Lecture Course. 223 



At the conclusion of the evening a hearty vote of thanks 

 was unanimously accorded to the Ottawa Electric Company for 

 supylying gratis electric current, wires, etc., during the evening. 

 To Mr. Wm. Scott and Mr. A. Dion especially, are the thanks 

 of the members of the two societies due for their great kindness 

 and interest in the matter. 



November 27TH, 1896, Ottawa Teachers' Association. — 

 Electrical Discharges in High Vacua,'' by Prof John Cox, 

 M.A., F.R.S.C, of the Physics Laboratories, McGill 

 University, Montreal. 



Professor Cox began by showing the insulating power of 

 dry air and the disruptive discharges which occurs when the 

 terminals are approached to a minimum distance. He then 

 caused the same discharge to take place in sealed tubes from 

 which the air had been exhausted in varying degrees, and 

 demonstrated Quet's observations upon the stratification of the 

 medium. He referred to the fact that De la Rue has proved by 

 the uniformity of potential that even in highly attenuated air 

 the discharge is a disruptive one, and that at no degree of 

 exhaustion is air a condnctor. The striae were shown in a large 

 number of Geissler tubes containing various gases highly rarified. 

 All the strata appear to start from the positive pole, and as they 

 successively detach themselves from it they occupy very con- 

 stant positions relatively. The potential necessary to cause a 

 current to pass (disruptively) diminishes until a certain attenua- 

 tion is reached, when it increases and the strata thicken and 

 diminish in number until no discharge passes, however high be 

 be the potential. The colours are reversed in order by reversing 

 the direction of the current. All these experiments were made 

 in tubes which, are highly rarified, still were far from perfectly 

 vacuous. Dr. Crookes was the first to carry the exhaustion of 

 tubes to a degree approaching perfect vacuum In this case the 

 stratification ceases, and a bluish light fills the entire tube. 

 When the vacuum approaches perfection the light proceeds from 



