AN
ORIGINAL THEORY
OR
NEW HYPOTHESIS
OF THE

UNIVERSE,

By THOMAS WRIGHT, of Durham.

One Sun by Day, by Night ten Thousand shine,
And light us deep into the Deity. Dr. Young.
LONDON:
Printed for the Author, and sold by H. Chapelle, in Grosvenor-Street.
MDCCL.

THE
PREFACE.

THE Author of the following Letters having been flattered into a Belief, that they may probably prove of some Use, or at least Amusement to the World, he has ventured to give them, at the Request of his Friends, to the Publick. His chief Design will be found an Attempt towards solving the Phænomena of the Via Lactea, and in consequence of that Solution, the framing of a regular and rational Theory of the known Universe, before unattempted by any. But he is very sensible how difficult a Task it is to advance any new Doctrine with Success, those who have hitherto attempted to propagate astronomical Discoveries in all Ages, have been but ill rewarded for their Labours, tho' finally they have proved of the greatest Benefit and Advantage to Mankind. This ungrateful Lesson we learn from the Fate of those ingenious Men, who, in ignorant Times, have unjustly suffered for their superior Knowledge and Discoveries; they who first conceived the Earth a Ball, were treated only with Contempt for their idle and ridiculous Supposition, as it was called; and he who first attempted to explain the Antipodes, lost his Life by it; but in this Age Philosophers have nothing to fear of this sort, the great Disadvantages attending Authors now, are of a widely different Nature, rising from the infinite Number of Pretenders to Knowledge in this Science, and much is to be apprehended from improper Judges, tho' from real ones nothing; for nothing is more certain than this, as much as any Subject exceeds the common Capacity of Readers, so much will the Work in general be condemned; the Air of Knowledge is at least in finding Fault, and this vain Pretence generally leads People, who have no real Foundation for their Judgment to argue from, to ridicule what they are too sensible they do not understand. Thus the same Disadvantages too often attend both in publick and private an exceeding good Production equally the same as a very bad one: But the Author is not vain enough to think this Work without Faults, has rather Reason to fear, from the Weakness of his own Capacity, that there may be many; but he hopes the Design of the Whole will, in some measure, plead for the Imperfection of the Parts, if the Merits of the Plan should be found insufficient for his full Pardon, in attempting so extensive a Subject.

In a System thus naturally tending to propagate the Principles of Virtue, and vindicate the Laws of Providence, we may indeed say too little, but cannot surely say too much; and to make any further Apology for a Work of such Nature, where the Glory of the Divine Being of course must be the principal Object in View, would be too like rendering Virtue accountable to Vice for any Author to expert to benefit by such Excuse. The Motive which induces us to the Attempt of any Performance, where no good Reason can be supposed to be given for the Omission, or Neglect of it, will always be judged an unnecessary Promulgation, and consequently every Attempt towards the Discovery of Truth, the Enlargement of our Minds, and the Improvement of our Understandings will naturally become a Duty. If therefore this Undertaking falls short of being instrumental towards the advancing the Adoration of the Divine Being in his infinite Creation of higher Works, and proves unable to answer all Objections that may possibly arise against it, yet will its Imperfections appear of such a Nature to every candid Reader, as to afford the Author a sufficient Apology for producing them to the World: And it is to be hoped farther, that where a Work is entirely upon a new Plan, and the Beginning, as it were, of a new Science, before unattempted in any Language, the Author having dug all his Ideas from the Mines of Nature, is surely entitled to every kind of Indulgence.

To those who are weak enough to think that such Enquiries as these are over-curious, vain, and presumptive, and would willingly, suitable to their own Ignorance and Comprehension, set Bounds to other People's Labours, I answer with Mr. Huygens, "That if our Forefathers had been at this Rate scrupulous, we might have been ignorant still of the Magnitude and Figure of the Earth; or that there was such a Place as America. We should not have known that the Moon is enlightened by the Sun's Rays, nor what the Causes of the Eclipses of each of them are; nor a Multitude of other Things brought to Light by the late Discoveries in Astronomy; for what can a Man imagine more abstruse, or less likely to be known, than what is now as clear as the Sun."

Had we still paid that Homage to a Name,

Which only God and Nature justly claim;

The western Seas had been our utmost Bound,

Where Poets still might dream the Sun was drown'd;

And all the Stars that shine in Southern Skies,

Had been admir'd by none but savage Eyes.

Besides the Nobleness and Pleasure of these Studies, Wisdom and Morality are naturally advanced, and much benefited by them, and even Religion itself receives a double Lustre, "to the Confusion of those who would have the Earth, and all Things formed by the shuffling Concourse of Atoms, or to be without Beginning." In Astronomy, as well as in natural Philosophy, though we cannot positively affirm every thing we say to be Facts and Truth, yet in so noble and sublime a Study as that of Nature, it is glorious, as Mr. Huygens says, even to arrive at Probability.

Notwithstanding then the Disadvantages which ever have attended all new Discoveries, either thro' the Ignorance of the Age, or the universal Passion of Ridicule in such contented Creatures, as can't comprehend, yet ever attacking with a fool-hardy Resolution, the advancing Ensigns of Knowledge, if Ignorance was Virtue, and Wisdom Vice; I say, regardless of this noisy Shore, it is sure our Duty to spring forward, and explore the secret Depths of Infinity, and the wonderful hidden Truths of this vast Ocean of Beings. But how the heavenly Bodies were made, when they were made, and what they are made of, and many other Things relating to their Entity, Nature, and Utility, seems in our present State not to be within the Reach of human Philosophy; but then that they do exist, have final Causes, and were ordained for some wise End, is evident beyond a Doubt, and in this Light most worthy of our Contemplation.

He who thro' vast Immensity can pierce,

See Worlds on Worlds compose one Universe,

Observe how System into System runs,

What other Planets, and what other Suns;

What varied Being peoples ev'ry Star;

May tell why Heav'n made all Things as they are.

To expect that so new an Hypothesis should meet with universal Approbation, would be an unpardonable Vanity; nor is it reasonable every Reader should think the Author obliged to remove all his Prejudices and Partialities, so far as to give him the perfect Picture of the Universe he likes best. In many Cases it would be so far from being better for the World, if all Men judged and thought alike, that Providence seems rather to have guarded against it as an Evil, than any how to have promoted it as a general Good: But the following Theory regards the Whole rather than Individuals: And the many worthy Authors cited in the Work, who have all greatly favoured this extensive Way of Thinking, will, I hope, be a sufficient Excuse for forming these obvious Conjectures into a Theory, especially where so great a Problem is attempted as the Solution of the Via Lacteal Phænomenon, which has hitherto been looked upon as an insurmountable Difficulty. How the Author has succeeded in this Point, is a Question of no great Consequence; he has certainly done his best; another, no Doubt, will do better, and a third perhaps, by some more rational Hypothesis, may perfect this Theory, and reduce the Whole to infallible Demonstration: The first System of the solar Planets was far from a true one, but it led the Way to Perfection, and the last we can never too much admire. It is well known, that the first System of the Planets was also but a Conjecture, yet none will deny that it was an happy one.

The Discovery of the Magnet Poles; the Government of the Tides; proportional Distance and Periods of the Planets, &c. have all their Uses, and undoubtedly were designed to be known. Ignorance is the Disgrace of Mankind, and sinks human Nature almost to that of Reptiles. Knowledge is its Glory and the distinguishing Characteristic of rational Creatures.

To Enquiries of this sort, then sure we may say with Milton, That

God's own Ear listens delighted.

The Subject is, no Doubt, the noblest in Nature, and as such, will always merit the Attention of the thinking Part of Mankind. Men of Learning and Science, in all Ages, have ever made it their peculiar Study. Towards the latter End of the Republic, and afterwards in the more peaceable Times of Trajan and the Plinys, we have no Reason to doubt but that Astronomy was in the highest Reputation: And notwithstanding Greece had been the chief Seat of the Philosophers, yet may we suppose Rome in those Days little inferior in the Knowledge of the Stars, when we find Men[A] of the first Figure in Life become Authors upon the Subject.

[A] Cicero translated the Phænomena of Aratus into Latin Verse. Julius Cæsar, as Pliny relates, wrote of Astronomy in Greek, and is said to have left several Books of the Motion of the Stars behind him, derived from the Doctrine of the Egyptians. Ant. Chris. 45. He with Sosigenes reformed the Roman Year, which was first invented by Numa Pompilius. Germanicus Cæsar also translated Aratus's Phænomena into Latin Verse Anno Dom. 15. Tiberius and Hadrian are also said to have wrote on Astronomy.

We have many Instances to shew, that Astronomy was in the greatest Repute amongst the Antients of all Ranks, and almost every where looked upon as one of the greatest, if not as one of the first Qualifications of their best Men. As a Confirmation of which, we find in the historical Accounts of the Argives, a very warm Contest betwixt the two Sons of Pelops 1205 Years before Christ, thus testified by Lucian: When the Argives, by publick Consent, had decreed that the Kingdom should fall to him of the two, who should manifest himself the most learned in the Knowledge of the Stars, Thyestes thereupon is said to have made known to them, the Constellation, or Sign of the Zodiack call'd Aries: But Atreus at the same time discovering to them the Course of the Sun, with his various Rising and Setting, demonstrating his Motion to be [B]contrary to that of the Heavens, or diurnal Motion of the Stars, was thereupon elected King.

[B] Hence arose the Fable of the Sun's going backwards in the Days of Atreus, as if struck with Abhorrence of his bloody Banquet. Vide Ovid's Metamorphosis.

To recite more of the most eminent Patrons and Professors of this kind of Learning here, will carry me too far from my present Purpose; for farther Information therefore, I shall refer the inquisitive Reader, to that curious Catalogue in Sherburn's Sphere of Manilius, where so many ruling [C]Men of all Ages and Nations swell, and illustrate the Number.

[C] Seven Emperors, nine Kings, and as many sovereign Princes. Charlemagne wrote Ephemerides, and named the Months and Winds in High Dutch, 770. Rich. II. &c.

In a Word, when we look upon the Universe as a vast Infinity of Worlds, acted upon by an eternal Agent, and crowded full of Beings, all tending through their various States to a final Perfection, and reflect upon the many illustrious Personages, who have, from time to time, thought it a kind of Duty to become Observers, and consequently Admirers of this stupendous Sphere of primary Bodies, and diligent Enquirers into the general Laws and Principles of Nature, who can avoid being filled with a kind of enthusiastic Ambition, to be acknowledged one of the Number, who, as it were, by thus adding his Atom to the Whole, humbly endeavours to contribute towards the due Adoration of its great and divine Author.

I judge it will be quite unnecessary to say any thing about the Order of the Work, since that would be only a Repetition of the Table of Contents, to which the Reader is referred, as to the properest Account that can here be given.

THE
CONTENTS.

LETTER the FIRST.

[Page 1]

LETTER the SECOND.

[9]

LETTER the THIRD.

[18]

LETTER the FOURTH.

[27]

LETTER the FIFTH.

[37]

LETTER the SIXTH.

[48]

LETTER the SEVENTH.

[58]

LETTER the EIGHTH.

[67]

LETTER the NINTH.

[77]

Directions for placing the PLATES.

Some of the Principal ERRATA.

Plate X. read the Characters of the Planets in this Order ♃ ☿ ♄ ♂ ♀

[Note: Transcriber made the corrections above in the text.]

A
LIST
OF THE
SUBSCRIBERS.

A.
Lord Anson.
Hon. Mr. Archer.
Charles Ambler, Esq.
B.
Duke of Beaufort.
Duke of Bedford.
Dutchess of Beaufort.
Lord Berkely, of Straton.
Miles Barne, Esq;
Lancelot Barton, Esq;
Hon. Antoine Bentinck.
Hon. John Bentinck.
Norbone Berkely, Esq;
John Brown, Esq;
—— Blaman, Esq;
Thomas Brand, Esq;
J. Bevis, M. D.
Rev. T. Bonney, A. M.
C.
Countess of Cunengesby.
Lord Cornwallis.
Lady Cornwallis.
Edward Cave, Esq;
John Chamock, Esq;
Hon. and Rev. Dr. Cowper.
Mr. Richard Chad.
Mr. Henry Chapell.
Is. Colepepper.
Mr. George Conyers.
D.
Rev. John Dealtary, A. M.
Mr. Samuel Dent.
F.
Charles Fitzrea Scudamore, Esq;
Kean Fitzgerald, Esq;
Thomas Fonnerau, Esq;
Robert Rakes Fulthorpe, Esq;
Mr. Samuel Farrant.
Mr. Paul Fourdrinier.
G.
Marchioness Grey.
Lord Glenorchy.
Francis Godolphin, Esq;
Roger Gale, Esq;
James Gibbon, Esq;
Ralph Goward, Esq;
Ralph Gowland, Esq;
Ralph Gowland, Junior, Esq;
Dr. Gregory.
Dr. Griffith.
Rev. John Griffith, A. M.
Rev. Middlemore Griffith.
H.
Lord Hardwick, Lord High Chancellor of Great-Britain.
Hon. James Hamilton.
Mr. Thomas Heath.
Mr. Thomas Holt.
John Hughes, Esq;
J.
Earl of Jersey.
Richard Jackson, Esq;
Rev. Mr. Jones.
K.
—— Knowles, Esq;
Dr. Kendrick.
Mrs. Kennon, 4.
L.
Lady Vicountess Limerick.
Sir William Lee, Bart.
William Lester, Esq;
Rev. Dr. Long, Master of Pembroke-hall, Cambridge.
William Lloyd, Esq;
Mr. Andrew Lawrence.
M.
R. J. Mead, M. D.
Richard Meyrick, M. D.
Owen Meyrick, Esq;
Pierce Meyrick, Esq;
N.
Duke of Norfolk.
Lord North.
Lord Bishop of Norwich.
Richard Nicholls, Esq;
Mrs. Norsa.
P.
Duke of Portland.
Earl of Pembroke, &c. 2.
Countess of Pembroke, &c.
Lady Palmerston.
Robert Money Penny, Esq;
Sir Francis Pool.
Sir John Pool.
John Probyn, Esq;
Rev. Mr. Pierce.
Mr. Dominick Pile.
Mr. Powel, of Cambridge.
R.
Dutchess of Richmond, &c. &c.
James Ralph, Esq;
Allan Ramsey, Esq;
William Read, Esq; 2.
Henry Reveley, Esq;
William Reveley, Esq;
S.
Sir George Savile.
—— Serle, Esq;
Rev. Dr. Smith, Master of Trinity College, Cambridge.
Miss Stonehouse.
William Symonds, Esq;
Mr. James Scot.
Mr. James Stephens.
T.
Lord Viscount Townshend.
John Temple, Esq;
James Theobald, Esq;
Charles Townshend, Esq;
Mrs. Mary Trevor.
Mr. James Thornton.
V.
Lord Viscount Villiers.
W.
Lady Frances Williams.
Miss Williams.
Miss Charlotta Williams.
Rev. Thomas White, A. M.
—— White, Esq;
Charles Louis Wiedmarkter, Esq;
Mr. Ward.
Y.
Hon. Philip York.
Dr. Arthur Young, Preb. of Cant.

LETTER the FIRST.

Opinions of the most eminent Authors whose Sentiments on the following Subject have been published in their Works.

SIR,

Reflecting upon the agreeable Conversation of our last Meeting, which you may remember chiefly turned upon the Stars, and the Nature of the planetary Bodies; a Subject, which is generally allowed to give true Pleasure to all those who take Delight in mathematical Enquiries; and having not a little Regard to the repeated Request in your late Letters, I have at length undertaken to explain to you, as far as I am able, my Theory of the Universe, and the Ideas I have form'd of the known Creation.

The Hypothesis upon which this new Astronomy is founded, and now reduced into a regular System, was the result of my Astronomical Studies[D] full fifteen years ago, hence I hope you will allow, I have more than observed Horace's celebrated Aphorism,

Nonumque prematur in annum.

[D] The first Scheme of this Hypothesis was plann'd in the Year 1734, representing in a Section of the Creation, eighteen Feet long and one broad, several thousand Worlds and Systems, and a great Number of emblematical Figures, now in the Author's Possession, together with a Scheme of the entire Creation, completed since, nine Feet long and six broad, more fully illustrating upon the same Construction the Innumerability of Systems and Worlds.

The Subject, I have often observed, you have listened to with a pleased Attention, and I am the more incouraged to explain it at large to you, as I am perswaded you don't want to be convinced of its valuable Uses and Importance.

I remember you have often told me, that to apply ourselves to the Study of Nature, was the surest and readiest Way to come at any tolerable Knowledge of ourselves, however difficult the Task might prove either in the Attempt, or the attaining it, and the less to be neglected, as it never fails to introduce a proper Knowledge of the Divine Being, as a certain Consequence along with it, and such a Knowledge, as will naturally make every Man, who has but a tolerable Share of common Sense, and is not a Slave to another's Reason, without any other Evidence or Motive, in all Stations, and under all Circumstances, Act justly, Live chearfully, and die full of Hope in the Expectation of a happy Sequel, in Futurity.

Eternity is written in the Skies:

Mankind's Eternity, nor Faith alone;

Virtue grows there ——

A learned Author on the Attributes, recommending these Studies as a reasonable and moral Service, says, "Sure, it is most becoming such imperfect Creatures as we are, to contemplate the Works of God with this Design, that we may discern the Manifestations of Wisdom in them; and thereby excite in ourselves those devout Affections, and that superlative Respect, which is the very Essence of Praise."

Who turns his Eye, on Nature's Midnight Face,

But must enquire —— what Hand behind the Scene,

What Arm Almighty, put these wheeling Globes

In Motion, and wound up the vast Machine?

The enchanting Idea Milton had of the Subjects of Astronomy whose truly sublime Way of thinking and writing perhaps was never so nearly equalled, or attempted before this Reverend Author's Night-Thoughts, appear'd is finely shewn in the Eighth Book of his Paradise Lost, where he makes his Adam, so earnestly attentive to the Angel Gabriel, as to ceasing to relate the Mysteries of Creation.

The Angel ended, and his Adam's Ear

So charming left his Voice, that he awhile

Thought him still speaking; still stood fix'd to hear.

Milton's own Ideas of the Universe too, which no doubt he had gathered from astronomical Authors, and had reconciled himself to, we are fully made acquainted with in the same Book, where the Arch-angel says, in answer to Adam's Enquiries.

——Other Suns perhaps

With their attendant Moons thou wilt descry

Communicating Male and Female Light,

Which two great Sexes animate the World,

Stor'd in each Orb, perhaps with some that live:

For such vast Room in Nature, unpossest

By living Soul, desert and desolate,

Only to shine, yet scarce to contribute

Each Orb a Glimpse of Light, convey'd so far

Down to this habitable, which returns

Light back to them, is obvious to Dispute.

But before I presume to plan my own Discoveries and Conjectures into a Theory, both in Justice to those who have in some measure been in the same Way of Thinking, and also as a Defence of myself for producing so new an Hypothesis to the World, which otherwise (though any Apology made to you I know will be unnecessary) may appear to too many but an idle Chimera of my own. I judge it will be highly proper, by way of strengthening my own Arguments, and adding more Weight to what I shall myself advance in the following Letters, to give you in this the Opinions of the most able Writers, whose Works I have read upon the Subject. I mean so far as relates to the now general received Notion, that the Stars are all Suns, and surrounded with planetary Bodies, with which I shall set out; and shew you, it is not a Thing merely taken for granted, but has ever been the concurrent Notion of the Learned of all Nations, as shall be further shewn, in its proper Place, and as nearly as Possibility will admit of, demonstrated to be Truth.

The following is an Extract from Mr. Toland, in his Account of the Works of

Jordanus Bruno.

"The Divine Efficacy (says this Author in his infinite Creation) cannot stand idle, without the Want of Will or Power; but any Imbecility in such a Being argues Imperfection, and since any finite Produce compared with Infinity is as nothing, or rather as the Beginning of Good, it must be no less idle, and invidious in producing a finite Effect, than in producing none at all.

"Hence, as all Finites, singly considered, are but as Commencements of something more to be expected.

"Omnipotence, in making the Creation finite, will appear to be no less blameable for not being willing, than for not being able, to make it otherwise; i. e. infinite, as being an infinite Agent upon a finite Subject, which is repugnant to Reason."

It follows then that, Creation must be not only extensively, but intensively indefinite, and beyond the Reach of the human Understanding to comprehend; and that the one is as necessary as the other, i. e. an infinite Expanse is as reconcileable to our Reason, as infinite Parts are to our Senses.

All the Attributes of the Divine Being are, as any one of them, incomprehensible to his Creatures; why should our Imagination then be supposed to extend beyond the divine Activity?

"Thus, adds the above Author, the Excellency of God is adequately magnified, and the Grandeur of his Empire made manifest; he is not glorified in one, but in numberless Suns; not in one Earth, or in one World, but in ten thousand thousand of infinite Globes."

An infinite Representation of an infinite Original, and a Spectacle befitting the Excellency and Eminence of him, that can neither be fully conceived, imagined, or comprehended.

What read we here? the Existence of a God?

Yes, and of other Beings, Man above,

Natives of Æther! Sons of higher Climes!

"If the Existence of this one World be good or convenient, it is not less good or convenient that there be infinite others like it.

"The infinite efficient Cause would be absolutely defective, without an infinite Effect; and besides, by conceiving the Infinity of the Universe and innumerable Beings, the Understanding rests satisfied, and is reconciled with the Idea of an Eternity; whereas, by asserting the contrary, it is unavoidably plunged into innumerable Difficulties, and unsolvable Inconveniencies, Paradoxes, and Absurdities."

Again, says the same Writer, "Did we but consider and comprehend all this, oh! to what much further Considerations and Comprehensions should we be carried! as we might be sure to obtain that Happiness by virtue of this Science, which in other Sciences is sought after in vain.

This Prospect vast, what is it? weigh'd aright,

'Tis Nature's System of Divinity,

And every Student of the Night inspires.

'Tis elder Scripture, writ by God's own Hand;

Scripture authentic! uncorrupt by Man.

"This then is that Philosophy, which opens the Senses, which satisfies the Mind, which enlarges the Understanding, and which leads Mankind to the only true Beatitude, whereof they are capable according to their natural State and Constitution; for it frees us from the sollicitous Pursuit of Pleasure, and from the anxious Apprehensions of Pain, making us to enjoy the good Things of the present Hour, and not to fear more, than we hope from the future; since that same Providence, or Fate, or Fortune, which causes the Vicissitudes of our particular Being, will not let us know more of the one, than we are ignorant of the other."

And farther, "From these Contemplations, if we do but rightly consider, it will follow, that we ought never to be dispirited by any strange Accidents, through Excess of Fear or Pain, nor ever be elated by any prosperous Event, through Excess of Hope or Pleasure; whence we have the Path to true Morality, and following it, we shall of course become the magnanimous Despisers of what Men of weak Minds fondly Esteem, and be wise Judges of the History of Nature, which would be written in our Minds, and consequently be chearful and strict Executioners of the divine Laws, which would thus be ingraved in the Center of our Hearts. Seeking, as it were, in ourselves, an Approbation of our own Action, which alone is capable of true Content and Happiness."

Christopher Huygens,

[E]

[E] The Pendulum Clock; the first Discovery of Jupiter's Satellites, and Saturn's Ring.

To whom the World is much indebted for many curious Inventions, and Discoveries, says in his Planetary Worlds, "I must be of the same Opinion with all the great Philosophers of our Age, that the Sun is of the same Nature with the fix'd Stars; and this will give us a greater Idea of the World than all other Opinions can. For then why may not every one of these Stars, or Suns, have as great a Retinue, as our Sun, of Planets, with their Moons to wait upon them? Nay, there is a manifest Reason why they should; for, if we imagine ourselves placed at an equal Distance from the Sun and fix'd Stars, we should then perceive no Difference at all betwixt them.

"Why then may we not make use of the same Judgment that we would in that Case; and conclude, that our Star has no better Attendance than the others? So that what we allowed the Planets upon the Account of our enjoying it, we must likewise grant to all those Planets that surround that prodigious Number of Suns. They must have their Plants and Animals, nay, their rational Creatures too, and those as great Admirers and as diligent Observers of the Heavens as ourselves; and must consequently enjoy whatever is subservient to, and requisite for such Knowledge.

"What a wonderful and amazing Scheme have we here of the magnificent Vastness of the Universe! So many Suns, so many Earths, and every one of them stock'd with so many Herbs, Trees, and Animals, and adorned with so many Seas and Mountains! And how must our Wonder and Admiration be increased, when we consider the prodigious Distance and Multitude of the Stars?"

The Opinion of Sir Isaac Newton.

This great Author, in his grand Scholia to the Principia, says:—"The most beautiful System of the Sun, Planets, and Comets, could only proceed from the Counsel and Dominion of an intelligent and powerful Being: And if the fix'd Stars are the Centers of other like Systems, these, being form'd by the like wise Counsel, must be all subject to the Dominion of One; especially, since the Light of the fix'd Stars is of the same Nature with the Light of the Sun, and from every System Light passes into all the other Systems. And least the Systems of the fix'd Stars should by their Gravity fall mutually on each other, he (the Divine Being) hath placed those Systems at immense Distances from one another."

The Opinion of Dr. Derham, in his Astro-Theology.

"The new System, says he, supposeth there are many other Systems of Suns and Planets, besides that, in which we have our Residence; namely, that every fix'd Star is a Sun, and incompassed with a System of Planets, both primary and secondary, as well as ours.

"These several Systems of the fixed Stars, as they are at a great and sufficient Distance from the Sun and us; so they are imagined to be at as due, and regular Distances from one another: By which means it is that those Multitudes of fixed Stars appear to us of different Magnitudes, the nearest to us large; those farther and farther, less and less; and that some, if not all of those vast Globes of the Universe, have a Motion, is manifest to our Sight, and may easily be concluded of all, from the constant Similitude and Consent that the Works of Nature have with one another."

To this we may add, that this System of the Universe, as it is physically demonstrable, is far the most rational and probable of any. Because,

"It is far the most magnificent of any, and worthy of an infinite Creator, whose Power and Wisdom, as they are without Bounds and Measure, so may they, in all Probability, exert themselves in the Creation of many Systems as well as one. And as Myriads of Systems are more for the Glory of God, and more demonstrate his Attributes than one; so it is no less probable than possible, there may be many besides this which we have the Privilege of living in." And as the strongest Confirmation of this, "we see it is really so, as far as it is possible it can be discerned by us, at such immense Distances as those Systems of the fixed Stars are from us; and we cannot reasonably expect more."

"Since the Sun and fix'd Stars, says Dr. Gregory, are the only great Bodies of the Universe that have any native Light, they are justly esteemed by Philosophers to be of the same Kind, and designed for the same Uses; and it is the Effect of a Man's Temper that sets a greater Value upon his own Things than he ought, that makes him judge the Sun to be the biggest of them all."

That, as an elegant[F] Writer observes, which we call the Morning, or the Evening Star, is, in reality, a Planetary World; which, with the four others, that so wonderfully, as Milton expresses it, "vary their mystick Dance, are in themselves dark Bodies, and shine only by Reflection; have Fields and Seas, and Skies of their own; are furnished with all Accommodations for animal Subsistence, and are supposed to be the Abodes of intellectual Life. Again, The Sun, with all its attendant Planets is but a very little Part of the grand Machine of the Universe. Every Star—is really a vast Globe, like the Sun, in Size and in Glory, no less spacious, no less luminous, than the radiant Source of our Day; so that every Star is the Center of a magnificent System, has a Retinue of Worlds irradiated by its Beams, and revolves round its active Influence; all which are lost to our Sight in immeasurable Tracts of Æther.

[F] Contemplations on the starry Heavens.

"Could we, says the same Author, wing our Way to the highest apparent Star—we should there see other Skies expanded, other Suns, that distribute their inexhaustible Beams of Day; other Stars, that gild the alternate Night; and other perhaps nobler Systems established; established in unknown Profusion, through the boundless Dimensions of Space. Nor does the Dominion of the great Sovereign end there, even at the End of this vast Tour, we should find ourselves advanced no farther than the Frontiers of Creation; arrived only at the Suburbs of the great Jehovah's Kingdom."

O for a Telescope his Throne to reach!

Tell me ye Learn'd on Earth! or Blest above!

Ye searching, ye Newtonian Angels! tell,

Where your great Masters Orb? His Planets where?

Those conscious Satellites, those Morning Stars,

First-born of Deity from central Love.

Many other Authorities might be produced from Writers of great Repute, were it necessary to trouble you with them[G]; but I believe those above will be abundantly sufficient for the present Purpose, if even an Apology were wanting for my own Conjectures. I shall therefore conclude this Letter with the following Passage out of Pope's Universal Prayer, and in my next shall proceed in the Work I have undertaken.

Yet not to Earth's contracted Span,

Thy Goodness let me bound;

Or think thee Lord alone of Man,

When thousand Worlds are round.

I am, &c.

[G] Particularly from Fontenelle, &c.

LETTER the SECOND.

Concerning the Nature of Mathematical Certainty, and the various Degrees of Moral Probability proper for Conjecture.

SIR,

Y

You know how much I am an Enemy to the taking of any thing for granted, merely because a Person of reputed Judgment, has been heard to say, it absolutely is so; an Ipse dixit, and implicit Faith in some Cases, may be both necessary and useful; but here, in Astronomy, I mean, every Man's Reason, by the Help of a very little Mathematicks, is able to bring wonderful Truths to Light without them; and Truths not only of the highest Importance to every Individual, but of a great and common Consequence to all Mankind: And as such, in all Ages of the World, have been judged worthy to be enquired into, by the best and wisest of Philosophers.

You are likewise very sensible how far the human Understanding is even at the best, from being infallible, and don't want to be told, how difficult it is in a Subject of this Nature to arrive at any tolerable Degree of Certainty, which before the Days of the sagacious Euclid, and the penetrating Archimedes, was a Thing not to be expected. And many things which were then but barely Objects of Conjecture and Probability, have since been demonstrated to be infallibly true. Time and Observation will undoubtedly, at last, discover every thing to us necessary to our Natures, and proper for us to know. As a Proof of which, we see human Wisdom daily increases; and while a Capacity continues to make ourselves still more acquainted with the manifest Wisdom and Power of God in the Works of his Creation, who is to tell us where to stop our Enquiries? Or who is so impious to set Bounds to a Science, which so evidently spreads through all Infinity, the Attributes of God, and an eternal Basis for future Hope?

This Branch, or rather Body of Astronomy, I believe you will find to be quite new; and though evident Truths, are the principal Thing to be regarded in it, yet as being in its infant State, where lineal Demonstration fails, as in some Cases it cannot be otherwise, I hope you will give me Leave to make use of a weaker Way of Reasoning, to convince you of the Point in Dispute, I mean of that by the Analogy of known and natural Things.

I shall be extremely unwilling to affirm any thing for a Fact, or Truth, without hearing, if not the real Evidence, at least a plausible Reason, next to a Conviction, or moral Certainty, along with it; and therefore I will here endeavour to explain to you what I mean by moral Certainty and also by mathematical Proof.

Mathematical Proof, or Certainty, proper for Conjectures, may, to almost every Capacity, be illustrated as follows:

Suppose you had accidentally found a very small Part of a visibly broken Medallion, with nothing more express upon it, than what is represented at Fig. 1. Plate I. a Person totally unacquainted with the mathematical Sciences, we may naturally conclude, would not be able to make any thing of it, or in the least comprehend what it originally was, or meant; but if an Astronomer should chance to see it, who of course we are to suppose knew the Order and Proportion of the planetary Orbits, he would immediately conclude, and with great Probability, on the Side of his Conjectures, that it might be Part of a Medal representing the Solar System. In such a Case may we not very naturally suppose he would reason thus?

The Arches A and B seem to be Portions of the respective Orbits of Saturn and Jupiter, and what may lead us to believe, that they are really so, and Part of the Solar System, is the oblique Curve C, which looks not unlike the Trajectory of a Comet.

This surely would be far from an irrational Conjecture, and consequently in some Degree probable: But this is not sufficient you'll say; To prove it we must have farther recourse to the Mathematicks, and a Mathematician would immediately thus demonstrate it to be true.

Plate I.

Plate II.

First, by compleating the Circles geometrically from the fourth Book of Euclid, by the Assistance of any three Points E. F. G. the original Figure will be restored, as at Fig. 2. And secondly, by assuming any two Points, as F, E in the Curve C, if admitted a Parabola, by a well-known Problem in Conic Sections the Heliocentric Portion X. Y. Z. will easily be projected and shewn, as in Fig. 3. Lastly, join this in Position to the former, and it will justly supply the Orbit, or Path of some one of the Comets; and if required, even what Comet may be discovered by comparing the Perihelion Distance Y. S. with their general Elements or Theories, in Dr. Hally's Synopsis of the Motion of these Bodies. And if a farther Confirmation of the Truth of these Conjectures were wanting, the small concentric Circles at D would now be allowed beyond a Contradiction, to represent the secondary Orbits of Saturn; and thus the first Presumption being carried thro' several corroborating Degrees of Probability, almost past a Dispute, would become a mathematical Certainty; and the above imperfect Piece of Medallion, would evidently appear beyond a Contradiction to be Part of a Representation of the said solar System, and such as is shewn in Plate II. Q. E. D. Thus in many Cases, it often happens, that from a very small Part of orbicular Things, we are able to determine the Form and Direction of the Whole: And hence you may conceive it no very difficult Task to a Mathematician, to describe the Orbits of all the Planets in the solar System, though he had never observed them but in one and the same Sign of the Zodiack; thus far I have thought it would not be amiss to explain to you the Nature of those Steps, by which we arrive at moral Certainty, and where the Subject will admit of it, Mathematical Conviction, which will not a little contribute to strengthen many of the Arguments hereafter made use of, and in some Degree serve to supply the Place of Proof, where infallible Demonstration cannot from the Nature of the Thing be discovered.

But besides the indisputable Principles of Geometry, the universal Law of Analogy and Similitude of things, have a Privilege to assist us, in Conjectures relating to the heavenly Bodies, and though not of equal Force with the former, is often as conclusive as the Subject requires. This sort of probable Evidence (as Dr. Butler observes,) is essentially distinguished from "Demonstrative by this, that it admits of Degrees; and of all Variety of them, from the highest moral Certainty to the very lowest Presumption; and that which chiefly constitutes Probability, is expressed in the Word Likely, or Natural Likeness, as to State or Being." This general Way of arguing, I think, is allowed to be evidently natural, just and conclusive, and unquestionably to have its Weight in various Degrees, towards determining our Judgment: For Instance, should any ignorant Person, endowed with rational Principles, cut open a Pomegranate of the natural Growth of England, and finding it full of small Globules, or Kernels, upon being presented with an every way similar Fruit, said to be the Produce of Italy, doubt of its being of the same Nature, and composed of like globular Seeds within; here indeed would be no mathematical Evidence to assist the Judgment, the Object of Proof being invisible, but sure from the external Similitude, the strongest Probability of their being also internally the same. Again,

Is it natural to suppose, that the first Person who found a Lark's Nest, and in it several of the Female's Eggs, should have any Apprehensions of finding none in the Nightingale's, only because he had never seen one before, I believe the most illiterate Person of the earliest Ages, who had Curiosity enough for such a Search, would be greatly disappointed in such a Case, and far from concluding that the Nightingale had none. Farther, should any one who had seen several Sorts of Fish taken out of the River Thames, or out of the Nyle, have any sort of Suspicion that he should find no such Creatures in the Seine or the Ganges, though it should be allowed that he had never seen any such Creatures that were known to come from thence. Ocular Demonstration, in such a Case, would sure be unnecessary, and an Evidence of the first, I believe would be abundantly sufficient to convince us of what we ought to look for at least in the last: But then the Fishes of different Seas, and of Rivers are not of the same Species you'll say; but as it were infinitely diversified through all the aqueous World, this is, and must be granted, and alike Variety of Species must also be granted, in the former Case of the Birds: But no Objection can possibly arise from any such Diversity, since we don't pretend to say, nor is it at all necessary, that the Beings in the sidereal Planets should be every where the same with these of our solar System, a Variety must every where be admitted, and will always be admired, where the Work is Nature's, and the Design God's.

All then that I here pretend to argue for, is a Universality of rational Creatures to people Infinity, or rather such Parts of the Creation, as from the Analogy and Nature of Things, we judge to be habitable Seats for Beings, not unlike the mortal human.

Every Animal, and every Vegetable, that, as it were, naturally exists by the Virtues, Properties, or Laws of the mineral Kingdom, has something of a secondary Nature, depending upon it as a Principle; and to say that the Stars, which are a certain visible sort of Cotemporaries in Space with the Sun, have no like planetary Bodies with ours moving round them, because we cannot possibly see them, is no less absurd and ridiculous, than to argue, that we can have no Reason to expect to find, in the proper Season, Grapes upon every Vine—Figs upon every Tree—Roses upon every Bush—only because some of them are at such a Distance, that neither Rose, Fig or Grape, can be discovered by the Eye.

This sort of Reasoning, though some perhaps may neglect it, I am perswaded you will look upon as abundantly sufficient for Things out of the Reach of Science to determine; and that the collective Body of Stars have not been discovered, to be together a proper Subject for such Conjectures before, can surely only proceed from the Want of Time, necessary to compleat the Observations proper for a Foundation to build such an Hypothesis, or Theory upon. This is the great Article in which the Moderns have so much, and ever will have, an Advantage over the Antients. And hence it will appear, That

The Improvements and Discoveries of latter Ages are not at all owing to the greater Capacity of the Moderns, but from the Advantages received, or arising from the Inventions and Progress made by the Ancients. We at first in a manner walked by their Leading-strings, and though many of them now are broke, or useless, none can deny, but that formerly they were of great Advantage in promoting and directing philosophical Enquiries.

In an Assembly of the most eminent Men of all Ages, if we may suppose such a Conference amongst the illustrious Dead, on Purpose to deliver their several Sentiments familiarly together, on the most interesting Subjects of natural Knowledge, who would not lament the Disadvantages, poor old Thales, an Hipparchus, or a Ptolomy, would lie under, who had nothing but the Eye of Reason to direct them, in Opposition to the Judgment of a Brahe, or a Galilæus, who reaped so much Benefit from their compound Opticks? But on the other hand, perhaps if the solar System, was the Topic of Discourse, a [H]Pythagorean might very pertinently say to a Newtonian, "You have not gone much farther in the Light with our Direction, than we did in the Dark alone; for you are still roving round the same Circles." Much might be said upon this Head; but I believe it would be a difficult Matter to do Justice to all Parties: So here I intend to leave them, only must observe, that Posterity will always have the Advantage over their Predecessors; and that After-ages, in all Probability, will reap so great a Benefit from the Invention and Improvement of Fluxions, that scarce any thing, which is the immediate Object of such Enquiry, will long lie concealed from a true mathematical Genius.

[H] The true System of the Planets have been discovered above two thousand Years.

For this, in which he has surpassed all the Antients, and greatly advanced the philosophical Sciences, the World is indebted to Sir Isaac Newton.

But as many of his Discoveries, such as relate particularly to the Laws of the planetary System, are but as so many Confirmations of the Conjectures and Imaginations of Astronomers and Philosophers before him, it perhaps will not be amiss to acquaint you a little with the Astronomy of the Antients concerning the Universe. And before I proceed to those of my own, shew you in the first Place how far their Speculations in the visible Creation have been carried; and with these I shall conclude this preparatory Epistle.

The Universe, or mundane Space, by which the Antients comprehend all Creation, has, from time to time, according to the Progress of Science, come under a sort of Necessity of being variously modell'd agreeable to the Opinion of the several Authors, who have judged themselves wise enough to write upon it with a mathematical Foundation: And the cosmical System, by which is meant the Co-ordination of its constituent Parts has undergone almost as many Changes as its Elements are even capable of; every Age of the World, as Knowledge has increased, either from improved Imagination, or repeated Observations, producing something new concerning it.

Milton, no doubt, had all this Diversity of Opinions in View, as appears from his supposed Pre-knowledge of Raphael, in the following Passage, Book. VIII.

Hereafter, when they come to model Heaven,

And calculate the Stars, how they will weild

The mighty Frame! how build, unbuild, contrive

To save Appearances, how gird the Sphere

With centric and eccentric scribbl'd o'er;

Cycle, and Epicycle, Orb in Orb.

But the following Synopsis, I believe, will abundantly convince you that from certain Observations only, we ought to form all our Notions of it, if we either hope to arrive at Truth, or expect our Ideas should be supported by Reason.

Aristotle was of Opinion, that the Universe, or Heaven, was all one World, and St. Chrysostom, Tertullian, St. Bonaventure, Tycho Brahe, Longomontanus, Kepler, Bulialdus and Tellez, were of an united Opinion, that this one Heaven, or Universe, was all sidereal and fluid. But Aegidius, Hurtadus, Cisalpinus, and Aversa, believing the same Heaven with them to be all one World, and that sidereal, yet on the contrary held it to be solid.

Clemens, Acacius, Theodoret, Anastasius, Synaita, Procopius, Suidus, S. Bruno, and Claudianus Mamertus, supposed the universal mundane Space as divided into two Heavens, namely,

The Empyræum created the first Day,

And the Firmament created the second Day.

Two Heavens were also held by Justin Martyr, the one sidereal, and the other aerial. The first supposed by St. Gregory Nyssene, to be that of the fixed Stars, and the last, that of the Planets. But Mastrius and Bellutus, though agreeing in the Number of Heavens, calls one the *Primum Mobile, and the other, the Starry Heaven.

Farther, St. Basil, St. Ambrose, Damascene, Cassiodorus, Genebrardus, Suarez, Tannerus, Hurtadus, Oviedus, Tellez, and Borrus, distinguished the Universe as divided into three Portions, or Heavens.

Again, St. Athanasius adds to those of the fix'd Stars, the Planets, and the Air, that of the Empyræum, and makes in all four Heavens.

But as the Number of the Heavens thus increases, and will become subdivided in the subsequent Account of them, to give you a better Idea of the Order of these celestial Portions of the mundane Space, it will not be amiss to form what remains of them into regular Sections of their proper Spheres and Systems.

See Plate III. in which Figure, the first represents a Section of the cosmical Theory of Oviedus and Ricciolus: Both consisting of five Heavens, viz.

Fig. II. represents that of venerable Bede and Rabanus, viz. of Seven Heavens.

Fig. III. Represents the Hypotheses of Eudoxus, Plato, Calippus, Cicero, Riccius, Philo, Remigius, Aben-Ezra, Carthusianus, Lyranus, Tostatus, Brugensis, Orontius, Cremoninus, Philalethæus, Amicus, and Ruvius; also the Babylonians and Egyptians.

Consisting of Eight Heavens,

All Sidereal, viz. The Sphere of the fix'd Stars, and those of the Seven Planets.

Fig. IV. is that of Macrobius, Haly Alpetragius, Rabbi-Josue, Rabbi Moyses, Scotus, Abraham Zagutus, Sacroboscus, Claromontius, Avigra, and Arraiga.

All of Nine Heavens,

Comprehend a Primum Mobile Q, or, according to Arriaga, a solid Empyræum. The Sphere, of fixed Stars A, and the seven Regions of the solar Planets.

Fig. V. is that of the great Alphonsus, Fernelius, Regiomontanus, Amicus, Maurolycus and Langius; also of Azabel, Thebit, and Isaac Israelita; and likewise of Gulielmus Parisiensis, and Johannes Antonius Delphinus.

Consisting of Ten Heavens, made up of

Note, Some Authors place the Sphere of Tripidation in Longitude below that of the Aplain, or Eighth Sphere.

Lastly, Fig. VI. is the Heaven of Petrus Alliacensis, the College of Conimbra, Martinensis, (and sometime) of Clavius; and also Johannes Warnerus, Leopoldus de Austriâ, Johannes Antonius Maginus; and lastly, of Clavius.

In all Eleven Heavens containing,

Plate III.

Thus you see how many various Opinions have from time to time been embraced concerning the Fabric and Formation of the visible Universe; all of which are now and have long been exploded; and although at first advanced by Men of the greatest Learning, and of the deepest Penetration in natural Knowledge, it does not appear from any one of their Opinions, that they had any the least Notion of infinite Space, but as it were confined the Divine Being to their limited Notions, as one may say in an Egg-shell. If therefore what I shall hereafter advance, extend so far without the known Creation, that you can possibly conceive no Bounds to the Works of infinite Wisdom and Power, I hope you will be in no Danger of looking upon it as more ridiculous, or absurd, than what so many of the wisest Men of every Age have thought proper to attempt, and have judged worthy of their Attention so long before me. If any thing less so, I shall think myself happy enough in having broke, or rather passed the narrow Limits to which the Creation has for so many Years been confined, in hopes of tempting Men of greater Talents to look up wards, and pursue so noble a Subject as far as the human Understanding is capable of comprehending it.

To the Opinions above might be added many more, particularly that of Johannes Baptista Turrianus, and Fracastorius, who increased the Number of Heavens to fourteen, viz. seven on each Side the Aplané.

But of this I have said enough; in my next I shall proceed to Matter better grounded,

And am, &c.

LETTER the THIRD.

Concerning the Nature, Magnitude, and Motion of the Planetary Bodies round the Sun, &c.

SIR,

T

The younger Pliny, if I remember right, somewhere says, that there is, or ought to be, a wide Difference betwixt writing to a Friend, and writing to the Publick: I have indeed pleased myself with the one, but am far from thinking myself qualified for the other; I must therefore rather intreat you, though perhaps you cannot possibly overlook all my Faults as an Author, to excuse them at least in the Friend, and by such kind of unlimited Indulgence, you will give me a much greater Chance to do the Subject some Justice, though I own I despair in this first Attempt, to reconcile every thing I advance to your more cool and impartial Reasoning. But to the Business:

As I have no Ambition to have the Substance of my Theory more admired by you than understood, which is too often the Case in Works of this Nature, I must beg leave to repeat to you Part of a former Discourse, which will refresh in your Ideas the principal Laws of the System of our Sun, and make you properly acquainted with such Things as are necessary to be known in the now-established Astronomy of [I]Copernicus, &c. before I proceed to any new Matter.

[I] Nicolaus Copernicus, stiled by Bulialdus, Vir absolutæ subtilitatis, was a Native of Thorn in Polish Prussia, and Canon of the Church of Frawenburgh; he was Scholar to Dominicus Maria of Ferrara, to whom he was Assistant in his astronomical Observations at Bologne, and Professor of the Mathematicks at Rome, in his noble Work, De Revolutionibus Orbium Cælestium; he fortunately revived, happily united, and formed into an Hypothesis of his own, the several Opinions of Philolaus, Heraclides Ponticus, and Ecphantus Pythagoreus, viz. after the Opinion of Philolaus he made the Earth to move about the Sun, as the Center of its annual Motion; and according to Heraclides and Ecphantus, he likewise gave it a diurnal Rotation round its own Axis: Which System has withstood all Opposition; and as Ricciolus, (though a Dissenter from it) observes, Per damna, per cædes, ab ipso sumit opes, animumque ferro.

The Sun, you are not to learn, is the reputed Center of our Planetary System, and may remember, that the Earth on which we live, and these five following Erratic Stars, viz. Saturn, Jupiter, Mars, Venus and Mercury, have been demonstrated to move round him in the Order and Manner following.

Saturn is found to complete one Revolution round the Sun in twenty-nine Years, one hundred and seventy-four Days, six Hours, and thirty-six Minutes; at the Distance of about seven hundred and seventy-seven Millions of Miles. Jupiter performs a like Revolution in about eleven Years, three hundred and seventeen Days, twelve Hours, and twenty Minutes; distant from the Sun about four hundred and twenty-four Millions of Miles. Mars compleats his Circuit in one Year, three hundred and twenty-one Days, twenty-three Hours, and twenty-seven Minutes; and his mean Distance is about one hundred and twenty-three Millions of Miles.

These three are called superior Planets, as being farther from the Sun than the Earth, and circumscribing its Orbit.

The Earth circumambulates her Orbit in one solar Year, viz. in three hundred and sixty-five Days, five Hours, forty-eight Minutes, and fifty-seven Seconds; at the mean Distance of eighty-one Millions of Miles.

The Radius of Venus's Orbit is about fifty-nine Millions of Miles; and that of Mercury nearly thirty-two Millions, ditto.

The Heliocentric Revolution of Venus, is made in two hundred and twenty-four Days, sixteen Hours, forty-nine Minutes, and twenty-seven Seconds; and that of Mercury, in eighty-seven Days, twenty-three Hours, fifteen Minutes, and fifty-four Seconds. These two last Planets are called inferior Ones, as being circumscribed by the Earth.

The Diameter of the Sun being demonstrated to be nearly seven hundred and sixty-three thousand Miles:

The proportional Magnitudes of all the above Planets will be found nearly as follows, viz.

Thus much I have thought proper to premise, and for your immediate Inspection, have added the following Schemes, that nothing may be wanting to give a general Idea of the Order of the celestial Bodies in our own System, before I attempt to lead you through the neighbouring Regions of the Stars to the more remote Tracts of Infinity.

PLATE IV.

Is a true Delineation of the solar System, with the Trajectories of three of the principal Comets, whose Periods and Orbits have been accurately determined, and are represented in their true Proportion and Position to one another, and the Order of the Planets round the Sun, marked with their respective Characters, viz. ♄, for Saturn, ♃, Jupiter, ♂, Mars, ♁, the Earth, ♀, Venus, and ☿, Mercury. The Scale being nearly five hundred and eighteen Millions of Miles to an Inch.

PLATE V.

Is a true Projection of the System of the known Comets; in which are represented nine of the chief Trajectories, from their Aphelii to their Perihelii, all in just Proportion and Position to the Orbits of Saturn and Jupiter, which are also represented by the two concentric Circles, supposed to be drawn round the Sun as their Center.

The Ellipsis, or Trajectory, marked A, shews the Position and Path of the Comet which appeared in the Year 1684, whose Period is supposed to be about fifty Years, and has been observed within the Region of the Planets once.

That mark'd B, is the Way of the Comet of 1682;
The Period conjectured to be about seventy-five
Years and a half, and has been observed thrice.
C, Way of the Comet of 1337;
The Period about 100 Years, observed once.
D, That of the Comet of 1661;
The Period about 129 Years, observed twice.
E, Tract of the Comet of 1618;
The Period about 160 Years, observed once.
F, Way of the Comet of 1677;
The Period about 200 Years, observed once.
G, Way of the Comet of 1744;
The Period about 300 Years, observed once.
H, Way of the Comet of 1665;
The Period about 400 Years, observed once.
I, Way of the Comet of 1680;
The Period about 575 Years, observed thrice.

Plate IV.

Plate V.

The Scale of this System is equal to one Third of the former.

Here I must observe to you, as a Thing I judge may prove of great Consequence with regard to the System of Comets, which is as yet very imperfect: That I am strongly of Opinion, that the Comets in general, through all their respective Orbits, describe one common Area, that is to say, all their Orbits with regard to the Magnitude of their proper Planes, are mathematically equal to one another; which, if it once could be proved, and confirmed by Observation, the Theories of all the Comets that have been justly observed, might easily be perfected, and their Periods at once determined, which now we can only guess at, or may wait whole Ages for more Certainty of. What leads me to believe, that this may prove to be really the Case is this.

I find by Calculation, that the Orbits of the two last Comets, whose Elements have been most corrected by Sir Isaac Newton and Dr. Hally, are to one another, according to their Numbers, nearly as [J]13 to [K]17, notwithstanding one of them is one of the most erratick that ever came under our Observation; and the other one of the most neighbouring to the Sun.

[J] 1316539,968282 Comet of 1680.

[K] 1708155,4644 Comet of 1682.

But it is well known to all Mathematicians, that the first of these Comets moved in so eccentric a Trajectory, that the least Error in its almost incredible Proximity to the Sun will produce a very sensible Difference in the Area of the Orbit: And accordingly, if we moderate the Perihelion Distance of this Comet, by making it but 1000 instead of [L]612, which is but increasing it a 1/35000th Part of the great Radius of the Orbit, (which is an Error every Astronomer will readily grant is very easily made) and we shall find the Orbits of the said two Comets to be exactly equal.

[L] The Number in Dr. Hally's Synopsis.

Further, I must inform you, that the Comet of 1682, which the above is compared with, seems to have been so accurately observed, that it does not appear to have altered its Perihelion Distance half a 68th Part in one intire Revolution. Now, if we can with any Show of Reason, and a Probability on our Side, bring the Areas of these two extream Comets, as I may call them, to an Equality, sure we may conclude, it is a Subject highly worthy to be more considered and enquired into.

PLATE VI.

Is a true Representation of the satellite Systems, proportionable to one another, and to the Orb of the Sun's Body, that a just Idea of the Distances of those secondary Planets, may be easier had from their respective primary ones.

S represents the solar Body with its Atmosphere. Fig. 1. is the System of Saturn from the same Scale. Fig. 2. that of Jupiter from ditto. And Fig. 3. the Orbit of the Moon round the Earth, in the same Proportion.

But as you can have but a very imperfect Idea of the Magnitude of these last Circles, with regard to the Body of the Earth or Moon,

PLATE VII.

Is a true Projection of their real Globes, at their proper Distance from each other, with their common Center of Gravity, and the Point and Line of equal Suspension betwixt them, viz.

A, represents the Globe of the Earth.
B, that of the Moon.
C, Point, and C D, Line of equal Suspension betwixt them.
E, Common Center of Gravity, which describes the Orbis Magnus.
E, F, and B, G, is the Orbit of the Moon.

Farther, that nothing may be wanting to give a true Notion of the whole together,

PLATE VIII.

Is a proportional Drawing of all the primary and secondary Planets together, distinguished by their Characters, proper to attend a Globe of twelve Inches Diameter, such a one being supposed to represent the Sun.

PLATE IX.

Is an exact Scheme of the principal known Comets, in just Proportion, to the Globe of the Earth represented at A, with the Nucleus, and Part of the Tail of the Comet of 1680, B, as it was observed in its Assent from the Sun, viz. a a the Comet's natural Atmosphere, z z z, the Denser Matter winding itself into the Axis of the Train x x, the inflam'd Atmosphere and Tail dilated near the Sun. C, represents the Ball of the Comet of 1682, D, that of 1665, E, that of 1742, and F, the Head of the Comet of 1744.

And again, that you may have some Notion of the apparent Magnitudes of all these Planets and Comets, &c. as they appear at the Earth,

Plate VI.

Plate VII.

Plate VIII.

Plate IX.

Plate X.

Plate XI.

Click on image to view larger sized.

PLATE X.

Represents the Sun and Moon in the just Proportion of their mean Diameters, with two of the Comets A and B, and the five erratick Planets, as they are observed at the Earth, in a middle State of their Distances from it.

For a more full and particular Description of all the Parts of the solar System, and of the home Elements of Astronomy in general, I refer you to my Clavis Cœlestis, &c. where every thing concerning the Planets, Comets, and Stars; and their real and apparent Motions, are at large represented, explained, and accounted for, for the Benefit of such as have not made the Mathematicks their regular Study.

Now, to convince you that the Planets are all in their own Nature no other than dark opaque Bodies, reflecting only the borrowed Light of the Sun, I must recommend to your Observation, this natural and simple Experiment, which almost any Opportunity of seeing the Moon a little before the Full, will put into your Power to make; but best and easiest when the Sun is in any of the North Signs, i. e. in Summer.

At such a time, the Sun being near setting, the Moon will appear in the eastern Hemisphere; and if there be any bright Clouds northward, or southward near her, you will plainly perceive, that the Light of the one is of the same Nature with that of the other; I mean the Light of the Moon, and that of the Cloud. To me there never appeared any Difference at all; and I am perswaded, were you to make but two or three Observations of this kind, which is from Nature itself, a sort of ocular Demonstration, you cannot fail of being convinced, that the Moon's Light, such as it is, without Heat, can possibly proceed from no other Cause than that which illumines the Cloud: For if the Clouds, whose Composition we know to be but a thin light Fluid, formed of condensed Vapours only, is capable of remitting so great a Lustre, how much more may we not allow the Moon, which, Length of Time, and many other Circumstances, have long confirmed to be a durable and solid Body.

The Increase of her Lustre, indeed, during the Absence of the Sun from us, to a less penetrating Genius than your's, may possibly afford some trifling Ground of Objection to the above Conclusions, as being drawn from the Phænomena of Day-light only; by reason in the Night, we have no Clouds in equal Circumstances to compare with her.

But this I need not tell you, is all owing to her being seen through a darker Medium, and not to any real Increase of natural Light emitted from the Sun. As a Proof of which, were it necessary, you need only, shut out the Rays of the Atmosphere, by the Help of a sufficiently long Tube; and the Moon, or any other celestial Body, will appear through it, as bright in the Day-time as in the Night.

Thus all light Bodies of inferior Lustre, whether shining by their own natural Radiences, or by a borrowed Reflection, partake of the same Advantage, when removed from the more potent Influence of a superior one; and hence it is, that the [M]Aura Ætherea shines out most manifest, when the Body of the Sun himself is hid, the Stars, and the Via Lactea most lively and numerous in the Absence of the Moon, and those Exhalations, or Meteors, vulgarly called Falling-stars, become only visible (like Glow-worms) in the Night.

[M] An Helios, or golden Light, always attending the Sun, and supposed to spread itself all round his Body in the Direction of his Equator, was very visible during the total Darkness of the Eclipse of 1715, and may be always seen about the Autumnal Equinox.

Here it may not be improper to tell you, that the Clouds are to us in effect no other than as so many Moons, whereby we have our artificial Day prolonged to us several Hours after the Sun is set, and likewise produced as much sooner before he rises; and were they to ascend by still stronger Power of Exhalation to an Elevation, all round the Atmosphere, so as to form a Sphere equal to four Times the Globe of the Earth, there would then be no such Thing as real nocturnal Darkness to any Part of the World.

The lunar Light then we may very justly conclude, proceeds originally from the Sun: And notwithstanding many more Arguments might be drawn from the Demonstration of her Phases, Eclipses, &c. to prove it, yet none of them need here be added, to what has been already said, to convince you of the Truth of it. This being granted, let us now consider what Effect this, or a like Quantity of borrowed Light, would have, when removed to a much greater Distance.

I may, I think, suppose, that you know so much of Opticks as to understand, that all visible Objects apparently decrease in Magnitude, as their Distance from the Eye increases. Consequently, that, if the Moon's Orbit was placed as far again from the Earth as it really is, her Globe, or rather Disk, would then seem to be but half as big as to us she now appears to be, and of course still farther, were she placed at ten times the Distance she is known to revolve at, her apparent Diameter would be reduced to a tenth Part only of what it now appears to be in her present Orbit, that is, one hundred Times less in visible Magnitude than her neighbouring Disk is found to be where it now is seen. And such, but something less, the two Planets Venus and Jupiter, which are frequently, in their Turns, our Morning and Evening Stars, appear to be through a common Telescope.

Now these two Planets, together with the other three, which we find moving in regular Orbits round the Sun, are all found subject to the same [N]Changes of Phænomena, in their various Aspects with the Sun; and who can doubt but that they are all of the same or like Nature? But you'll say, perhaps, how are we sure that Venus and Jupiter have no native Light of their own, since many of the ancient Philosophers, and in particular Anaximander, allowed even the Moon to have some; and besides, in Philosophy, as well as in Logick, I think you hold there is no proving a Negative, at least at such a Distance.

[N] Venus and Mercury in every Heliocentrick Revolution, perform all the Changes of our Moon in a like Gradation and Defection of Light, both horned and gibos'd.

To make you conceive the Impossibility of such a Light, and next to a Demonstration, convince you of the Unnaturalness of such a Supposition, I must put you in mind, that some time ago, when I was last in the Country with you, I think it was about the latter End of Autumn, near the Winter Solstice, as we were walking one Evening, I bid you take notice of the Moon, which was then near setting, and about two Days old. You may remember, her whole Globe appeared to us very conspicuously within a manifest Circle. You immediately told me, that that kind of Phænomenon the Country People called a Stork, or the old Moon in the new one's Arms. This I then endeavoured to explain to you, and I think made you sensible it was intirely an Effect of the Earth's, and an Appearance always to be expected at that Time of the Year. The Earth being then in the State of a Full-Moon to that Part of the lunar Orbit, and near her Perihelion, at which time, the Earth sends back a Reflection to the [O]Moon twenty-five times more potent than that of the Moon to us.