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a u n 
A U R 
A U R 
Tycho, forty according to Hevelius, and 
sixty-six in the Britannic catalogue. 
This is one of the forty-eight asterisms 
mentioned by all antient astronomers; and 
represented by the figure of an old man in a 
kind of sitting posture, with a goat and her 
kids in his left hand, and a bridle in his right. 
Besides the hcedi, this constellation includes 
another Star, called capella; which is the 
bright one near the shoulder, and supposed to 
be the mother of the hcedi, and the nurse ot 
Jupiter. The hcedi, or the two stars in the 
arm of Auriga, were regarded by the ancients 
as affording presages of the weather ; and 
these were so much dreaded on account of 
the storms and tempests that succeeded their 
rising, that they are said to have shut up the 
navigation at this season. 
AUR1UM abscissio, in antiquity, cutting 
off ears, was a punishment inflicted by the 
Saxon law on those who robbed churches, 
and afterwards on every thief, and at length 
on other criminals. 
AURORA BOREALIS, northern light, 
or streamers, a kind of meteor appearing in 
the northern part of the heavens, mostly in 
the winter season, and in frosty weather. It 
is usually of a reddish colour, inclining to 
yellow; and sends out frequent coruscations 
of pale light, which seem to rise from the ho- 
rizon in a pyramidal undulating form, and 
shooting with great velocity up to the zenith. 
It appears often in form of ail arch, which is 
partly bright and partly dark, but generally 
transparent: and the matter of it is not found 
to have any effect on the rays of light, which 
pass freely through it. Dr. Hamilton ob- 
serves that he could plainly' discern the 
smallest speck in the Pleiades through the 
density of those clouds which formed part of 
the aurora borealis in 1763, without the least 
diminution of its splendour, or increase of 
twinkling. Philos. Essays, p. 106. 
Sometimes it produces an iris. Hence M. 
Godin judges that most of the extraordinary 
meteors and phenomena in the skies, related 
as prodigies by historians, as battles, and the 
like, may probably enough be reduced to the 
class of aurora boreales. Hist. Acad. R. 
Scien. for 1762, p. 405. 
This kind of meteor never appears near 
the equator ; but, it seems, is as frequent to- 
wards the south pole as towards the north, 
having been observed there by' voyagers. 
See Philos. Trans. No. 461, and vol. 54; also 
Forster’s Account of his Voyage round the 
World withCapt. Cook, in which he describes 
their appearance as observed for several nights 
together, in sharp frosty weather ; which was 
much the same as those seen in the north, 
excepting that they were of a lighter colour. 
It seems that meteors of this kind have 
appeared at some times more frequently than 
at other'; They were so rare in England, or 
else so little regarded, that none are recorded 
in our annals since that remarkable one of 
November 14, 1574, till the surprising aurora 
borealis of March 6, 1716, which appeared 
for three nights successively, but by far more 
strongly on the first; except that five small 
ones were observed in the years 1 707 and 1708. 
Hence it would seem that the air or earth, or 
both, are not at all times disposed to produce 
this phenomenon. 
The extent of these appearances is also 
amazingly great. That in March 1716 was 
visible from the west of Ireland to the confines 
of Russia and the east of Poland, extendingat 
least near 30 degrees of longitude, and from 
about the 50th degree in latitude over al- 
most all the north of Europe; and in all 
places, at the same time, it exhibited.the like 
wondrous appearances. 
Father Boscovich has determined the 
height of an aurora borealis, which was ob- 
served by the marquis of Polini the 16th of 
December, 1737, and found it was 825 miles 
high ; and Mr. Bergman, from a mean of 30 
computations, makes the average height of 
the aurora borealis amount to 70 Swedish, or 
469 English, miles. But Euler supposes the 
height to be several thousands of miles ; and 
Mairan also assigns to them a very elevated 
region. 
In Sweden and Lapland the aurorae boreales 
are not only singularly beautiful, but afford 
travellers, by their almost constant effulgence, 
a very fine and brilliant light during the whole 
night. In Hudson’s-buy, the light ot the au- 
rora borealis is said to be equal to that ot a full 
moon: and in the north-eastern parts of Sibe- 
ria, we are told, these northern lights are 
observed to begin with single bright pillars, 
rising in the north, and almost at the same 
time in the north-east, which, gradually in- 
creasing, comprehend a large space ot the 
heavens, rush about from place to place with 
incredible velocity, and finally almost cover 
the whole sky up to the zenith, and produce 
an appearance in tire heavens of a vast ex- 
panded tent, glittering with gold rubies and 
sapphire. A more interesting spectacle can- 
not be conceived ; but whoever sees such a 
northern light for the first time could not be- 
hold it without terror. For however fine the 
illumination may be, it is attended, as it is said, 
with a hissing noise through the air, as if the 
largest fire-works were playing off. lode- 
scribe what they then hear, the natives make 
use of the expression spolochi chodjat, that is, 
the raging host is passing. The hunters who 
pursue the foxes are frequently overtaken with 
these lights; and their dogs are then so much 
terrified, that they will not move, but lie ob- 
stinately on the ground till the noise is passed. 
See Phil. Trans, vol. lxxiv. 
Many attempts have been made to deter- 
mine the cause of this phenomenon. Dr. 
Halley imagines that the watery vapours or 
effluvia, exceedingly rardied by subterra- 
neous fire, and tinged with sulphureous 
streams, which many naturalists have sup- 
posed to be the cause of earthquakes, may 
also be the cause of this appearance; or that 
it is produced by a kind of subtile matter 
freely pervading the pores of the earth, and 
which, entering into it nearer the southern 
pole, passes out again with some force into 
the tether, at the same distance from the 
northern. This subtile matter, by becoming 
more dense, or having its velocity increased, 
may perhaps 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. 
Philos. Trans. No. 347. See also Mr. Cotes’ s 
description of this phenomenon, and Lis me- 
thod of explaining it by streams emitted from 
the heterogeneous and fermenting vapours of 
the atmosphere, in Smith’s Optics, p. 69 ; or 
Philos. Trans, abr. vol. 6, part 2. 
Ever since the identity of lightning and 
the electric matter lias been determined, how- 
ever, philosophers have been naturally led to 
seek for the explication of aerial meteors in 
the principles of electricity ; and there is. now 
no doubt that most of them, and especially 
the aurora borealis, are electrical phenomena. 
Besides the more obvious and known appear- 
ances which constitute a resemblance between 
this meteor and the electric matter by which 
lightning is produced, it has been observed, 
that the aurora occasions a very sensible fluc- 
tuation in the magnetic needle ; and that 
when it has extended lower than usual in the 
atmosphere, the flashes have been attended 
with various sounds of rumbling and hissing, 
especially in Russia and the other more 
northern parts of Europe, as noticed by Sig. 
Beccariaand M. Messier. Mr. Canton, .soon 
after he had obtained electricity from the 
clouds, offered a conjecture that the aurora 
is occasioned by the dashing of electric tire 
positive towards negative clouds at a great 
distance, through the upper part of the atmo- 
sphere, where the resistance is least : and he 
supposes that the aurora which happens at 
the time when the magnetic needle is disturb- 
ed by the heat of the earth, is the electricity 
of the heated air above it : and this appears 
chiefly in the northern regions, as the altera- 
tion in the heat of the air in those parts is the 
greatest. Nor is this hypothesis wholly im- 
probable, when it is considered that electri- 
city is the cause of thunder and lightning; 
that it has been extracted from the air at the 
time of the aurora borealis; that the inhabit- 
ants of the northern countries observe it re- 
markably strong when a sudden thaw suc- 
ceeds very cold severe weather; and that the 
tourmalin is known to emit and absorb the 
electric fluid only by the increase or dimi- 
nution of its heat. Positive and negative 
electricity in the air, with a proper quantity 
of moisture to serve as a conductor, will ac- 
count for this and other meteors sometimes 
seen in a serene sky. Mr. Canton afterwards 
contrived to exhibit this meteor by means of 
the Torricellian vacuum, in a glass tube about 
three feet long, and sealed hermetically. 
When one end of the tube is held in the 
hand, and the other applied to the conductor, 
the whole tube will be illuminated from end 
,to end, and will continue luminous without 
Interruption for a considerable time after it 
has been removed from the conductor. If, 
after this, it is drawn through the hand either 
way, the light will be remarkably intense 
through the whole length of the tube. And 
though a great part of the electricity is dis- 
charged by this operation, it will still flash 
at intervals, when held only at one extremity, 
and kept quite still ; but if, at the same time, 
it is grasped by the other hand in a different 
place, strong flashes of light will dart from 
one end to the other; and these will continue 
24 hours or more, without a fresh excitation. 
Sig. Beccaria conjectures that there is a con- 
stant and regular circulation of the electric 
fluid from north to south; and he thinks 
that the aurora borealis may be this electric 
matter performing its circulation in such a 
state of the atmosphere as renders it visible, 
or approaching nearer than usual to the 
earth : though probably this is not the 
mode of its operation, as the meteor is ob- 
served in the southern hemisphere with the 
same appearances 'as in the northern. Dr. 
Franklin supposes that the electric lire dis- 
charged into the polar regions, from litany 
