AURORA BOREALIS. 



113 



Their dogs are then so much frightened that they 

 will not move, but lie obstinately on the ground till 

 the noise has passed. Commonly clear and calm wea- 

 ther follows this kind of northern lights. I have heard 

 this account not from one person only, but confirmed 

 by the uniform testimony of many who have spent 

 part of several years in these very northern regions, 

 and inhabited different countries from the Yenisei to 

 the Lena ; so that no doubt of its truth can remain. 

 This seems, indeed, to be the real birth-place of the 

 aurora borealis. 



Maupertuis describes a very remarkable aurora which 

 he saw at Oswer-Zornea, on the 18th December 

 1 736, and which he says excited his admiration, not- 

 withstanding the many extraordinary appearances of 

 this kind to which he had been accustomed to in the 

 Arctic regions. An extensive region of the heavens 

 towards the south appeared tinged of so lively a red, 

 that the whole constellation Orion seemed as if dyed 

 in blood. This light was for some time fixed, but 

 soon became moveable ; and after having successively 

 assumed all the tints of violet and blue, it formed a 

 dome, of which the summit nearly approached the 

 zenith in the south-west. Its splendour was so great, 

 as to be in no degree affected by the strong light of 

 the moon. Maupertuis adds, that he observed only 

 two of these red northern lights in Lapland, which are 

 of very rare occurrence in that country, although the 

 aurora there assumes a great variety of tints ; hence 

 they are considered by the natives as of portentous 

 omen, and as the forerunners of some great calamity. 

 This account of the noises attending the aurora 

 borealis has been corroborated by other testimonies. 

 They have been heard at Hudson's Bay, and in Swe- 

 den ; and Muschenbroek mentions, that the Green- 

 land whale fishers assured him they had frequently 

 heard the noise of the aurora borealis ; but adds, that 

 no person in Holland had ever experienced this phe- 

 nomenon. Mr Cavallo, however, declares, that he 

 lias repeatedly heard a crackling sound proceeding 

 from the aurora borealis. (Elem. oJ~Sat.andV.xper. 

 Phil. vol. iii. p. 449.) And Mr Nairne mentions, 

 that, being in Northampton at the time when the 

 northern lights were remarkably bright, he is con- 

 fident he perceived a hissing or whizzing sound. Mr 

 Belknap, also, of Dover, in New Hampshire, North 

 America, testifies to the same fact. Amer. Trans. 

 vol. ii. p. 196. 



The aurora is by no means confined to the northern 

 hemisphere. In the high southern latitudes, it was 

 long ago observed, that there is a similar phenome- 

 non. (See Phil. Trans. No. 461. and vol. liv. No. 

 53.) And, if the existence of the aurora australis 

 was before in some measure doubtful, it has been com- 

 pletely ascertained by the second voyage round the 

 world performed by Captain Cooke. " On February 

 17. 1773," says Mr Forster, who accompanied Cooke 

 in the capacity of naturalist, " in south lat. .58, a 

 beautiful phenomenon was observed during the pre- 

 ceding night, which appeared again this and several 

 following nights. It consisted of long columns of a 

 clear white light, shooting up from the horizon to the 

 eastward, almost to the zenith, and gradually spread- 

 ing over the whole southern part of the sky. These 

 columns were sometimes bent sideways at their upper 

 extremities ; and though in most respects similar to 

 VOL. III. part I. 



the northern lights of our hemisphere, yet differed 

 from them in being always of a whitish colour ; where- 

 as ours assume various tints, especially those of a fiery 

 and purple hue. The sky was generally clear when 

 they appeared, and the air sharp and cold, the ther- 

 mometer standing at the freezing point." 



Various attempts have been made to determine the 

 height of the aurora borealis, but with very little suc- 

 cess. Bergman, from a mean of thirty computations, 

 makes the height of this phenomenon to be 72 Swe- 

 dish, or about 468 English miles. Father Boscovich 

 calculated the height of an aurora borealis, observed 

 on the 16th December 1737, by the Marquis of Po- 

 leni, to have been 825 miles : Mairan supposed the far 

 greater number of auroras to be at least 600 miles 

 above the surface of the earth ; and Euler assigned 

 them an elevation of several thousands of miles. Dr 

 Blagden, however, limits their height to about 100 

 miles, which he supposes to be the region of fire-balls ; 

 remarking that instances are upon record, in which 

 the northern lights have been seen to join, and form 

 luminous balls, darting about with great velocity, and 

 even leaving a train behind them like common me- 

 teors. Phil. Trans, vol. lxxiv. p. 227. 



Respecting the cause of this beautiful phenomenon, 

 a great variety of theories have been proposed. When 

 the science of meteorology was in an imperfect state, 

 it was natural to ascribe the aurora borealis to fiery 

 or sulphureous vapours exhaled from the bowels of 

 the earth, and rising into the region of the air ; and 

 Muschenbroek is at pains to point out certain chemical 

 mixtures which send forth a phosphorescent steam or 

 vapour, in many respects resembling the northern 

 lights. Dr Halley, also, at first proposed a similar 

 theory : conceiving that the watery vapours which 

 are rarefied aud sublimed by subterraneous fire, might 

 carry along with them sulphureous vapours suffi- 

 cient to produce this luminous appearance in the 

 atmosphere. He soon, however, abandoned this 

 hypothesis, which is evidently very insufficient to 

 account for the phenomena ; and supposed that 

 the aurora borealis might be occasioned by the circu- 

 lation of the magnetic effluvia of the earth from one 

 pole to the other. It was an hypothesis of this phi- 

 losopher, that the earth is a hollow sphere, inclosing 

 within it another sphere, which has a strong magne- 

 tic virtue, to two poles which are nearly but not per- 

 fectly coincident with the poles of the world. The 

 inner sphere he supposed to have a slow revolution on 

 its axis, independent of the diurnal rotation of the 

 earth, by which he accounted for the variation of the 

 magnetic needle ; and he supposed that there is a con- 

 stant circulation of the magnetic fluid from the north 

 to the south pole through the air ; which is counter- 

 balanced by a circulation from the south to the north 

 pole, through the pores of the earth. The magnetic 

 effluvia, darting upwards from the north pole into the 

 higher regions of the atmosphere, acquire such aa 

 impetus as to render the circumambient ether lumi- 

 nous ; and give rise to all the phenomena of the au- 

 rora borealis. It has never, however, been shewn, 

 that magnetic effluvia can in any case produce light ; 

 and according to this theory, the aurora ought at the 

 south pole to direct itself towards the earth ; where- 

 as Mr Forster found it moving rapidly towards the 

 zenith, just ae it does in the northern hemisphere. 



Aurora 

 Borealis. 



