604 



In carbonic acid vacua the discharge at first appears in the form 

 of a wavy line ; it is strongly affected on the approach of a magnet 

 or by the hand, but does not generally present the stratified ap- 

 pearance ; if this be present, it is only near the positive terminal : 

 sometimes in the course of a few minutes, but often not until after 

 several days, stratifications are visible, which, as the carbonic acid 

 becomes absorbed, increase ; they subsequently assume a conical 

 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 ^-th 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 diffi- 

 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 Jj-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 



