P.t A


( 817 )


PT 7 A


encompars'd Vith a  hantgeabic Atmoffphee; they have, of
confuenAe, Waters, Seas, &c. as well as dry Lad, and     2
are Bodies like the Moon, and therefore like the Earth.
Q.E.D.
PAnd hence, nothing hinders but that the Planets may be  i
concluded to be inhabited.
As to the Planetary Inhabitants; Huygens in his Co/mat ro-
"os argues very plaufibly for their Exiflence, from the fimi- I
litude of the Planets with our Earth; thole7 like this, being
opake, denle, uneven, round, heavy, illumined and warm'd
by the Sun ;having Night and Day, Summer and Winter, &c.
Wolfius deduces fomething relating hereto from Arguments
of another kind.-Thus e. gr. 'Tis fcarce to be doubted, that
the Inhabitants of Yupiter are much larger than thofe of the
Earth-; and in effed of the Giant Kind. For it is {hewn in
Optics, that the Pupil of the Eye dilates in a firong
Light, and contrals in a weak one; wherefore, fince in ;u-
piter the Sun's Meridian Light is much feebler than on the
Earth, by reafon of cupiter's greater Diftance from the Sun i
the Pupil will need to be much more dilatable in the Inha-
bitants of Yupiter, than in thofe of the Earth. But the Pu-
pil is obferv'd to have a conflant Proportion to the Ball of
the Eye; and the Eye to the reft of the Body fo that in
Animals, the larger the Pupil the larger the Eye, and the
larger the Body.
To afcertain the Size of thefe jovial Inhabitants, it may
be obferv'd that the Diftance of J2upiter from the Sun, is
to the Earth's Diftance from the fame, as z6 to 5; the In-
tenfity of the Sun's Light ia Jupster is to its Intenfity on the
Earth, in a duplicate Ratio of 5 to 26; but 'tis found by
Experience, that the Pupil dilates in a Ratio greater than
that wherein the Intenfity of Light decreafes; otherwife, a
Body at a great Dilance might be feen as clearly as a nearer:
The Diameter, therefore, of the Pupil in its greatefi Dilata-
tion, in Jupiter, is to its Diameter in the like Rfate in the
Earth, in a Ratio greater than that of 5 to 26.-If then
we put it, as Ic to z6, or as 5 to 13: fince the ordinary
Stature of the Inhabitants of the Earth is computed at 5
Englijh Feet, 4 Inches and .0; (which Wolfius tells us is his
own Height) the ordinary Stature of _upiter's Inhabitants
will be found 14 Feet 3, which is very nearly the fize of
the Giant Og, mention'd by Mofes, whofe Iron Bed was 9
Cubits long and its Breadth 4. See GIANT.
The Motion of the P L A N E T S.
That the Planets do all revolve round the Sun as their
Center, and not round the Earth, is evident from a thoufand
phrenomena.- 10 The Orbit wherein Venus, e. gr. moves,
does certainly encompafs the Sun, and therefore in defcribing
that Orbit) the Planet muft turn round the Sun. See 0 R-
B IT.
That her Orbit includes the Sun, appears hence that Ihe
is Sometimes above the Sun, fometimes below it, Sometimes
beyond it, andfometirnes on this fide; all which are evident
from the Circumftances of her Phafes.  See PHASES.
That ffie does not move round the Earth is no lefs appa-
rent from her being ever obferved in the fame Quarter with
the Sun, never receding from him above 450.-She never
therefore comes to be in oppofition to the Sun; no, not to
be in a Quartile Afpe&, or to have a Quarter of the Heavens
between them; both which, like the Earth, {he muff fre-
.quently have, did (he attend and move round the Earth.
20 That Mercury revolves round the Sun appears in like
manner from his Phafes, which refemble thofe of Venus and
the Moon; and from its Neighbourhood to the Sun, from
whom Mercury never recedes fo far as Venus does.
30 That the Orbit of Mars includes the Sun, is evident
from that Planet's being found both in Conjunition and Op-
pofition with the Sun; and in both Cafes fhining with a
fill Face.-Indeed, from the fame Circumfiances it appears,
that the Orbit of Afars encompaffes the Earth; but then,
it follows, likewife, from Mars's Diameter appearing fiveu
times as big when in Oppofition, as when in ConjunCtion,
that he is feven times nearer the Earth, in the latter than
the former Pofition. The Earth therefore is far from being
the Center of Mars's Motion; but Mars is ever nearly at
the fame Diftance from the Sun-Again, Mars view'd
from the Earth moves very irregularly; is fometinmes feen
to proceed flower, fometimes falter; fornetimes ftands ftill,
fometimes goes backward; (the Reafons whereof, fee. under
the Article 0 paT I c Irregularity) but view'd from the Sun,
will ever appear to move with the fame confiant uniform
Tenor; whence 'ris evident, he refpefts the Sun, not the
Earth, as the Centter of his Motion.
4f0 The fame Appearances whence AMars is fhewn to re-
volve round the Sun as a Center, are likewife obferv'd in
Japiter and Satarn7; whence the fame Conclufion may be
made of them.
Lafily, that the Earth revolves round the Sun, as a Cen-
ter, is evident from her Place which we have obfervd to be
betwen the Orbits of   arrs and Menus; an4 from the Phxr


nomena of the fiuperior Planets view'd therefro .-if thie
Earth flood flill we fhould never fee thofe Planetr either
llationary or retrograde; the Earth therefore moves, but
it is fill found between the Orbits of Mars and Venus which
encompafs the Sun; therefore the Earth too encompaffes
the Sun.
To this Afironomical Denionftration, may be added a
Phyfical D monftration, of the Earth's Motion fr6m Sir lfiac
Meiton.-lt appears from abundant Obfervation, that either
the Earth turns round the Sun, or the Sun round the Earth,
fo as to defcribe equal Area's in equal times: But he demon-
ftrates, that Bodies revolving about one another by fuch
Law, do of Necefity gravitate towards each other. (See
GRAVITATION. Whence if the Sun gravitate to the Earth,
AMon and Re-affion being ftill equal, the Earth will like-
wife gravitate toward the Sun. (See RE-Ac-moN.) But
he proves, further, that two Bodies gravitating towards each
other, without direaly approaching one another in right
Lines, muft both of them turn round the common Center
of Gravity of both.-The Sun and Earth, therefore, do
both revolve round one common Center.-But the Earth
being but a Point in comparifon of the Sun, the common
Center of Gravity of the two, will be within the Sun's
Body, and not far from its Genter.-Tbe Earth, thereftre,
revolves round a Point, within the Body of the Sun ; and there-
fore round the Sun. See EARTH and SUN.
The Orbits of the Planers are all Ellipfes i one of whofe
Foci is in the Sun.-This, Kepler firfl found from 7ycho's
Obfervations; before him all Afironomers took the Plane-
tary Orbits for eccentric Circles. See ORBIT, ELLIPSIS,
ECCENTRIC.
The Planes of thefe Orbits do all interreq in the Sun;
nor are their Extremities far a-part.-In effe&, they are but
little inclined to one another; and the greateft Angle any
of them makes with the Plane of the Earth's Orbit, i. e. of
the Ecliptic, is that of A'feieray, which lies at an Angle of
60  2';i that of Venus is 30 23I; that of Mars 1f0 s zi
that of Jupiter 1f so'; and that of Saturn f 30W.
The Line wherein the Plane of each Orbit cuts thit of th-
Earth, is call'd the Line of the Nodes; and the two Points
wherein, the Orbits themfllves.touch that Plane, the Nodes.
See NODE.
The Diftance between the Center of the Sun, and the
Center of each Orbit, is call'd the Eccentricity of the Planer.
See ECCENTRICITY.
And the Angle at which each Plane cuts that of the Ecli-
ptic, the Inclination of the Plane. See PLANE, INCL INA-
rIoN, and ECLIPTIC.
To account for the Motion of the Planets about the Sun;
there needs nothing but to fuppofe an uniform projeftile
Motion, in firait Lines, at firfl given themn; and a Power of
Attraffion or Gravitation, fuch as we obferve in all the great
Bodies in our Syflem.-For a Body A, (Tab. Aftronomy,
Fig. 6.4 proceeding uniformly along the Line A B; will,
by the Intervention of the attrafting Body C, be every Mo-
ment diverted out of its reftilinear, and bent into a curvi-
linear, Path ; according to the Laws of Central Forces. See
CENTRAL Force.
If, then, the projeffile Motion be perpendicular to a Line
C A, drawn from. the attradting Body C; and its Velocity fo
proportion'd to the Force of Attration of A, as that the
centripetal and centrifugal Forces are equal, i. e. that the
Conatus to fall to the central Body C, in a right Line, A C;
and that to proceed in the Direaion of the Tangent, A B,
balance each other: The Body will revolve in a circular Or-
bit AO, y, J&, (*c. SeeCENTRIPETAL and CENTRIFUGAL.
'Tis not improbable, that at the Beginning, this was the
State of things; and that the Velocities imprefs'd on the lr-
veral Planets were fo combin'd with their relpeftive Maflls
and Diffances from the Sun at which they were to roll; as
that their Momenta Ihould counter-balance the Sun's attra-
&five Force, and be precirely counter-balanced thereby:
whence the primitive Orbits muff have been perfet Circles,
from which they don't even now deviate very far; the Ec-
centrity of the Earth's Orbit being only  , of its Semidia-
meter. See ECCENTRICITrY.
If the Planet's projeffile Motion be not perfectly adju-
fled to the Sun's Attrafion -, the Orbit defcribed will be an
Ellipfis.-If it be too fwift, the Orbit will be greater th in
a Circle, and the nearer Focus coincide with the central Bo-
dy; if too flow, the Orbit will be lefs than a Circle, and
the further Focus coincide with the central Body.
Indeed the Form of the Planetary Orbits, does not only
depend on the Adjulfment of the firift projeftile Velocity
with the Sun's Artrafion, but alfo on the Direffion wherein
that Motion was originally inprefs'd.if that Dire~tion
were according to the Tangent A B, as above -fIppofe, and
the central Forces exaftly balanced, the Orbit wOutd be cir-'
cular; but if that DireCtion were oblique, in an y manner,
Whether afcending to or defending from the Sun, the Pla-
! et, notwithilanding any Adufnent of. its Velocity to
the Attraation, would be an Ellipfis. Ste PRoJEc~-ra.
The