278 DR. MERTON AND PROF. NICHOLSON ON PHENOMENA OF HYDROGEN AND HELIUM. 
2. A study has been made of the relative intensity distribution in the spectra of 
Helium and Hydrogen under different conditions of excitation. 
3. It has been found that under certain specified conditions there is a transfer of 
energy from the longer to the shorter wave-lengths in any given series, and that 
under such conditions the associated series, and in particular the Diffuse series, are 
relatively enhanced at the expense of the Principal series. 
4. It has also been found that the distribution of intensity found in certain celestial 
spectra can be approximately reproduced in the laboratory. 
5. A study has been made of the separations of the components of lines of the 
Balmer series of Hydrogen, and the mean values of the separations of the doublets 
constituting the lines H a and H^ have been found to be respectively 0'132 A.U.,and 
o 
0’033 A.U. These values are consistent with the separations appropriate to Principal 
series, and the first is in precise agreement with the value deduced by Buisson and 
Fabry. 
Note on the Band Spectrum of Helium .—We have made a number of observations 
of the pinkish glow which surrounds the cathode in a Helium tube excited by the 
ordinary discharge. The cathode glow in Helium presents a very striking appearance 
when viewed through coloured screens which transmit only a narrow region of the 
spectrum. Through a violet screen the dark space around the electrode is clearly 
defined and surrounded by a uniform glow. Viewed through a screen which transmits 
red rays only, the appearance is entirely changed, the “ dark space ” being in fact the 
region in which the red rays are predominant. The band spectrum of Helium is 
relatively strong in the cathode glow, though not intrinsically so strong as with the 
“ bulb discharge In this connection we may mention that we have definite 
evidence from the relative intensities of the bands in the “bulb discharge ” and the 
cathode glow that this spectrum is capable of sub-division. Apart from theoretical 
considerations, this circumstance may be of importance in modifying the conclusion 
that the spectrum in question is absent from celestial spectra. 
* Curtis, ‘Roy. Soc. Proc.,’ A, vol. 89, p. 146, 1913. 
fRESE.UEB 
O SEP.1S17 
