11(1 



AURORA 



pearance of an aurora. If the aurora were bright, he 

 says the gale came on within 2t hours, but was of 

 no long continuance ; if the light was faint and dull, 

 the gale was less violent, and longer in coming on ; 

 but longer also in duration. His observations were 

 made in the English channel, where such winds are 

 very dangerous, and by attending to the aurorae, he 

 says, that he often escaped shipwreck, while others 

 suffered. As we have supposed a stream of electri- 

 city to be constantly passing through the mass of the 

 earth, from the equator towards the poles, it is evi- 

 dent, that a wind may be occasioned by this electri- 

 city finding a ready vent at some promontory, or 

 head-land. And should we suppose one of those 

 vents situated on the coast of France, or in the Bay 

 of Biscay, the electric matter that has been received 

 at the equator, during an aurora borealis, will be dis- 

 charged there, for some time after ; and consequent- 

 ly will occasion a wind from that quarter, which will 

 be south-west iri the English channel. According, 

 however, to the different situations of these electrical 

 vents, winds may blow in very different directions in 

 different quarters of the world. ( 



The most unaccountable of all the circumstances 

 respecting the aurora borealis, is, that it is not much 

 more than a century since this phenomenon has been 

 observed to occur with any degree of frequency in 

 our latitudes. We find indeed a few remarkable at- 

 mospheric phenomena recorded by the ancients, 

 which maybe reckoned examples of this meteor, viz. 

 in Aristotle's Meteor. 1. i. c. 4, 5. ; and Sehec. Quest. 

 Nat, 1. i. c. 15. Pliny also (1. ii. c. 27.) speaks of 

 a bloody appearance of the heavens, which seemed 

 like a fire descending upon the earth, seen in the third 

 year of the 107th Olympiad ; and of a light seen in 

 the night-time, equal to the brightness of day, in the 

 consulship of Cxcilius and Papyrius (1. ii. c. 33. ) both 

 which may be referred to the aurora borealis. But, 

 with such trilling exceptions as these, the whole of 

 antiquity is absolutely silent on this subject. Dr 

 Halley informs us, that he had begun to despair of 

 witnessing this beautiful phenomenon, when the re- 

 markable aurora of 1716 made its appearance. This 

 philosopher has given us a historical detail of the se- 

 veral observations of this meteor, in which he says, 

 that the first account of it upon record, in an English 

 work, is in a book entitled, A Description of Meteors, 

 by W. F. D. D., reprinted at London, in 1654, 

 which speaks of " burning spears" being seen Jan. 

 .'SO. 1560. The next appearance of a like kind is re- 

 corded by Stow, and occurred on October 7. 1564. 

 [n 157 !, according to Stow and Camden, an aurora 

 was seen for two successive nights, viz. the 14th and 

 1 5th of November. The same phenomenon was twice 

 ten in Brabant in 1575, viz. on the 13th of February 

 and- the 28th of September; and the circumstances 

 accompanying it wcVe described by Cornelius Gem- 

 ma, who compares them to spears, fortified cities, and 

 armies fighting in the air. In 1580 and 1581, this 

 phenomenon was repeatedly observed at Baknang, 

 ii the county of Wirtemberg, in Germany. But 

 from this time to 1621, we have no such phenome- 

 non on record, when it was seen all over Prance on 

 September 2., and is particularly described by Gas- 

 . Ii in his Physics, under the title of Aurora Bo- 



13 O 11 E A L I S. 



r a al it . In November 162:5, another was seen all over 

 ny, and is particularly described by Kepler. 

 Since that time, for more than eighty years, we have 

 no account of any such phenomenon being observed ; 

 but in 1707, Mr Neve observed one of short conti- 

 nuance in Ireland ; and in the same year, a similar 

 appearance was seen by Romer at Copenhagen ; while, 

 during an interval of eighteen months, in the years 

 1707 and 1708, this sort of light had been seen n* 

 less than five times. The aurora of 1716, which Dr 



Halley particularly describes, was remarkably bril- 

 liant. It was also visible over a prodigiou?\ract of 

 country ; being seen from the west of Ireland to the 

 confines of Russia, and the east of Poland ; extend- 

 ing near 30 of longitude, and from about the 50th 

 degree of north latitude, over almost all the north of 

 Europe ; and in all places exhibiting, at the same 

 time, appearances similar to those observed in Lon- 

 don. 



It appears, then, to be certainly established, that 

 the aurora was of very rare occurrence in our lati- 

 tudes till about a century ago ; for it cannot be sup- 

 posed that so beautiful and striking a phenomenon 

 would have passed unnoticed, and unrecorded, during 

 the two preceding centuries, while men of science, 

 and particularly astronomers, were so busily employed 

 in examining every remarkable appearance of the 

 heavens ; or that the philosophers of Greece and 

 Rome would have remained silent concerning sd b. 

 tiful a meteor, had it been in any degree familiarly 

 known to them. It is in vain to account for their 

 silence by saying, that they inhabited latitudes which 

 are scarcely ever Visited by this appearance ; for the 

 Romans not only vjsited, but long resided in the 

 north of Germany, and in Britain, where the aurora 

 is now frequently seen in great splendour. 



The following ingenious theory has been proposed, 

 with a view to resolve this difficulty. There is a very 

 remarkable analogy between the phenomena of elec- 

 tricity and those of magnetism, and, apparently, an in- 

 timate dependence of the one upon the other. There 

 are two species of electricity, a positive and a ne- 

 gative, and two species of magnetic polarity, a north 

 and a south. A body positively electrified repel > 

 another body positively electrified, and attracts one 

 that is electrified negatively ; while the north pole of 

 one magnet repels the north pole, and attracts the 

 south pole of another. The electric shock will de- 

 prive a magnetic needle of its power, or communicate 

 it to it again, according to the direction in which it 

 is laid; and, during a thunder storm, the magnetic 

 needle is observed to be powerfully agitated. Thus 

 the intimate connection between electricity and mag- 

 netism seems to be satisfactorily established. Again, 

 that imaginary line, or circle, winch traverses the 

 earth irregularly from the north to.vards the south, 

 and is called the line of no variation, because the 

 magnetic needle, when placed upon it, points truly 

 to the poles, is observed to have a gradual, and pretty 

 regular, revolution around the earth, performed in 

 about 1000 years ; 60 ^hat, when 1000 years have 

 elapsed, the line of no variation will have reached the 

 same situation which it occurt'ed at the beginning of 

 that period. This line seems to have a sort ot con- 

 tioul over the confiscations of the aurora, which are 



