Spectrum of Hydrogen Positive Rays. 243 



Balmer series H^ and H y (H a does not appear, as the plaies 

 used were not sensitive to the red). From this it seems 

 certain that the Balmer series is due to the hydrogen atom. 



Exhaust 



It is harder to deduce the electrical condition of the atoms 

 which are giving out this light. In the positive rays there 

 are, besides the positively charged particles, particles which 

 have become neutralized, and even some which have acquired 

 a negative charge. There are thus three kinds of particles 

 and tour types of change of state — namely, neutralization 

 of positive and negatively charged particles and the cor- 

 responding ionizations. Since these are all going on 

 simultaneously, any of these changes or conditions may he 

 the cause of the emission of light. In view, however, of the 

 excess of neutral and positively charged particles in the 

 positive rays, it seems natural to suppose that the emission 

 of the Balmer series is caused either by the neutralization of 

 the positively charged atom, or by its collisions with other 

 particles without neutralization, or by the splitting off of an 

 electron from the neutral atom. From theoretical con- 

 siderations the second is very improbable, owing to the 

 siriallness of the nucleus, whose characteristic frequencies, if 

 any, would be expected to be of an order far beyond those of 

 the visible spectrum. It would theoretically be possible to 

 decide between the other two alternatives by sweeping all the 

 charged particles out of a beam of positive rays by an electric 

 or magnetic field, and examining how the luminosity re-estab- 

 lished itself further along the beam. It would be necessary, 

 however, to separate the "resting' 3 from the "moving 3 ' 

 spectrum, as the existence of the former, due presumably to 

 the dissociation of the molecules of the gas in the observation- 

 chamber by the impact of the rays, would mask the effect. 

 Bohr's theory suggests strongly that it is the neutralization 

 which causes the emission of light, but the point cannot be 

 regarded as quite conclusively settled. In addition there is 

 the possibility (cf. the phenomenon of resonance potential) 



