OXYGEN IN THE SUN.—Herren Runge and Paschen have recently suggested (Astrophysical Journal, No. 5) a criterium by which the presence of oxygen in the sun may be directly ascertained. They have found that in a vacuum tube filled with oxygen, the line at 7775, discovered by Piazzi Smyth, has two components, the strongest being the most refrangible and the weakest the least refrangible; the wave-lengths of the three are 7772˙26, 7774˙30, and 7775˙97. In the solar spectrum about this region there are, comparatively speaking, few lines, but, corresponding with the above wave-lengths, there is a triplet which has the same characteristic intensities. Herren Runge and Paschen think that their origin is probably not atmospheric, for the spectrum of the oxygen vacuum tube differs widely from the absorption spectrum of atmospheric oxygen. Mr. F. McLean has examined his photographs of the high and low sun, and has found that these lines do not depend on the altitude ot the sun, which fact still further points to a solar origin. A crucial test would be to examine the opposite limbs of the sun, and find out whether any displacement of the lines occurs.