The Spectrum of Hydrogen Positive Rays. 559 



decreased from 7*18 to 1*64, -corresponding to a pressure in 

 the observation chamber of 0*035 mm. Ho-. For a given 

 potential — 20,000 volts, say, — an increase of pressure from 

 0*035 to 0'10 mm. Hg produced a diminution of the ratio 

 between moved and unmoved intensity from 3*22 to 1*24. 



Mr. Thomson has not separated moved and unmoved 

 intensity, but only drawn his conclusions from the fact 

 that under varied conditions he gets a variation of the ratio 

 between the intensity of the line-spectrum and the second 

 (band-) spectrum of hydrogen. But it follows, from what is 

 already said, that this ratio can be greatly varied as an effect 

 of variations of pressure and velocity, and with a high pressure 

 in the observation chamber and a large velocity of the rays 

 tlie second spectrum appears on the plate very prominent 

 relative to the line-spectrum, and this effect teas found under 

 conditions where no JJoppler effect of the second hydrogen 

 spectrum was to be observed. 



Now the hvdrogen spectrum given by Thomson cor- 

 responds to discharges in tubes of different form with a 

 different length of the dark space, and probably also 

 differences of pressure in the observation chamber ; and 

 there is then every reason to believe that the changes he 

 observes with regard to the ratio between the intensity of 

 the series lines and that of the many-lined spectrum may be 

 regarded only as an effect of velocity and pressure variations. 



Mr. Thomson's interpretation of his results could only 

 have any weight when it was proved that the effective 

 potential of the tube and the pressure in the observation 

 chamber were the same in both cases. 



In connexion with the question regarding the origin of 

 the moved intensity, discussed by Mr. Thomson, I should 

 like to point out that the same problem has been treated by 

 the author in the papers referred to. 



From certain observations* I was able to draw the 

 conclusion that the unmoved intensity was produced from the 

 direct bombardment of gas molecules by the positive rays. 



Further, I made experiments that showed f that at any 

 rate a considerable part of the moved intensity is produced 

 by the neutral part of the positive ray bundle, and that 

 a complete ionization is not necessary to bring a neutral 

 atom to emit light. I shall here briefly describe my experi- 

 mental arrangement, and give results of calculations which 

 I made some time ago, but which have not previously been 

 published. 



* L. Vegard, Ann. d. Phys. vol. xli. p. 638 (191:5). 



t L. Vegard, ibid, vol.xxxix. p. 162 (1912), and vol. lii. p. 86 (1917). 



