An investigation into the Nature and occurrence of the auroral Green line λ 5577 Å

The wave-length at 5577 Å, which is the most prominent line in the spectrum of the auroral light, and which is the characteristic line of the spectrum of the light from the night sky, has been the subject of extensive research. Its wavelength has been measured very accurately by Babcock* and has been found to be 5577·350 ± 0·005 Å. In 1923 Prof. Vegard,f in Norway, put forward the view that the line had its origin in the luminescence of solid nitrogen suspended in a state of fine division in the upper atmosphere, but that view, in the light of a rigid investigation, has been found to be untenable. In 1925 McLennan and ShrumJ announced that they had been able to obtain a green spectral line at λ 5577 Å from the electrical discharge in a tube containing a mixture of helium and oxygen, and that its wave-length agreed with that found by Babcock for the line in the spectrum of the night sky. Later they obtained it quite strongly in a mixture of neon and oxygen, and in addition they found at a still later time that it could be observed faintly in the spectrum of the electrical discharge in low pressure oxygen presumably pure. During the past year we have been engaged in a research to elucidate further the nature of this elusive radiation at λ 5577 Å, and to locate more definitely its origin and mode of occurrence.