western part of its Orbit, as Mr. Huygens well obferves (a). These Satellites we may reafonably conclude to be of a prodigious Bulk, for the reflecting of Light, and for their other Miniftrations to Saturn, because otherwise they could not be seen at so great a Distance as the Earth; and particularly one of them (6) is of that Magnitude, and ap (a) The Reason why Saturn's fifth Satellite pears not on the Eaftern, but Western Part of its Orbit, Mr. Huygens very fagaciously (like himfelf) conjectures to be, because this Satellite, as the Moon doth to the Earth, always turns one and the fame Side to Saturn, and because this Satellite hath, he imagines, only one Part of its Surface clear, and the greatest Part obscure, and not able to reflect fufficient Light to us; therefore all the Time that obfcure Part is turned towards us (which is whilft the Satellite is in the Eastern Parts of its Orbit) it disappears: But in the Weftern Parts it appears, because the bright Sides lie towards us. Cofmotheor. p. 118. (b) It is the fourth Satellite, or Outermoft but one (called from its firft Discoverer, the Hugenian Satellite) that is fo vifible. its its Light fo brisk and vivid, that it appears very illuftrious through our longer Glaffes, and may be difcerned with our fhorter. As to the Distances, the Periods, and Latitudes of those Satellites, they being confentaneous to what I have already taken Notice of in Jupiter, I fhall not infift upon them, but pass to another provifion made for the great Distance of that Planet; which is a Thing fo fingular to Saturn, so unufual in all the reft of the Creation, and fo amazing, that it is an evident and noble Demonftration of the great CREATOR's Art and Care; and that is Saturn's Ring. Concerning which these Things are obfervable. 1. The prodigious Size of it, its great Breadth and vaft Compafs. This we may make a Judgment of, by comparing it with Saturn himfelf. And fuppofing the Diameter of Sa turn turn to be as is before determined, 93451 English Miles, the Diameter of his Ring will be 210265 fuch Miles, and its Breadth about 29200 (c); an amazing Arch to an Eye placed in that Planet. 2. The due and convenient Diftance of it from Saturn it felf; not closely adhering to it, because that would annoy a large portion of Saturn's Globe, by depriving it of the Sun's Rays, but environing it at about the Diffance of its Breadth; by which Means the Sun's Light and Heat are permitted to enter between the Planet and its Ring, whilft other Rays are, at the fame Time, reflected upon the Planet by the Ring. (c) Mr. Huygens in his Syftema Saturn. p. 47. and Cofmotheor.p.109. determines the Diameter of Saturn's Ring to the Diameter of Saturn, to be as 9 to 4; and the breadth of the Ring, and Distance of the Ring from Saturn's Body, to be nearly equal, and accordingly thefe Numbers are defined here. 3. The 3. The Thickness of the Ring, which is hardly, if at all perceivable by us; which is as great a Benefit, as its edging Shade would be an Annoyance, was the Ring thick. 4. Its Smoothnefs and Aptitude to reflect Light and Heat (d) is a wonderful Convenience in it. Was it full of Mountains and Valleys, and I may add Waters too, as in our Earth, and probably the Moon likewife, the Reflexions would be too weak to render the Ring visible unto us, at fo great a Distance as we are; but perceiving its Light to be fo lively and ftrong, as to render both it felf, and Saturn very illuftrious, it is a Demonftration of the Aptitude of its Structure, and Smoothnefs, for the Reflexion of Light and Heat to the Planet it ferves. (d) See Huygen. Syft. Saturn. p. 70. 5. As the periodical Revolutions of the Earth are an excellent and providential Contrivance, for those useful and neceffary Mutations we have of the Seasons of the Year, fo no doubt but the fame Benefits accrue to those Revolutions, which Saturn hath about the Sun. It is vifible, that as Saturn changes its place in its Orbit, fo its Ring receives a variety of Aspects (e) not only with respect to us, but to the Sun. Thus in one part of the Orbit it appears with a (f) larger Ellipfis, fo as to exhibit a large (e) Every 14 or 15 Years Saturn's Ring hath the fame Face; appearing at one Time with large open Anfa, at another Time with no Ring at all. Which Appearances is obtained by gentle Progreffes from the one to the other Face. As, if the Anfe are the largest, they gradually diminish, until no Anfe or Apertures are to be feen in the Ring, and at laft no Ring at all also. See Fig. 8. (f) This Mr. Huygens fhews, is when Saturn is 20 Degrees in Gemini and Sagittary. This was the |