3. It is opacous, not transparent or diaphanous like Chrystall or glasse,[1] as _Empedocles_ thought, who held the Moone to bee a globe of pure congealed aire, like haile inclosed in a spheare of fire, for then. [Sidenote 1: _Plut. de fa. lunæ._] 1. Why does shee not alwaies appeare in the full? since the light is dispersed through all her body? 2. How can the interposition of her body so darken the Sun, or cause such great eclipses as have turned day into night,[1] that have discovered the stars, and frighted the birds with such a sudden darknesse, that they fell downe upon the earth, as it is related in divers Histories? And therefore _Herodotus_ telling of an Eclipse which fell in _Xerxes_ time, describes it thus:[2] ὁ ἥλιος ἐκλιπὼν τὴν ἐκ τοῦ οὐρανοῦ ἕδρην ἀφανὴς ἦν. The Sunne leaving his wonted seate in the heavens, vanished away: all which argues such a great darknesse, as could not have beene, if her body had beene perspicuous. Yet some there are who interpret all these relations to bee hyperbolicall expressions, and the noble _Tycho_ thinkes it naturally impossible, that any eclipse should cause such darknesse, because the body of the Moone can never totally cover the Sunne; however, in this he is singular, all other Astronomers (if I may believe _Keplar_) being on the contrary opinion, by reason the Diameter of the Moone does for the most part appeare bigger to us then the Diameter of the Sunne. [Sidenote 1: _Thucid._ _Livii._ _Plut. de fa. Lunæ._] [Sidenote 2: _Herodot. l. 7 c. 37._] But here _Julius Cæsar_[1] once more, puts in to hinder our passage. The Moone (saith he) is not altogether opacous, because ’tis still of the same nature with the Heavens, which are incapable of totall opacity: and his reason is, because perspicuity is an inseparable accident of those purer bodies, and this hee thinkes must necessarily bee granted, for hee stops there, and proves no further; but to this I shall deferre an answere, till hee hath made up his argument. [Sidenote 1: _De phænom. Lunæ. c. 11._] We may frequently see, that her body does so eclipse the Sunne, as our earth doth the Moone; since then the like interposition of them both, doth produce the like effect, they must necessarily be of the like natures, that is a like opacous, which is the thing to be shewed; and this was the reason (as the Interpreters guesse) why _Aristotle_ affirmed the Moone to be of the earths nature,[1] because of their agreement in opacity, whereas all the other elements save that, are in some measure perspicuous. [Sidenote 1: _In lib. de animalib._] But the greatest difference which may seeme to make our earth altogether unlike the Moone, is, because the one is a bright body, and hath light of its owne, and the other a grosse dark body which cannot shine at all. ’Tis requisite therefore, that in the next place I cleare this doubt, and shew that the Moone hath no more light of her owne than our earth. Proposition 5.