1891.] 



liquid electrodes in vacuum tubes. 



245 



Table V. 



Crookes' space 



^__ X 



Type Height 

 above 

 rim. 



(a) 



(b) 



C°) 



(d) 



(d) 



(d) 

 (d) 



H 2 S0 4 cathode 



Distance 

 above 

 rim of 

 top of 



negative 

 glow. 



4 



6 



7 + 

 7 + 

 13 

 10 + 

 13 + 

 15 + 



Al. cathode 



1-5 

 1-5 



2 

 2-5 



17 + 



18 + 

 24 + 

 30 + 



Distance 



above 



rim of 



head of 



positive 



discharge. 



5 



6 



7 



7 



10 

 10 

 13 

 15 

 absent 

 absent 

 17 

 18 

 24 

 30 



Length 



of 



Crookes' 



space. 



Distance 



above 



cathode 



of top of 



negative 



glow. 



17 



2-5 

 4 



4'5 



5 



5 



7 

 8 



23 



Distance 

 above 



cathode 

 of head of 



positive 

 discharge. 



11 



17 

 19 

 22 



29 



40 

 38 



dubious 



50 

 dubious 

 dubious 



None of the distances admitted of very accurate observation 

 because the positions of the various parts of the discharge, especially 

 the head of the positive column over an Al. cathode, were seldom 

 quite stationary. At the lower pressures in the table the blue 

 light surrounding the red column over an H 2 S0 4 cathode extended 

 up the tube AE to above the level of the horizontal tube. When, 

 however, the interrupter was adjusted to give a slower and more 

 noisy spark the red column sometimes completely disappeared. 

 It also sometimes faded out when the discharge was kept passing 

 for some time. In either case there appeared from about 20 to 

 40 mm. above the H 2 S0 4 cathode a considerably darker blue than 

 elsewhere verging towards black. This darker band always accom- 

 panied the types (6) and (c) of discharge with which the red 

 column was not observed. Once or twice this column instead of 

 being red w r as white. In general its outline appeared straight and 

 regular, but on at least one occasion it showed numerous short 

 horizontal projections like hairs. 



The colour of the positive column at the higher pressures and 

 until the Crookes' space over the Al. cathode attained a length of 

 1 or 2 mm. was always red. At lower pressures when red its 

 colour was much fainter, and at the lowest pressures it generally 

 tended to white or even blue. The striae were most conspicuous 

 when the colour w r as white, but they were seldom very distinct. 

 At the lowest pressures only faint phosphorescence was observed in 



19—2 



