The spectrum of helium has been very carefully studied by Runge and Paschen.
The careful measurements of Kayser and Runge of the carbon bands show that the successive differences in the frequencies do (1900), I, p. 399.
The question has been fully discussed by C. Runge in the second volume of Kayser's Handbuch (see also Magneto-Optics), and we may therefore content ourselves with the mention of the law discovered by Th.
Preston that all the lines of the same series show identical effects when measured on the frequency scale, arfrl the fact recently announced by Runge 3 that even in the more complicated cases mentioned some simple relation between the distances of the components exists.
Runge and F.