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bath thence deduced the Motion os Jus iter abouthis Axis ; and that M.CaJfmiat first opposed it: But that Spot was Ohferved in England a good while before.

4. There are two Sorts oF Spots at certain times to be Feen in the DiFqueos Jupiter. One Sort are nothing but the Skadows of his Satellites but the By M. Caffiniother have forne resemblance to thole that are scen in the Moon\ and they are 8 ‘perhaps of the fame Nature wirh thole that are called Belts. They Move 3°'.^. a7.front the Eastern to the Western Limb • their apparent Motion is unequal, 82./.and Fwifter near the Center than the Circumference; and they never are sowell Feen as when they approach to the Center, they being very narrow andalmost imperceptible when they approach to the Circumference; whichmakes us believe, that they are flat and Füperficial to Jupiter.

Among thcse Spots there is none so sensible, as that which is situate inthe Northern-part of the Southern Bclt. its Diameter is about the tenthpart of that of Jupiter ; and at the time that its Center is nearest to that ofJupiter , it is Distant from it about the third part of the Scmidiametcr of thatPlanet.

M. CaJJini, aster he had made many Observations of this Spot during theSummer of the Year 166y, four.d, that the Pcriod of its apparent Bevolutionis of 9 11 56h He continued to ObFerve it till the Beginningof 1666, whenJupiter approach’d to the Beams of the Sun But after he was got free of theSun-Beams it was difficult to be diFccrn'd. This gave grounds that it mightbe of the Nature of the Spots of the Sun ( which after having appeared fora while, difäppear for ever ) M. Caffini ceased at length to ObFerve them.

But Jan.it). i6yx. {st. n.) when he ObFerv’d Jupiter , at 4!^ in the Mor-ning, he pereeived in the Fame Place ot his DiFque the Figure of the FanteSpot, adhering to the Farne Southern Bclt. It was already gone beyond theMoiety of this Belt, and he Fäw it advance littleby little towards the WesternLimb, to which it seemed to be very near at 6}* 1 .

By the Celerity of its Motion near the Center, and by the Place where hehad begun to Fee it, hejudged that it might have been in the midst of the Belt at4K 3 y'in the Morning. And as he prepared himFelf to make Ephemerides ofits Motion for that Tear i6yx, he pereeived, that in thole, he madefor the Year t666, this Spot had been in the midst of Jupiter the Farne Day,nam«Jy the I9 th of Jan. at the fame Hour. So that in Fix Years, of whichone is a Bistextile, it is found to have made, in respect of the Earth, at käst5194 Revolutions, each of 9 h 55' 58^, compeniating one Revolution byanother; and at most 5x94 Revolutions of 9h yl^; forafmuch as he wasaflured of the preciFeness of one Mcan Bevolution ty one eighth of a Minute.

Until then he had never Feen an immediate Return of this Spot after 9hours and y6 minutes, because it had not happened, that Jupiter after theApparition -of the Spot had stayed, in one and the Farne Night, long enoughabove the Horizon, at least at a Füfhcient height, to obFerve him with due Di-stinctness. He had only concluded the time of this stcvolution by Returnsobserved after about xo, 30, and 50 hours; and he had more precisely limi-red it by Observations more distant. But the Night after Mar. 1, at 7 ^ inthe Evening, he Faw this Spot ist the midst of the Belt ; and the fame Night at

5^x6*.