A study of the presence or absence of nitrogen bands in the auroral spectrum

Abstract
In a previous paper I showed that the negative, bands of nitrogen were actually stronger than the green aurora line on the occasion of the auroral display of May 13-14, 1921, which was a typical aurora, in the sense that it was accompanied by conspicuous solar and magnetic disturbance. In contrast with this, the nitrogen bands were not observed at all in the numerous photographs which showed the green line in the night sky on ordinary nights in the south of England. The point deserved much closer scrutiny, as it might be expected to throw light on whether the ordinary night sky effect was to be classed with the northern lights or not. To get additional evidence, I proceeded to Shetland in mid-October, 1921. Dr. G. C. Simpson, F. R. S., and Dr. A. Crichton Mitchell very kindly gave me facilities for working at the meteorological observatory near Lerwick, and Mr. J. Crichton, the officer in charge, did everything possible to help, and continued the exposures throughout the winter after 1 had left. Indeed, all the most successful photographs were taken by him, and forwarded to me for discussion.

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