that the fame may be deduced by certain Confequences from the Obfervations that have been made concerning them, as every Mathematician knows, and as literally appears in the Syft. Saturn. p. 77 and 81, of Mr. Huygens; fo that upon the whole Matter, it depends only on the Greatness and Distance of the Earth with refpect to the Sun, not to know the Proportion only, but the true Meafure thereof, of which Aftronomers are in a manner fo much Mafters, that they can be fure that neither the Planets themfelves nor their Distances are fupposed too great.

If it be then known that there is no Miftake of any Importance made herein, the swiftness of their Motion may be eafily computed from the time of their Revolution: As for Inftance, a Cannon-bullet runs, according to the Experiments of Merfennus, (quoted by Huygens in his Cofmotheoros, P. 125) 100 French Toifes of fix Foot, in the space of a Second; and according to the most accurate Admeasurement of the French, the Diameter of the Earth amounts to 6,538,594 of the faid Toifes or Fathoms,

Accordingly then a Cannon-Bullet would run the length of the Earth's Diameter in about 65,386 Seconds, that is, full 18 Hours; from whence it follows, that it would run in one Year, confifting of 365 Days, 486 of the like Diameters, and 40 thereof in a Month of 30 Days.

Now it appears above, that (Tab. XXII. Fig. 1, and 2.) the length between the Sun and Earth, or the Line A S, being fuppofed' to be 10,000 Diameters (which is lefs than what is allowed by Meff. Huygens and la Hire) the Distance of Venus from the Sun, or the Line S C, will amount to 7000 of the said Diameters; and if now we take the Revolution CIR for a Circle, of which CS is the half Diameter, the whole one CR

will

will be 14000 of the Earth's Diameters; and fup pofing the Ratio of the whole Diameter to the Circumference of a Circle, according to what is known, As 113 To355; the Circumference CIR of this Diameter CR, which Venus finishes in 7 Months, will be 43,982 Diameters of the Earth.

But it is found before, That a Bullet runs 300 of the like Diameters in 7 Months, or in the Time of Ventis's Revolution. Thus it appears, that the Velocity of Venus, with respect to that of a Cannon-Bullet is, As 43,982 To 300 or; that Venus moves 146 times fafter than the faid Bullet.

After the like manner, and with very little Trouble too, we may compute, that fince Jupiter's Distance from the Sun, or the Semidiameter of its Way (fuppofing it likewife to be exactly circular) amounts to 51,000 Diameters of the Earth, and that the Time of its Revolution is 12 Years; it moves about 55 times, at least a good deal above 54, faster than a Cannon-Bullet, that fhall run in one Year 486 of the like Diameters, as has been fhewn above. We fuppofe here the Courses of the Planets to be uniform, tho' Aftronomers find that they move one while fafter and another flower; but forafmuch as they perform their Revolutions in about the faid Time, this Calculation is fure enough.

SECT. LXIV. The Swiftness of one of Jupiter's Moons.

Is we now fuppofe with Mr. Caffini, (See the Cofmotheoros, p. 101) that the nearest of Jupiter's Moons is diftant from it 2; Diameters of that Planet, and that its Revolution is performed in one Day, eighteen Hours, twenty eight Minutes, and thirty fix Seconds; the whole Diameter of the faid Revolution, will be 5, and the Circumference

cumference, fuppofing it to be exactly circular, will be 17 Diameters of Jupiter.

Now one Diameter of Jupiter is equal to 20 Diameters of the Earth; the Revolution therefore of this nearest Moon is 356 of the faid Diameters, and according to the fuppofed Time of the Revolution this runs in one Day in its Way about Jupiter, 201 Diameters of the Earth; and Jupiter, according to its before-fuppofed Distance and Time of its Revolution runs 73 Diameters in its Orbit about the Sun in the faid Space of a Day; fo that this Moon runs in its Orbit about twice or thrice as fast as Jupiter itself, and confequently a great deal above 100 times fafter than a Cannon-Bullet, tho' it be as big as the Earth itfelf: See Huygens's Cofmotheoros, p. 101.

SECT. LXV. The amazing Force that is requifite to move Jupiter.

Now if one would form an Idea of the amazing Greatness of that Power by which the faid Planet is moved, it having been proved before, that the Diameter of Jupiter is 20 times greater than that of the Earth, it follows that the former Planet is 8000 times bigger than the latter.

Now thofe who understand Mechanicks know, that by multiplying the Mafs of two Bodies, each of 'em by its own Velocity, the Proportion of the Powers that move them, may be learned from thence: Suppofing then that the Earth's Magnitude to be as an Unit, and the Velocity of the Cannon-Bullet to be likewife as an Unit, the Force that muft move the Earth with the fame Swiftnefs as a Cannon-Bullet is moved, must also be as an Unit, because an Unit multiplied by itself produces only an Unit.

And in this Comparison the Globe of Jupiter

muft

must be fuppofed as 8000, and its Velocity as 54, because it moves in its Orbit 54 times swifter than a Bullet; which being multiplied with the other, gives 432,000 for the Force that moves Jupiter.

So that it is irrefragably proved hereby, that the Force which moves Jupiter, and confequently the Strength of that Planet it self is at least 432,000 times as great as that which is capable of caufing the Earth to move with the same Velocity as a Bullet is discharged from a Cannon.

We suppose here the Denfity of the Parts of which the Earth and Jupiter are compofed to be equal; tho' fome reckon that of the Earth to be greater than Jupiter's; yet this difference will not hinder the faid Number from remaining a great many thousands of Times more; but this is not the Place to make fo nice an Enquiry in.

SECT. LXVI. Convictions from the Whole.

Now they that hitherto doubt whether there be a mighty Creator and Director of this Univerfe, let them fit down by themselves, and ferioufly confider, Firft, How thefe Planetary Globes, fo amazing in their Magnitudes, are whirl'd about the Sun with so dreadful a Velocity, so far furpaffing the almost unconceivable Motion of a Cannon-Bullet.

Secondly, How other Planets, or Moons, each of which will hardly yield in Magnitude to the Earth, are carried with a yet greater Swiftness about the aforefaid Planets.

Thirdly, That neither the Motion of Jupiter in his Orbit, nor of the rest of the Planets, can be performed but by a Force fo many thousand times greater than that mighty Strength by which a Globe as large as the whole Earth is driven with the fame Velocity as a Bullet shot out of a Cannón

And

And if this laft Force, whereby the Earth can be fo fwiftly moved, furpaffes all human Conception, what fhall we fay of that which moves the Planet Jupiter in the Heavens?

SECT. LXVII. The Evafions of Atheists, and their Pretences.

I KNOW very well, that in order to elude the Proof of an All-ruling God, which is fo terrible to Atheists, thofe miferable Wretches are wont to conceive the Motions of these vast heavenly Globes, as they were fo many round little Balls, floating and circulating in a Veffel of Water, which happens when the Water is put into a Circular Motion; and they are not a little confirmed in fuch Fancies, by the Figures with which Aftronomers are used to reprefent the Struature of the World, as may be feen in Tab. XXII. Fig. 1, and 2. where we find the Revolutions of the Planets reprefented like the forementioned Balls in Water, upon one and the fame Plane ; infomuch that there does not feem to be wanting any other Direction for their Motions than only conceiving a circular Motion of the Matter in which they fwim, and the rather, because if one moves the Water in a round Veffel swiftly about with a Stick, we may often obferve fome of the little Particles thereof whirling about their own Axis, and at the fame time carried about the common Center; from whence they infer, That the Moons alfo of Saturn and Jupiter may be likewife carried about their refpective Planets, as here at F and H, without any particular Direction.

And thus thefe deplorable Difputers are ufed to contemplate, and to account for the Wonder$ produced in the Heavens, without confidering VOL. III. Eee

them