.346 Mr. J. B. B. Burke on the 



In connexion with this point it may be noticed that 

 P. Lewis, in a paper in Wied. Ann. July 1900, has suggested 

 that the phosphorescence produced by the discharge may be 

 due to an effect on the glass and not in the gas, since if 

 •a portion of the glass tube be heated it ceases to shine, and 

 the phosphorescence appears again when the discharge is 

 sent, as soon as the glass has cooled down. Bat it is well 

 known that phosphorescence of many substances is destroyed 

 by heating ; for as Becquerel has shown they then give out 

 the energy, that has been stored up in them, with greater 

 intensity, and therefore in a shorter time. The same may 

 be expected to occur in a gas when it is brought in contact 

 with the hot surface of the glass. A similar effect was 

 observed by J. J. Thomson (loc. cit.), but he attributed it to 

 a chemical change produced in the gas by heating the tube. 

 Moreover, the phosphorescence also depends upon the nature 

 of the gas in the tube (see Art. (8)), so that, bearing these 

 various points in mind, namely that the glow can travel down 

 brass tubes with the same facility as along glass ones ; that 

 phosphorescent jets may be produced ; and finally that the 

 phosphorescence depends upon the nature of the gas, there is 

 conclusive evidence that the phosphorescence is a volume- 

 effect in the gas. 



However, the phosphorescent molecules in the gas may 

 have an attraction for the walls of the tube so that there may 

 be a concentration of phosphorescent gas near the surface of 

 the glass, notwithstanding the facts that have already been 

 adduced, showing that the phosphorescence is a volume-effect : 

 for it is by no means necessary that the distribution of phos- 

 phorescent molecules throughout the gas should be uniform; 

 and this is the only explanation, that appears satisfactory, 

 of the effect described on page 345, that the glow does not 

 travel down the tube except w T ith great difficulty when the 

 latter projects into the bulb a few cms. : and since the glow is a 

 volume-effect in the gas, what must happen is that the greater 

 number of the phosphorescent molecules glide along close to 

 the walls of the tube, although they can exist quite apart from 

 the walls and be blown about in a stream of gas, or in a jet. 



(4) It can be shown that the glow is not the result of 

 recombination of ions, produced by the spark, as these travel 

 down the tube. Thus the tube in fig. 2 had a number of 

 wire -gauze electrodes 1, 2, 3, along it The electrodes 

 were circular pieces of wire-gauze and fitted closely into 

 the tube. When these were connected to a terminal of a 

 Wimshurst, it was found that the glow still travelled down the 

 tube every time the ring-discharge passed in the bulb, quite 



