been able to perceive any Attendance of Mcons, as in the other fuperior Planets; not fo much probably because there are none, but becaufe they are small, or they reflect a weak Light, and are at a great Distance from us. And as for Venus and Mercury, there may be no Occafion for any Attendants, by reafon of their proximity to the Sun. But in the two higheft, or more diftant Planets, Jupiter and Saturn, we have a very noble, and entertaining Scene of the CREATOR's Glory. For whereas those two Planets are at a much greater Distance, than any of the other Planets, from their Fountain of Light and Heat, the Sun; and as confequently their Heat and Light are abated in proportion to the Square of their Distances; fo to make them amends, they are furrounded with a more grand Retinue, of Secondary Planets, or Moons; Jupiter

Jupiter with four, Satrrn with five, as 'tis imagined; and probably more (a).

And an admirable Remedy this is, not only for the great Diflance of thefe two Planets from the Sun, but alfo for the tardity of the periodick Motion in their refpective Orbits. For whereas Saturn revolves round the Sun but once in near thirty

(a) Mr. Huygens in his Cofmotheor. p. 99. gives this Account of the Discovery of the Satellites of Jupiter and Saturn, That it is well known the Dif covery of the Circumjovials is owing to Galileo; that the brightest and outermoft Circumfaturnial he happened to fee with a 12 Foot Glafs in the Year 1655; that the reft are owing to Caflini, who first faw them with a Glass of Campani's grinding, of 36 Feet, and afterwards with one of as many Feet above an hundred. That the Third and Fifth, Caffini fhewed him in 1672, and afterwards oftner. That Caffini acquainted him, by Letter afterwards, with his Difcovery of the First and Second in 1684. That the two laft are not easily difcerned, and he cannot fay be ever faw them. That befides thefe Five, be fufpects there may be One or more lie concealed. Of which fee Chap. 7. following

Years, and Jupiter but once in near twelve, it comes to pass that the places near the two Poles of those Planets, have a Night of near fifteen Years in Saturn, and fix in Jupiter, fuppofing their Axes inclined to the Planes of their Orbits, as it is in our own Globe. But fuppofing (as it is imagined) that their Axes are not fo much inclined, and that their Days and Nights, their Winters and Summers, are nearly equal; in this refpect, the Cafe would be worse, than in the long Nights, in the other Cafe: But in both Cafes, the polar Parts of both those Planets, would be difmal Regions of Darknefs, when fo long detained from the kindly Vifits of the Sun. But an admirable Remedy is found, and a glorious Scene of the great CREATOR's Works appears therein, as will be manifeft by confidering par

ticulars

ticulars in each of those two fuperiour Planets.

CHAP. VI.

Of Jupiter's Moons, Days, and Seasons.

IN

N speaking concerning the fuperior Planets in particular, I fhall begin with Jupiter. The Distance of this Planet from the Sun, is reckoned to be 343 millions of Miles farther from the Sun than we are; and by that Means, the Sun's Light and Heat are 27 times lefs there than with us, and its apparent Diameter, five times lefs (b). And confidering

(b) Gregorii Aftron. L.6. Prop. 5. Mr. Huygens makes the Light and Heat but 25 times lefs, and the apparent Diameter 5 times. Cofmoth. p. 103.

how vaft a Globe Jupiter is, having its Superficies 100 Times, yea (according to Mr. Huygens's Computations) 400 Times bigger than that of the Earth; in this Cafe, what vaft Tracts of that Globe muft needs lie in profound Darkness, and Defolation, had no Remedy been provided! But there are divers provided. One is by the frequent Rotations of Jupiter round his own Axis; which being performed in lefs than 10 Hours, it comes to pass, that what is wanting in the Strength, and Degree of Light and Heat, is compenfated by the frequent Returns there

of.

The other Remedy is by the Increafe of the Number of Moons about Jupiter, who is attended (as I faid) with four, as we who are nearer the Sun, are with one. Concerning which these four Things are remarkable.

1. Their