242 



Mr Ghree, On some experiments on 



[June 1, 



whether the two were actually in contact. Possibly they may 

 have been separated by a thin hollow conical dark space. 



At this stage the tube containing an Al. cathode showed a 

 positive column whose diameter was several times greater than 

 that of the column just described. Further, the head of the 

 positive column over an Al. cathode had the usual convexity, and 

 was separated by a distinct Faraday space from the negative glow. 

 As the exhaustion proceeded an ordinary Crookes' space appeared 

 over an Al. cathode, and the other phenomena seemed of the usual 

 type. Over an H 2 S0 4 cathode, however, the phenomena seemed 

 of an exceptional kind. 



The liquid surface was of course concave, the depression of 

 the vertex below the rim being about If mm. Thus on looking 

 sideways at the tube one saw a curved dark line answering to 

 a vertical section of the liquid surface. Between this and the 

 horizontal plane through the rim of the surface there appeared 

 a blue tint. This might have proceeded from a luminous film 

 over the liquid surface or merely from the reflexion of the glow 

 further up the tube. Now supposing a Crookes' space to exist, 

 the surface separating it from the negative glow would by analogy 

 from other cases be expected to resemble in form the liquid 

 surface. Thus so long as the thickness of this space was less than 

 the sagitta of the liquid meniscus, one would have expected the 

 blue negative glow to pass near the axis of the tube into the 

 blue of the liquid surface, while close to each of the tube walls 

 one would look for a dark space shaped like a right-angled 

 triangle, with a curved hypothenuse answering to the surface 

 of the negative glow. Let us call this type (a). An idea of 



(6) 



C 



I) 



(<0 



C 



Fig. 2. 



B 



E 



it will be easily derived from (b), fig. 2, by supposing ACB non- 

 existent. The spaces HAD and KBE are to be supposed black, 

 while below DABE and above HABK blue prevails for some 

 distance. DABE represents the liquid rim cutting the surface 

 HABK of the negative glow in the straight line AB. At lower 

 pressures one would have expected to see the length AB 

 gradually diminish, till finally there appeared over the whole 



