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VII. On Phenomena Relating to the Spectra of Hydrogen and Helium. 
By T. R. Merton, D.Sc. ( Oxon ), Lecturer in Spectroscopy, University of London, 
King's College, and J. W. Nicholson, M.A., D.Sc., Professor of Mathematics 
in the University of London. 
Communicated hy Prof. A. Fowler, F.R.S. 
[Plates 2 and 3.] 
Received June 16,—Read June 29, 1916. 
Contents. 
Section 
(I.) Introductory. 
(II.) Methods of measurement. 
(III.) Determination of the photographic intensities of lines. 
(IV.) The density of the wedge as a function of wave-length. 
(V.) Determination of the intensities of lines in terms of the intensity of the radiation from 
the positive crater of the carbon arc. 
(YI.) The energy in an emission line. 
(VII.) The Helium spectrum under different conditions. 
(VIII.) Transfer of energy in the Hydrogen spectrum.•. 
(IX.) The spectrum of Neon. 
(X.) Photographic intensities in the carbon arc. 
(XI.) Relative intensities of Helium lines on an absolute scale. 
(XII.) The nature of the Balmer series. 
(XIII.) Theoretical considerations on the basis of the quantum theory. 
(XIV.) The Lummer Gehrcke plate. 
(XV.) The law of intensity distribution in a line excited by the ordinary discharge . . . . 
(XVI.) Isolation of components of a line. 
(XVII.) Separation of the components of H a . 
(XVIII.) The structure of H^. 
(XIX.) Discussion of results. 
(XX.) Summary. 
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(I.) Lntroductory. 
In recent years the spectra of Hydrogen and Helium have been perhaps more closely 
studied than those of any other element, owing partly to the importance of these 
substances in celestial bodies, and partly to the supposed simplicity of their atoms 
YOL. CCXVII.-A 555. 2 L [Published August 11, 1917. 
