244 Mr Chree, On some experiments on [June 1, 



regular tuft, and in his figure c the appearance of a bundle of rays 

 projecting into a dark Faraday space. In fact if in these figures 

 all to the left of the plane through the rim of the cathode were 

 removed there would be a considerable resemblance to the pheno- 

 mena illustrated by my (b) and (c) fig. 2. The principal difference 

 is that with Crookes' electrode there appears to have been a 

 Faraday space limiting a distinct and, except in the plane of 

 symmetry, thin negative glow, whereas with the H 2 S0 4 cathode 

 no such distinct Faraday space was seen. 



I would also call attention to Crookes' fig. 2, p. 643, Phil. 

 Trans., 1879, as showing a concentration of negative glow in 

 positions opposite the hollows of a corrugated cathode. 



The resemblance of the boundaries of ACB in (b) and (c) 

 fig. 2 to caustic surfaces unquestionably suggests that we may 

 have here to do with some species of emission from the surface 

 separating the liquid and gas, each element of the surface acting 

 as a source more or less independent of its neighbours. If, as 

 seems to be the case with the molecular streams 1 , the direction of 

 emission from the elements near the rim deviates more than else- 

 where from the normal to the surface, one can easily see that there 

 would be a crossing of the trajectories near the axis of the tube, 

 even close to the liquid surface. 



The sudden change noticed when the type (c) fig. 2 appeared, 

 might be accounted for by the discharge leaving at first from only 

 a portion of the liquid surface, or possibly it may be connected 

 with the rise of the small bubbles accompanying the electrolysis 

 which take some short time to reach the surface. 



The following table gives results from several series of observa- 

 tions, all data in a horizontal line being taken in immediate 

 succession with a constant rate of make and break. All the dis- 

 tances are in millimetres. Except at the highest pressures even 

 the approximate position of the upper end of the negative glow 

 could not be fixed. Such an entry as "7 +" in the column headed 

 "Distance... glow" means that the glow reached to some unde- 

 termined height above the point of the red column. In the case 

 of the H 2 S0 4 cathode all the distances were measured from the 

 rim as the most convenient starting-point. It ought to be remem- 

 bered, however, in instituting any comparisons that in the axis of 

 the tube the true liquid surface was some If mm. below the rim. 

 The negative glow in type (d) had a considerably greater curva- 

 ture than the liquid surface, so that its distance from that surface, 

 measured parallel to the axis of the tube, was least in the axis. 



1 See Goldstein, Wied. Ann. 15, 1882, pp. 254—277, specially pp. 274—5. 



