A S T R O 
taught in the Italian f’chool, before Ariflotle and his two 
cotemporary philosophers, Eivdo'jsus and Callippus, had 
given it all the perfection which it is capable of receiving* 
Though rude and inartificial, it is capable of connecting 
together, in the imagination, the grandeft and the molt 
feemingly disjointed appearances in the heavens. The 
motions of the molt remarkable objects in the celeftial re¬ 
gions, the Sun, the Moon, and the fixed (tars, are fufficiently 
connected with one another by this hypothecs. The eclipfes 
of thefe two great luminaries are, though not fo eafily cal¬ 
culated, as ealily explained, upon this ancient, as upon 
the modern, fyfiem. When thefe early philofophers ex¬ 
plained to their difciples the very fimple caufes of thole 
dreadful phenomena, it was under the feal .of the mod fa- 
cred fecrecy, that they might avoid the fury of the peo¬ 
ple, and not incur the imputation of impiety, when they 
thus took from the gods the direction of t.hofe events, 
which were apprehended to be the mod terrible tokens of 
their impending vengeance. The obliquity of the eclip¬ 
tic, the confequent changes of the feafons, the vicillitudes 
of day and night, and the different lengths of both days 
and nights, in the different feafons, correfpond too, pretty 
exactly, with,this ancient doctrine. And if there, had 
been no other bodies difcoverable in the heavens befides 
the Sun, the Moon, and the fixed fiars, this old hypo'the- 
fis might have ftood the examination of all ages, and have 
gone down triumphant to the remotefl poflerity. 
If it gained the belief of mankind by its plaufibility, it 
attracted their wonder and admiration; fentiments that 
(till more confirmed their belief, by the novelty and beau¬ 
ty of that view of nature which it prefented to the ima¬ 
gination. Before this fyftem was taught in the world, the 
earth was regarded as, what it appears to the eye, a vaft 
rough and irregular plain, the bafis and foundation of the 
univerfe, furrounded on all lides by the ocean, and whofe 
roots extended themfelves through the whole of that in¬ 
finite depth which is below it. The fky was conlidered as 
a folid hemifphere, which covered the earth, and united 
with the ocean at the extremity of the horizon. The Sun, 
the Moon, and all the heavenly bodies, rofe out of the 
eafiern, climbed up the convex fide of the heavens, and 
defeended again into the weftern ocean, and from thence, 
by fome fubterraneous paflages, returned to their firfi cham¬ 
bers in the eaft. Nor was this notion confined to the peo¬ 
ple, or to the poets who painted the opinions of the peo¬ 
ple: it was held by Xenophanes, the founder of the Elea- 
tic philofophy, after that of the Ionian and Italian fchools, 
the earlieft that appeared in Greece. Thales of Miletus 
too, who, according to Arifiotle, reprefented the Earth as 
floating upon an immenfe ocean of water, may have been 
.nearly of the fame opinion ; notwithftanding what we are 
told by Plutarch and Apuleius concerning his aftronomical 
difeoveries, all of which mud plainly have been of a much 
later date. To iliofe who had no other idea of nature, be¬ 
sides what they derived from fo confufed an account of 
things, how agreeable muft that fyfiem have appeared, 
which mprefented the Earth as diftinguifhed into land and 
water, felf-balanced and fufpended in the centre of the 
univerfe, furrounded by the elements of air and ether, and 
covered by eight polilhed and cryflalline fpheres, each of 
which was diftinguilhed by one or more beautiful and lu¬ 
minous bodies, and all of which revolved round their com¬ 
mon centre, by varied, but by equable and proportionable, 
motions. It feems to have been the beauty of this fyfiem 
that gave Plato the notion of fomething like an harmonic 
proportion, to be difeovered in the motions and diftances 
of the heavenly bodies; and which fuggefted to the ear¬ 
lier Pythagoreans, the celebrated fancy of the muficof the 
fpheres: a wild and romantic idea, yet fucli as does not 
ill correfpond with that admiration, which fo beautiful a 
fyftem, recommended too by the graces of novelty, is apt 
to infpire. 
Whatever are t,he defeils which this account of things 
■labours under, they are fucli, as to the firfi obfervers of 
the heavens could not readily occur. If all the motions 
Vol. II. No.74. 
N O M Y. 429 
of the five planets cannot, the greater part of them may, 
be ealily connected by it; they and all their motions are the 
leaft remarkable objects in the heavens; the greater part 
of mankind take no notice of them at all; and a fyftem, 
whofe only defe6t lies in the account which it gives of 
them, cannot thereby be much difgraced in their opinion. 
It was, however, to remedy thofe defects, that Eudoxus, 
the friend and auditor of Plato, found it neceflary to in- 
creafe the number of the celeftial fpheres. Each planet 
is fometimes obferved to advance forward in that eaftward 
courfe which is peculiar to itfelf, fometimes to retire back¬ 
wards, and fometimes again to ftand ftiLl. To fuppofe 
that the fphere of the planet fliould by its own motion, if 
one may fay fo, fometimes .roll forwards, fometimes roll 
backwards, and fometimes do neither the one nor the 
other, is contrary to' all the natural propenfities of the 
imagination, which accompanies with eafe and delight any 
regular and orderly motion, but feels itfelf perpetually ' 
flopped and interrupted, when it endeavours to attend to 
one fo defultory and uncertain. It would purfue, natu¬ 
rally and of its own accord, thediredl or progreffive move¬ 
ment of the fphere, but is every now and then (hocked, 
and turned violently out of its. natural career, by the re¬ 
trograde and ftationary appearances of the planet, betwixt 
which and its more ufual motion, the fancy feels a want 
of connexion, a gap or interval, which it cannot fill up, 
but by fuppofing lome chain of intermediate events to join 
them. The hypothefis of a number of other fpheres re¬ 
volving in the heavens, befides thofe in which the lumi¬ 
nous bodies themfelves were infixed, was the chain with 
which Eudoxus endeavoured to fupply it. He beftowed 
four of thefe fpheres upon each of the five planets; one 
in which the luminous body itfelf revolved, and three 
others above it. Each of thefe had a regular and conftant, 
but a peculiar movement of its own, which it communi¬ 
cated to what was properly the fphere of the planet, and 
thus occafioned that diverfity of motionsobfervable inthofe 
bodies. One of thefe fpheres, for example, had an ofcil- 
latory motion, like the circular pendulum of a watch. As 
when you turn round a watch, like a fphere upon its axis, 
the pendulum will, while turned round along with it, (till 
continue to ofcillate, and communicate to whatever body 
is comprehended within it, both its own ofcillations and 
the circular motion of the watch ; fo this ofcillating fphere, 
being itfelf turned round by the motion of the fphere above 
it, communicated to the fphere below it, that circular as 
well as its own ofcillatory motion; produced by the one, 
the daily revolutions ; by the other, tiiedireft, ftationary, 
and retrograde, appearances of the planet, which derived 
from a third fphere that revolution by which it performed 
its annual period. The motions of all thefe fpheres were 
in themfelves conftant and equable, fiich as the imagina¬ 
tion could eafily attend to and purfue, and which connect¬ 
ed together that othenvife incoherent diverfity of move¬ 
ments obfervable in the fphere of the planet. The motions 
of the Sun and Moon being more regular than thofe of 
the five planets, by afiigning three fpheres to each of them, 
Eudoxus imagined he could connect together all the di- 
verfity of movements difcoverable in either. The motion 
of the fixed ftars being perfectly regular, one fphere he 
judged fufficient for them all. So that, according to this 
account, the whole number of celeftial fpheres amounted 
to twenty-feven. Callippus, though fomewhat younger, 
the cotemporary of Eudoxus, found that even this num¬ 
ber was not enough to connect together the vaft variety of 
movements which he difeovered in thofe bodies, and there¬ 
fore increafed it to thirty-four. Arifiotle, upon a'yet more 
attentive obfervation, found that even all thefe fpheres 
would not be fufficient, and therefore added twenty-two 
more, which increafed their number .to-fifty-fix. Later 
obfervers difeovered (till new motions, and new inequali¬ 
ties, in the heavens. New fpheres w ere therefore (till to 
be added to the fyftem, and fome of them to be placed 
even above that of the fixed ftars. So that in the fixteenth 
century,when Fracoftorio,fmitten with the eloquence of Pl a . 
4 P ' _ to 
