April 28th, I goS?^ Proceedings. xxv 



Ordinary Meeting, April 28th, 1908. 



The President, Professor H. B. Dixon, M.A., F.R.S., in the Chair. 



The thanks of the members were voted to the donors of the 

 books upon the tables. 



Mr. Thomas Thorp, F.R.A.S., described a simple means for 

 producing the characteristic glow in insulated vacuum tubes. If 

 a vacuum tube be rubbed with the dry hand a very faint 

 phosphorescent glow is observed in the dark, but if it be covered 

 with a thin film of celluloid — say, by coating it with a solution 

 of celluloid in acetone — the glow is much more easily induced. 

 If instead of rubbing the vacuum tube itself, a glass plate coated 

 with celluloid be rubbed and the vacuum tube brought near it 

 from either side, the glow will be induced for several to and fro 

 movements of the tube. Again, if the vacuum tube be inserted 

 in a larger glass tube, the glow will be induced in like manner 

 on rubbing the latter with the dry hand, but much more 

 intensely if it has a celluloid coating. A still better effect is 

 produced if the glass itself is rubbed with a sleeve of thin 

 celluloid. Adopting the latter arrangement and securing a 

 Neon vacuum tube in its interior, the characteristic glow is very 

 pronounced and from ten to twenty distinct discharges are given 

 for each stroke of the rubber, as may be plainly seen by giving 

 the tube a sideway motion when rubbing. The Neon tube was 

 suspended at about the centre of the outer tube by means of dry 

 corks, and was not earthed in any way. The explanation 

 appears to be, that in the disturbance set up by the friction, the 

 electric field produced causes the transference of the free 

 electrons in the walls of the exhausted tube from one position to 

 another, and these by colliding with the gaseous molecules 

 having relatively long free paths, are the source of the energy 

 directly producing the glow. 



Professor F. E. Weiss, D.Sc, F.L.S., exhibited some 

 interesting botanical specimens brought by him from the Riviera, 



