1891.] liquid electrodes in vacuum tubes. 241 



As I hardly follow his description of the appearances at the 

 cathode I give his own words : " Von der negativen Fliissigkeits- 

 oberflache selbst erhebt sich in einigem Abstande von derselben 

 ein schwach conischer Lichtring, ahnlich wie die Flamme eines 

 ringformigen Brenners," p. 131. With increasing exhaustion : 

 " um so mehr verlangert sich dieser negative Lichtcylinder, und 

 ura so grosser wird sein Abstand von der Flrissigkeitsober- 

 flache," p. 132. At very low pressures he observed the pheno- 

 mena to be much the same at both electrodes. 



In this case my observations commenced as soon as the 

 pressure was sufficiently reduced for the discharge to become 

 visible in a dim light. This invariably occurred when the alu- 

 minium was cathode, and the luminosity took the form of a 

 thin purplish negative glow. At somewhat lower pressures the 

 Al. tube was fairly luminous whether it contained the cathode 

 or anode, the H 2 S0 4 surface when cathode showing a thin blue 

 glow. The horizontal tube and a small portion of the tube AE 

 below D then showed a red spark discharge. The greater portion 

 of the latter tube remained however dark, except that at in- 

 tervals red twig-like discharges passed down it. At this stage 

 the spark in the tube DF was most twig-like and of least diameter 

 at that end which was nearest the cathode, whether Al. or H 2 S0 4 . 

 The pressure had to be further reduced to a considerable extent 

 before luminosity could be detected at the H 2 S0 4 surface when 

 anode. When the discharge was first clearly seen at an H 2 S0 4 

 anode it took the form observed at pretty low pressures with 

 an Hg. anode. Throughout the greater portion of the tube the 

 positive column appeared as a solid cylinder of considerably less 

 diameter than the interior of the tube, but near its base this 

 cylinder increased in diameter so as just to fill the tube on 

 reaching the liquid surface. 



At this stage the appearance in the tube AE over an H 2 S0 4 

 cathode took the following form. A column of very small 

 diameter, usually bright red in colour, extended down the axis of 

 the tube to within a short distance of the liquid surface. The 

 end of this column was sometimes truncated, but frequently it 

 presented a sharp point like that of a pencil. Over the liquid 

 surface, completely occupying the cross-section of the tube, there 

 existed the ordinary blue negative glow. At first this was sepa- 

 rated by several millimetres of a dark, presumably Faraday, space 

 from the red column, but as the exhaustion proceeded while the 

 head of the column retired from the H 2 S0 4 surface the negative 

 glow overtook it. With progressing exhaustion the point and a 

 gradually increasing length of the red column were immersed in 

 the blue glow. The difference in colour rendered the red column 

 conspicuous through the blue glow, but I am unable to say 



