external diameter 

 of 6 mm. and a total length of 160 mm. Thus the total distance 

 between the electrodes was about 50 cm. These measurements 

 were not made with any great exactness and the surfaces of the 

 electrodes were not kept at a perfectly constant level. The 

 tube CHP led to the mercury pump, GH being vertical, and 

 HP parallel to DF. This tube was of about the same diameter 

 asDE. 



Supposing the tube AD to have a liquid electrode, this was 

 connected with the exterior by a fine wire whose top was about 

 1 cm. below the liquid surface, and which passed down air-tight 

 through the bottom of the tube. 



The point to which Professor Thomson originally directed my 

 attention was the question whether there was any change in- 

 troduced in the liquid surface by the discharge which altered 

 the subsequent character of the luminous appearances. As my 

 results on this point are intelligible only when the form of the 

 discharge has been described, their discussion is postponed to a 

 later part of the paper. 



There were three sets of experiments on mercury. In the 

 first both electrodes were mercury surfaces ; in the second one 

 was mercury, and the other an uncovered platinum wire ex- 

 tending some 2 cm. up the axis of one vertical tube ; in the 

 third set the platinum wire was replaced by a flat horizontal 



