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encompafs'd with a changeable Atmofphere - , they have, of noniena of the fuperior planets view'd therefrom. — -If the
confequence, Waters, Seas, &c. as well as dry Land, and Earth ftood ftill we fhould never fee thofe Planets either
are Bodies like the Moon, and therefore like the Earth, ftationary or retrograde ; the Earth therefore moves, but
O.E.D. it is Hill found between the Orbits of Mars and Venus which
And hence, nothing hinders but that the Planets may be encompafs the Sun ; therefore the Earth too encompaffes
concluded to be inhabited. t the Sun.
As to the Planetary Inhabitants -, Huygcns in his Cofmetheo- To this Aftronomical Demonstration, maybe added a
res argues very plauiibly for their Exiftence, from the (imi- Physical Demonftration, of the Earth's Motion from Sir Ifiiac
litude of the Planets with our Earth', thofe, like this, being Newton.— -It appears from abundant Obfervatio:i, that either
opake, denfe, uneven, round, heavy, illumined and warm'd the Earth turns round the Sun, or the Sun round the Earth,
by the Sun ■, having Night and Day, Summer and Winter, &c. fo as to defcribe equal Area's in equjl times : But he demori-
ffo/jSaj deduces fomething relating hereto from Arguments ftrates, that Bodies revolving about one another by fuck
of another kind.— Thus e.gr. 'T's fcarce to be doubted, that the Inhabitants of "Jupiter are much larger than thofe of the Earth-, and in erfeft of the Giant Kind. For it is Ihewn in Optics, that the Pupil of the Eye dilates in a ftrong Light, and contracts in a weak one ; wherefore, fince in Ju- piter the Sun's Meridian Light is much feebler than on the Earth, by reaibn of Jupiter's greater Diftance from the Sun ;
Law, do of Necessity gravitate towards each other. (S . Gravitation. Whence if the Sun gravitate to the Earth, Action and Re-aftion being ftill equal, the Earth will like- wife gravitate toward the Sun. (See Re-action.) But he proves, further, that two Bodies gravitating towards each other, without directly approaching one another in right Lines, muff both of them turn round the common Center
the Pupil will need to be much more dilatable in the Inha- of Gravity of both.— i he Sun and Earth, therefore, do bitants of Jupiter, than in thofe of the Earth. But the Pn- both revolve round one common Center. — But the Earth pil is oblerv'd to have a conftant Proportion to the Ball of being but a Point in comparifon of the Sun, the common
the Eye-, and the Eye to the reft of the Body fo that i 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 oblerv'd that the Diftance of Jupiter from the Sun, is to the Earth's Diftance from the fame, as 26 to 5 ; the In- tensity of the Sun's Light in Jupiter 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
Center of Gravity of the two, will be within the Sun's Body, and not far from its Center.— The Earthy therefore, revolves round a Point, within the Body of the Sun ; and there- fore round the Sun. See Earth and Sun.
The Orbits of the Planets are all Elliples:, one of whofe Foci is in the Sun.— This, Kepler firft found from Tycho's Obfervationsi before him all Aftronomers took the Plane- tary Orbits for eccentric Circles. See Oreit, Ellipsis, Eccentric.
The Planes of thefe Orbits do all interfeft in the Sun ; Body at a great Diftance might be (ten as clearlyasa nearer: nor are their Extremities fir a-part. — In effect, they are but The Diameter, therefore, of the Pupil in its greateft Dilata- little inclined to one another; and the greateft Angle any
tion, in Jupiter, is to its Diameter in the like ftate in the
Earth, in a Ratio greater than that of 5 to 26 If then
we put it, as 10 to 26, or as 5 to 13 : fince the ordinary Stature of the Inhabitants of the Earth is computed at 5 Englifi Feet, 4 Inches and ,'„ -, (which Wolfius tells us is his own Height) the ordinary Stature of Jupiter's Inhabitants
Of them makes with the Plane ol the Earth's Orbit, /. e. of the Ecliptic, is that of Met cury, which lies at an Angle of 6° 52' ; that of Venus is 3° 23' ; that of Man i° 52' ; that of Jupiter i° 20' ', and that of Saturn z° 30'.
The Line wherein the Plane of each Orbit cuts that of the Earth, is call'd the Line of the Nodes; and the two Points
will be found 14 Feet f , which is very nearly the fize of wherein the Orbits themlelves touch that Plane, the Nodes. the Giant Og, mention'd by Mofes, whofe Iron Bed was 9 See Node.
The Diftance between the Center of the Sun, and the
Center of each Orbit, is call'd the Eccentricity of the Planet.
See Eccentricity.
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 Phenomena. 1° The Orbit wherein Venus, e. gr. moves,
And the Angle at which each Plane cuts that of the Ecli- ptic, the Inclination of the Plane . See Plane, Inclina- tion, and Ecliptic.
To account for the Motion of the Planets about the Sun ;
does certainly encompafs the Sun, and therefore in defcribing there needs nothing but to fuppofe an uniform projeftile
that Orbit, the Planet muft turn round the Sun. See Or- Motion, in ftrait Lines, at firft given them -, and a Power of
b 1 t. Attraction or Gravitation, fuchas we obferve in all the great
That her Orbit includes the Sun, appears hence that (he Bodies in our Syftem.— For a Body h, (Tab. Aflronomy,
is fometimes above the Sun, fometimes below it, fometimes Fig. 6.) proceeding uniformly along the Line AB; will,
beyond it, andfometimes on this fide ; all which are evident by the Intervention of the attracting Body C, be every Mo-
frorh the Circumftances of her Phafes. See Phases. ment diverted out of its rectilinear, and bent into a curvi-
That (he does not move round the Earth is no lefs appa- linear, Path ; according to the Laws of Central Forces. See
rent from her being ever obferved in the fame Quarter with Central Force.
the Sun, never receding from him above 45 She never If, then, the projeftile Motion be perpendicular to a Line
therefore comes to be in oppofition to the Sun ; no, not to CA, drawn from the attracting BodyC-, and its Velocity fo
be in a Quartile Afpeft, or to have a Quarter of the Heavens proportion'd to the Force of Attraction of A, as that the
between them-, both which, like the Earth, (he muft fre- centripetal and centrifugal Forces are equal, i. e. that the
.quently have, did ilie attend and move round the Earth. Conatus to fall to the central BodyC, in a right Line, AC;
2° That Mercury revolves round the Sun appears in like and that to proceed in the Direction of the Tangent, A B,
manner from his Phafes, which referable thofe of Venus and balance each other : The Body will revolve in a circular Or-
the Moon ; and from its Neighbourhood to the Sun, from bit A/3, y, J*, &c. See Centripetal and Centrifugal. whom Mercury never recedes fo far as Venus does. 'Tis not improbable, that at the Beginning, this was the
3 That the Orbit of Mars includes the Sun, is evident State of things-, and that the Velocities impreis'd on the le-
from that Planet's being found both in Conjunction and Op- veral Planets were fo combin'd with their refpeftive MaiTes
pofition with the Sun-, and in both Cafes mining with a and Diftances from the Sun at which they were to roll ; as
full Face. Indeed, from the fame Circumftances it appears, that their Momenta (hould counter-balance the Sun's attra-
tliat the Orbit of Mars encompaffes the Earth ", but then, it follows, likewife, from Mars's Diameter appearing liven times as big when in Oppofition, as when in Conjunction, tliat 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
ftive Force, and be precifely counter balanced thereby : whence the primitive Orbits muft have been perfect Circles, from which they don't even now deviate very far ; the Ec- centrity of the Earth's Orbit being only -,4J„ of its Semidia- meter. See Eccentricity. If the Planet's projeftile Motion be not perfectly adju-
the fame Diftance from the Sun. Again, Mars view'd fted to the Sun's Attraction -, the Orbit defcribed will be an
from the Earth moves very irregularly ; is fometimes feen Ellipfis.- — if it be toofwift, the Orbit will be greater th m
to proceed (lower, fometimes falter-, fometimes (lands ftill, a Circle, and the nearer Focus coincide with the central Bo-
fometimes goes backward ; (the Reafons whereof, fee, under dy ; if too flow, the Orbit will be lefs than a Circle, and
the Article Optic Irregularity) but view'd from the Sun, the further Focus coincide with the central Body,
will ever ap n -' t to move with the fame conftant uniform Indeed the Form of the Planetary Orbits, does not only
Tenor ; whence 'tis evident, he refpefts the Sun, not the depend on the Adjuftment of the firft projeftile Velocity
Earth, as the Centvr of his Motion. with the Sun's Attraction, but alfo on the Direction wherein
4° The fame Appearances whence Mars is Ihewn to re- that Motion was originally imprefs'd If that Direction,
volve round the Sun as a Center, are likewife obferv'd in were according to the Tangent A B, as above fuppofed, and
Jupiter and Saturn; whence the fame Conclufion may be made of them.
Laftly, that the Earth revolves round the Sun, as a Cen
the central Forces exactly balanced, the Orbit would be cir- cular ; but if that Direftion were oblique, in any manner, whether afcending to or defending from the Sun, the Pla-
ter, is evident from he- Place which we have obferv'd to be net, notwithstanding any Adjuftment of its Velocity to between the Orbits of Man and Venus ; and from the Plvx- the Attraction, would be an Ellipfis. See Projectile.
The
