ASTRONOMY. 
in diale&ic, and for the fectirity and fublimitv^of their 
moral dodrines, thofe fages feem never to have had any 
high reputation for their knowledge ot the heavens; nei¬ 
ther is the name ol any one of them ever counted in the ca¬ 
talogue of the great aftronomers, and ft odious obfervers 
of the ftars, among the ancients. I hey rejected the doc¬ 
trine of the folid fpheres; and maintained, that thecelef- 
tial regions were filled with a fluid ether, of too yielding 
a nature to carry along with it, by any motion of its own, 
bodies fo immenfely great as the Sun, Moon, and five pla¬ 
nets. Tliefe, therefore, as well as the fixed ftars, did not 
derive their motion from the circumambient body, but had 
each of them, in itfelf, and peculiar to itfelf, a vital prin¬ 
ciple of motion, which direded it to move with its own 
peculiar velocity, and its own peculiar diredion. It was 
by this internal principle, that the fixed ftars revolved di- 
redly from eaft to weft in circles parallel to the equator, 
greater or lefs according to their diflance or nearnefs to 
the poles, and with velocities lo proportioned, that each 
of them finifhed its diurnal period in the fame time, in 
fomething lefs than twenty-three hours and fifty-fix minutes. 
It was by a principle of tlie fame kind, that the Sun moved 
weftwards, (for they allowed of no eaftward motion in the 
heavens,) but with lefs velocity than the fixed ftars, fo as 
to finifh his diurnal period in twenty-four hours, and, con- 
fequently, to fall every day behind them by a fpace of the 
heavens nearly equal to that which he paft'es over in tour 
minutes; that is, nearly equal to a degree. T his revolution 
of the Sun, too, was neither diredly weft-wards, nor exact¬ 
ly circular; but, after the futnmer folltice, his motion be¬ 
gan gradually to incline a little fouthwards, appearing in 
his meridian to-day farther fouth than yefterday, and to¬ 
morrow (till farther fouth than.to-day; and thus continu¬ 
ing every day to deferibe a fpiral line round the Earth, 
which carried him gradually farther and farther fouth¬ 
wards till he arrived at the winter folftice. Here, this 
fpiral line began to change its diredion, and to bring him 
gradually, everyday, farther and farther northwards., till 
it again reftored him to the fummer folftice. In the fame 
manner they accounted for the motion of the Moon, and 
that of the five planets, by fuppofing that each of them 
revolved weftwards, but with directions and velocities that 
were botli different from one another, and continually va¬ 
rying; generally, however, in fplierical lines, lomewhat 
inclined to the equator. 
This fyftem feems never to have had the vogue. The 
fyftem of concentric, as well as that of eccentric, fpheres, 
gives fome fort ot reafon, botli for the conftancy and equa¬ 
bility of the motion of the fixed ftars, and for the variety 
and uncertainty of that of the planets. Each ot them be- 
ftow fome fort of coherence upon thofe apparently disjoint¬ 
ed phenomena. But this other fyftem feems to leave them 
pretty much as it found them. Afk a Stoic, Why all the 
fixed ftars perform their daily revolutions in circles paral¬ 
lel to each other, though of very different diameters, and 
with velocities fo proportioned, that they all finifh their 
period at the fame time, and through the whole courleof 
it preferve the fame diftance and fituation w ith regard to 
one another ? He can give no other anfwer, but that the 
peculiar nature, or, it one may fay fo, the caprice, of each 
ftar direds it to move in that peculiar manner. His fyf¬ 
tem affords him no principle of connection by which lie 
can join together, in his imagination, fo great a number of 
harmonious revolutions. But either of tiie other two iyf- 
tems, by the fuppofition of the folid firmament, affords 
this eafily. He is equally at a lofs to canned together the 
peculiarities that are obferved in the motions of the other 
heavenly bodies; the fpiral motion of them all; tlveir al¬ 
ternate progreffion from north to fouth, and from fouth to 
north ; the fometimesaccelerated, and again retarded, mo¬ 
tions of the Sun and Moon; the dired, retrograde, and 
fiationary, appearances.of the planets. All thefe have, in 
his fyftem, no bond of union, but remain as loofe and in¬ 
coherent in the fancy as they at firft appeared to the fenfes, 
before philofophy had attempted, by giving them a new 
arrangement, by placing them at different diftances, by af- 
figning to each fome peculiar but regular principle of mo¬ 
tion, to methodize and difpofe them into an order that 
fliould enable the imagination to pafs as fmoothly, and 
with as little embarraftment, along them, as along the moll 
regular, familiar, and coherent, appearances of nature. 
Such were the fyftems of aftronomy that, in the ancient 
world, appear to have been adopted by any confiderable 
party. Of all of them, the fyftem of eccentric fpheres 
was that which correfponded moft exactly with the appear¬ 
ances of the heavens. It was not invented till after thofe 
appearances had been obferved, w ith fome accuracy, for 
more than a century together; and it was not completely 
digefted by Ptolemy till the reign of Antoninus, after a 
much longer courfe of obfervations. We cannot wonder, 
therefore, that it was adapted to a much greater number 
of the phenomena than either of the other two fyftems 
which had been formed before thofe phenomena were ob¬ 
ferved with any degree of attention; which, therefore,, 
could connect them together only while they were thus re¬ 
garded in the grofs, but which, it could not be expected, 
fliould apply to them when they came to be conlidered in 
the detail. From the time of Hipparchus, therefore,.this 
fyftem feems to have been pretty generally received by all 
thofe who attended particularly to the ftudy of the hea¬ 
vens. That aftronomer firft made a catalogue of the fixed 
ftars; calculated, for fix hand red years, the revolutions of 
the Sun, Moon, and five planets ; marked the places in the 
heavens in which, during all that period, each of thofe 
bodies fliould appear; afeertained the times af. the edipfes^ 
of the Sun and Moon, and the particular, places of the 
Earth in which they fliould be vifible.. His calculations 
were founded upon this fyftem ; and as the events corref¬ 
ponded to his predictions, with a degree of accuracy which, 
though inferior to what aftronomy has lince arrived at, was 
greatly luperior to any thing which tlie world had then 
known, they afeertained, to all aftronomers and mathema¬ 
ticians, the preference of his fyftem above all thole which 
had been current before it. 
It w as, how ever, to aftronomers and mathematicians on. 
ly that they afeertained this; fur, notwitliftanding the evi¬ 
dent fuperiority of this fyftem to all thofe with whicii the 
world was then.acquainted, it was never, adopted by any¬ 
one fed of philofophers. Indeed philofophers, long be¬ 
fore the days of Hipparchus, feem to have abandoned the- 
ftudy of nature, to employ themfelves chiefly in ethical,, 
rhetorical, and dialectical, queftions. Each party of them 
had, perhaps, by this time, completed their peculiar fyftem 
or theory ot the univerfe, and no human confideration, 
could then have induced them to give up any part of it. 
That fupercilious and ignorant contempt with.which they 
regarded all mathematicians, among whom they counted 
aftronomers, Items even to have hindered them from en¬ 
quiring fo far into their dodrines as to know what opinions 
they held. Neither Cicero nor Ser.eca, who have fo of¬ 
ten occafion to mention the ancient fyftems of aftronomy, 
take any notice of that of Hipparchus. His name is not 
to be found in the writings of Seneca. It is mentioned 
but once in thofe of Cicero, in a letter to Atticus, but 
without any note of approbation as a geographer, and not 
as an aftronomer. Plutarch, when he counts tip, in his. 
fecund book concerning the Opinions of Philofophers, all 
the ancient fyftems of aftronomy, never mentions this, the 
only tolerable one w hich was known in his-time, Thofe 
three authors, it feems, converted only with the writings 
of philofophers. The elder Pliny indeed, a man whole 
curiofity extended itfelf equally to every part of learning, 
del’cribes the fyftem of Hipparchus, and never mentions 
its author without fome note of that High admiration w hich 
he had fo juftly conceived for his merit. Such profound 
ignorance in thefe profefled inftrudors of mankind, with 
regard to fo important a part of the learning of tlieir own. 
times, is indeed very extraordinary. 
Syftems in many relpeds refemble machines. A ma¬ 
chine is a. little fyftem created to perform, as well as to 
conncft - 
