Page:Micrographia - or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon.djvu/356

Rh is Eclipsed, for it alwayes passes between the lines 1 2, and 3 4.

To which I say, That if the Air be such, as I have newly shewn it to be, and consequently cause such an inflection of the Rays that fall into it, those dark Penumbra's F Y Z Q, H X V T, and O R P S, will all vanish. For if we suppose the Air indefinitely extended, and to be no where bounded with a determinate refracting surface, as I have shewn it uncapable of having, from the nature of it; it will follow, that the Moon will no where be totally obscured, but when it is below the Apex N, of the dark blunt Cone of the Earth's shadow: Now, from the supposition, that the Sun is distant about seven thousand Diameters, the point N, according to calculation, being not above twenty five terrestrial Semidiameters from the Center of the Earth: It follows, that whensoever the Moon eclipsed is totally darkned, without affording any kind of light, it must be within twenty five Semidiameters of the Earth, and consequently much lower then any Astronomers have hitherto put it.

This will seem much more consonant to the rest of the secundary Planets; for the highest of Jupiter's Moons is between twenty and thirty Jovial Semidiameters distant from the Center of Jupiter; and the of Saturn much about the same number of Saturnial Semidiameters from the Center of that Planet.

But these are but conjectures also, and must be determin'd by such kind of Observations as I have newly mention'd.

Nor will it be difficult, by this Hypothesis, to salve all the appearances of Eclipses of the Moon, for in this Hypothesis also, there will be on each side of the shadow of the Earth, a Penumbra, not caus'd by the Refraction of the Air, as in the Hypothesis of Kepler; but by the faint inlightning of it by the Sun: For if, in the sixth Figure, we suppose E S Q, and G S R, to be the Rays that terminate the shadow from either side of the Earth; E S Q coming from the upper limb of the Sun, and G S R from the under; it will follow, that the shadow of the Earth, within those Rays, that is, the Cone G S E, will be totally dark. But the Sun being not a point, but a large area of light, there will be a secondary dark Cone of shadow E P G, which will be caus'd by the earth's hindring part of the Rays of the Sun from falling on the parts G P R, and E P Q of which halved shadow, or Penumbra, that part will appear brightest which lyes nearest the terminating Rayes G P, and E P, and those darker that lye nearest to G S, and E S: when therefore the Moon appears quite dark in the middle of the Eclipse, she must be below S, that is, between S and F; when she appears lighter near the middle of the Eclipse, she must pass some where between R Q and S; and when she is alike light through the whole Eclypse, she must pass between R Q, and P. Rh Errata