^4® ASTRO 
Bat, whatever moves in a circle is conftantly endea¬ 
vouring to fly ofl' from the centre of its revolution ; for 
the natural motion of all bodies is in a ftraight line. All 
the particles of matter therefore, in each of thofe greater 
vortices, were continually prefling from the centre to the 
circumference, with more or lei's force, according to the 
different degrees of their bulk and folidity. The larger 
and more folid globules of the fecond element forced them- 
felves upwards to' the circumference, while the fmaller, 
more yielding, and more aClive, particles of the firft, which 
could flow even through the interftices of tire fecond, were 
forced downwards to the centre. They were forced down¬ 
wards to the centre, notwithftanding their natural tendency 
was upwards to the circumference ; for the fame reafon 
that a piece of wood, when plunged in water, is forced 
upwards to the furface, notwithftanding its natural ten¬ 
dency is downwards to the bottom ; becaufe its tendency 
downwards is lefs ftrong than that of the particles of water, 
which therefore, if one may fay fo, prefs in before it, and 
thus force it upwards. But, there being a greater quantity 
of the firft element than was neceflary to fill up the inter- 
frices of the fecond, it was necelfarily accumulated in the 
centre of each of thefe great circular ftreams, and formed 
there the fiery and aClive fubftance of the Sun. For, ac¬ 
cording to that philofopher, the folar fyftems were infinite 
in number, each fixed ftar being the centre of one : and 
lie is among the firft of the moderns, who thus took away 
the boundaries of the ttniverfe ; even Copernicus and Kep¬ 
ler themfelves having confined it within what they fup- 
pofed the vault of the firmament. 
The centre of each vortex being thus occupied by the 
moft aCtive and moveable parts of matter, there was ne- 
ceftarily among them, a more violent agitation than in any 
other part of the vortex, and this violent agitation of the 
centre cherifhed and fupported the movement of the whole. 
But, among<the particles of the firft element, which fill 
up the interftices of the fecond, there are many which, 
from the prelfure of the globules on all lides of them, ne- 
ceflarily receive an angular form, and thus conftitute a 
third element of particles lefs fit for motion than thofe of 
the other two. As the particles, however, of this third 
element were formed in the interftices of the fecond, they 
are neceftarily fmaller than thofe of the fecond, and are 
therefore, along with thofe of the firft, urged down towards 
the centre, w here, w hen a number of them happen to take 
hold of one another, they form fuch fpots upon the furface 
of the accumulated particles of the firft element, as are 
often difeovered by telefcopes upon the face of that Sun 
whichenlightensandanimatesour particular fyftem. Thofe 
fpots are often broken and difpelled, by the violent agita¬ 
tion of the particles of the firft element, as has hitherto 
happily been the cafe with thofe which have fucceffively 
been formed upon the face of our Sun. Sometimes, how¬ 
ever, they encruft the whole furface of that fire which is 
accumulated in thecentre; and, the communication betwixt 
the molt aCtive and moft inert parts of the vortex being thus 
interrupted, the rapidity of its motion immediately begins 
to languiih, and can no longer defend it from being fwal- 
lovved up and carried away by the fuperior violence of fome 
other like circular ftream ; and in this manner, what w as 
onee a Sun becomes a planet. Thus the time was, ac¬ 
cording to this fyftem, when the Moon was a body of the 
fame kind with the Sun, the fiery centre of a circular 
ftream of ether, which flowed continually round her; 
but, her face having been crufted over by a congeries of 
angular particles, the motion of this circular ftream began 
to languifh, and could no longer defend itfelf from being 
abforbed by the more violent vortex of the Earth, which 
was then too a Sun, and which chanced to be placed in its 
neighbourhood. The Moon therefore became a planer, 
and revolved round the Earth. In procefs of time, the 
fame fortune, which had thus befallen the Moon, befel 
alfo the Earth ; its face was encrufted by a grofs and in¬ 
active fubftance ; the motion of its vortex began to lan- 
guifli, and it was abforbed by the greater vortex of the 
N O M y. 
Sun: but, though the vortex of the Earth had thus become 
languid, it ftill had force enough to occafion both the di¬ 
urnal revolution of the Earth, and the monthly motion of 
the Moon. For a fmall circular ftream may eafily be con¬ 
ceived as flowing round the body of the Earth, at the 
fame time that it is carried along by that great ocean of 
ether which is continually revolving round the Sun; in 
the fame manner, as in a great whirlpool of water, one 
may often fee feveral final! whirlpools which revolve round 
centresof their own, and at the fame time are carried round 
the centre of the great one. Such was the caufe of the 
original formation and confequent motions of the planetary 
fyftem. When a folid body is turned round its center, 
thofe parts of it, which are neareft, and thofe which are 
remoteft from the centre, complete their revolutions in. 
one and the lame time. But it is otherwife with the revo¬ 
lutions of a fluid : the parts of it which are neareft the 
centre complete their revolutions in a ftiorter time than 
thofe which are remoter. The planets therefore, all float¬ 
ing in that immenfe tide of ether which is continually let¬ 
ting in frc*m weft to eaft round the body of the Sun, com¬ 
plete their revolutions in a longer or fhortertime, according 
to their nearnefs or diftance from him. There was, how¬ 
ever, according to Des Cartes, no very exaCt proportion 
obferved betwixt the times of their revolutions and their 
diftances from the centre. For that nice analogy, which 
Kepler had difeovered betwixt them, having not yet been 
confirmed by the obfervations of Caflini, was, as I before 
took notice, entirely difregarded by Des Cartes. Accor¬ 
ding to him too their orbits might not be perfectly circular, 
but be longer one way than the other, and thus approach 
to an ellipfe. Nor yet was it neceflary to fuppofe, that 
they deferibed this figure with geometrical accuracy, or 
even that they deferibed always precifely the fame figure. 
It rarely happens, that nature can be mathematically exaCt 
with regard to the figure of the objects (he produces, upon 
account of the infinite combinations of impulfes, which 
mud confpire to the production of each of her effects. No 
two planets, no two animals of the fame kind, have ex¬ 
actly the fame figure, nor is that of any one of them per¬ 
fectly regular. It was in vain, therefore, that aftronomers 
laboured to find that perfeCt conftancy and regularity in 
the motions of the heavenly bodies, which is to be found 
in no other parts of nature. Thefe motions, like all others, 
muft either languiih or be accelerated, according as the 
caufe which produces them, the revolution of the vortex 
of the Sun, either languifhes, or is accelerated ; and there 
are innumerable events which may occalion either the one 
or the other of thofe changes. 
It was thus, that Des Cartes endeavoured to render fa¬ 
miliar to the imagination, the greateft difficulty in the Co- 
pernican fyftem, the rapid motion of the enormous bodies 
of the planets. When the fancy had thus been taught to 
conceive them as floating in an immenfe ocean of ether, it 
was quite agreeable to its ufual habits to conceive, that 
they ihould follow the ftream of this ocean, how rapid 
foever. This was an order of fucceflion to which it had 
been long accuftomed, and with which it was therefore 
quite familiar. This account too of the motions of the 
heavens, was connected with a vaft, an immenfe, fyftem, 
which joined together a greater number of the moft dif- 
cordant phenomena of nature than had been united 
by any other hypothefis; a fyftem in which the principles 
of connection, though perhaps equally imaginary, were, 
however, more diftinCt and determinate, than any that 
had been known before ; and which attempted to trace to 
the imagination, not only the order of fucceflion by which 
the heavenly bodies were moved, but that by which they, 
and almoft all other natural objeCts, had originally been 
produced. The Cartefian philofophy is wow indeed almoft 
univerfally rejected, while the Copernican fyftem conti¬ 
nues to be univerfally received. Yet it is not eafy to 
imagine, how much probability and coherence this ad¬ 
mired fyftem was long fuppofed to derive from that ex¬ 
ploded hypothefis. Till Des Cartes had ptiblifhed his 
principles. 
