434 Royal Society : — 



form, and lastly, the clear cloud-like character of the best Torricel- 

 lian vacua. Under certain conditions the stratifications disappear, the 

 whole length of the tube being filled with luminosity ; when in this 

 state, if the outside of the tube is touched, pungent sparks can be 

 perceived ith of an inch in length, and the peculiar blue phos- 

 phorescent light, that in the ordinary state is perceptible at the 

 negative, is perceptible at both terminals, and a galvanometer shows 

 that the discharge is no longer conductive. 



After noticing the difficulty of obtaining in carbonic acid vacuum- 

 tubes precisely the same results, the author describes one experiment 

 in which moisture was purposely introduced ; in this tube the strati- 

 fied discharge was very clear and distinct. He states (and describes 

 the illustrative experiment) that under certain conditions the stratifi- 

 cations entirely disappear, the vacuum insulating the discharge. 

 Carbonic acid vacuum-tubes were prepared, into which arsenious 

 acid, iodine, bromine, pentachloride of antimony, bichloride and 

 bisulphide of carbon were severally introduced, and the results ob- 

 tained are described. 



In Torricellian vacua the author was necessarily limited in the 

 size of the glass vessels employed, but with carbonic acid this difli- 

 culty no longer exists ; in one vessel of 7 inches internal diameter, 

 the stratified discharge was observed to fill the entire space ; in 

 another, the discharges were made to pass in the middle of the vessel 

 through a small hole in the centre of a glass diaphragm. 



After many trials, the author ascertained that if the negative ter- 

 minal is covered with glass tubing (open at each end) to about -g^th 

 of an inch beyond the terminal of the wire, the stratifications are 

 destroyed. In this state the negative discharge appears to issue 

 with considerable force through the orifice ; this discharge can be 

 deflected by the magnet, and wherever it impinges, a brilliant blue 

 phosphorescent spot is perceivable, which spot is in a short time 

 sensibly heated. The author remarks that in this experiment there 

 is the appearance of a direction of a force emanating from the 

 negative. 



In some of the vacuum-tubes beyond the clear cloud-like stratifica- 

 tions, but nearer the negative terminal, several faint striae can be 

 obtained : on repeating Mr. Grove's experiment (Phil. Mag. July 

 1858), of allowing the discharge to pass between two metallic points 

 attached to the coil, the author observed that these faint striae »'«- 

 variably disappeared. 



Stratifications remarkably sensitive to induction on the approach 

 of the hand were obtained in a glass cylinder of about A\ inches dia- 

 meter, in which the wires were hermetically sealed 21 inches apart. 



From the absorption of carbonic acid by caustic potassa, not only 

 were vacua obtained far more perfect than by the Torricellian method, 

 but the process can be made so gradual as to occupy several 

 weeks, or even months, thus enabling the experimenter to examine 

 the phenomena of the stratified discharge under a variety of con- 

 ditions, several of which the author describes ; in this manner the 

 non-transferring condition for the electrical discharge in a vacuum 



