is the same constant as in the Balmer spectrum of hydrogen. From analogy with the Balmer- and Pickering-spectra, Nicholson has suggested that the lines in question are due to hydrogen.
It is seen that the lines discussed by Nicholson are given by the above formula if we put
. The lines in question correspond to
; if we for
put
, we get lines coinciding with lines of the ordinary Balmer-spectrum of hydrogen. If we in the above formula put