On the 12th April 8h, while observing the part of the moon called Palus Mœotis by Nevelius, with an excellent Newtonian reflector of 6 inches aperture, at a particular part of the Palus, which he minutely describes, he saw, with powers 70 and 130, “a very conspicuous spot wholly enveloped in black nebulous matter, which, as if carried forward by a current of air, extended itself in an easterly direction, inclining a little towards the south, rather beyond the margin of Mœotis.” April 13th 8h to 9h, the cloudy appearance was reduced both in extent and intensity, and the spot from which it seemed to issue had become more distinctly visible. On April 17th scarcely a trace of the nebulous matter remained; but so long after as June 10th 8h “a little blackness” remained about the spot. Mr. Emmett suggested “smoke of a volcano or cloudy matter.” A copy of the drawing annexed to the paper is given on Plate X. fig. 10 (black patch on moon). If this observation was (as it certainly appears to be) critical and exact, there must have been a disturbance of the moon’s surface, indicating some sort of cloud- or vapour-supporting atmosphere; and probably, for the purposes of Auroræ, an atmosphere of a very rarefied condition would suffice[10]. [Sidenote: Prof. Alexander’s evidence in favour of a lunar atmosphere.] According to the ‘New York Tribune,’ at a recent semi-annual meeting of the American Academy of Sciences, Professor Alexander “brought forward a variety of evidence tending to indicate some envelope like an atmosphere for the moon. The evidence was principally drawn from observations during eclipses. The explanations usually offered for the bright band seen around the moon at such times was fully considered, and shown to be inadequate, though good as far as they would apply. The ruddy band of light is much too broad to be the sun’s chromosphere. It was most apparent in those instances where the moon was nearest the earth. It would best be accounted for by supposing an atmosphere to the moon, a thin remnant of ancient nebulosity, comparable to that which accompanies the earth and gives rise to the appearance of the Aurora Borealis.” Is it not, however, possible that the appearance might have arisen from Auroræ in action within the region of the earth’s own atmosphere during the passage of the sun’s rays through it at the time of the eclipse? The whole subject is difficult of explanation, and should be one of the points for attention on the occasion of the next total Lunar eclipse. It seemed to me appropriate for introduction into the present history of the Aurora, whatever its solution may ultimately be. [Sidenote: Mars and Jupiter.]