[ROBERTSON] ELECTRODELESS DISCHARGE 155 



tion is tolerably strong and it may be that in them is found the origin 

 of a portion of the secondary. But the problem is far from solution 

 and one can only make suggestions and continue observations. 



In regard to another point it has been difficult to give any ex- 

 planation. It has been stated above that the red discharge (showing 

 the Balmer lines relatively strongly developed) formed the inner 

 portion of the discharge ring, the outer being pink. Now the ex- 

 pression^ from which one may calculate the value of the electric 

 intensity at any point within a coil of co-planar turns shows that the 

 field is weaker nearer the centre of the coil. (Conditions, of course, 

 are altered when a discharge takes place in the gas, but one may 

 reasonably expect that the discharge region would have a shielding 

 effect and, therefore, if anything, still further weaken the field at the 

 centre.) Why is it, then, that the red discharge, which is evidence 

 of an "excess of atomic hydrogen, is on the inner portion of the ring? 

 The question is all the more puzzling because in iodine, as noted 

 above, the reverse was the case. The inner portion of the ring showed 

 the lines less strongly developed as one would expect to be the case 

 in the weaker field. The writer has no explanation to offer. It 

 looks as if the walls of the bulb for some reason either made it easier 

 for atoms to re-combine or made dissociation more difficult.* In this 

 connection it is interesting to note that in Professor Wood's^ paper 

 on the spectra of hydrogen in long vacuum tubes a condition is de- 

 scribed in which the tube showed a red discharge at the centre with 

 a whitish appearance at the ends. There may, however, be no 

 connection between the two cases. 



The writer has under way further work and hopes to obtain 

 more conclusive evidence regarding some of the questions raised. 



Queen's University. , 



June 8, 1922. 



*Berge.n Davis, loc. cit. 



«R. W. Wood, Phil. Mag., Nov., 1921, p. 729. 



*Note added September 14th, 1922:— 



During the summer I have learned that according to Langmuir, there is much 

 evidence to support the view that glass acts as a catalyser in promoting the com- 

 bination of hydrogen atoms into molecules. 



