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h* s Equinoctial Parts, and makes his Meridians! mic h Elliptical, so as to be diiccrnable by the Te-lescope.

The Sun’s Heat in Jupiter, is at most not above°ie twenty fifth part of what it is with us; andC | tqueni[y ’twould be very uncomfortable livingtlCrc (if at all possible) for Men of our Constituti-on - And yet some are very fond of thinking Jupi-/f) an excellent place to live in.

1 he Distance of Jupiter from the Sun, is aboveVe times as great as that of the Earth from theUn >lee Gregory's Ajlron. and consequently the Dia-nicttr °f the Sun to any Eye in Jupiter, will ber ° c a Ehh part of what it appears to us, andtherc-his Disk will be above 25 times less, and infame Proportion will his Eight and Heat

. 1 he Artificial Day and Night (each of 5 Hours)the fame length in Jupiter, all over his Sur-ace ; because the Axis ot his Diurnal Revolution,5 nearly at Right Angles to the Plane of his Annual

’bit round the Sun.

Altho' Jupiter hath 4 Primary Planets below him,j q c an Eye placed there, and of no sharper Sight

an one of ours, could never behold any one of

th

unless as Spots tranliting over the Sun’s Diskhen they happen to be between the Jovial Eyes r,t * the Sun : For Aims which goes furthest of alleotn the Sun, will not in Jupiter be seen above 1 3Purees from him ; and fince that Planet is butihitll. and resects but a weak Eight, so near the

Sin

h it cannot be visible : So that Saturn is the on-

^ Vianet that can be seen in Jupiter, except hisa sour Moons or Satellites,g she Sun’s Parallax seen from Jupiter, will scarcee ^nsible any more than Saturn's ; neither beingr ’ Uc h above zo Seconds. So that the Sun’s appa-' nt diameter in Jupiter, will not be above 6 Mi-phtes. But the outermost of his Satallites will ap-a hnost as great as the Moon doth to us, vi%.of ^ t ’’nts the Diameter, asd z; times the Diskorfi ^ un ’ ^ ccn f rom ’be fame Planet: And if thetviif 1 ' Satellites are not less than the outermost, they^ Yet appear rmteh greater : (And the Learnedt r - tiugcns conceives them not much ’els than ourhj. n h) and give the Planet a good Eight in thetan S ’ w hich also can never there be very

r - Gregory, (from whence this comparative”oni° n0rn y ' s collected) faith also, That an Astro-the r*- Placed in Jupiter, would easily compareDi distances of the four Inferior Planets with theUs ^ters of Jupiter, as we do the Distances of

the Planets, by comparing them with theaj^-terof the Earth : And this would be donetfi c Jp’ e sour nearest ones, easier than we computeter* p^ ance of the Moon by the Earth’s Diame-°f th T> r tbe Horizontal Parallax of the remotestg rca c Planets seen from Jupiter, is above twice asir 0 ,^ as the Horizontal Parallax of the Moon seenL; e a t *’ c Earth; and therefore must be very fensi-fi ttY j considerable. And tho’ the Globe of Ju-y Ct si. % Va b 1 y large, in comparison of our Earth ;fit Cr ^ .tin’s Parallax, when he’s beheld from Ju-qu en \.' VVI /^ not be quite 20 Seconds, and confc-Sat Ur ^ . car , ce sensible : Nor will the Parallax ofnext to w ben in Opposition to the Sun, andtwin 1° be much greater ; and therefore

efti tri „ r e \ er Y difficult for the Jovial Astronomer toth^t Plan C Obb^uce of Saturn,or of the Sun from

Indeed, if he can discover that Jupiter movesround the Sun, he may be able (as the Doctorstrews, Prop. 3.) to determine the Ratio of the Di-stance of Jupiter and Saturn from the Sun, other-wise not.

Our Jovial Astronomer therefore, by the help ofhis Senses would distinguish two kinds of Planets;four nearer to him, which arc the Satellites, andtwo (as the Sun and Saturn ) more remote ; andthele latter would appear with a lesser Diameter,the former with a greater. Of the Remotest, theSun would appear in Diameter about six Minutes,but the Diameter of Saturn would scarce be ■! of aMinute. ^

Of the four nearer Planets, or Satellites, thefourth would appear to an Eye in Jupiter, of theBigness the Moon doth to us: That is, with a Di-ameter five times greater, and a Disk twenty fivetimes greater than the Sun doth there. Besides,the four nearer, and apparently greater ones, willbe distinguish’d from the more remote and lesserot,es, in this, that in the nearer Planets the Squaresof the Periodick Times, are as the Cubes of theirDistances from the Center of Jupiter, which wou’dby no means be true, if any one of the greaterwere compared with any one of the lesser. Andaltho’ the nearer these Planets are, they appear thegreater ; yet the Sun will be immensely morebright then they ; for from their Faces, which de-pend upon their Situation, with respect to the Sun,they will appear like so many Moons J Frontwhence a Spectator in Jupiter will have four kindsof Months, according to the Number of Moons.There will be contained above 2407 of the leastMonths in a Year ; and about half the Numberof Months next to these; the Number of theMonths ot the third Satellite contain’d in a Year,will be nearly subduple of the second, or fubqua-druple of the first, and the Months of the greatestwill be about 254, So that altho’ the Notation ofTime, be much more intricate in Jupiter, by rea-son of the great Number of Days which theirYear contains, yet it is much facilitated by thesefour Kinds of Months; for in the least Monththere are only 4 Days and a quarter, but in thegreatest something more then 40.

Besides, these Moons suffer an Eclipse when theybeing in Opposition to the Sun, happen ro fall intothe Shadow of Jupiter ; and again, when they(being in Conjunction with the Sun, project theirShadows to Jupiter, they make an Eclipse of theSun to an Eye placed in that Region of Jupiter ,where the Shadow falls (which Region is a verysmall part of Jupiter's Surface) just as our Moondoes; but because the Orbits of those Moons a-bout Jupiter, are in a Plain which is cnclined to,or makes an Angle with Jupiter’s Orbit about theSun, and are all of ’cm nearly in the fame Plain*excepting the second which deviates a little ; uponthis account I fay their Eclipses are Central, andconsequently most lasting, when'the Sun is in oneof the Nodes of those Moons. But when the Sunis out of this Position, the Eclipses may be Total,tho’ not Central, because the Breadth ot Jupiter’sShadow, is nearly decuple the Breadth of any ofthe Satellites, and the apparent Diameter of anyof those Moons, is nearly quintuple the apparentDiameter of the Sun. And this remarkable inequa-lity of the Diameters, and rhe small Inclination thePlain of the Orbits of the Satellites has to the Plainof Jupiter’s Orbit round the Sun, is the reason whyin each Revolution there happens Eclipses both ofZ z z X the