He also describes (Parry’s First Voyage) an Aurora seen at Melville Island, and says the light was estimated as equal to that of the moon when a week old. Besides the pale light, _which resembled the combustion of phosphorus_, a slight tinge of red was noticed when the Aurora was most vivid; but no other colours. This Aurora was repeatedly seen _on the following day_. [Sidenote: Procter suspects Aurora is formed in a mist. M’Clintock: Aurora is never visible in a perfectly clear atmosphere.] Mr Procter, in a letter to me, suspects that the Aurora is generally formed in a sort of “mist or imperfect vapour;” and this mist or imperfect vapour seems in many instances to form part of the Aurora, and to partake of its self-luminous character. M’Clintock does not imagine that the Aurora is ever visible in a perfectly clear atmosphere. He has often observed it just silvering or rendering luminous the upper edge of low fog or cloud-banks, and with a few vertical rays feebly vibrating. [Sidenote: Aurora of Feb. 4, 1874. Illuminated fog-cloud. Capt. Oliver’s meteor-cloud. Auroral display, 24th Oct., 1870. Streamers of phosphorescent cloud.] An instance of apparent phosphorescence is supplied by the Aurora of the 4th February, 1874 (_antè_), when a bright cloud of light was seen which gave the impression of an “_illuminated fog-cloud_.” Captain S. P. Oliver saw at Buncrana, Co. Donegal, on February 4, 1874, what he describes as a meteor-cloud, viz. “a broad band of silvery white and luminous cloud.” This appearance, as described by another correspondent, was evidently an imperfectly formed (perhaps actually forming) Auroral arc. The great Auroral display of the 24th of October, 1870, as seen by me, included, according to my notes made at the time, “streamers of opaque white phosphorescent cloud, very different from the more common transparent Auroral diverging streams of light.” [Sidenote: Aurora of Feb. 4, 1872, at Frant. Radii of phosphorescent light.] Describing the Aurora of February 4, 1872, at Frant, Dr. Allnatt says:—“At a later hour of the night the canopy of cirro-stratus had separated, and was transformed into luminous masses of radiant cumulus. At 10.40 the Aurora reappeared in the N., and sent luminous radii of white _phosphorescent_ light from the periphery of a segment of a perfectly circular arch”[7]. [Sidenote: The author’s description of same Aurora. Masses of phosphorescent vapour.] Again, February 4th, 1872, as described by me, the first signs of the Aurora were (in dull daylight) a lurid tinge upon the clouds, which suggested the reflection of a distant fire; while scattered among these, “torn and broken masses of white vapour having a phosphorescent appearance” reminded me of a similar observation in October 1870. [Sidenote: Day Auroræ must have a phosphorescent glow. Ångström considers yellow-green line due to fluorescence or phosphorescence. Oxygen and some of its compounds phosphorescent.]