Part 6

The Inhabitants of Venus have much the ſame Face of Things as thoſe in Mercury, only they never ſee him in oppoſition to the Sun, which is occaſioned by his never removing above 38 degrees, or thereabouts, from it. The Sun appears to them larger by half in his Diameter, and above twice in his Circumference, than to us: and by conſequence affords them but twice as much Light and Heat, ſo that they are nearer our Temperature than Mercury. Their Year is compleated in ſeven and a half of our Months. In the Night our Earth, when ’tis on the other ſide of the Sun from Venus, muſt needs ſeem much larger and lighter to Venus than ſhe doth ever to us; and then they may eaſily ſee, if their Eyes be not weaker than ours, our conſtant Attendant the Moon. I have often wonder’d that when I have view’d Venus when ſhe is neareſt to the Earth, and reſembled an Half-moon, juſt beginning to have ſomething like Horns, through a Teleſcope of 45 or 60 Foot long, ſhe always appeared to me all over equally lucid, that I can’t ſay I obſerved ſo much as one Spot in her, tho’ in Jupiter and Mars, which ſeem much leſs to us, they are very plainly perceiv’d. For if Venus had any ſuch Thing as Sea and Land, the former muſt neceſſarily ſhow much more obſcure than the other, as anyone may ſatisfy himſelf, that from a very high Mountain will but look down upon our Earth. I thought that perhaps the too brisk Light of Venus might be the occaſion of this equal appearance; but when I uſed an Eye-glaſs that was ſmok’d for the Purpoſe, it was ſtill the ſame Thing. What then, has Venus no Sea, or do the Waters there reflect the Light more than ours do, or their Land leſs? Or rather (which is moſt probable in my Opinion) is not all that Light we ſee reflected from an Atmoſphere ſurrounding Venus, which being thicker and more ſolid than that in Mars or Jupiter, hinders our ſeeing any thing of the Globe it ſelf, and is at the ſame time capable of ſending back the Rays that it receives from the Sun? For it is certain that if we looked on the Earth from the outſide of the Atmoſphere, we ſhould not perceive ſuch a difference as we do from a Mountain; but by reaſon of the interpoſed Atmoſphere, we ſhould obſerve very little Diſparity between Sea and Land. ’Tis the ſame Thing that hinders us from ſeeing the Spots in the Moon as plain in the Day as in the Night, becauſe the Vapours that ſurround the Earth being then enlighten’d by the Rays of the Sun, are an Impediment to our Proſpect.

[In Mars.]

But Mars, as I ſaid before, has ſome Parts of him darker than other ſome. By the conſtant Returns of which his Nights and Days have been found to be of about the ſame length with ours. But the Inhabitants have no perceivable Difference between Summer and Winter, the Axis of that Planet having very little or no Inclination to his Orbit, as has been diſcover’d by the Motion of his Spots. Our Earth muſt appear to them almoſt as Venus doth to us, and by the Help of a Teleſcope will be found to have its Wane, Increaſe, and Full, like the Moon: and never to remove from the Sun above 48 Degrees, by whoſe Diſcovery they ſee it, as well as Mercury and Venus, ſometimes paſs over the Sun’s Disk. They as ſeldom ſee Venus as we do Mercury. I am apt to believe, that the Land in Mars is of a blacker Colour than that of Jupiter or the Moon, which is the reaſon of his appearing of a Copper Colour, and his reflecting a weaker Light than is proportionable to his diſtance from the Sun. His Body, as I obſerved before, tho’ farther from the Sun, is leſs than Venus. Nor has he any Moon to wait upon him, and in that, as well as Mercury and Venus, he muſt be acknowledged inferiour to the Earth. His Light and Heat is twice, and ſometimes three times leſs than ours, to which I ſuppoſe the Conſtitution of his Inhabitants is anſwerable.

[Jupiter and Saturn the moſt eminent of the Planets both for bigneſs and attendants.]

If our Earth can claim pre-eminence of the fore-mention’d Planets, for having a Moon to attend upon it, (for its Magnitude can make but a ſmall difference) how much Superiour muſt Jupiter and Saturn be to thoſe three and the Earth alſo? For whether we conſider their Bulk, in which they far exceed all the others, or the Number of Moons that wait upon them, it’s very probable that they are the chief, the primary Planets in our Syſtem, in compariſon with which the other four are nothing, and ſcarce worth mentioning. For the eaſier Conception of their vaſt Diſparity, I have thought fit to add a Scheme of our Earth, with the Moon’s Orbit, and the Globe of the Moon itſelf, and the Syſtems of [Fig. 3.] Jupiter and Saturn, where I have drawn every thing as near the true Proportion as poſſible. Jupiter you ſee is adorned with four, and Saturn with five Moons, all placed in their reſpective Orbits. The Moons about Jupiter we owe to Galilæo, ’tis well known: and any one may imagine he was in no ſmall Rapture at the Diſcovery. The outermoſt but one, and brighteſt of Saturn’s, it chanc’d to be my lot, with a Teleſcope not above 12 foot long, to have the firſt ſight of in the Year 1655. The reſt we may thank the induſtrious Caſſini for, who uſed the Glaſſes of Joſ. Campanus’s grinding, firſt of 36, and afterwards of 136 foot long. He has often, and particularly in the Year 1672, ſhew’d me the Third and Fifth. The Firſt and Second he gave me notice of by Letters in the Year 1684; but they are ſcarce ever to be ſeen, and I can’t poſitively ſay, I had ever that Happineſs; but am as ſatisfied that they are there, as if I had; not in the leaſt ſuſpecting the Credit of that worthy Man. Nay, I am afraid there are One or Two more ſtill behind, and not without reaſon. For between the Fourth and Fifth there’s a Diſtance not at all proportionable to that between all the others: Here, for ought I know, there may be a Sixth; or perhaps there may be another without the Fifth that may yet have eſcaped us: for we can never ſee the Fifth but in that part of his Orbit, which is towards the Weſt: for which we ſhall give you a very good reaſon.

Perhaps when Saturn comes into the Northern Signs, and is at a good height from the Horizon (for at the writing of this he is at his loweſt) you may happen to make ſome new Diſcoveries, good Brother, if you would but make uſe of your two Teleſcopes of 170 and 210 Foot long; the longeſt, and the beſt I believe now in the World. For tho’ we have not yet had an opportunity of obſerving the Heavens with them (as well by reaſon of their Unwieldineſs, as for the Interruption of our Studies by your Abſence) yet I am ſatisfied of their Goodneſs by our trial of them one Night, in reading a Letter at a vaſt diſtance by the Help of a Light. I cannot but think of thoſe times with Pleaſure, and of our diverting Labour in poliſhing and preparing ſuch Glaſſes, in inventing new Methods and Engines, and always puſhing forward to ſtill greater and greater Things. But to return to the Figures, of which there remains ſomething further to be ſaid.

[The proportion of the Diameter of Jupiter, and of the Orbs of his Satellites, to the Orbit of the Moon round the Earth.]

I have there made the Diameter of Jupiter about two third parts of our diſtance from the Moon: for the Diameter of Jupiter is above twenty times bigger than that of the Earth; which is about a thirtieth part of the Moon’s diſtance. The Orbit of the outermoſt of Jupiter’s Satellites is to that of the Moon round the Earth, as 8 and ½ is to 1. And each of theſe Moons, by the Shadow they make upon Jupiter, cannot be leſs than our Earth. Their [The Periods of Jupiter’s Moons.] Periods, that I may not omit them, are according to Caſſini’s Account theſe. That of the inmoſt is one day, 18 hours, 28 minutes, and 36 ſeconds. The Second ſpends 3 days, 13 hours, 13 min., 52 ſeconds in going round him. The Third 7 days, 3 hours, 59 min., 40 ſec. The Fourth 16 days, 18 hours, 5 min., 6 ſec. The Diſtance of the innermoſt from Jupiter himſelf is 2⅚ of his Diameters. That of the Second is 4 and a half: Of the Third 7 and one ſixth part: Of the Fourth 12 and two thirds, of the ſame [And Saturn’s.] Diameters. The Innermoſt of Saturn’s Satellites moves round him in 1 day, 21 hours, 18 min., 31 ſec. The Second in 2 days, 17 hours, 41 min., 27 ſec. The Third in 4 days, 13 hours, 47 min., 16 ſec. The Fourth in 15 days, 22 hours, 41 min., 11 ſec. The Fifth in 79 days, 7 hours, 53 min., 57 ſec. Their Diſtances from the Center of Saturn are, that of the firſt almoſt one, that is 39 fortieth parts of the Diameter of his Ring; that of the ſecond one and a quarter of thoſe Diameters; of the third one and three quarters of them; of the fourth four, or according to my Calculation, but 3 and a half; of the 5th 12, which were found with vaſt Pains and Labour.

Now can any one look upon, and compare theſe Syſtems together, without being amazed at the vaſt Magnitude and noble Attendance of theſe two Planets, in reſpect of this little Earth of ours? Or can they force themſelves to think, that the wiſe Creator has diſpoſed of all his Animals and Plants here, has furniſh’d and adorn’d this Spot only, and has left all thoſe Worlds bare and deſtitute of Inhabitants, who might adore and worſhip him; or that all thoſe prodigious Bodies were made only to twinkle to, and be ſtudied by ſome few perhaps of us poor Mortals?

[This proportion true according to all modern Obſervations.]

I do not doubt but there will be ſome who will think we are very much miſtaken about the Magnitude of theſe Planets. For will you pretend to make them who are taken up in admiring the Largeneſs of this Globe, its multitude of Nations, Cities, and Empires; can you pretend I ſay to make them ever believe that there are Places in compariſon of which the Earth is as inconſiderable as this Figure would make it? But they ought to be inform’d, that theſe Proportions are thoſe which the beſt Aſtronomers of this Age have agreed upon. For if the Earth be diſtant from the Sun ten or eleven thouſand of its own Diameters, according to the Accounts of Monſieur Caſſini in France, and Mr. Flamſted in England, wherein they made uſe of very exact Obſervations of the Parallaxes of Mars; or if, according to a very probable Conjecture of mine, it be diſtant twelve thouſand, then the Magnitudes of the other Orbs will very near anſwer the Proportions here ſettled.

[The apparent magnitude of the Sun in Jupiter, and a way of finding what Light they there enjoy.]

But to return to Jupiter. The Sun appears to them who are upon it five times leſs than to us, and conſequently they have but the five and twentieth part of the Light and Heat that we receive from it. But that Light is not ſo weak as we imagine, as is plain by the Brightneſs of that Planet in the Night; and alſo from hence, that when the Sun is ſo far eclipſed to us, as that only the 25th part of his Disk remains uncovered, he is not ſenſibly darken’d. But if you have a mind exactly to know the Quantity of Light that Jupiter enjoys, you may take a Tube of what Length you pleaſe. Let one end of it be cloſed with a Plate of Braſs, or any ſuch thing, in the middle of which there muſt be a Hole, whoſe Breadth muſt have the ſame proportion to the length of the Tube, as the Chord of 6 Minutes bears to the Radius; that is, about as one is to 570. Let the Tube be turned ſo to the Sun, that no Light may fall upon a white Paper placed at the End of it, but what comes through the little Hole at the other end of the Tube. The Rays that come through this will repreſent the Sun upon the Paper of the ſame Brightneſs that the Inhabitants of Jupiter ſee it in a clear Day. And if removing the Paper you place your Eye in the ſame Place, you will ſee the Sun of the ſame Magnitude and Brightneſs as you would were you in Jupiter.

[And in Saturn.]

If you make the Hole twice as little in breadth, you will ſee the ſame in Saturn. And altho’ his Light be but the hundredth part of ours, yet you ſee it makes him ſhine tolerably bright in a dark Night. But in both theſe Planets, if there ever be any cloudy Days, it muſt be very dark in compariſon of us; yet without doubt the Inhabitants have no more reaſon to complain of the want of Light, than our Owls and Batts, to whom the Twilight or the Night itſelf is more agreeable than the Brightneſs of the Day.

[In Jupiter their days are five Hours.]

But it’s a little ſtrange, that when Jupiter is ſo much bigger than our Planet, their Days and Nights ſhould be but five of our Hours. By this we may ſee that Nature has not obſerv’d that proportion that their Bulk ſeems to require, ſeeing in Mars the Days are very little different from ours. But in the length of their Years, that is, in the Revolution of the Planets round the Sun, there is an exact proportion to their diſtances from the Sun followed. For as the Cubes of their Diſtances, ſo are the Squares of their Revolutions, as Kepler firſt ſound out. Which proportion the Moons of Jupiter and Saturn keep in their Courſes round thoſe [Always of the ſame length.] Planets. As the Years and Days in Jupiter are different from ours in this reſpect, ſo are the Days in another; namely, that they are all of the ſame length. For they there enjoy a perpetual Equinox, their Axis having little or no inclination to their Orbit, as the Earth’s has, as has been diſcovered by Teleſcopes. The Countries that lie near their Poles have little or no Heat, by reaſon the Rays of the Sun fall ſo obliquely upon them; but then they are freed from the Inconveniency that ours are troubled with, of tedious long half-year Nights, and have the conſtant returns of Day and Night every five Hours. Indeed ſuch ſhort Days would not be agreeable to us, but we think our ſelves much better done by, that ours are more than twice as long, tho’ upon no other account, but that whatever is our own, we are apt to imagine, muſt be beſt.

The reſt of the Planets are ſo near the Sun (Mars himſelf never being above 18 degrees from it) that in Jupiter they have the ſight only of Saturn. But we cannot deny but that their four Moons ſtand them in greater ſtead than our one doth us, if ’twere only that they ſeldom know any ſuch Thing as to be without Moonſhiny Nights. And they are of great Advantage to them, as we ſaid before, in their Navigation, if they have any ſuch thing. Not to mention the pleaſant Sights of their frequent Conjunctions and Eclipſes, Things that they are ſeldom a Day without.

Saturn enjoys all thoſe Pleaſures and Advantages in a ſtill higher Degree, as well for his five Moons, as for the delightful Proſpect that the Ring about him affords his Inhabitants Night and Day. But we will give an account of their Aſtronomy, as we have done of the reſt of the Planets.

[They ſee the fix’d Stars juſt as we do.]

And firſt of all we ſhall obſerve what we might have remark’d before, but which will be more ſtrange here, that the fix’d Stars appear to them of the ſame Figure and Magnitude, and with the ſame degree of Light that they do to us: and this, by reaſon of their immenſe diſtance, of which we ſhall have occaſion to ſpeak by and by. In compariſon with which the Space that a Bullet-ſhot out of a Cannon could travel in 25 Years, would be almoſt nothing.

Their Aſtronomers have all the ſame Signs of the Bear, the Lion, Orion, and the reſt, but not turning upon the ſame Axis with us: for that’s different in all the Planets.

As Jupiter can ſee no Planet but Saturn, ſo Saturn knows of no Planet but Jupiter; which appears to him much as Venus doth to us, never removing above 37 Degrees from the Sun. The Length of their Days I cannot determine: But if from the Diſtance and Period of his innermoſt Attendant, and comparing it with the innermoſt of Jupiter’s, a Man may venture to give a Gueſs, they are very little different from Jupiter’s, 10 Hours or ſomewhat leſs. But whereas in Jupiter theſe are equally divided between Light and Darkneſs, the Inhabitants of Saturn muſt perceive a more ſenſible difference than we, eſpecially between Summer and Winter. For our Axis inclines to the Plane of the Ecliptick but 23 degrees and a half, but there’s above 31. Upon this Account his Moons muſt decline very much from the Path that the Sun ſeems to move in, and his Inhabitants can never have a full Moon but juſt at the Equinoxes; Two of which fall out in 30 of our Years. ’Tis this Poſition of the Axis too that is the Cauſe of thoſe delightful Appearances, and wonderful Proſpects that its Inhabitants enjoy: For the better underſtanding of which I ſhall draw a Figure of Saturn with his Ring about him: in which the Proportion between the Diameters of the Globe and Ring is as 9 to 4. And the empty Space between them is of the ſame Breadth with the Ring itſelf. All Obſervations conſpire to prove that That is of no great Thickneſs, altho’ if we ſhould allow it ſix hundred German Miles, I think, conſidering its Diameter, we ſhould not overdo the Matter.

Suppoſe then, agreeable to what has been ſaid, the Globe of Saturn, [Fig. 4.] whoſe Poles are A, B. G N is the Diameter of the Ring, as you view it ſideways, repreſenting a narrow Oval. Thoſe that live about the Poles within the Arches C A D, E B F, each of which are 54 Degrees, (if the Cold will ſuffer any Body to live there) never have a Sight of the Ring. [The Appearances of the Ring in Saturn.] From all other parts it is continually to be ſeen for fourteen Years and nine Months, which is juſt half their Year. The other Half it is hid from their View. Thoſe then that dwell between the Polar Circle C D, and the Equator T V, all that time that the Sun enlightens the Part oppoſite to them, have every Night the Sight of a Piece of it H G L, much in the Shape of a ſhining Bow, which comes from the Horizon, but is darken’d in the Middle by the Shadow of Saturn G H, which reaches moſt commonly to the outermoſt Rim of it. But after Midnight that Shadow by little and little begins to move towards the right Hand to thoſe in the Northern, but the Left to thoſe in the Southern Hemiſphere. In the Morning it diſappears, leaving behind it a Likeneſs indeed of a Bow, but much paler and weaker than our Moon is in the Day time. For they, as I ſaid before, have an Atmoſphere, or an Air ſurrounding them enlightened by the Sun. Otherwiſe Night and Day they would have their Ring, their Moons, and all the fix’d Stars, equally conſpicuous. Another thing that muſt make the Sight of their Ring very curious, is, that by ſome Spots in it, it is diſcover’d to turn round upon it ſelf: A thing that thoſe that are ſo near cannot but take notice of, when we that live at this Diſtance can deſcry a great Inequality, the inſide of it being brighter much than the outſide is. When the Shadow of the Globe falls upon that part of the Ring G H, the Shadow of the Ring at the ſame time darkens another Part of the Globe about P F, which otherwiſe would have the Sun upon it. So that there is always a Zone of the Globe P Y F E, ſometimes of a larger extent than at others, which is depriv’d of the Sight both of the Sun and Ring for a conſiderable time, the latter of which hides ſome part of the Stars from it too. And certainly an amazing Thing it muſt be, all of a ſudden to have the Sun intercepted and to become as dark as Midnight, without ſeeing any Cauſe of ſuch an Accident. All which time their Moons are their only Comfort. The other half of the Year the Hemiſphere T B V enjoys the ſame Light that T A U before did, and then this undergoes thoſe long Eclipſes that That before ſuffer’d. At the Equinoxes, when the Sun is in the ſame Plane with the Ring, the Inhabitants of Saturn cannot well perceive it: no not even we with our Glaſſes, by reaſon of its Darkneſs. This happens when Saturn, view’d from the Sun, is advanced one and twenty degrees and a half in Virgo or Piſces, as I have ſhow’d formerly in my Syſtem of Saturn: Where there is an Account given of the Riſings of the Sun above the Ring, throughout all the Saturnian Year.

With Saturn in this Scheme you have the Globes of the Earth and Moon drawn in their true proportion, to put you in mind again of a Thing worth remembring, viz. how very ſmall our Habitation is when compar’d with that Globe or the Ring about it. And now any one, I ſuppoſe, can frame to himſelf a Picture of the Night in Saturn, with two Arches of the Ring, and five Moons ſhining about, and adorning him. This then is what I had to ſay to the primary Planets.

We are now come a little lower, to make an enquiry into the Attendants of theſe Planets, eſpecially our own. And here we ſhall not only conſider their Aſtronomy, but ſhall alſo ſearch into their Furniture and Ornament, if they are found to have any ſuch thing, which we have deferred conſidering till now.

[Very little to be ſaid of the Moon.]

And here one would think that when the Moon is ſo near us, and by the Means of a Teleſcope may be ſo nicely and exactly obſerv’d, it ſhould afford us Matter for more probable Conjectures than any of the other remote Planets. But it is quite otherwiſe, and I can ſcarce find any thing to ſay of it, becauſe I have not a Planet of the ſame Nature before my Eyes, as in all the primary ones I have. For they are of the ſame kind with our Earth; and ſeeing all the Actions, and every thing that is here, we may make a reaſonable Conjecture at what we cannot ſee in thoſe Worlds.

[The Guards of Jupiter and Saturn of the ſame nature with our Moon.]

But this we may venture to ſay, without fear, that all the Attendants of Jupiter and Saturn are of the ſame Nature with our Moon, as going round them, and being carried with them round the Sun juſt as the Moon is with the Earth. Their Likeneſs reaches to other Things too, as you’ll ſee by and by. Therefore whatſoever we can with reaſon affirm or conjecture of our Moon (and we may ſay a little of it) muſt be ſuppos’d with very little Alteration to belong to the Satellites of Jupiter and Saturn, as having no reaſon to be at all inferior to that.

[The Moon hath Mountains.]

The Surface of the Moon then is found, by the leaſt Teleſcopes of about three or four Foot, to be diverſified with long Tracts of Mountains, and again with broad Valleys. For in thoſe Parts oppoſite to the Sun you may ſee the Shadows of the Mountains, and often diſcover the little round Valleys between them, with a Hillock or two perhaps riſing out of them. Kepler from the exact roundneſs of them would prove that they are ſome vaſt work of the rational Inhabitants. But I can’t be of his mind, both for their incredible Largeneſs, and that they might eaſily be occaſioned by natural Cauſes. Nor can I find any thing like Sea there, tho’ he and many others are of the contrary Opinion I know. For thoſe vaſt Countries which appear darker than the other, commonly taken for and called by the Names of Seas, are diſcover’d with a good long Teleſcope, to be full of little round Cavities; whoſe Shadow falling within themſelves, makes them appear of that Colour: and thoſe large Champains there in the Moon you will find not to be always even and ſmooth, if you look carefully upon them: neither of which two [But no Sea.] Things can agree to the Sea. Therefore thoſe Plains in her that ſeem brighter than the other Parts, muſt conſiſt, I ſuppoſe, of a whiter ſort of Matter than they. Nor do I believe [Nor Rivers.] that there are any Rivers, for if there were, they could never eſcape our Sight, eſpecially if they run between the Hills as ours do. Nor have they [Nor Clouds.] any Clouds to furniſh the Rivers with Water: For if they had, we ſhould ſometimes ſee one part of the Moon darkened by them, and ſometimes another, whereas we have always the ſame Proſpect of her.

[Nor Air, and Water.]