LONDON. Royal Society, June 23.—J. C. McLennan and J. H. McLeod: On the wave-length of the green auroral line iarthe oxygen spectrum. In 1925, McLennan and Shrum found a line in the spectrum of highly purified oxygen of wave-length λ 5577.35±0.15, and provisionally identified it with the green auroral line. Reinvestigation with a Fabry-Perot interferometer now determines the wave-length of this line as 5577.341±0.004. Babcock's value for the wavelength of the auroral line being 5577.350±0.005, there would thus seem to be no doubt as to the identity of the lines. Apparently oxygen as well as nitrogen is present in those regions of the upper atmosphere whence the auroral light is transmitted.