AURORA BOREALIS. 



lumns of a clear white light, shooting 1 up 

 from the horizon to the eastward, almost 

 to the zenith, and gradually spreading on 

 the whole southern part of the sky. These 

 columns were sometimes bent sideways 

 at their upper extremities ; and though in 

 most respects similar to the northern 

 lights (aurora boreaflis) of our hemi- 

 sphere, yet differed from them in being 

 always of a whitish colour, whereas ours 

 assume various tints, especially those of a 

 fiery and purple hue. The sky was ge- 

 nerally clear when they appeared, and the 

 air sharp and cold, the thermometer 

 standing at the freezing point." 



The periods of the appearance of these 

 northern lights are very inconstant. In 

 some years they occur very frequently, 

 and in others they are more rare ; and it 

 has been observed, that they are more 

 common about the time of the equinoxes 

 than at other seasons of the year. Dr. 

 Halley ( see Philos. Trans. No. 347, p. 406,) 

 has collected together several observa- 

 tions, which form a kind of history of this 

 phenomenon. After having particularly 

 described the various circumstances 

 which attended that observed by himself 

 and many others, in March 1716, and 

 which was singularly brilliant, he pro- 

 ceeds with informing us, that the first ac- 

 count of similar phenomena, recorded in 

 the English annals, is that of the appear- 

 ance -vhich was noticed January 30, 1560, 

 and called " burning spears," by the. au- 

 thor of a book entitled "A Description 

 of Meteors," by W. F. D. D. reprinted at 

 London, in 1654. The next appearance 

 of a like kind, recorded by Stow, occurred 

 on October, 7, 1564. In 1574, as Camden 

 and Stow inform us, an aurora borealis 

 was seen for two successive nights, viz. 

 14th and 15th of November, with appear- 

 ances similar to those observed in 1716, 

 and which are now commonly noticed. 

 The same phenomenon was twice seen 

 in Brabant, in 1775, vis. on the 13th of 

 February and the 28th of September ; 

 and the circumstances attending it were 

 described by Cornelius Gemma, who 

 compares them to spears, fortified cities, 

 and armies fighting in the air. In the 

 year 1580, M. Mastline observed these 

 phasmata, as he calls them, at Baknang, 

 in the county of Wirtemberg, in Germa- 

 ny, no less than seven times in the space 

 of twelve months; and again at several 

 different times, in 1581. On September 

 2d, 1621, the same phenomenon was seen 

 over all France ; and it was particularly 

 described by Gassendus, in his " Physics," 

 who gave it the name of " aurora borea- 



VOL.II. 



lis." Another was seen all over Germany 

 in November, 1623, and was described by 

 Kepler. Since that time, for more than, 

 eighty years, we have no account of any 

 such phenomenon, either at home or 

 abroad. In 1707, Mr. Neve observed one 

 of small continuance in Ireland ; and in 

 the same year, a similar appearance was 

 seen by Romer, at Copenhagen; and dur- 

 ring an interval of eighteen months, in 

 the years 1707 and 1708, this sort of 

 light had been seen no less than five times. 

 Hence it should seem, says Dr. Halley, 

 that the air or earth, or both, are not at 

 all times disposed to produce this pheno- 

 menon, though it is possible it may hap- 

 pen in the daytime, in bright moon shine, 

 or in cloudy weather, and so pass unob- 

 served. Dr. Halley further observes, that 

 the aurora borealis of 1716, which he de- 

 scribed, was visible from the west of Ire- 

 land to the confines of Russia, and to the 

 east of Poland ; extending at least near 

 30 of longitude, and from about the 50th 

 degree of north latitude, over almost all 

 the North of Europe ; and in all places, at 

 the same time, it exhibited appearances 

 similar to those which he observed at 

 London. He regrets, however, that he 

 was unable to determine its height, for 

 want of contemporary observations at dif- 

 ferent places. 



Father Boscovich has determined the 

 height of an aurora borealis, observed on 

 the 16th of December, 1737, by the Mar- 

 quis ot'Poleni, to have been 825 miles; 

 and Mr. Bergman, from a mean, of thirty 

 computations, makes the average height 

 of the aurora borealis to be 72 Swedish, 

 or (supposing a Swedish mile to be about 

 6^ English miles) 468 English miles. Eu- 

 ler supposes the height to be several 

 thousands of miles; and Mairan also as- 

 signs to these phenomena a very elevated 

 region, the far greater number of them 

 being, according to him,about 200 leagues 

 above the surface of the earth. Dr. Blag- 

 den, speaking of the height of some fiery 

 meteors, (Phil. Trans, vol. Ixxiv. p. 227,) 

 says, that " the aurora borealis appears to 

 occupy as high,if notahigher,regionhbove 

 the surface of the earth, as may be judged 

 from the very distant countries to which it 

 has been visible at the same time;" he adds 

 that " the great accumulation of electric 

 matter seems to lie beyond the verge of 

 our atmosphere, as estimated by the ces- 

 sation of twilight." However, the height 

 of these meteors, none of which appear 

 to have ascended so high as 100 miles, is 

 trivial, compared with the elevations 

 above ascribed to the aurora borealis. 



