40 6 ASTRO 
ton, in Suffolk, and an account was given of it as follows : 
It was feen at half pad eight in the evening, nearly in the 
pole of the ecliptic ; compoling a rhomboides or lozenge- 
fhaped figure with 0 and y Draconis, and a (tar of the 4th 
magnitude in the left heel of Hercules. It was then dif- 
tintlly vifible to the naked eye as a faint flar. With a 
good telefcope, it appeared to mod advantage when a pow¬ 
er of about forty was ufed. It was then a diffufed rnilky 
hazinefs, like the nebula of Andromeda. Its motion in 
twenty-four hours was about twelve degrees. It had no 
diftinft nucleus; but its fouthern fide was mod luminous, 
and feveral dars were feen didinftly through it. On the 
26th, at 8h. 53' it was above a. Ophinchi, with four de¬ 
grees greater altitude than that dar ; the comet being $o° 
5'. It had feventy-three degrees polar didance, and was 
very near an unnamed dar, from which it was palling fouth- 
ead. Its right afcenfion twenty degrees of Sagittarius. In 
pading near its node it came very near to the Earth, and, 
when fird feen, it was returning from the Sun, having 
paffed its perihelion fome weeks. Its afcending node is 
calculated in the fign twenty-eight degrees of Aquarius, 
and its perihelion didance computed at near one-fixteenth 
of the Earth’s, confequently nearer to the Sun than Venus. 
If the comet was, when neared to the Earth, on the 16th 
of Augnd, about five or fix millions of miles from 11s, or 
more than twenty times the Moon’s didance, which appears 
to have been the cafe, its obferved apparent diameter could 
hardly be lefs than one-third larger than the Moon. This 
would make it about 3000 miles in diameter, and fomewhat 
conliderably larger than Mercury. If the perihelion place 
could be reconciled, the other elements would bring this 
comet to a very near agreement with that of 1596 and 1699, 
fo as to make it probable they might be one and the fame. 
This would give a period varying from 103A to io8£ years. 
From what has been difeovered in general concerning 
comets, it is podible they may fometimes approach fonear 
to the primary planets, as to catife aneclipfe of the Sun to 
thofe planets; and, as the body of a comet bears a much 
larger proportion to the bulk of a primary planet than any 
fecondary, it is plain that a cometary eclipfe would both 
be of much longer continuance, and attended with much 
greater darknefs, than thatoccafioned by the Moon ; and, 
if we fuppofe the primary planet and comet to be moving 
both the fame way, the duration of fuch an eclipfe would 
be prodigioufly lengthened ; and thus, inftead of four mi¬ 
nutes, the Sun might be totally darkened to the inhabi¬ 
tants of certain places for as many hours. Hence we may 
account for that prodigious darknefs which we fometimes 
read of in hiftory, at times when no eclipfe of the Sun by 
the Moon could pofiibly happen. Such are thofe men¬ 
tioned by Herodotus, lib.vii. c.37, and lib.ix. c. 70; 
likevvife the eclipfe mentioned by Dion, which happened 
a little before the death of Auguftus; and it is obferva- 
ble, that Seneca noticed a comet the fame year. It is re¬ 
markable, however, that no comet hath ever been obfer¬ 
ved pafilng over the dilk of the Sun like a fpot, as Venus 
and Mercury are; yet this muft certainly happen, when 
the comet is in its perihelion, and the Earth on the fame 
fide of its annual orbit. Such a phenomenon well deferves 
the watchful attention of altronomers, as it would be a 
greater confirmation of the planetary nature of the comets 
than any thing hitherto obferved. 
Of the ZODIACAL LIGHT. 
The zodiacal light is a pyramid of light which fome¬ 
times appears in the morning before fun-rife. It has the 
Sun for its bafis, and in appearance refembles the aurora 
borealis, and the tails cf comets. Its lides are not ftraight, 
but a little curved, its figure refembling a lens feen edge¬ 
ways. It is generally feen here about Oflober and March, 
that being the time of our Ihortefi twilight; for it cannot 
be feen in the twilight; and, when the twilight lafts a 
confiderable time, it is withdrawn before the twilight ends. 
Ib was obferved by M. Caflini, in 1683, a little before the 
vernal equinox, in the evening, extending along the eclip- 
N O M Y„ 
tic from the Sun. He thinks, however, that it has appear¬ 
ed formerly, and afterwards difappeared, from an obfer- 
vation of Mr. J. Childrey, in a book publilhed in 1661, 
entitled, Britannia Baconica. He fays, that “ in February, 
for leveral years, about fix o’clock in the evening, after 
twilight, he law a path of light tending from the twilight 
towards the Pleiades, as it were touching them. This is to 
be feen whenever the weather is clear, but bell when the 
Moon does not Ihine. I believe this phenomenon has been 
formerly, and will hereafter appear always at the above- 
mentioned time of the year. But the caufe and nature of 
it I cannot guefs at, and therefore leave it to the enquiry 
ot pofierity.” From this defeription, there can be no 
doubt but that this was the zodiacal light. He fufpefls 
alio, that this is vvliat the ancients called trabrs, which 
word they ufed for a meteor, or imprellion in the air like 
a beam. Pliny, lib. ii. p. 26, fays, “ Emicant trabes, 
quos docos vocant.” Des Cartes alfo fpeaks of a pheno¬ 
menon of the fame kind. M. Facio obferved it immedi¬ 
ately after the difeovery by M. Cafiini, and fufpefled that 
it has always appeared. It was foon after obferved by M. 
Kirch and Eimmart in Germany. In the year 1707, on 
April 3, it was obferved by Mr. Derham in Eifex. It 
appeared in the weftern part of the heavens, about a quar¬ 
ter of an hour after fun-let, in the form of a pyramid, 
perpendicular to the horizon. The bafe of this pyramid 
he judged to be the Sun. Its vertex reached fifteen or 
twenty degrees above the horizon. It was throughout of 
a dulky red colour, and at firfi appeared pretty vivid and 
drong, but faintell at the top. It grew fainter by degrees, 
andVanilhed about an hour after fun-fet. This folar at¬ 
mosphere has alfo been feen about the Sun in a total folar 
eclipfe, a luminous ring appearing about the Moon at the 
time when the eclipfe was total. 
To illufirate this fubjefl. let HO R, in the annexed fi¬ 
gure, be the horizon, S the Sun 18 0 below twilight; then 
will A I O reprefent the appearance and pofition of the zo¬ 
diacal light feen at Paris on the laft day of February, and 
zge will reprefent the lame the next morning before the 
beginning of twilight, the Sun-being at S', as determined 
by M. de Mairan, in his treatife de I’Aurore Boreale. The 
diltance S A was then about 90°, and IO about 20°. The 
A 
axis A Z, az, coincide with the Sun’s equator, and there¬ 
fore makes an angle of about 75 0 with the ecliptic. There¬ 
fore, as the angle which the ecliptic makes with the hori¬ 
zon changes at different times of the day, the angle which 
the axis of this light makes with the horizon will alfo be 
variable. Hence, if we determine the angle which the 
ecliptic makes with the horizon at any time, it will give 
us ths pofition. If we fet a celellial globe to the hour, it 
