Page:Micrographia - or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon.djvu/355

Rh First, From the irregular surface of the Moon, and from several Parallaxes, that unless the Dichotomy happen in the Nonagesimus of the Ecliptick, and that in the Meridian, &c. all which happen so very seldom, that it is almost impossible to make them otherwise then uncertainly. Besides, we are not yet certain, but that there may be somewhat about the Moon analogus to the Air about the Earth, which may cause a refraction of the light of the Sun, and consequently make a great difference in the apparent dichotomy of the Moon. Their way indeed is very rational and ingenious; and such as is much to be preferr’d before the way by the Horizontal Parallax, could all the uncertainties be remov’d; and were the true distance of the Moon known.

But because we find by the Experiments of Vendiline, Reinoldus, &c. that Observations of this kind are very uncertain also: It were to be wisht, that such kind ot Observations, made at two very distant stations, were promoted. And it is so much the more desirable, because, from what I have now shewn of the nature of the Air, it is evident, that the refraction may be very much greater then all the Astronomers hitherto have imagined it: And consequently, that the distance of the Moon, and other Planets, may be much lesse then what they have hitherto made it.

For first, this Inflection, I have here propounded, will allow the shadow of the Earth to be much shorter then it can be made by the other Hypothesis of refraction, and consequently, the Moon will not suffer an Eclipse, unless it comes very much nearer the Earth then the Astronomers hitherto have supposed it.

Secondly, There will not in this Hypothesis be any other shadow of the Earth, such as Kepler supposes, and calls the Penumbra, which is the shadow of the refracting Atmosphere; for the bending of the Rays being altogether caus’d by Inflection, as I have already shewn, all that part which is ascribed by Kepler, and others after him, to the Penumbra, or dark part, which is without the umbra terræ, does clear vanish; for in this Hypothesis there is no refracting surface of the Air, and consequently there can be no shadows, such as appear in the ninth Figure of the 37. Scheme, where let A B C D represent the Earth, and E F G H the Atmosphere, which according to Keplers supposition, is like a Sphære of Water terminated with an exact surface E F G H, let the lines M F, L B, I D, K H, represent the Rays of the Sun; ’tis manifest, that all the Rayes between L B, and I D, will be reflected by the surface of the Earth B A D, and consequently, the conical space B O D would be dark and obscure; but, say the followers of Kepler, the Rays between M F, and L B, and between I D, and K H, falling on the Atmosphere, are refracted, both at their ingress and egress out of the Atmosphere, nearer towards the Axis of the spærical shadow C O, and consequently, inlighten a great part of that former dark Cone, and shorten, and contract, its top to N. And because of this Reflection of these Rays, say they, there is superinduc’d another shell of a dark Cone F P H, whose Apex P is yet further distant from the Earth: By this Penumbra, say they, the Moon Rh