X. Bakerian Lecture.— On the Spectrum of Hydrogen. 
By T. B. Merton, D.Sc., F.R.S., Professor of Spectroscopy in the University of Oxford, 
and S. Barratt, B.A., Balliol College, Oxford. 
Received January 13,—Read March 9, 1922. 
[Plate 3.] 
Contents. 
Section Page. 
(1) Introductory.369 
(2) Experimental..373 
(3) Wave-length Measurements.373 
(4) The Continuous Spectrum.376 
(5) The Classification of the Lines.376 
(6) Comparison of the Secondary Hydrogen Spectrum with the Solar Spectrum.378 
(7) The Widths of Spectrum Lines.378 
(8) Theoretical .380 
(9) Experimental Results.381 
(10) The Separation of Gases in Vacuum Tubes.383 
(11) On Impurities in Vacuum Tubes .386 
(12) Summary.387 
(13) Tables of Wave-lengths and Wave-numbers .388 
(1) Introductory. 
Modern theoretical investigations have met with signal success in providing an explana¬ 
tion for the production of the primary spectrum of Hydrogen, generally known as the 
Balmer series, but the many-lined or secondary spectrum has hitherto proved to be a 
much more formidable problem. There can be little doubt that a completely satis¬ 
factory explanation of its genesis will mark an important step in our knowledge oi 
the origin of spectra. The detection of regularities amongst such a vast number of lines 
is in itself an exceedingly difficult task, and one for which it is essential that the data 
relating to wave-lengths should be accurate and complete. 
Although some of the early investigators were of the opinion that the secondary 
spectrum was to be referred to impurities in the discharge tube, it is now generally 
VOL. CCXXII.—A 603. 3 F [Published April 27, 1922. 
