Note on Vegard's theory of the aurora

Prof. Vegard has recently published in considerable detail his theory of upper atmosphere, according to which, above the ordinary atmosphere, there is an extensive region of frozen nitrogen dust. He claims that this explains the heights at which auroræ are said to be observed, and it has also him to experiments which have given what he is provisionally content regard as a laboratory source for the green auroral line at 5578 Å, in solid nitrogen. It is the purpose of this paper to show that his theory is inadequate the purpose for which it is designed, impossible thermodynamically, not ally supported by his laboratory experiments, and finally not even necessary, ce it is not difficult to devise alternatives, free in varying degrees from his ore questionable assumptions, which do account more or less for observation without introducing any difficulties that he avoids. It will also be shown that otographs of the spectrum of gaseous oxygen, excited under peculiar contions, have been obtained which indicate a possibility that 5578 may really due to this element (a result that has already been suspected by some ysicists), but even if this is disproved these photographs at least surpass appearance those of Vegard, even if reproduced on a larger scale than he nployed. The essential points of Vegard’s theory are as follows:—Auroræ are said be observed up to 600 or 700 km. height. (The evidence for this is not at present available here, and may be unexceptionable, but one can imagine that the difficulties of observation are considerable.) No gas can reasonably be supposed to rise to such a height unless it is helped by an electric force. A large of one electron per molecule would result in too high a volume-charge. Therefore, the molecules must be grouped in clusters; this can only happen the nitrogen is actually condensed. Therefore there must be a region of solid nitrogen dust extending from 90 km. to about 600 km. The difficulties attending this view do not appear to have received adequate attention.