236 Mr GJiree, On some experiments on [June 1, 



bright. This is clearly a variety of the phenomena observed by 

 Goldstein and by Spottiswoode and Moulton, but it seems worth' 

 noticing as the tube GBP did not lead to an anode. The Hg. 

 column in the pump did not lead to earth, and further the 

 luminosity in BP decreased as the distance from H increased, 

 which it would hardly have done if the pump had acted as anode. 



Deposit on the tubes. 



In the tube BG containing the platinum there were two, 

 generally distinct, principal areas of deposit on the glass. When 

 the platinum had served for some time as cathode there was a 

 dense black deposit from a little above the level of the top of 

 the wire downwards, and a second less dense deposit separated 

 in general from the lower by an almost perfectly clean and 

 sharply denned area only about 1 mm. broad but extending 

 right round the tube. Roughly speaking, the upper deposit ex- 

 tended to about the highest level attained by the extremity of 

 the Faraday space, but there were traces of it further up the 

 tube. Thus the portions of the walls of this tube where the 

 deposit was thickest were precisely those where the phosphor- 

 escence was strongest ere the darkening of the glass reduced 

 its brightness. At the same time phosphorescence was con- 

 spicuous on the narrow patch of clean glass separating the two 

 principal areas of deposit, and also in the upper portion of the 

 tube FG where no deposit was seen. 



In the tube AE the permanent deposit extended in general 

 from 20 or 30 to 80 or 90 mm. above the Hg. surface, none ap- 

 pearing in the neighbourhood of E. It was nowhere so thick as 

 that on the other tube. Looking at it in strong light one could 

 see small drops of mercury scattered about, but its exact com- 

 position was not determined. There were other deposits of a 

 more temporary character near the Hg. surface. One had the 

 appearance of dew spreading up the tube for a few millimetres 

 when the Hg. was made cathode, and gradually creeping down 

 when the current was stopped, taking only a short time to dis- 

 appear. It was seen only at low pressures. In some cases 

 there was a sort of white deposit separated from the Hg. surface 

 by a clear space of a few millimetres, which increased apparently 

 as the exhaustion proceeded. On readmitting air to the tube 

 this last form of deposit in great measure disappeared. What 

 has been called above the permanent deposit had a blackish 

 colour and was but little affected by the readmission of air. 

 These deposits by obscuring the portions of the tube where the 

 Faraday and Crookes' spaces had to be looked for, increased very 

 much the difficulty of reaching final conclusions as to the existence 

 of these spaces at the lowest pressures. 



