4 oo ASTRO 
happened on July 25th, 1766, in the evening, about four 
digits eclipfed ; and, after two periods more, it will hap¬ 
pen on Auguft 16th, 1802, early in the morning, about 
live digits, the centre coming from the north frozen con¬ 
tinent, by the capes of Norway, through Tartary, China, 
and Japan, to the Ladrone (Hands, where it goes off. 
Again, in 1820, Ad guff 26 th, between one and two, it 
will be a great eclipfe at London, about ten digits ; but, 
happening fo near the equinox, the centre will leave every 
part of Britain to the weft, and enter Germany at Embden, 
pairing by Venice, Naples, Grand Cairo, and fet in the 
gulf of Baffora near that city. It will be no more vifible 
till 1874, when five digits will be qbfcured (the centre 
being now about to leave the Earth) on September 28th. 
lit 1892, the Sun will go down eclipfed in London; and 
again, in 1928, the pallage of the centre will be in the 
expanding though there will be two digits eclipfed at Lon¬ 
don, Odlober the 31ft of that year, and about the year 
2090 the whole penumbra will be worn off; whence no 
more returns of this eclipfe can happen till after a revo¬ 
lution of ten thoufaod years. 
From thefe remarks on the entire revolution of this 
eclipfe, we may gather, that a thoufand years more or lefs 
(for there are Come irregularities that may protraft or 
lengthen this period 100 years) complete the whole ter- 
reftrial phenomena of any fingle eclipfe : and fince twenty 
periods of fifty-four years -each, and about thirty-three 
days, comprehend the .entire extent of their revolution, it 
is evident, that the times of the returns will pafs through 
a circuit of one year and ten months, every Chaldean pe¬ 
riod being ten or eleven days later, and of the equable ap¬ 
pearances, about thirty-two or thirty-three days. Thus, 
though this eclipfe happens about the middle ot July, no 
other fubfequent eclipfe of this period will return till the 
middle of the fame month again3 but wear conftantly 
.each period ten or eleven days forward, and at laft appear 
in winter ; but then it begins to ceafe from affe&ing us. 
Another conclufion from this revolution may be drawn, 
that there w ill feldom be any more than two great eclipfes 
,of the Sun in the interval of this period, and thefe follow 
fometimes next return, and often at greater diftances. 
That of 1715 returned again in 1735 very great ; but this 
prefent eclipfe will not be great till the year 1820, which 
is a revolution of four Chaldean periods : fo that the ir¬ 
regularities of their circuits mull undergo new computa¬ 
tions to aflign them exactly. 
Nor do all eclipfes come in at the fouth pole : that de¬ 
pends altogether on the pofition of the lunar nodes, which 
•will bring in as many from the expanfum one way as the 
other ; and fuch eclipfes will wear more lbutherly by de¬ 
grees, contrary to what happens in the prefent cafe. The 
eclipfe, for example, of 1736, in September, had its cen¬ 
tre in the expanfum., and let about the middle of its ob- 
feurity in Britain; it will wear in at the north pole, and, 
in the year 2600, or thereabouts, go off into theexpanfum 
on the fouth fide of the Earth. The eclipfes therefore 
which happened about the creation are little more than 
half-way yet of their ethereal circuit; and will be 4000 
years before they enter the Earth any more. This grand 
revolution feems to have been entirely unknown to the an¬ 
cients. A longer period than the above-mentioned, for 
comparing and examining eclipfes which happen at long 
intervals of time, is 557yr. 2jd. iSh. 30'. 11". in which 
time there are 6890 mean lunations; and the Sun and node 
meet again fo nearly as to be but 1 j" diftant.; but then it 
ir not the lame ecliple that returns, as in the iliorter pe¬ 
riod above-mentioned. 
Of COMETS. 
Of all the celeftial bodies, comets have given rife to the 
greateft number of fpeculations and conjectures. Their 
lirange appearance has in all ages been a matter of terror 
to the uninformed, who I ave generally looked upon them 
to be evil omens, and forerunners of war, peltilence, &c. 
Thus, in ancient times, they were imagined toLe prodi- 
N O M Y. 
gies hung out by the immediate hand of God in the hea¬ 
vens, - and intended to alarm the world. Their nature be¬ 
ing now better underftood, they are no longer terrible : but 
as there are Hill many w ho think them to be lupernatural 
warnings, portents of future events, it may not be impro¬ 
per to obferve, that the nrchitedt of the univerfe has fra¬ 
med every part according to divine order, and fubjedted 
all things to laws and regulations ; that he does not hurl 
at random ftars and worlds, and diforder the fyftem of the 
whole glorious frame, to produce falfe apprehenlions of 
diftant events, fears without foundation and without ufe. 
Religion glories in the tell of realon, of knowledge, and 
of true wifdom ; it is every way connected with, and is al¬ 
ways elucidated, by them. From philofophy we may learn, 
that, the more the works of the fuprenie Author of the 
univerfe are underftood, the more he mult be adored ; and 
that his fuperintendancy over every portion is niore clearly 
evinced, and more fully exprelfed, by their unvaried 
courfe, than by ten thoufand deviations. 
The exiltence of an univerlal connection between all 
parts of the fiderial heavens is now generally admitted. 
Comets undoubtedly form a part of this great chain ; but 
of the part they occupy, and of the ufes for which they 
exift, we are in a great meafure ignorant. It is a portion 
of fcience whofe perfection is referved for feme diftant 
day, when thefe bodies, and their vail orbits, may, by 
long knd accurate obfervation, be added to the known 
parts of the folar fyftem ; when aftronomy will appear with 
new lights, after all our dilcoveries, great as we at pre¬ 
fent imagine them to be. Upon the whole, the aftronomy 
of comets is very imperfect; for but little can be known 
with certainty where but little can be feen. Comets af¬ 
ford few obfervations on which to ground conjecture, and 
are for the greateft part of their courfe beyond the reach 
of human vifion. They are fometimes called blazingJlars, 
becaufe they are ufually attended with a long train of light, 
tending always oppofite to the Siin, and of a fainter luftre 
the farther it is from tire body of the comet. And hence 
arifes the divifion of comets, into three kinds, viz. bearded, 
tailed ,, and hairy ; though, in reality, this divifion rather re¬ 
lates to the fevcral circumftances of the fame comet, than 
to the phenomena of feveral. Thus, when the comet is 
eaftward of the Sun, and moves from him, it is faid to be 
bearded, becaufe the light precedes it in the manner of a 
beard, as ftiewn at Jig.S, of the Aftronomical-Plate V. 
When the comet is weft ward of the Sun, and fets after 
him, it is faid to be tailed, becaufe the train of light fol¬ 
lows it in the manner of a tail, as (hewn at Jig. 9. And, 
laftly, when the Sun and comet are diametrically oppofite, 
the Earth being between them, the train is hid behind the 
body of the comet, excepting the extremities, which, be¬ 
ing broader than the body of the comet, appear as it were 
around it, like a border of hair, or coma, from whence the 
comet derives its name. This form of it is ftiewn at Jig. 
10, in the fame Plate. But there have been comets whofe 
difk was as clear, round, and well-defined, as that of Jupiter, 
without either tail, beard, or coma. 
Philofophers and aftronomers, of all ages, have been 
much divided in their opinions as to the nature of comets. 
Diodorus Siculus and Apollonius Myndius, in Seneca, 
inform us, that many of the Chaldeans held them to be 
lafting bodies, having dated revolutions as well as the pla¬ 
nets, but in orbits vaftly more exteniive ; on which account 
they are only vifible while near the Earth, but difappear 
again when they go into the higher regions. Others of them 
were of opinion, that the comets were only meteors raifed 
very high in the air, which bla,ze for a while, and difap¬ 
pear when the matter of which they confift is confumed or 
difperfed. Some of the Greeks, before the time of Ari- 
ftotle, fuppofed that a comet was a vaft heap or aftemblage 
of very (mall ftars meeting together, by reafon of the ine¬ 
qualities of their motions, and fo uniting into a vifible 
mafs, by the union of al! their (jnall lights; which mull: 
again difappear, as thofe ftars feparated, and each pro¬ 
ceeded in its courfe. Pythagoras, however, accounted 
them 
