Baumhauer (Compt. Rend. vol. lxxiv. p. 678) advances, as regards Polar Auroræ, the proposition, that not only solid masses large and small, but clouds of “uncondensed” (meteoric) matter probably enter our atmosphere. If from our knowledge of the meteoric stones which fall to the earth’s surface we may draw any conclusion respecting the chemical constitution of these clouds of matter, it would appear that they may contain a considerable portion of the magnetic minerals iron and nickel. Let such a cloud approach our earth, regarded as a great magnet, it would be attracted towards the Pole, and, penetrating our atmosphere, the particles which have not been oxidized, and are in a state of extremely fine division, would by their oxidation generate light and heat, producing the polar Auroræ. Baumhauer suggests it would be interesting in support of this theory to detect in the soil of polar areas the presence of nickel. The presence of iron and nickel in meteoric masses in considerable quantities is frequent; and cases are also on record by Eversmann of hailstones containing crystals of a compound of iron and sulphur, by Pictet of hailstones containing nuclei which proved to be iron, and by Cozari of hailstones containing nuclei of an ashy-grey colour, the larger ones of which were attracted by the magnet, and found to contain iron and nickel. Nickel was found by Reichenbach in parts of Austria on hills consisting of beds of sandstone and limestone, and quite free from metallic veins. [Sidenote: Mr. Lefroy’s description of a phenomenon ascribed by him to streams of cosmic dust.] Mr. J. W. N. Lefroy, in ‘Nature,’ describes a phenomenon seen by him at Fremantle, West Australia, in the month of May, which he designates “A Lunar Rainbow, or an Intra-lunar convergence of Streams of slightly illuminated Cosmic Dust?” It lasted about three quarters of an hour, and consisted of one grand central feather, of very bright white cloud, springing out of the horizon at W.N.W., and crossing the meridian at about 20° north of the zenith, with a width of 7° to 8°. On either side of this was a system of seven or eight minor beams of light, extending from the W. to the E. horizon, subtending a chord common to themselves and to the main stream, and converging towards the axis of the central stream so as to intersect it at a point about 30° or 40° below the western horizon, at which the whole system subtended an azimuth of about 20°. Near the zenith, where its transverse section was a maximum, that section subtended an angle of about 40°.