AURORA BOREALIS

AURORA BOREALIS, or AURORA SEPTENTRIONALIS, the northern dawn or light; is an extraordinary meteor, or luminous appearance, showing itself in the night time, in the northern part of the heavens. See METEOR. 'Tis usually of a reddish colour, inclining to yellow, and sends out frequent coruscations of pale light, which seem to rise from the horizon in a pyramidal undulating form, and strike, with great velocity, up to the zenith.

This kind of meteor never appears near the equator, and was so rare in England, that none are recorded in our annals since that remarkable one, November 14, 1574, till the surprising Aurora Borealis, March 6, 1716, which appeared for three nights successively, but by far more strongly on the first—Indeed, in the years 1707 and 1708, five small ones were observed in little more than eighteen months. Hence it should seem that the air or earth, or both, are not at all times disposed to produce this phenomenon; for though 'tis possible it may happen in the day-time, in bright moonshine, or in cloudy weather, and so pass unobserved; yet that it should appear so frequent at some times, and so seldom at others, cannot well this way be accounted for—That in March 1716, was visible to the west of Ireland, confines of Russia, and to the east of Poland; extending at least near 30° of longitude, and 900° in latitude, that is, over almost all the north of Europe; and in all places at the same time, it exhibited the like wondrous circumstances.



A sufficient number of observations have not yet been made by the curious, to enable them to assign the cause of this phenomenon, with any certainty—Dr. Halley, however, imagines that watery vapours, or effluvia, rarified exceedingly by subterraneous fire, and tinged with sulphurous streams, which naturalists suppose to be the cause of earthquakes; may also be the cause of this appearance: Or, that 'tis produced by a kind of subtle matter, freely pervading the pores of the earth, and which entering into it near the southern pole, passes out again with some force into the aether at the same distance from the northern; the obliquity of its direction being proportioned to its distance from the pole. This subtle matter, by becoming some way or other more dense, or having its velocity increased, may be capable of producing a small degree of light, after the manner of effluvia from electric bodies, which by a strong and quick friction, emit light in the dark: To which sort of light this seems to have a great affinity. Phil. Trans. No. 347.

AURORA BOREALIS