must be such hollow and deep places whereto the rays cannot reach. But when the moon is got farther off from the sun, and come to that fulness as this line B B doth represent her under; then do these parts also receive an equal light, excepting only that difference which doth appear betwixt their sea and land. And if you do consider how any rugged body would appear being enlightened, you would easily conceive that it must necessarily seem under some such gibbous unequal form, as the moon is here represented. Now for the infallibility of these appearances, I shall refer the reader to that which hath been said in the sixth proposition.

But Cæsar la Galla affirms, that all these appearances may consist with a plain superficies, if we suppose the parts of the body to be some of them diaphanous, and some opacous; and if you object that the light which is conveyed to any diaphanous part in a plain superficies, must be by a continued line; whereas here there appear many brighter parts among the obscure at some distance from the rest: to this he answers, it may rise from some secret conveyances and channels within her body, that do consist of a more diaphanous matter; which being covered over with an opacous superficies, the light passing through them may break out a great way off; whereas the other parts betwixt, may still remain dark. Just as the river Arethusa in Sicily, which runs under ground for a great way, and afterwards breaks out again. But, because this is one of the chiefest fancies, whereby he thinks he hath fully answered the argument of this opinion, I will therefore set down his answer in his own words, lest the reader might suspect more in them than I have expressed *. Non est impossibile cæcos ductus diaphani & perspicui corporis, sed opaca superficie protendi, usque in diaphanam aliquam ex profundo in superficiem emergentem partem, per quos ductus lumen longo postmodum interstitio erumpat, &c. But I reply, if the superficies betwixt these two

* Cap. 11.

two enlightened parts remain dark because of its opacity; then would it always be dark, and the sun could not make it partake of light more than it could of perspicuity. But this contradicts all experience, as you may see in Galilæus, who affirms that when the sun comes nearer to his opposition, then that which is betwixt them both, is enlightened as well as either. Nay, this opposes his own eye-witness; for he confesses himself that he saw this by the glass. He had said before, that he came to see those strange sights discovered by Galilæus his glass, with an intent of contradiction; and you may read that confirmed in the weakness of this answer, which rather bewrays an obstinate, than a persuaded will; for otherwise sure he would never have undertook to have destroyed such certain proof with so groundless a fancy.

That instance of Galilæus*, would have been a better evasion, had this author been acquainted with it; who might then have compared the moon to that which we call mother of pearl, which though it be most exactly polished in the superficies of it, yet will seem unto the eye as if there were divers swellings and risings in its several parts. But yet, this neither would not well have shifted the experiment of the perspective. For these rugged parts do not only appear upon one side of the moon, but as the sun does turn about in divers places, so do they also cast their shadow. When the moon is in her increase, then do they cast their shadows to the east. When she is in the decrease, and the sun on the other side of her, then likewise may we discover these brighter parts casting their shadows westward. Whereas in the full moon there are none of all these to be seen.

But it may be objected, that it is almost impossible, and altogether unlikely, that in the moon there should be any mountains so high as those observations make them. For do but suppose, according to the common principles, that the moon's diameter unto the earth's, is very near to the

Syst. mund. col. 1.

proportion of two to seven. Suppose withal that the earth's diameter contains about 7000 Italian miles, and the moon's 2000 (as is commonly granted.) Now Galilæus hath observed, that some parts have been enlightened, when they were the twentieth part of the diameter distant from the common term of illumination. From whence it must necessarily follow, that there may be some mountains in the moon so high, that they are able to cast a shadow a hundred miles off. An opinion that sounds like a prodigy or a fiction; wherefore it is likely that either those appearances are caused by somewhat else besides mountains, or else those are fallible observations; from whence may follow such improbable, inconceivable consequences. But to this I answer;

1. You must consider the height of the mountains is but very little, if you compare them to the length of their shadows. Sir Walter Rawleigh* observes that the mount Athos, now called Lacas, casts its shadow 300 furlongs, which is above 37 miles; and yet that mount is none of the highest. Nay Solinus † (whom I should rather believe in this kind) affirms that this mountain gives his shadow quite over the sea, from Macedon to the isle of Lemnos, which is 700 furlongs, or 84 miles, and yet according to the common reckoning it doth scarce reach 4 miles upwards in its perpendicular height.

2. I affirm that there are very high mountains in the moon. Keplar and Galilæus think that they are higher than any which are upon our earth. But I am not of their opinion in this, because I suppose they go upon a false ground, whilst they conceive that the highest mountain upon the earth is not above a mile perpendicular.

Whereas it is the common opinion, and found true enough by observation, that Olympus, Atlas, Taurus and Emus, with many others, are much above this height. Tenariffa, in the Canary islands, is commonly related to be above 8 miles perpendicular, and about this height (say

Hist. 1. 1. cap. 7. sect. 11.

+ Poly. Hist. c. 21.

some) is the mount Perjacaca in America.

*

Sir Walter Rawleigh seems to think that the highest of these is near 30 miles upright: nay Aristotle, speaking of Caucasus in Asia, affirms it to be visible for 560 miles, as some interpreters find by computation; from which it will follow, that it was 78 miles perpendicularly high; as you may see confirmed by Jacobus Mazonius +, and out of him in Blancanus the Jesuit. But this deviates from the truth more in excess than the other doth in defect. However, though these in the moon are not so high as some amongst us ; yet certain it is they are of a great height, and some of them at the least four miles perpendicular. This I shall prove from the observation of Galilæus, whose glass can shew to the senses a proof beyond exception; and certainly that man must needs be of a most timorous faith, who dares not believe his own eye.

By that perspective you may plainly discern some enlightened parts (which are the mountains) to be distant from the other about the twentieth part of the diameter. From whence it will follow, that those mountains must necessarily be at the least four Italian miles in height.

Hist. l. 1. c. 7. sect. 11. Meteor. 1. 1. c. 11.

+ Comparatio Arist. cum. Platone, sect. 3. c. 5. Expost in loc. Matth. Arlis loc. 148.

For let B D E F be the body of the moon, A B C will be a ray or beam of the sun, which enlightens a mountain at A, and B is the point of contingency; the distance betwixt A and B must be supposed to be the twentieth part of the diameter, which is an 100 miles, for so far are some enlightened parts severed from the common term of illumination. Now the aggregate of the quadrate from A Ba hundred, and B G 1000 will be 1010000; unto which the quadrate arising from A G must be equal; according to the 47th proposition in the first book of elements. Therefore the whole line A G is somewhat more than 104, and the distance betwixt H A must be above 4 miles, which was the thing to be proved.

But it may be again objected, if there be such rugged parts, and so high mountains, why then cannot we discern them at this distance? Why doth the moon appear unto us so exactly round, and not rather as a wheel with teeth?

I answer, by reason of too great a distance; for if the whole body appears to our eye so little, then those parts which bear so small a proportion to the whole, will not at all be sensible.

But it may be replied, if there were any such remarkable hills, why does not the limb of the moon appear like a wheel with teeth, to those who look upon it through the great perspective, on whose witness you so much depend? Or what reason is there that she appears as exactly round through it, as she doth to the bare eye? certainly then either there is no such thing as you imagine, or else the glass fails much in this discovery.

To this I shall answer out of Galilæus.

1. You must know, that there is not merely one rank of mountains above the edge of the moon, but divers orders, one mountain behind another, and so there is somewhat to hinder those void spaces which otherwise, perhaps, might appear.

Now where there be many hills, the ground seems even to a man that can see the tops of all. Thus when the sea