A S T R O N O M Y. 
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metaphyfical evaflons the followers of Copernicus endea¬ 
voured to elude this objection, which, before the dodlrine 
of the corhpofition of motion had been explained by Ga¬ 
lileo, was altogether unanfwerable. They allowed, that 
a ball dropped from the malt of a fliip under fail would 
not fall at the foot of the malt, but behind it ; becaufe 
the ball, they faid, was no part of the fliip, and becaufe 
the motion of the (hip was natural neither to itfelf nor to 
the ball. But the (tone was a part of the earth, and the 
diurnal and annual revolutions of the Earth were natural 
to the whole, and to every part of it, and therefore to the 
Bone. The (tone, therefore, having naturally the fame 
motion with the Earth, fell precifely at the bottom of the 
tower. But this anfwer could not fatisfy the imagination, 
which (till found it difficult to conceive how thefe motions 
could be natural to the Earth ; or how a body, which had 
always prefented itfelf to the fenfes as inert, ponderous, 
and averfe to motion, fhould naturally be continually wheel¬ 
ing about both its own axis and the Sun with fuch violent 
rapidity. It was, belides, argued by Tycho Brahe, upon 
the principles of the fame philofophy which had afforded 
both the objedtion and the anfwer, that even upon the 
fuppofition, that any fuch motion was natural to the whole 
body of the Earth, yet the fione, which was feparated 
from it, could no longer be actuated by that motion. The 
limb, which is cut off from an animal, lofes thofe animal 
motions which were natural to the whole: the branch, 
which is cut off from the trunk, lofes that vegetative mo¬ 
tion which is natural to the whole tree. Even the metals, 
minerals, and (tones, which are dug out from the bofom 
of the Earth, lofe thofe motions winch occafioned their 
produftion and increafe, and .which were natural to them 
in their original Bate. Though the diurnal and annual 
motion of the Earth, therefore, had been natural to them 
while they were contained in its bofom ; it could no longer 
be fo when they were feparated from it. 
Tycho Brahe, the great rellorer of the fcience of the 
heavens, who had fpent his life and waited his fortune 
upon the advancement of aftronomy, whofe obfervations 
were both more numerous and more accurate than thofe of 
all the aftronomers who had gone before him, was himfelf 
fo much affefted by the force of this objection, that, tho’ 
he never mentioned the fyfiem of Copernicus without (ome 
note of the high admiration he had conceived for its au¬ 
thor, he could never himfelf be induced to embrace it; 
yet all his agronomical obfervations tended to confirm it. 
They delnouftratcd, that Venus and Mercury were fome- 
times above and fometimes below the Sun; and that, con¬ 
fequently, the Sun, and not the Earth, was the centre of 
their periodical revolutions. They (hewed, that Mars, 
when in his meridian, at midnight, was nearer to the 
Earth than the Earth is to the Sun ; though, when in 
conjunction with the Sun, he was much more remote from 
the Earth than that luminary ; a difcovery which was ab- 
folutely inconfiftent with the fyfiem of Ptolemy, which 
proved, that the Sun, and not the Earth, was the centre 
of the periodical revolutions of Mars, as well as of Venus 
and Mercury; and which demonftrated, that the Earth 
was placed betwixt the orbits of Mars and Venus. They 
made the fame thing probable with regard to Jupiter and 
Saturn; that they, too, revolved round the Sun; and that, 
therefore, the Sun, if not the centre of the univerfe, was 
at leafi that of the planetary fyfiem. They proved, that 
comets were fuperior to the Moor,, and moved through 
the heavens in all poflible directions ; an obfervation in¬ 
compatible with the folid fpheres of Arifiotle and Pur- 
bach, and which, therefore, overturned the phylical part, 
at leafi, of the eftablifited aftronomy. 
All thefe obfervations, joined to his averfion to the fyf- 
tem, and perhaps, notwithfianding the generofity of his 
•character, fome little jealoufy of the fame of Copernicus, 
luggefted to Tycho the idea of a new hypothelis, in which 
the Earth continued to be, as in the old account, the im¬ 
moveable centre of the univerfe, round which the firma- 
.gpeut revolved every day from eaft to welt, and, by fome 
(ecret virtue, carried the Sun, the Moon, and the five pla¬ 
nets, along with it, notwithfianding their immenfe difiance 
and notwithfianding there was nothing betwixt it and them 
but the mofi fluid ether. But, although all thefe (even 
bodies thus obeyed the diurnal revolution of the firma¬ 
ment, they had each of them, as in the old fyfiem, a con¬ 
trary periodical eaftward revolution of their own, which 
made them appear to be every day, more or lefs, left be¬ 
hind by the firmament. The Sun" was the centre of the 
periodical revolutions of the five planets ; tire Earth that 
of the Sun and Moon. The five planets followed the Sun 
in his periodical revolution round the Earth, as they did 
the firmament in its diurnal rotation. The three fuperior 
planets comprehended the Earth within the orbit in which 
they revolved round the Sun, and had each of them an 
epicycle to conned together, in the Came manner as in 
the fyfiem of Ptolemy, their direCt, retrograde, and-(la - 
tionary, appearances. As, notwithfianding their immenfe 
difiance, they followed the Sun in his periodical revolu¬ 
tion round the Earth, keeping always at an equal difiance 
from him, they were necefiarily brought much nearer to 
the Earth when in oppofition to the"Sun than when in 
conjundtion with him. Mars, the neared of them, when 
in his meridian at midnight, came within the orbit which 
the Sun deferibed round the Earth, and confequently was 
then nearer to the Earth than the Earth was to the Sun. 
The appearances of the two inferior planets were explain¬ 
ed, in the fame manner as in the fyfiem of Copernicus, 
and confequently-required no epicycle to conned them. 
The circles in which the five planets performed their pe¬ 
riodical revolutions round the Sun, as well as thofe in 
which the Sun and Moon performed theirs round tire 
Earth, were, as both in the old and new hypothefis, eccen¬ 
tric circles, to conned together their differently accelera¬ 
ted and retarded motions. 
Such was the fyfiem of Tycho Brahe, compounded, as 
is evident, Out of thofe of Ptolemy and Copernicus; hap¬ 
pier than that of Ptolemy, in the account which it ‘fives 
of the motions of the two inferior planets ; more complex", 
by luppofing the different revolutions of all the five to be 
performed round two different-centres ; the diurnal round 
(he Earth, the periodical round the Sun ; but, in every 
refped, more complex and more incoherent than that of 
Copernicus. Such, however, was the difficulty that man¬ 
kind felt in conceiving the motion of the Earth, that it 
long balanced the reputation of that otherwife more beau¬ 
tiful fyftem. It may be faid, that thofe who confidered 
the heavens only, favoured the fyfiem of Copernicus, 
which conneded fo happily all the appearances which prcl 
fented themfelves there: but that thofe who looked upon 
the Earth, adopted the account of Tycho Brahe, which 
leaving it at reft in the centre of the univerfe, did lefs 
violence to the uftial habits of the imagination. The learn¬ 
ed were, indeed, fenfible of the intricacy and of the many 
incoherences of that (yftem ; that it gave no account why 
the Sun, Moon, and five planets, fimuld follow the revo¬ 
lution of the firmament; or why the five planets, notwith¬ 
fianding the immenfe difiance of the three fuperior ones, 
(liould obey the periodical motion of the Sun; or why the 
Earth, though placed between the orbits of Mars and 
Venus, (fiould remain immoveable in the centre of the fir¬ 
mament, and conftantly refift the influence of whatever it 
was, which carried bodies that were fo much larger than 
itfelf, and that were placed cn all tides of it, periodically 
round the Sun. Tycho Brahe died before he had fully- 
explained his fyftem. His great and merited renown di(- 
poled many of the learned to believe, that, had his life 
been longer, he would have connedled together many of 
thefe incoherences, and knew methods of adapting his 
fyftem to fome other appearances, with which none of his 
followers could conned! it. 
The objection to the fyftem of Copernicus, which was 
drawn from the nature of motion, and that was mod in¬ 
filled on by Tycho Brahe, was at laft fully anfwered by 
Galileo; not, however, till about thirty years after the 
death 
