3*9 ASTRO 
ecilpfesby the mean motions of the fun and moon obferved 
5000 years fince ; and that their accuracy, with regard to 
the folar motion, far exceeds that of the bed Grecian af- 
tronomers. They had alfo fettled the lunar motions by 
computing the fpaee through which that luminary had 
pa (Ted in 1,600,984 days, or a little more than 4383 years. 
M. Bailly alfo informs us, that they make ufe of the cycle 
of nineteen years, the fame as that afcribed by the Greeks 
to Mefon ; that their theory of the planets is much better 
than Ptolemy’s, as they do not fuppofe the earth in the 
centre of the celedial motions, and believe that Venus and 
Mercury move round the fun ; and that their adronomy 
agrees with the mod modern difcoveries as to the decreafe 
of the obliquity of the ecliptic, the acceleration of the 
motion of the equinoctial points, See. In the 2d vol. of 
the Tran factions of the Royal Society of Edinburgh is alfo 
a learned and ingenious didertation on the adronomy of the 
Brahmins of India, by profedor Playfair; in which the 
great accuracy and high antiquity of the fcience, among 
them, is reduced to the greated probability. It hence 
appears that their tables and rules of computation have 
peculiar reference to an epoch, and to obfervations, three 
or four thoufand years before Ohrid ; and many other in- 
dances are there adduced, of their critical knowledge in 
the other mathematical fciences, employed in their pre¬ 
cepts and calculations. 
Adronomy, it feeiiis, was not unknown to the Ameri¬ 
cans ; though in their divilion of time, they made ufe only 
of the folar and not of the lunar motions. And that the 
Mexicans, in particular, had a drange predilection for the 
number thirteen, by means of which they regulated almod 
every thing : their diorted periods confided of thirteen 
days ; their cycle of thirteen months, each containing 
twenty days ; and their century of four periods, of thir¬ 
teen years each ; and this excellive veneration for the num¬ 
ber thirteen, arefe, according to Siguenza, from its being 
the number of their greater gods. And it is very remark¬ 
able, that the Abbe Clavigero aflerts it a faff, that, hav¬ 
ing difcovered the excels of a few hours in the folar above 
the lunar year, they made ufe of intercalary days, to bring 
them to an equality, as edablifhed by Julius Caslhr in the 
Roman calendar; but with this difference, that, indead 
of one day every four years, they interpofed thirteen days 
every fifty-two years, which produces the fame effect. 
Mod authors, however, fix the origin of adronomy and 
adrology, either in Chaldea or in Egypt ; and accordingly 
among the ancients we find the word Chaldean often tiled 
for adronomer, or, which was the fame thing, ddrologer. 
Indeed both of thefe nations pretended to a very high an¬ 
tiquity, and claimed the honour of producing the fird cul¬ 
tivators of this fcience. The Chaldeans boaded of their 
temple or tower of Belus, and of Zoroader, w hom they 
placed 5000 years before the dedruTion of Troy ; while 
the Egyptians boaded ot their colleges of prieds, where 
adronomy was taught, and of the monument of Ofyman- 
dvas, in which, it is laid, there was a''golden circle of 365 
cubits in circumference, and one cubit thick, divided 
into 363 equal parts according to the days of the year, &c. 
From Chaldea and Egypt, adronomy palled into Phoenicia, 
and this people applied it to the purpofes of navigation, 
fleering their courie by the north polar (far; and hence 
They became mailers of the fea, and of almod all the com¬ 
merce in the world. 
The Greeks, it is probable, derived their adronomieal 
knowledge chiefly from the Egyptians and Phoenicians, by 
means of feveral of their countrymen- who villted thole 
nations for the purpofe of learning the different fciences. 
By what we can collect from the hidorical fragments of 
thole early ages, it appears, that though mankind were un¬ 
acquainted with the true principles of adronomy, they had 
neverthelefs formed many rational conclufions with refpeCt 
to the celedial phenomena. Thole even who fuvveyed the 
heavens.with the moll carelefs attention, necelfarily diftin- 
guifhed in them three different forts of objects; the Sun, 
*he Moon, and the Stars. Thefe lad, appearing always-in 
N O M Y. 
the fame fituation, and at the fame didance with regard to 
one another, and deeming to revolve every day round the 
earth in parallel circles, which widened gradually from the 
poles to the equator, were naturally thought to have all the 
marks of being fixed, like fo many gems, in the concave 
fide of the firmament, and of being carried round by the 
diurnal revolutions of that foil'd body : for the azure Iky, 
in which the dars teem to float, was readily apprehended, 
upon account of the uniformity of their apparent motions, 
to be a folid body, the roof or outer wall of the uikverfe, 
to whole infide all thole little fparklifig objefts were at¬ 
tached. From this original idea of adronomy, we fliali 
trace its progrefs to the prelent time, in the language and 
order of the much-admired podhuinous work of Dr. 
Adam Smith. 
The Sun and Moon, often changing their didance and 
fituation, in regard to the heavenly bodies, could not be 
apprehended, even by the earlieft adronomers, to be at¬ 
tached to the fame fphere with them. They adigned, 
therefore, to each of them, a fphere of its own; that is, 
fuppofed each of them to be attached to the concave fide 
of a folid and tranlparent body, by whofe revolutions they 
were carried round the earth. There was not indeed, in 
this cafe, the fame ground for the fuppofition of Inch a 
fphere as in that of the fixed dars ; for neither the Sun nor 
the Moon appears to keep always at the fame didance with 
regard to any one of the other heavenly bodies. But, as 
the motion of the dars had been accounted for by an hy- 
pothefis of this kind, it rendered the theory of the hea¬ 
vens more uniform, to account for that of the Sun and 
Moon in the fame manner. The fphere of the Sun they 
placed above that of the Moon ; as the Moon was evident¬ 
ly feen in eclipfes to pafs betwixt the Sun and the Earth. 
Each of them was fuppofed to revolve by a motion of its 
own, and at the fame time to be affedted by the motion of 
the fixed dars. Thus, the Sun was carried round from 
ead to welt by the communicated movement of this outer 
fphere, w hich produced his diurnal revolutions', and the 
vicillitLides of day and night; but at the fame time he had 
a motion of his own, contrary to this, from wed to ead, 
which occafioned his annual revolution, and the continual 
Ihifting of his place with regard to the fixed dars. This 
motion was more eafy, they thought, when carried on 
edgeways, and not in direct: oppolition to the motion of the 
outer fphere, which occafioned the inclination of the axis 
of the fphere of the Sun to that of the fphere of the fix¬ 
ed dars; this again produced the obliquity of the ecliptic, 
and the conlequent changes of the fea Tons, The Moon, 
being placed below the fphere of the Sub, had both a 
Ihorter courie to finiih, and was lefs oblhuded by the con¬ 
trary movement of the fphere of the fixed dars, front 
which (he was farther removed. She finilhed her period, 
therefore, in a fliorter time, and required but a month, in- 
ftead of a year, to complete it. 
The dais, when more attentively furveved, w ere fome 
of them obferved to be lefs condant and uniform in their 
motions than the red, and to change their (filiations with, 
regard to the other heavenly bodies; moving generally eaff- 
wards, yet appearing fome times to (land dill, and fome- 
times even to move wedwards. Tlrefe, to the number of 
five, were didinguidled by the name of planets, or wan¬ 
dering dars, and marked with the particular appellations 
of Saturn, Jupiter, Mars, Venus, and Mercury. As, like 
the Sun and Moon, they feem to accompany the motion of 
the fixed dars from ead to well, but at the fame time to 
have a motion of their own, which is generally from wed 
to ead ; they were each of them, as well as thole two great 
lamps of heaven, apprehended to be attached to the infide 
of a folid concave and tranlparent fphere, which had a 
revolution of its own, that was almod dirc-ctly contrary to 
the revolution of the outer heaven, but which, at the fame 
time, was hurried along by the fuperior violence and ra¬ 
pidity of this lad. 
This is the fydem of concentric fpheres, the fird regu¬ 
lar fydem of adronomy which the world beheld, as it was 
taught 
