The Spectra of Aurora and Corona

Abstract

So much attention has been drawn to the correspondence between the spectrum of the corona and that of the aurora, as to lead one to suppose that they were almost identical; or, at least, that the principal auroral line was also seen in the corona. But even this is not at all the case. As the readers of NATURE are aware, the light of the aurora is almost monochromatic, giving a spectrum of one bright line in the yellowish green (wavelength about 557), and three or four very faint bands, which are more refrangible. These last are only occasionally visible, and indeed, Angstrom, in 1869, had seen them but once, and that momentarily. It is with one of these faint bands that the 1,474 corona line (wave length 531.6) is said to coincide, and not with the bright line (wave length 557), which is entirely absent in the corona spectrum. Two more of the auroral bands are near to the F and G hydrogen lines, which are visible in the corona, but it is yet doubtful whether they coincide. It is not impossible that a faint H spectrum may be produced in the aurora by the moisture of the air, but I incline to attribute them to the low temperature air spectrum mentioned in my letter of February 7, and which has bands in nearly the same positions. From the extreme faintness of the auroral bands, it is of course impossible to measure their positions with great accuracy.