vifible, they again appear to rife in or near the fame Place as they did at firft. Now by reafon of Mercury's Nearness to the Sun, and of Saturn's great Distance from him, no Obfervations of this kind have hitherto been made on them, and therefore their diurnal Motion, or Revolution round their own Axis, tho' probable, is not yet abfolutely determined.

As the Ecliptic Line is the Orbit or annual Path of the Earth, fo each Planet has its proper Orbit, whose Plane differs fome few Degrees from the Plane of the Orbit of the Earth; and to a Spectator's Eye placed in the Center, would interfect or cut the Earth's Orbit at two oppofite Points or Nodes. To reprefent this more plainly to your Imagination, fuppofe, fays Mr. Watts, as many Hoops as there are Planets, thrust through with several strait Wires, and thereby join'd in different Places to the Hoop that reprefents the Plane of the Ecliptic, i. e. the Earth's Orbit; and then let those Hoops be turn'd more or lefs obliquely from the Plane of the Ecliptic: For all the feveral Orbits or Paths of the Flanets do not cross or interfect the Ecliptic in the fame Point, nor at the fame Angles; but their Nodes or Interfections of the Ecliptic are in different Parts of the Ecliptic, and alfo make different Angles with it.

Each of the primary Planets moves round the Sun in a Line which forms an Ellipfis, which I will here show you how to defcribe.

Fix upon any Plane two Pins, as at A and B. To thefe tie a String ACB fomewhat longer than their Diftançe

from

from one another. Then apply a third Pin D in the Double of the Thread, fo as to hold it ftrain'd, and in that manner carrying this Pin about, the Point of it will defcribe an Ellipfis. If through the Points AB the ftrait Line EABF be drawn, and terminated at the Points E and F, this is the longeft Line that can be drawn within the Figure, and is called the greater Axis of the Ellipfis. The Line GH, drawn perpendicular to this Axis EF, fo as to pafs thro' the middle of it, is called the leffer Axis. The two Points A and B are called Focus's. Now each primary Planet moves round the Sun in a Line of this kind, the Place of the Sun being in one of the Focus's. Suppofe A to be the Place of the Sun, then E is the Point wherein the Planet will be nearest to the Sun, and at F it will be the most remote. The Point E is call'd the Perihelion of the Planet, and F the Aphelion. In G and H the Planet is faid to be in its middle or mean Distance, because the Distance AG or AH is truly the middle between AE the leaft, and AF the greatest Distance.

Of the fix primary Planets, it hath not been obferv'd that more than three are attended with Secondaries, Moons, or Satellites, viz. the Earth, Jupiter, and Saturn.

The Moon is a fecondary Planet to the Earth, and performs her Revolution round it, in fomewhat less than 28 Days, at about thirty Diameters of the Earth's Distance from it; and in the Space of a Year is carry'd along with the Earth round the Sun.

*Jupiter has four Satellites attending him. The firft or innermost of which performs its Revolution in about 1 Day 18 Hours, at a Distance from the Center of that Planet equal to about 5 Semi-diameters of Jupiter's Body, The next Satellite revolves round Jupiter in about 13 Days 13 Hours, at the Distance from Jupiter of about 9 of that Planet's Semi-diameters. The third performs its Period nearly in 7 Days 3 Hours, at the Distance of about 14 Semi-diameters. The fourth, which is the outermoft, makes its Period in about 16 Days 16 Hours, at a Distance of about 25 Semi-diameters.

Saturn has five Satellites attending him, which perform their Periods round him as follows. The innermoft is diftant about 4 of Saturn's Semi-diameters, and revolves round him in about 1 Day 21 Hours. The next is diftant about 5 Semi-diameters, and makes its Period in 2 Days 17 Hours. The third is about 8 Semi-diameters diftant, and performs its Revolution in near 4 Days 11 Hours. The fourth is near 18 Semi-diameters diftant, and moves round Saturn in about 15

• Vide Pemberton's View of Newton's Philofophy,

15 Days 22 Hours. The outermost is removed to the Diftance of 56 Semi-diameters, and makes its Revolution in about 79 Days 7 Hours. Befides thefe Satellites, there belongs to Seturn another Body of a very fingular Kind. This is a fhining, broad, and flat Ring, which encompaffeth the Planet round about, without adhering in any Place to its Body. But what Laws this Ring is fubject to, or what Ufes it may ferve, are yet unknown.

The Reafon for taking fuch particular Notice of the Diftance of the primary Planets from the Sun, and of the fecondary Planets from their refpective Primaries, is this; these feveral Distances are requifite to be known, in order to apprehend more clearly the Excellency of the Copernican System; according to which, the Motions of all the Planets, both Primary and Secondary, are regulated by one general Law, viz. The Squares of the periodical Times of

Primary

Secondary

Planets are one to another, as the Cubes

the { }
of their Distances from the {

Sun,

Center of their Primary.

Far beyond this Solar System are placed the fixed Stars, at fuch an immense Distance, that the beft Telescopes reprefent them but as Points: They are called fixed Stars, becaufe from all Ages they have not been obferv'd to change their Situation, Hence, fays Mr. Wells, it is ufual to denote the Place of any of the intermediate Celeftial Bodies, by affigning what Part of the Sphere of the fixed Stars they appear to us to be in, or more properly under. And accordingly it is ufual to diftinguish that Tract of the Sphere of the fixed Stars, under which all the Planets move, by the Afterifms or Constellations that lie in that Tract; which being fancy'd to reprefent feveral Things, are therefore called Signs; and because the Things reprefented by them are most of them + Zodia, or Animals, hence all this Tract is ftil'd the Zodiac. Now the Orbit, wherein the Earth performs its annual Period (and which the Sun feems to move round every Year) runs under the very middle of the Zodiac; whence this middle Part of the Zodiac is of special Note in Aftronomy, and is therefore diftinguifh'd by a peculiar Name, being called the Ecliptic. This, as well as the whole Zodiac, is divided into twelve Parts, diftinguifh'd by the Conftellation or Sign, to which each Part was formerly affign'd. The Names and Characters of the faid Signs are as follows.

A Greek Word, fignifying living Creatures.

Avics.

Aries Taurus.

Gemini. Cancer. Leo. Virgo. Libra.

From the Obfervations of those who have endeavour'd to find the Parallax of the Earth's Orbit, it may be demonstrated, that the nearest of the fixed Stars are at least 100,000 Times farther from us, than we are from the Sun. Nay fo inconceivable is the Space betwixt us and them, that Aftronomers have computed the Distance of Sirius, or the DogStar, which is thought the neareft, to be no less than 2,200000,0000co Miles, i. e. two Billions and two hundred thousand Millions of Miles. So that a Cannon-Ball in its fwifteft Motion, would be above fix hundred thousand Years in travelling to it.

If a Spectator was placed as near to any fixed Star as we are to the Sun, that Star would in all Probability appear to him as big as the Sun appears to us; and our Sun would feem no bigger than a fixed Star. Since the Sun therefore differeth nothing from a fixed Star, why may not the fixed Stars be reckon'd as fo many Suns, and every Star be fupposed the Center to a Syftem of inhabited Planets and Worlds like ours? For who can conceive that all those noble and majestic Globes were only intended as Lights or Ornaments to this diminutive Ball which we inhabit?"

But these grand Objects! thefe amazing Systems! their Numbers, Motions, Magnitudes! are much too vaft and too fublime for the Capacity of the human Mind to form an adequate Conception of them. Yet let me hope that you will fo contemplate them, as to raise and kindle in your Heart, Love, Praise and Adoration to the fupreme Creator.

PART

PART IV.

CHRONOLOGY

G.

AND

HISTORY.

H

Governor. Pupil.

ITHERTO, my young Pupil, I have confined myself to fuch Inftructions as may be filed Preliminary, and were intended to prepare you for Studies of a higher Nature. It now remains that I enter upon the more important Part of my Tafk; to principle your Mind with found Knowledge, to form you to Wisdom and Virtue, and guide you thro' the Paths of Learning and the Sciences. May I flatter myself with the fame ready Attention here, the fame Defire to learn and improve, as I have all along experienced in the Course of the Leffons already given you?

P. Doubtless you may; for in our feveral Conversations together, you have frequently intimated, that the Subjects then handled, tho' useful in themselves, yet chiefly merited Attention, as preparatory to other Things of greater Moment and Confequence. This Confideration made me liften to you with Pleafure, and I have waited impatiently for the Time when I was to enter upon more ferious Studies.

G. I am pleased to find you fo well difpofed. You difcover a Judgment and Understanding much above your Years; and as I plainly fee that my past Instructions have not been wholly unprofitable, I proceed with the greater Chearfulnefs. And now that I am to lead you regularly thro' the most important Branches of human Learning, I fhall begin with giving you Directions for that Study, which above all others conduces to make a Man knowing, prudent and virtuous. For this is the capital Point in Education, and what ought to be eftablifhed as the Ground-work of all our other Improvements, if we mean that they fhall be either profitable to ourselves,

or