, and let
vary, we get a series which includes
of the series observed by Fowler, and denoted by him as the first and second principal series of the hydrogen spectrum. If we put
, we get the series observed by Pickering in the spectrum of
Puppis. Every second of the lines in this series is identical with a line in the Balmer series of the hydrogen spectrum; the presence of hydrogen in the star in question may therefore account for the fact that these lines are of a greater intensity than the rest of the lines in the series. The series is also observed in the experiments of Fowler, and denoted in his paper as the Sharp series of the hydrogen spectrum. If we finally in the above formula put
