The Discovery of a World in the Moone/Chapter 12

by John Wilkins

Proposition 11.

That as their world is our Moone, so our world is their Moone.

I Have already handled the first thing that I promised according to the Method which Aristotle uses in his Booke de Mundo, and shew'd you the necessary parts that belong to this world in the Moone. In the next place 'tis requisite that I proceed to those things which are extrinsecall unto it, as the Seasons, the Meteors, and the Inhabitants.

1. Of the Seasons;

And if there be such a world in the Moone, 'tis requisite then that their seasons should be some way correspondent unto ours, that they should have Winter and Summer, night and day, as wee have.

Now that in this Planet there is some similitude of Winter and Summer is affirmed by Aristotle^[1] himselfe, since there is one hemispheare that hath alwaies heate and light, and the other that hath darknesse and cold. True indeed, their daies and yeeres are alwaies of one and the same length, but tis so with us also under the Poles, and therefore that great difference is not sufficient to make it altogether unlike ours, nor can we expect that every thing there should be in the same manner as it is here below, as if nature had no way but one to bring about her purposes. Wee may easily see what great differences there are amongst us, betwixt things of the same kinde. Some men^[2] (say they) there are, who can live onely upon smells, without eating any thing, and the same Plant, saith Besoldus hath sometimes contrary effects. Mandragora which growes in Syria inflames the lust, wheras Mandragora which grows in other places doth coole the blood & quench lust.

Now if with us there be such great difference betwixt things of the same kinde, we have no reason then to thinke it necessary that both these worlds should be altogether alike, but it may suffice if they bee correspondent in something onely, however it may be questioned whether it doth not seeme to be against the wisedome of providence, to make the night of so great a length, when they have such a long time unfit for worke? I answere no, since tis so, and more with us also under the poles; and besides, the generall length of their night is somewhat abated in the bignesse of their Moone which is our earth. For this returnes as great a light unto that Planet, as it receives from it. But for the better proofe of this, I shall first free the way from such opinions as might otherwise hinder the speede of a clearer progresse.

Plutarch^[3] one of the chiefe patrons of this world in the Moone, doth directly contradict this proposition; affirming, that those who live there may discerne our world as the dregges and sediment of all other creatures, appearing to them through clouds and foggy mists, and that altogether devoid of light, being base and unmoveable, so that they might well imagine the darke place of damnation to be here situate, and that they onely were the inhabiters of the world, as being in the midst betwixt Heaven and Hell.

To this I may answere, 'tis probable that Plutarch spake this inconsiderately, and without a reason, which makes him likewise fall into another absurditie, when he sayes our earth would appeare immoveable, whereas questionlesse though it did not, yet would it seeme to move, and theirs to stand still, as the Land doth to a man in a Shippe; according to that of the Poet:

Provehimur portu, terræque urbesque recedunt.

And I doubt not but that ingenuous Authour would easily have recanted if hee had beene but acquainted with those experiences which men of latter times have found out, for the confirmation of this truth.

2. Unto him assents Macrobius, whose words are these; Terra accepto solis lumine clarescit, tantummodò, non relucet. "The earth is by the Sunne-beames made bright, but not able to enlighten any thing so farre." And his reason is, because this being of a thicke and grosse matter, the light is terminated in its superficies, and cannot penetrate into the substance; whereas the moone doth therefore seeme so bright to us, because it receives the beames within it selfe. But the weaknesse of this assertion, may bee easily manifest by a common experience, for polished steele (whose opacity will not give any admittance to the rayes) reflects a stronger heate then glasse, and so consequently a greater light.

3. 'Tis the generall consent of Philosophers, that the reflection of the Sunne-beames from the earth doth not reach much above halfe a mile high, where they terminate the first region, so that to affirme they might ascend to the moone, were to say, there were but one region of aier, which contradicts the proved and received opinion.

Unto this it may be answered:

That it is indeed the common consent, that the reflexion of the Sunne-beames reach onely to the second region, but yet some there are, and those too Philosophers of good note, who thought otherwise. Thus Plotinus is cited by Cœlius, ^[4] {{lang|la|Si concipias te in sublimi quopiam mundi loco, unde oculis subjiciatur terræ moles aquis circumsufa, & solis syderumque radiis illustrata, non aliam profecto visam iri probabile est, quam qualis modo visatur lunaris globi species. "If you did conceive your selfe to bee in some such high place, where you might discerne the whole Globe of the earth and water, when it was enlightned by the Sunnes rayes, 'tis probable it would then appeare to you in the same shape as the moone doth now unto us." Thus also Carolus Malapertius,^[5] whose words are these, Terra hæc nostra si in luna constituti essemus, splendida prorsus quasi non ignobilis planeta, nobis appareret. "If wee were placed in the moone, and from thence beheld this our earth, it would appeare unto us very bright, like one of the nobler Planets." Unto these doth Fromondus assent, when he sayes,^[6] Credo equidem quod si oculus quispiam in orbe lunari foret, globum terræ & aquæ instar ingentis syderis a sole illustrem conspiceret. "I believe that this globe of earth and water would appeare like some great Starre to any one, who would looke upon it from the moone." Now this could not be, nor could it shine so remarkably, unlesse the beames of light were reflected from it. And therefore the same Fromondus expresly holds, that the first region of ayre is there terminated, where the heate caused by reflexion begins to languish, whereas the beames themselves doe a passe great way further. The chiefe argument which doth most plainely manifest this truth, is taken from a common observation which may be easily tryed.

If you behold the Moone a little before or after the conjunction, when she is in a sextile with the Sunne, you may discerne not onely the part which is enlightned, but the rest also to have in it a kind of a duskish light, but if you chuse out such a scituation, where some house or chimney (being some 70 or 80 paces distant from you) may hide from your eye the enlightned hornes, you may then discerne a greater and more remarkeable shining in those parts unto which the Sunne beames cannot reach; nay there is so great a light, that by the helpe of a good perspective you may discerne its spots. Inso much that Blancanus the Jesuite speaking of it sayes,^[7] Hæc experimentia ita me aliquando fefellit, ut in hunc fulgorem casu ac repente incidens, existimarim novo quodam miraculo tempore adolescentis lunæ factum esse plenilunium.,"This experiment did once so deceive mee, that happening upon the sight of this brightnesse upon a sudden, I thought that by some new miracle the Moone had beene got into her full a little after her change."

But now this light is not proper to the Moone, it doth not proceed from the rayes of the Sunne which doth penetrate her body, nor is is caused by any other of the Planets and Starres. Therefore it must necessarily follow, that it comes from the earth. The two first of these I have already proved, and as for the last, it is confidently affirmed by Cælius^[8], Quod si in disqu sitionem evocet quis, an lunari syderi lucem fœnerent planetæ item alii, asseveranter asiruendum non fœnerare. "If any should aske whether the other Planets lend any light to the Moone; I answer they doe not".^[9] True indeed, the noble Tycho discussing the reason of this light attributes it to the Planet Venus, and I grant that this may convey some light to the Moone, but that it is not the cause of this whereof wee now discourse, is of it selfe sufficiently plaine, because Venus is some times over the Moone, when as shee cannot convey any light to that part which is turned from her.

It doth not proceede from the fixed starres for then it would retaine the same light in eclipses, whereas the light at such times is more ruddy and dull. Then also the light of the Moone would not be greater or lesser, according to its distance from the edge of the earths shadow, since it did at all times equally participate this light of the starres.

Now because there is no other body in the whole Universe, save the earth, it remaines that this light must neccslarily be caused by that which with a just gratitude repaies to the Moone, such illumination as it receives from her.

And as loving friends equally patcicipate of the same joy and griefe, as doe these mutually partake of the same light from the Sunne, and the same darknesse from the eclipses, being also severally helped by one another in their greatest wants: For when the Moone is in conjunction with the Sunne, and her upper part receives all the light, then her lower Hemispheare (which would otherwise be altogether darke) is enlightened by the reflexion of the Sunne beames from the earth. When these two planets are in opposition, then that part of the earth which could not receive any light from the Sunne beames, is most enlightened by the Moone, being then in her full; and as she doth most illuminate the earth when the Sunne beames cannot, so the gratefull earth returnes to her as great, nay greater light when shee most wants it; so that alwaies that visible part of the Moone which receives nothing from the Sunne, is enlightened by the earth, as is proved by Galilæus, with many more arguments, in that Treatise which he calls Systema mundi. True indeed, when the Moone comes to a quartile, then you can neither discerne this light, not yet the darker part of her body, but the reason is, because of the exuperancy of the light in the other parts, Quippe ilustratum medium speciem recipit valentiorem^[10], the clearer brightnesse involves the weaker, it being with the species of sight, as it is with those of sound, and as the greater noise drownes the lesse, so the brighter object hides that which is more obscure. But they doe alwaies in their mutuall vicssitudes participate of one anothers light; so also doe they partake of the same defects and darknings, for when our Moone is eclipsed, then is their Sunne darkened, and when our Sunne is eclipsed, then is their Moone deprived of its light, as you may see affirmed by Mæslin.^[11] Quod si terram nobis ex alto liceret intueri, quomadmodum deficientem lunam ex longinquo spectare possumus, videremus tempere eclipsis solis terræ aliquam partem lumine solis deficere, eodem plane modo sicut ex opposito luna deficit, "If wee might behold this globe of earth at the same distance as we doe the Moone in her defects, wee might discerne some part of it darkened in the Sunnes eclipses, just so as the Moone is in hers." For as our Moone is eclipsed by the interposition of our earth, so is their Moone eclipsed by the interposition of theirs. The manner of this mutuall illumination betwixt these two you may plainly discerne in this Figure following.

Where A represents the Sun, B the Earth, and C the Moone; Now suppose the Moone C to be in a sextile of increase, when there is onely one small part of her body enlightened, then the earth B will have such a part of its visible Hemispheare darkened, as is proportionable to that part of the Moone which is enlightened; and as for so much of the Moone, as the Sun beames cannot reach unto, it receives light from a proportionall part of the earth which shines upon it, as you may plainly perceive by the Figure.

You see then that agreement and similitude which there is betwixt our earth and the Moone. Now the greatest difference which makes them unlike, is this, that the Moone enlightens our earth round about, whereas our earth gives light onely to that Hemispheare of the Moone which is visible unto us, as may be certainly gathered from the constant appearance of the same spots, which could not thus come to passe, if the Moone had such a diurnall motion about its own axis, as perhaps our earth hath. And though some suppose her to move in an epicycle, yet this doth not so turne her body round, that we may discerne both Hemispheares, for according to that hypothesis, the motion of her eccentrick, doth turne her face towards us, as much as the other doth from us.

But now if any question what they doe for a Moone who live in the upper part of her body? I answer, the solving of this is the most uncertaine and difficult thing that I know of concerning this whole matter. But yet I will give you two probable conjectures.

1. Perhaps, the upper Hemispheare of the Moone doth receive a sufficient light from those planets about it, and amongst these Venus (it may be) bestowes a more especiall brightnesse since Galilæus hath plainly discerned that she suffers the same increases and decreases, as the Moone hath, and 'tis probable that this may be perceived there without the help of a glasse because they are farre neerer it than wee. When Venus (saith Keplar) lies downe in the Perige or lower part of her supposed Epicycle, then is she in conjunction with her husband the Sunne, from whom after she hath departed for the space of ten moneths, shee gets plenum uterum, and is in the full.

But you'll reply, though Venus may bestow some light when she is over the Moone, and in conjunction, yet being in opposition, she is not visible to them, and what shall they then doe for light?

I answer, then they have none: nor doth this make so great a difference betwixt those two Hemispheares as there is with us, betwixt the places under the poles, and the line, but if this bee not sufficient, then I say in the second place that

2. Perhaps there may be some other enlightened body above the Moone which we cannot discerne, nor is this altogether improbable because there is almost the like observed in Saturne, who appeares through this glasse with two lesser bodies on each side, which may supply the office of Moones, unto each hemispheare thus:

So in this world also there may be some such body, though wee cannot discerne it, because the Moone is alwaies in a streight line, betwixt our eye and that. Nor is it altogether unlikely that there should bee more moones to one Orbe, because Jupiter also is observed to have foure such bodies that move round about him.

But it may seeme a very difficult thing to conceive, how so grosse and darke a body as our earth, should yeeld such a cleare light as proceeds from the Moone, and therefore the Cardinall de Cusa^[12] (who thinkes every Starre to be a severall world) is of opinion that the light of the Sunne is not able to make them appeare so bright, but the reason of their shining is, because wee behold them at a great distance through their regions of fire which doe set a shining lustre upon those bodies that of themselves are darke. Vnde si quis esset extra regionem ignis terra ista in circumferentia suæ regionis per medium ignis lucido stella appareret. "So that if a man were beyond the region of fire, this earth would appeare through that as a bright Starre." But if this were the onely reason then would the Moone bee freed from such increases and decreases as she is now lyable unto.

Keplar thinkes that our earth receives that light whereby it shines from the Sunne, but this (saith he) is not such an intended cleare brightnesse as the Moone is capable of, and therefore hee guesses, that the earth there is of a more chokie soyle like the Ile of Creete, and so is better able to reflect a stronger light, whereas our earth must supply this intention with the quantity of its body, but this I conceive to be a needlesse conjecture since our earth if all things were well considered, will be found able enough to reflect as great a light. For

I. Consider its opacity, if you marke these sublunary things, you shall perceive that amongst them, those that are most perspicuous, are not so well able to reverberate the Sunne beames as the thicker bodies. The rayes passe singly through a diaphanous matter, but in an opacous substance they are doubled in their returne and multiplyed by reflexion. Now if the moone and the other Planets can shine so clearely by beating backe the Sunne beames, why may not the earth also shine as well, which agrees with them in the cause of this brightnesse their opacity?

2. Consider what a cleare light wee may discerne reflected from the earth in the middest of Summer, and withall conceive how much greater that must bee which is under the line, where the rayes are more directly and strongly reverberated.

3. Consider the great distance at which wee behold the Planets, for this must needs adde much to their shining and therefore Cusauus (in the above cited place) thinkes that if a man were in the Sunne, that Planet would not appeare so bright to him, as now it doth to us, because then his eye could discerne but little, whereas here wee may comprehend the beames as they are contracted in a narrow body. Keplar beholding the earth from a high mountaine when it was enlightened by the Sunne confesses that it appeared unto him of an incredible brightnesse, whereas then the reflected rayes entered into his sight obliquely; but how much brighter would it have appeared if hee might in a direct line behold the whole globe of earth and these rayes gathered together? So that if wee consider that great light which the earth receives from the Sunne in the Summer and then suppose wee were in the Moone, where wee might see the whole earth hanging in those vast spaces where there is nothing to terminate the sight, but those beames which are there contracted into a little compasse; I say, if wee doe well consider this, wee may easily conceive, that our earth appeares as bright to those other inhabitants in the Moone, as theirs doth to us.

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1. De gen. animal. l. 4.12
2. Plat. de. fac. De naturâ populorum. c. 3.
3. Plut. de fac. lunæ.
4. Ant. lect. l. 1. c. 4.
5. Præfat. ad Austrica syd.
6. Meteor. l. 1. c. 2. Art. 2.
7. De Mundi fab. p. 3¹.c. 3.
8. Progym. 1
9. l. 20. c. 5.
10. Scal exerc. 62.
11. Epit. Astro. l. 4. part. 2.
12. De doct. ig. l. 2. c. 12.