As that part of our aire which is neerest to the earth, is of a thicker substance than the other, by reason ‘tis alwayes mixed with some vapours, which are continually exhaled into it. So is it equally requisite, that if there be a world in the Moone, that the aire about that, should be alike qualified with ours. Now, that there is such an orbe of grosse aire, was first of all (for ought I can reade) observed by Meslin, afterwards assented unto by Keplar and Galilaeus,1 and since by Baptista Cisacus, Sheiner with others, all of them confirming it by the same arguments which I shall onely cite,2 and then leave this Proposition.
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‘Tis not improbable that there should be a sphere of grosser aire about the Moone; because ‘tis observed, that there are such kind of evaporations which proceed from the Sun it selfe. For there are discovered divers moveable spots, like clouds, that doe encompasse his body: which those Authors, who have been most frequently versed in these kind of experiments and studies, doe conclude to be nothing else but evaporations from it. The probabilitie and truth of which observations may also bee inferred from some other appearances. As,
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It hath been observed that the Sunne hath sometimes for the space of foure days together,3 appeared as dull and ruddy almost as the Moone in her Ecclipses; In so much that the Starrs have been seene at midday. Nay, he hath been constantly darkned for almost a whole yeare, and never shined, but with a kind of heavy and duskish light, so that there was scarse heate enough to ripen the fruits. As it was about the time when Caesar was killed. Which was recorded by some of the Poëts. Thus Virgil, speaking of the Sunne.
Ille etiam extincto miseratus Caesare Romam,4
Cum caput obscurâ nitidum ferrugine texit,
Impiaque aeternam timueruut saecula noctem.
He pittying Romé when as great Caesar dyde,
His head within a mourning vaile did hide.
And thus the wicked guilty world did fright,
With doubtfull feares of an eternall night.
Ovid likewise speaking of his death —Solis quoque tristis imago Lurida sollicitis praebebat lumina terris.5 —The Suns sad image then Did yeeld a lowring light to fearefull men.
Now these appearances could not arise from any lower vapor. For then 1. They would not have been so universall as they were, being seene through all Europe; or else 2. that vapor must have covered the starres as well as the Sunne, which yet notwithstanding were then plainly discerned in the day time. You may see this argument illustrated in another the like case. Chap. 12. Hence then it will follow, that this fuliginous matter, which did thus obscure the Sunne, must needs bee very neere his body; and if so, then, what can we more probably guesse it to be, than evaporations from it?
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‘Tis observed, that in the Suns totall Ecclipses, when there is no part of his body discernable, yet there dos not always follow so great a darknesse, as might bee expected from his totall absence. Now ‘tis probable, that the reason is, because these thicker vapors, being enlightned by his beames, doe convey some light unto us, notwithstanding the interposition of the Moone betwixt his body and our earth.
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This likewise is by some guest to be the reason of the crepusculum or that light which wee have before the Suns rising.
Now, if there be such evaporations from the Sunne, much more then from the moone, which does consist of a more grosse and impure substance. The other arguments are taken from severall observations in the Moon herselfe, and doe more directly tend to the proofe of this proposition.
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‘Tis observed, that so much of the Moone as is enlightned, is alwayes part of a bigger circle, than that which is darker. The frequent experience of others hath proved this, and an easie observation may quickly confirme it. But now this cannot proceede from any other cause so probable, as from this orbe of aire; especially when we consider how that Planet shining with a borrowed light, doth not send forth any such rayes as may make her appearance bigger than her body.
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When the Moone being halfe enlightned, begins to cover any Starre, if the Starre bee towards the obscurer part, then may it by the perspective be discerned, to bee neerer unto the center of the moone, than the outward circumference of the enlightned part. But the moone being in the full; then dos it seeme to receive these starres, within its limbe.
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Though the Moone doe sometime appeare the first day of her change when so much as appeares enlightned, cannot be above the 80 part of her diameter, yet then will the hornes seeme at least to be of a fingers breadth in extension. Which could not bee, unlesse the ayre about it were illuminated.
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‘Tis observed in the Solary ecclipses, that there is sometimes a great trepidation about the body of the Moone, from which wee may likewise argue an Atmo-sphaera, since we cannot well conceive what so probable a cause there should be of such an appearance as this, Quod radii Solares à vaporibus Lunam ambientibus fuerint intercis[…],6 that the Sunne-beames were broken and refracted by the vapours that encompassed the Moone.
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I may adde the like argument taken from another observation which will be easily tried and granted. When the Sunne is eclipsed, we discerne the Moone as shee is in her owne naturall bignesse; but then she appeares somewhat lesse than when she is in the full, though she be in the same place of her supposed excentrick and epicycle; and therfore Tycho hath calculated a Table for the Diameter of the divers new Moones. But now there is no reason so probable, to salve this appearance, as to place an orbe of thicker aire, neere the body of that Planet, which may bee enlightned by the reflected beames, and through which the direct rayes may easily penetrate.
But some may object, that this will not consist with that which was before delivered, where I said, that the thinnest parts had least light.
If this were true, how comes it to passe then, that this aire should bee as right as any of the others parts, when as tis the thinnest of all?
I answer, if the light be received by reflection only, then the thickest body hath most, because it is best able to beate backe the rayes; but if the light be received by illumination (especially if there be an opacous body behinde, which may double the beames by reflexion) as it is here,7 then I deny not but a thinne body may retaine much light; and perhaps, some of those appearances, which wee take for fiery comets, are nothing else but a bright cloud enlightned; So that probable it is, there may be such aire without the Moone; & hence it comes to passe, that the greater spots are only visible towards her middle parts, and none neere the circumference; not but that there are some as well in those parts as elsewhere, but they are not there perceiveable, by reason of those brighter vapours which hide them.
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