Astronomical Dialogues Between a Gentleman and a Lady

Front matter

Astronomical Dialogues

Between a

GENTLEMAN

To the Lady Cairnes

TO THE

Lady CAIRNES.

MADAM, As the Design of these Dialogues carries them naturally into the Patronage of the Fair Sex; so your own Merit, and my Duty, determine them to your Ladyship.

To you Madam! who are blest with all those Natural Graces and Genteel Accomplishments, which justly command universal Esteem; while Persons of true Taste and thorough Knowledge of Life, with Pleasure see even those exceeded by intellectual Beauties, and such as claim Addresses of this Nature. For what can be more engaging than to find at Lady Cairne's Table, the greatest Liberality and Elegance of Entertainment, outdone by improving Conversation; and the Understanding more regaled than the Senses?

But I know I must forbear; and not offend such a Modesty as your's, even with Truth: However, I can't help shewing that I am neither insensible of what all the World admires, nor ungratéful for the Obligations you have so generously conferr'd on,

Madam,

Your Ladyship's

most humble Servant,

J. HARRIS.

The Preface

THE

PREFACE.

This Book was most of it written a good while ago: And being supposed to be lost for some Years, was lately retrieved, and reviewed by its Author, with the Disinteressedness of a Stranger. However, I liked it so well, as to resolve upon its present Publication, with some few Emendations and Additions. Of which latter sort the Description of the famous Orrery of , is the most considerable.

I wrote it in this diverting Way, in pursuit of a Design, which, as I have made the general Business of my Life, so I can look back upon its Success with Pleasure, viz. The engaging Persons of Birth and Fortune in a warm Application to useful and real Learning: To induce them to detach some of their happy Leisure from being lost by Sports, Play, or worse Avocations, and to dedicate it to the Improvement of their Minds.

For I have often been ashamed and shocked to see, how awkwardly the few Modest have lookt, in Conversations where they could bear no part; and how insolently others have despised what they neglected to understand.

But what glorious Improvements might one expect from Persons of Fortune and Leisure, if they would addict themselves to these Things? Who can bear the expence of Good Instruments for Cælestial Observations.

For tho' there can hardly be above a Score in an Age who have pursued these Studies thoroughly: Yet such great Lengths have been run in spite of all Disadvantages, as may easily convince us, what to have hoped for, if Great Men would now and then divert themselves this way.

The Reader will easily see that the Conversation in these Dialogues is feigned, and in Imitation of Those of the excellent Mr. Fontenelle, On the Plurality of Worlds. And that the Digressions, Reflexions, Poetry and Turns of Wit, are introduced to render Those Notions pleasing and agreeable, which perhaps without such a kind of Dress, would appear too crabbed and abstracted.

However, I don't perplex my Fair Astronomer with any thing but the true System of the World: I mislead her by no Notions of Chrystalline Heavens, or Solid Orbs: I embarrass her with no clumsey Epicycles, or imaginary and indeed impossible Vortices: But I shew her at first the Cælestial World just as it is; and teach her no Hypotheses, which, like some other things taught at Places of great Name, must be unlearned gain, before we can gain True Science.

And as I think it practicable to explain and teach any Science in this Facetious way (Facete enim & commode dicere quid vetat?) so perhaps I may hereafter, if God grant me Health, Ease and Leisure, make some other Attempts of this kind. For the Lady may well be supposed, tho' the Sight of the Globes first struck her Fancy and turned her Desires this way, to have made Excursions into other Parts of Mathematicks, and to have discoursed with her Friend on those Subjects. And perhaps all Those Dialogues may not be lost, as these had like to have been; but may, if these find a suitable Encouragement, be communicated also to the World.

Multaq; prætera tibi possum Commemorando, Argumenta, fidem dictis conradere nostris: Verum animo satis hæc Vestigia parva sagaci Sunt; per quæ possis cognoscere cætera tute. >>Lucret. Lib. I.

First Dialogue

Astronomical Dialogues

BETWEEN A

Gentleman and a Lady.

It is now about seven Years ago, since I presented the most Engaging Lady M… with Mr. Fontenelles Book of the Plurality of Worlds: And I remember well what she said a few Days after.

I have look'd over your Book, Sir, said she, as my way is, first cursorily, and I intend to give it a very careful second Reading; but I perceive by it, you have cut out much more Trouble for your self, than perhaps you imagin'd: For I find there are many things previously necessary to the understanding it, which you must oblige me with explaining; but, continued she, a Conversation of that kind with me, I doubt, will be too dull and tedious, since I am not bless'd with any of those shining Qualifications, with which Mr. Fontenelle hath complimented M. la Marquiese; I should indeed, said she, except those two, which I suppose, in Complaisance to our Sex, he makes the Foundation of Philosophy, viz. Ignorance and Inquisitiveness for those I'm sure, I have in Perfection, as you have long experienced.

I need not mention the Return I made, nor how prettily she changed the Discourse to something more general, when she found I was going to say just things of her; those that knew her, don't want to be reminded of the many Beauties, both of Mind and Body, which render'd Lady M… one of the most agreeable Persons of her Sex; which yet were she living, tho' a just Debt to her Merit, I must not have said, for fear of offending her Modesty.

All that is necessary to introduce what follows, is, to inform you, That some Years before her Death, when I went to visit that accomplish'd Lady at her Country Seat; I was a little surprised to find her, the next Morning after my Arrival, studiously viewing a pair of large Globes, Which stood in the Drawing-Room, looking into the Garden, and which I used to make my Place of Study.

Good Morrow, said I, Madam, what! hath Fontenelle made an Astronomer of you in good earnest? Are you really contemplating the Order and Motions of the Heavenly Bodies? Or are you rather seeking on the Earthly Globe, where to make new Conquests?

The Historians foolishly represent Alexander the Great, as Weeping, that he could carry his no further than over all the World; but I'm sure, were he present now, to see you in that Posture commanding the Globe, and giving what Turns you please to it; that Thought of your humble Servant's would appear just enough;

O! Sir, said she, your Servant, I doubt you did not rest well last Night? What did your Imagination carry you into the Poetical Regions of Fairy-Land, that you awake with Verses in your Mouth this Morning? But to speak seri- ously, I wonder you don't blush to paint so much beyond the Life, and yet suppose the Picture to be like any one; you affect to imitate our great Painters, if we sit to them, they make us all handsome; but they do it to shew themselves, not us, and they don't care so much whether it be like or no, so it be but a fine Picture; and in this our own Vanity too often indulges them.

But pray, added she, let us lay aside all these Fooleries; and be so good as to be serious with me for an Hour or two: I have a great Mind to be let a little into the Knowledge of these Instruments, the Globes; and to know something of the first Principles and Rudiments of Astronony; or else I find I shall lose half the Beauties of that very entertaining Book Mr. Fontenelles Plurality of Worlds, which you formerly obliged me with, as well as perhaps be led into some Errors by it: And don't despise and neglect me because I am a Woman. I have heard you sometimes say, you thought that there was no difference of Sexes in Souls; nay, that our Parts and Natural Capacities were often equal, at leasi, if not superior, to those of Men. But perhaps there were some particular Reasons for your saying so then, which now altering or ceasing, your Judgment and Opinion may have done so too.

I was going to assure her, that I was still of the same Sentiments, when putting on a forbidding Look, with a serious Countenance the proceeded thus:

These Globes, Sir, came too late to accompany a Relation of mine to India, his Ship having sailed before they were finished, which is the Reason you see them here; and I have ordered them to be set out this Morning, and shall do so from Day to Day, tho' without obliging you to what Fontenelle had with the French Lady, an entire Week's Conference. But I have a great Mind to learn, from my Friend, something of the Nature and Use of them; for they appear to be made and finished up with that Curiosity and Care, that sure some very useful Knowledge is to be learnt from them, and is it not barbarous in you Men to confine it all to your selves?

Madam, said I, you will give me a new Rise to value any thing that I understand; if I can render it acceptable to you.

Well then, Sir, said she, all Compliments apart, both to your self and me, pray let us go to our Business, the Tea won't be ready this Hour, and there is a little too much Dew for us to take a Walk in the Garden. Let me understand then, first the Difference between these two Globes, and why one hath the Cities, Countries, and Places of the Earth drawn on it, like a Map; and the other Circles and Stars, and these odd uncouth Figures of Beasts, Birds and Fishes: Pray why do they turn round? What doth this Brass Hoop signify in which they hang? For I perceive that it also hath Numbers engrav'd upon it: And what doth this broad wooden thing serve for, that hath the Days of the Month and other Letters, as well as Figures, pasted upon it?

I am glad, said I, Madam, by the warm Manner of your Enquiry, to find that you are in earnest; and I have often wished that the same Curiosity and Love of Knowledge would inspire more of the fair Sex, for it would mightily enlarge their Empire and Power over ours, by endowing them with more real and lasting Beauties, such as would improve with Time, and strengthen even in Age itself. But as to your present Questions, Madam, I will give you the most Satisfactory Returns I can.

And first, Madam, it will be necessary to acquaint you with the Meaning of the Word Globe; and what the Properties, in general, of such a Figure or Body, are.

Your Ladyship is to understand then, that a Globe is a round Body of such a Nature, that every Part of its Surface or Out-side, is at an equal Distance from one Point within it, which is called the Center. This Body also is sometimes named a Sphere, with regard to Astronomical Speculations; and this Science which you are now inquiring into, is hence called The Doctrine of the Sphere.

I Think I understand you; laid she, the Figure of a Globe is not flattish like that of a Cheese or a common Ninepin Bowl; but rather like a Boy's Marble, or a Bullet cast in a Mould.

Exactly right, Madam, said I, and further you are to know, that a strait Line supposed to be drawn thro' the Center of this Globe any where, from one opposite Point of the Surface to the other, is called a Diameter. I Thank you, said she, for that Explication, Sir, I have often met with the Word, but never knew fully what Diameter signified before: But now I know what the ingenious Mr. Butler meant when speaking of the Moon, he saith, that Sydrophil knew

And now I know what the Plummer meant the other Day, when he talk'd of a Pipe of Lead of such a Diameter; I now know the Meaning of Diametrically opposite, &c. But, pray, Sir, go on.

You will next see easily, Madam, said I, that if a Globe were at Liberty, and any Power or Force at hand to move it, it would easily turn or roll round any one of its Diameters, as this Globe doth round this Wire; which particular Diameter, is called therefore its Axis; as being the Axle-tree on which it turns. But tho' this be true of the Nature of a Globe in general, yet the Axis, as we call it, of the Earth and Heavens, by the Will of our All-wise Creator, is one fixed and determinate Line; and about this the fixed Stars are usually supposed to revolve, without ever changing their Distance, or deviating from one another or from it.

I Am mightily pleased, returns she, with the Nature of these Globes, because they are unbiassed and indifferent, as to this or that particular Way of Turning; and I fancy it to be a good Emblem of the Freedom of our Minds in the State of Innocence, when they first came out of Nature's Hands; they were then perfectly at Liberty to move any way, which they lik'd best; and I dare say, that all the wrong Biasses and particular Turns that we find in any of them, are owing to the Weight or Power, as you call it, of our own corrupt Affections.

You moralize excellently well, said I, Madam, and are very just in your Notions of the Deity.

But she went on, and said; Yet I think we might be glad to receive from the first Mover and Author of all Things, such a determinate Way of moving, as you say God hath given to the Heavens and the Earth; for our own whimsical Motions, Turnings and Shiftings, seem to be as unaccountable as they are various.

But pray, said she, let me understand what you say as to the present Point a little further; Do the Heavens and the Earth all really move round about one Axis, as these two Globes do round theirs? And are the Poles thus beautifully described by Mr. Dryden, the two Ends of this Axis?

Poles.

Shall I ever come to know what these Poles, and Dragons, and Bears, mean?

Very easily, Madam, said I, and you will find that the Motion of the Earth alone round its Axis will sufficiently account for all the rest; for these fixed Stars don't in Reality move at all, but only appear so to do. And you must know, that there is one Star, or a Point very near it, towards which this Pole, or End of the Earth's Axis, (which is called the North-Pole) doth always point: This is the Star here on this Celestial Globe, and if it be fair, and the Sky clear, in the Evening, I will shew it you in the Heavens: 'Tis said, by Astronomers, to be in the Tip of the Tail of the Little Bear, a Constellation of Stars so called; you see there are seven of these Stars in all, placed on the Globe within the Picture or Figure of a Bear: The Reason of the Figure I will tell you hereafter.

Pray, said she, good Sir, don't take it amiss if I interrupt you with one Question: Is this Tip of the Bears Tail, that celebrated Tip of Cardan the Conjurer; who, as Butler saith,

Firmly believ'd great States depend, Upon the Tip of th' Bears Tail's End,

That as she whisk'd it tow'rds the Sun, Strow'd mighty Empires up and down.

The very same, Madam, said I.

Go on then, said she.

This Star here by the Wire, Madam, said I, we call the Pole Star, and the Point near it, thro' which the Wire runs, the North Pole of the World. And let the Earth be where it will, in its Annual Course round the Sun, this North Point on the Earth, and here placed on the Globe, will always be either exactly or nearly under that North Pole Star or Point, in the Heavens. But of this more when I shall further explain to you the Motions of the Earth; and this Position of the Earth's Axis is so firmly fixed and determined by the Author of Nature, that from it there hath never yet been observed any considerable Variation.

Pray, Sir, said she, proceed: When I come to look over Fontenelle again, I perceive I shall understand him and you much better.

Madam, said I, the outward Figures of these two Globes you see are nearly alike; but tho' they are hung also, and fitted up alike, yet they are almost as different from one another in their Natures and Properties, as are the different Regions that they represent.

This Globe which is designed to shew the Face of the Earth; and which therefore is called the Terrestrial Globe, is truly and properly a Representation of it, round or spherical as that nearly is, and it hath the Sea and the Land, with all the Regions, Countries, Nations, Islands and Cities drawn upon it; just in that Order and Figure, that they are, in Reality, on the Face of the Earth itself; and it is, if carefully drawn, a true Map, or Description, of what is usually called The World: whereas all those flat Maps and Charts, which you see drawn upon Paper, cannot be accurately so, tho' they are exact enough for common Use.

That Word World, said she, I can't get over without reflecting, what weak, vain, and silly Mortals we are: We too often take this poor Spot of Earth to be the only World worth inquiring after; and so we can but acquire a little of its Dirt, we neglect all Care for an Eternal Mansion in the Heavens. And further, I have no Patience with Ptolomy, I think they call him, and his Astronomers, that will needs have the mighty Sun, and all that infinite Orb of fixed Stars, to be made only for the sake of this little dirty Planet, as I remember somebody calls it; and to have no other Use nor End, but only to dance round it, which yet, as I have heard, is a meer Point, and scarce visible to an Eye placed in some of the other Planets.

But to go on with my Lesson: Good Sir, said she, is the Figure of the Earth thus really round? and have you any good Reasons to make you think so? For I must own I had not till now a Notion of its being round like a Ball; I took it rather to be round in Compass like a Dish or Plate.

Very many and substantial ones, Madam, said I, and you will be fully convinced by them, when they occur to your Reading hereafter, if you proceed on in that Way you are now going: But, however, the Sun shining so bright into this Room, will furnish me now with one Argument to make that Notion plain to you. You see, Madam, when I hold any solid Body in this Light of the Sun, its Shadow will be nearly like the Shape and Form of that of the Body; when I hold this Book in the Light, its Shadow will be square at the Sides, as the Book is; but when I hold this Orange in the same Light, the Shadow, you see, hath a round Edge; and therefore since in the Eclipses of the Moon, the Shadow of the Earth, which you know, Madam, occasions the Moon's being covered with Darkness, appearing always exactly round or circular, we justly conclude that the Figure of the Earth is round or spherical too, or else the Termination or Out-Line of its Shadow could never be always in a Circular Form.

I Thank you for this easy and natural Explication, said the Lady, which I think I comprehend; and I am beholding to the Sun, that great Fountain of Light, or rather to Him that made it, for being now instrumental to dispel the Darkness I had in my Mind before about this Affair; however, being no Persian, I shall not worship the Sun for it. But pray, Sir, go on with an Explication of the other Globe.

That, Madam, is called the Celestial one, said I, because 'tis designed for a Representation of the Firmament, and the Concave Arch of the Heavens; and indeed it doth well enough exhibit to us the fixed Stars, and the Tracks or Circles of the Sun and Planets apparent Motions, if you get a right Notion of it, as this Figure, which we call an Armillary Sphere, will I think help you to obtain: In order to which you must now imagine your Eye placed within at the Center of the Globe, or on the little Ball there in the Figure which represents the Earth; and that the Spherical Surface of it, on which you see the Stars there painted and gilded were transparent like Glass; so that you could actually see thro' it, not only all the Circles drawn upon it, but also all the Stars above in the Heavens, as they really appear there in a bright Night. And if you imagine further, Madam, that strait Lines were drawn from every Star in the Firmament to your Eye so placed, as before, in the Center of this Globe, those Lines would pass thro' and cut the Spherical Surface of the Globe in proper Points to paint, or to place the Pictures of the Stars upon.

I Think, I conceive you right, said the Lady, so that if there were Holes in the Surface of this Globe in those Places where these Stars are painted upon it, and that my Eye were within at the Center, and the Globe turn'd, so as to conform itself to the present Position of the

Heavens above; I should see every Star there thro' its corresponding Hole in the Globe.

You are perfectly right, Madam, said I, and Ptolomy himself, could not have expressed it better. And just in that Central Point (and just such a Point as that is it) do Astronomers of his Sect suppose the Earth to be placed, as you see in the Figure, in the middle of the Sphere of the fixed Stars, which seem to revolve round about it, once in 24 Hours, because the Earth doth turn round her own Axis, tho' a contrary Way, in the same Time.

Of this, replied Clarella, I have gotten a tollerable Notion from what you said before, and from the French Author: But, pray, let us now go on with our Globes here; What is the Meaning of this broad Wooden Circle placed round each of them, and what is it called?

Madam, said I, it is called The Horizon; which is a Greek Word that signifies a Limiter or Determiner. And to conceive it right, imagine your self placed, as before, on this poor little Earth, within that immense Celestial Globe; which you are to suppose now to be millions of Millions of times greater than it really appears to be: Then you know, if you look round you on the Earth, its Surface will extend every way from your Eye, like a vast Plain; which will be under your Feet, and to which your Body will be perpendicular, or upright: this Plain stretching all round you every way as far as your Eyes can fee, in a flat open Country where no Hills interpose: Or on the Surface of the Sea, will seem to divide or cut the Concave Orb of the Stars, or the Sky, into two Parts (which they call Hemispheres; the one seemingly above this Plain; which therefore they call the Upper, and the other apparently below it: Which therefore they call the Lower Hemisphere. Such a Plain is this is call'd the Horizon: And if it be really that which any one's particular Eye makes upon any occasional View, 'tis call'd the Sensible Horizon: But if you imagine this Plain, as you may easily do, to pass through the very Center of the Earth on the Surface of which you then stand, 'tis called the Real or Rational Horizon; because that doth really or actually divide the Starry Regions into two equal Hemispheres; and both these Horizons are well enough represented by that wooden Cir- cle, which you now lay your fair Hand upon.

I Hope I take you right, said she; and now begin to understand better the Meaning of many Expressions which have often occurr'd to me before, but with less Light. But why do you so cautiously use the words apparently above and below?

Because, said I, Madam, there is in reality no such thing as any Difference between above and below: The Heavens are every where above or without what they contain; but we, taking our Ideas of things from ourselves, do agree to call that above or uppermost which is over our Heads, and that below, which is beneath us, or down under our Feet: And therefore as we call that Concave Half of the Region of the Fixed Stars, which we see above our Horizon, the Upper Hemisphere; so the other Half takes the Name of the Lower Hemisphere.

I am mightily pleased, said the Lady, with these Celestial Beings that are so perfectly above all the poor Trifles of Place and Station; with which we Mortals make such a bustle here below: Especially those of our Sex; as I will honestly own to you, now you are my Master and Teacher; for as Butler hath justly observ'd';

But let us go on. I perceive, said the Lady, that these Horizons will always vary as we shift the place of our View.

Yes, Madam, said I, and so will the Hemispheres too that they determine.

And yet, said she, we are often so vain as to take our little narrow View or Horizon for the Bounds of all that is to be seen; and judge, that what is not within our Hemisphere, to be either nothing at all, or at least not worth our knowing or enquiring after; for we are always so vain as to despise what we do not understand. But I interrupt you with my impertinent Reflections; pray, Sir, go on.

I beg you to take notice farther, said I, Madam, that when the Sun, or any Star or Planet, appears at the Eastern Edge of our Horizon, we say it is Rising; and when it is got quite above it, we say it is Risen, or is Up. On the contrary if it appear towards the Western Edge of it we say it is Setting; and when it is gotten below it, we say it is Set. And this Rising and Setting always respects the sensible, and not the Real Horizon.

But what is the meaning of these Circles, demands she, which I see drawn here upon the Board of the Horizon, and on both Globes alike?

The outermost of them, Madam, said I, represents the Points of the Compass, as they are called by our Seamen; who make use of an Instrument called the Compass, to steer their Ships by at Sea.

Pray let me know a little more of that matter, said she, for 'tis a Thing I have heard much talk of.

You have seen, no doubt, Madam, said I, a Loadstone; and know that it hath that wonderful Virtue, among others as strange, that if a Needle or long Iron-Wire be drawn rightly over it, that Needle will ever after that, when at liberty, point, as they call it, due North and South.

You are now, said she, so very good, that I think I must feed your Vanity, by owning, that I was once much pleased with some Verse of yours occasionally given me; but am more so now, because I understand them better; after you had talked in your usual way of Love and Constancy and I know not what; you thus, as I remember, concluded,

Madam, said I, you do Me and my Trifles a great deal of Honour——

Hush! said she, not a word! I won't now allow you one Syllable of Trifling; be quiet and go on with your Lecture.

Please to let me inform you then, Madam, said I, that such a Wire as this, so touch'd, as they call it, or directed by the power of the Magnet, or Loadstone, they put into a round piece of Pasteboard, on which they draw a Circle; dividing it as this on the wooden Horizon of the Globe is, first into four Quarters, for East, West, North and South, placing the Point of North over that End of the wire which will point that way; then they divide each Quarter into Halves, and by that means they make in the whole 32 Divisions, which they call Points; and which are there and here expressed by the Initial Letters of their Names after this manner: [See Fig. II] And therefore the Use of that Circle on the Horizon of the Globes is to shew, on what Point of the Compass the Sun, or any Star or Planet apparently Rises or Sets; as I shall shew you more fully hereafter.