OBSERVATIONS ON THE AURORA BOREALIS.

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the spectator. There can he no doubt of the electric origin of the Aurora Borealis,since many of its characteristics can be beautifully imitated by the electricalapparatus. The violet tint is easily produced by an electrical discharge throughhighly attenuated air ; but the green, the blue, the orange, the yellow, and the deepred cannot be imitated by any form of electrical experiment hitherto known, in whichthe light is shown in common air, however much it may be attenuated. But thesecolours may easily be accounted for under the supposition of an abundance of aqueousvapour in the regions of an auroral display—a concession by no means unreasonablewhen we take into account the season of the year (from about the autumnal to thevernal equinox) in which such spectacles are most frequent, the hazy appearance ofthe sky at the time, and the occurrence of wet weather that usually follows.

By looking over my journal for several years past, I find that the grandest displaysof the Aurora Borealis have been closely followed by wet weather; and the followingextract from the description of an Aurora which I observed in the vicinity of London,on the evening of September 3rd, 1839, will probably appear more eminently calculatedto develop the true character of the spectral colours accompanying the Aurora Borealisthan any other attempt at explanation hitherto on record. The observations were madewhilst walking from Brixton to my residence in Pomeroy-street, Old Kent Road:—

“ The sky was partially covered with thin vapoury clouds, which had an obviousinfluence on the colour, and the apparent horizontal motion of the light, which waseasily discerned to he behind or beyond these thin clouds of vapour, and assumed adeeper tinge of redness as the vapour became more dense between it and the spectator.As this was the first time of my observing a red light during the display of an AuroraBorealis, I became anxious to know the cause, for I never saw the electrical light, inartificially-attenuated air, anything like the colour of the light which I observed onthis occasion. It was sometimes of a deep crimson, at other times of an almost fieryred; then pink, very light pink, next the yellowish white colour which the Aurora mostusually displays, and so on for several alternate successions. At other times it wouldseem to reverse the order of colours, beginning with the white light, and passingthrough the different red tints down to a perfect crimson, and then return graduallyto the ordinary white. I had several opportunities of observing the curious changesof colour in the auroral light before I arrived at Camberwell. Just before I enteredthe Grove, at Camberwell, then about half-past nine o’clock, the northern sky wasilluminated throughout an immense horizontal range with a rich red light; but whenI arrived at the Church-yard, about five minutes afterwards, the red light had nearlydisappeared, a small portion only remaining on the northern edge of a thin fleece ofvapour, at a considerable height above the western horizon, being succeeded by seve-ral fine groups of the usual white streamers.”*

* Aurora Borealis, No. 6, page 497.

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