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



of being fused to the pump as it was during the other experi- 

 ments, was connected to it by some thick-walled india-rubber 

 tubing. The mode of altering the surface was simply by shaking 

 or vigorously tapping the tube. With the head of the positive 

 column from 9 to 30 mm. above the cathode, the stage at which 

 the Faraday space was most distinct, no certain change in its 

 position was observed to follow the alteration of the surface. 



The only stage of exhaustion at which a distinct effect of any 

 kind was observed was that where the Faraday space seems to 

 be in the act of disappearing. On first starting the current, 

 especially with a slow break and noisy spark, there appeared 

 more or less uniform whiteness in the cathode tube and in- 

 distinct striae in the anode tube. After the discharge had 

 passed a short time, the colour tended to fade out of a portion 

 of the cathode tube., roughly speaking, between 30 and 90 mm. 

 over the Hg. surface, and phosphorescence became much more 

 conspicuous, especially in this part of the tube ; also the striae 

 in the anode tube became more distinct. A shaking or sharp 

 tapping of the tube instantly restored the more or less uniform 

 white colour throughout the cathode tube and tended to obliterate 

 the striae in the other tube. The effect lasted only a short time, 

 the discharge gradually reverting to the appearance it presented 

 before the disturbance. This phenomenon invariably presented 

 itself under the conditions stated. The only explanation that 

 occurs to me — suggested by the views of Messrs E. Wiedemann 

 and H. Ebert — is that, at least at certain stages of exhaustion, 

 the condition at the cathode surface which leads to the pro- 

 jection of molecular streams takes some time for its full develop- 

 ment, and that on its development the successive discharges 

 follow one another more rapidly and consist each of a smaller 

 quantity of electricity. The shaking of the tube and consequent 

 distribution of fresh mercury over the cathode surface restores 

 the original conditions, which are less favourable to the production 

 of molecular streams. 



Electrodes H 2 S0 4 and Al. 



In the next set of experiments the electrode in AE was some 

 pure sulphuric acid, the aluminium plate electrode in the other 

 tube being retained. 



Some experiments with sulphuric acid electrodes have been 

 described by Paalzow 1 . He gives an interesting account of the 

 electrolysis of the acid, and of spectroscopic observations on the 

 discharge. He observed the positive discharge to start from the 

 line of separation of the fluid surface and the wall of the tube. 



1 Wied. Ann. 7, 1879, pp. 130—135. 



