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OBSERVATIONS ON THE AURORA BOREALIS.

movements of it amongst the attenuated air and aqueous vapour, illuminating themas it spreads in various directions, according as their different parts are prepared forits reception and diffusion. It is no unusual circumstance to observe preparations, asit were, during the evening, before daylight has disappeared, for a display of auroralbeams or streamers after nightfall. These preludes consist of certain arrangements ofthin streaks of nubiferous matter, floating at high altitudes, and often stretching quiteacross the heavens, and appearing to converge at two opposite points near the horizon,forming what some people call “ Noah’s Ark.” These streaks or bands of vapour,when traversed by the electric fluid at the night time, become luminous conductors,and form streamers of the Aurora Borealis—displaying different degrees of brilliancy,in correspondence with the attenuation of the nubiferous arrangement and the quan-tity of electric fluid flowing through it. From this simple fact, which I have myselfwitnessed, and from the high probability that similar arrangements of still more atten-uated aqueous vapour are frequently formed at altitudes where they are far beyondthe reach of observation, until illuminated by electrical disturbances, there can appearno great degree of extravagance by supposing that most, if not all, streamers assumetheir peculiar forms from a like cause. It is possible, however, that on many occasionsthe electrical disturbances may take place even at higher altitudes, and the light betransmitted through the thinnest bands of these nubiferous arrangements, whichwould give the appearance of streamers, or luminous beams, as decidedly as if theywere themselves the conductors or channels of electrical transmission.

The streamers, which mostly constitute a conspicuous feature in the Aurora Borealis,are not often suddenly formed ; they generally spring from some definite speck in theheavens, and wax gradually to their full dimensions, and then as gradually fade away.Some streamers, it is true, shoot rapidly to their full growth, and almost as suddenlydisappear; but in all cases they can be seen expanding lengthwise, whatever may bethe rapidity of their growth. They sometimes lengthen in both directions, but mostfrequently in one direction only—a circumstance more favourable to the idea of thenubiferous bands being the media of transit than in the capacity of transparent screens,permeated by an electric light from above.

In many displays of the Aurora, floods of streamers appear to flow upwards,from everypart of a luminous bow, which crosses the meridian in the north, and stretch to vari-ous angles of altitude towards the spectator—some of them reaching to his zenith,whilst others terminate their career before they arrive midway but; in no instance dostreamers spring into existence mature or full grown. This fact also gives counten-ance to the idea of their consisting of streaks or bands of thin aqueous vapour, gradu-ally, though rapidly in some cases, illuminated longitudinally by transmissions of theelectric fluid. This view is still further supported by the fact that, in whatever direc-tion streamers may be elongated, the point from which they spring is the most