534 ASTRO 
grade motion. To *xplain thefe appearances, the fyftem 
of Ptolemy ftippofed each of thefe planets to be at the 
upper part of their Several epicycles, in the one caie; and 
at the lower, in the other. But it afforded no fatisiaftory 
principle of conneftion, which could lead the mind eafily 
to conceive how the epicycles of thofe planets, whole 
Spheres were fo diftant from the Sphere of the Sun, (hould 
thus, if one may fay So, keep time to his motion. The 
fyftem of Copernicus afforded this eaftly, and like a more 
Simple machine, without the affiftance of epicycles, con- 
netted together, by fewer movements, the complex ap- 
pearances^of the heavens. When the Superior planets ap¬ 
pear nearly in conjunction with the ouu, they aie then in 
the Side of their orbits, which is almolt oppofite to, and 
mod diftant from, the Earth, and therefore appear fmalleft, 
andVaft fenfible to the eye. But, as they then revolve 
in a direction which is almolt contrary to that ot the 
Earth, they appear to advance forward with double ve¬ 
locity ; as a (hip, that Sails in a contrary direction to ano¬ 
ther, appears from that other to fail both with its own 
velocity and the velocity of that from which it is feen. 
On the contrary, when thofe planets are in oppolition to 
to the Sun, they arc on the fame (ide of the Sun with the 
Earth, are neareft it, molt fenlible to the eye, and revolve 
in the fame direction with it; but, as their revolutions 
round the Sun are (lower than that of the Earth, they are 
neceffarily left behind by it, and therefore feem to revolve 
backwards; as a (hip which fails flower than another, tlio’ 
it Sails in the fame direction, appears from that other to 
fail backwards. After the lame manner, by the fame an¬ 
nual revolution of the Earth, he connected together the 
direCt and retrograde motions of tiie two inferioi planets, 
as well as the llationary appearances of all the five. 
There are fome other particular phenomena ol the two 
inferior planets, which correfpond Itill better to this fyl- 
tem, and Hill worfe to that of Ptolemy. Venus and Mer¬ 
cury feem to attend conftantly upon the motion ol the 
Sun, appearing, Sometimes on the one fide, and Sometimes 
on the other, of that great luminary ; Mercury being al- 
moft always buried in its rays, and Venus never receding 
above forty-eight degrees from him, contrary to w hat is 
obferved in the other three planets, which are often feen 
in the oppofite fide of the heavens, at the greateft poflible 
diflance from the Sun. The fyftem of Ptolemy accounted 
for this, by fuppoling that the centres ot the epicycles of 
thefe two planets were always in the lame line with thole 
of .he Sun and the Earth; that they appeared therefore 
in conjunction with the Sun when either in the upper or 
lower part of their epicycles, and at the greateft diflance 
from him when in the (ides of them. It alTigned, how¬ 
ever, no reafon why the epicycles ot thefe two planets 
ftiould obferve fo different a rule from that which takes 
place in thofe of the other three, nor for the enormous 
epicycle of Venus, whofe fides mull have been forty-eight 
decrees diftant from the Sun, while its centre was in con- 
junClion with him, and whofe diameter mull have covered 
more than a quadrant of the great circle. But how eafily 
all thefe appearances coincide with the hypotlielis, which 
reprefents thofe two inferior planets revolving round the 
Sun in orbits comprehended within the orbit ot the Earth, 
is too obvious to require an explanation. 
Thus far did this new account of things render the ap¬ 
pearances of the heavens more completely coherent than 
had been done by any of tiie former fyftems. It did this, 
too, by a more Ample and intelligible, as well as a more 
beautiful, machinery. It reprel'ented the Sun, the great 
enlightener of the univerfe, w hole body was alone larger 
tl\an all the planets taken together, as eltabliftied immove¬ 
able in the centre, (hedding light and heat on all the worlds 
that circulated around him in one unitoim direction, but 
in longer or (liorter periods according to their different 
distances. It took away the diurnal revolution ot the fir¬ 
mament, whofe rapidity., upon the old hypotlielis, was 
beyond what even thought could conceive. It not only 
delivered the imagination from the embarruftment of epi- 
N O M Y. 
cycles, but from the difficulty of conceiving thefe two 
oppofite motions going on at the fame time, which the 
fyftem of Ptolemy and Ariltotle bellowed upon all the 
planets; I mean, their diurnal weftward and periodical 
eaftward revolutions. The Earth’s revolution round its 
own axis took away the necelTity for fuppoling the firft, and 
the fecond was eafily conceived when by itfelf. The five 
planets, which feem, upon all other fyftems, to be objects 
of a fpecies by themlelves, unlike to every thing to which 
tfie imagination has been accuftomed, when ftippofed to 
revolve along with the Earth round the Sun, were natu¬ 
rally apprehended to be objeils of the fame kind with the 
Earth, habitable, opaque, and enlightened only by the 
rays of the Sun. And thus this hypotlielis, by clafling 
them in the fame fpecies of things, with an object that is 
of all others the molt familiar to us, took off that won¬ 
der and uncertainty which the Itrangenefs and Angularity 
of their appearance had excited ; and thus far better an- 
fwered the great end of philofophy. 
Neither did the beauty and (implicity of this fyftem a- 
lone recommend it to the imagination ; the novelty and 
unexpedlednefs of that view of nature, which it opened to 
the fancy, excited more wonder and furprife than the 
ftrangeft of thofe appearances, which it had been invented 
to render natural and familiar, and thefe fentiments ftill 
more endeared it. For, though it is the end of philo¬ 
fophy, to allay that wonder, which either the unufual or 
leemingly disjointed appearances of nature excite, yet Ihe 
never triumphs fo much, as when, in order to conned! to¬ 
gether a few, in themfelves, perhaps, inconfidtrable ob¬ 
jects, fhe has, if 1 may lay fo, created another conftitution 
of things, more natural indeed, and fitch as the imagina¬ 
tion can more eafily attend to, but more new, more con¬ 
trary to common opinion and expedtation, than any of 
thofe appearances themfelves. As, in the inftance before 
us, in order to conned! together fome feeming irregulari¬ 
ties in the motions of the planets, the mod inconlklerable 
objedts in the heavens, and of w hich the greater part of 
mankind have no occalion to take any notice during the 
whole courfe of their lives, Ihe has, to talk in the hyper¬ 
bolical language of Tycho Brahe, moved the Earth from 
its foundations, Hopped the revolution ot the firmament, 
made the Sun Hand ftill, and lubverted the whole order 
of the univerfe. 
Such were the advantages of this new hypothefls, as 
they appeared to its author, when he firft invented it. 
But, though that love of paradox, fo natural to the learn¬ 
ed, and that pleafure, which they are fo apt to take in 
exciting, by the novelty of their ftippofed difeoveries, the 
amazement of mankind, may, notwithftanding what one 
of his difciples tells ns to the contrary, have had its 
weight in prompting Copernicus to adopt this fyftem ; yet, 
when he had completed his Treatife of Revolutions, and 
began coolly to conlider what a ftrange dodfrine he was 
about to offer to the world, he fo much dreaded the pre¬ 
judice of mankind againft it, that, by a fpecies of conti¬ 
nence of all others the mol! difficult to a philofopher, he 
detained it in his clofet for thirty years together. At laft, 
in the extremity of old age, he allowed it to be extorted 
from him, but died as loon as it was printed, and before 
it was publiftied. 
When it appeared in the world, it was aimed univer- 
fally diliipproved, as well by the learned as by the igno¬ 
rant. The natural prejudices of fenfe, continued by edu¬ 
cation, prevailed too much with both, to allow them to 
give it a fair examination. A few difciples only, whom 
he himfelf had inftruCied in his doifrine, received it with 
efteem and admiration. One of them, Reinhcldus, formed, 
upon this hypotlielis, larger and more accurate aftronomi- 
cal tables than what accompanied the Treatife of Revo¬ 
lutions, in which Copernicus had been guilty of fome er¬ 
rors in calculation. It foon appeared, that thofe Prutenic 
Tables, as they were called, correfponded more exactly 
with the heavens, than the Tables of Alphonfus. This 
ought naturally to have formed a prejudice in favour of 
