On the ionisation potentials of magnesium and other metals, and on their absorption spectra

In a paper recently published by the writer, on the single-line spectrum of magnesium, experiments were described in which it was found that when magnesium vapour in a vacuum was bombarded by electrons it was possible if the electrons possessed the requiste amount of kinetic energy to cause the vapour to emit a radiation consisting of the single spectral line λ = 2852.22 Å. U. At the time these experiments were made and the paper was written it was not known by the author whether this line was the first member of the series whose frequencies are given byν = (1.5, S) - (m, p 2 ), or of the series whose frequencies are represented byν = (1.5, S) - (m , P). Since the single line spectra of mercury, zinc and cadmium consisted of the single spectral line whose frequency is given byν = (1.5, S) - (2,p 2 ), it was assumed that the line λ = 2852.22 Å. U. also had a frequency represented by this formula. On the basis of this assumption it was deduced from well-known data regarding the magnesium series spectra that the wave-length of the line whose frequency isν = (1.5, S) - (2, P) should be approximately λ = 2073.36 Å. U. As in some experiments made by the writer, in collaboration with Mr. Evan Edwards, it had been shown that the absorption spectra of the vapours of mercury, zinc, and cadmium consisted of bands at lines whose frequencies were given byν = (1.5, S) - (2,p 2 ), andν = (1.5, S) - (2, P), it was expected that the absorption spectrum of magnesium vapour would also exhibit bands at λ = 2852.22 Å. U. and λ = 2073.36 Å. U.