of Hydrogen Positive Rays. 567 



of the rays. This does not explain the marked correlation 

 which I showed to exist between the ratio of the intensities 

 of the spectra, and the proportion between the atoms and 

 molecules of hydrogen in the rays as determined by direct 

 analysis. In point of fact, the difference in pressure was in 

 the reverse direction to that required for his explanation, the 

 pressure being lower during the experiments when the second 

 spectrum was obtained. While there were undoubtedly varia- 

 tions in the potential difference used in the discharge, the 

 resulting variation in energy of the rays was small compared 

 with the range in energy at any instant, which, as determined 

 from the electrostatic deflexion of the rays, was often 3 or 4 

 to 1. 



The close connexion between the two resting spectra found 

 by Prof. Vegard is to be expected on my theory as long as 

 the positive rays are all of one kind — that is, as long as there 

 is only one " moved " spectrum. They presumably corre- 

 spond, the series spectrum to dissociation with ionization 

 (partial or complete) and the second spectrum to ionization 

 only, of the gas in the observation chamber, with the sub- 

 sequent return of the electron which is the actual source of 

 the light emitted. As long as the particles forming the rays 

 were of the same nature, the ratio of the numbers of collisions 

 of these two types might be expected to be the same. 



As mentioned in my previous paper, the failure to find any 

 "moved" second spectrum is a point which needs explanation ; 

 but J still think that the use of cylindrical tubes of compara- 

 tively small diameter is largely responsible, as in similar 

 circumstances I too got a purely atomic beam of rays. 



Professor Vegard suggests no alternative theory as to the 

 nature of the carriers of the second spectrum, and the mole- 

 cular theory will seem much the most probable, especially in 

 view of the recent work of Mr. Saba *, at least until it can 

 be shown that rays which when analysed show the presence 

 of appreciable numbers of molecules give no (i moved" second 

 spectrum. 



My experiments were not such as to throw light on the 

 electric condition of the atoms which emit the series spectrum, 

 and I fully accept Professor Vegard's conclusion that light 

 is emitted both when the positively charged atom is neutralized 

 and when the neutral atom collides with the molecules of the 



gas. 



Yours faithfully, 



Corpus Ohristi College, Gr. P. THOMSON, M.A. 



Cambridge. 



* Phil. Mag. June 1S20. 



2P2 



