[182] “Brilliant and active coruscations of the Aurora Borealis,” says Captain Back, “when seen through a hazy atmosphere, and exhibiting the prismatic colours, almost invariably affected the needle. On the contrary, a very bright Aurora, though attended by motion, and even tinged with a dullish red and a yellow in a clear blue sky, seldom produced any sensible change, beyond, at the most, a tremulous motion. A dense haze or fog, in conjunction with an active Aurora, seemed uniformly favourable to the disturbance of the needle, and a low temperature was favourable to brilliant and active coruscations. On no occasion during two winters was any sound heard to accompany the motions. The Aurora was frequently seen at twilight, and as often to the eastward as to the westward; clouds, also, were often perceived in the day-time, in form and disposition very much resembling the Aurora.”--_Narrative of the Arctic Land Expedition._ [183] Faraday: _On the Diamagnetic character of Flame and Gases_. [184] “The Aurora Borealis is certainly in some measure a magnetical phenomenon; and if iron were the only substance capable of exhibiting magnetic effects, it would follow that some ferruginous particles must exist in the upper regions of the atmosphere. The light usually attending this magnetical meteor may possibly be derived from electricity, which may be the immediate cause of a change in the distribution of the magnetic fluid, contained in the ferruginous vapours which are imagined to float in the air.”--Lecture on Magnetism: Young’s _Lectures on Natural Philosophy_, p. 533. [185] _On the supposed influence of Magnetism and Chemical Action_; by Robert Hunt.--Philosophical Magazine, vol. xxxii. No. 215, 1849.