Page:Philosophical Transactions - Volume 001.djvu/183

 it in relation to the Sun, in respect whereof, its motion is regular, he considers the same in relation to the Earth, where We observe it; and shews by the means of his Tables, what is to be added or substracted, to know, at what time the said Spot is to come into the middle of Jupiter's Diske, according as he is Oriental or Occidental. He hath also considered it in relation to an unmovable point, which he has supposed to be the first point of Aries, because we thither refer here upon Earth the beginning of all the Celestial motions, and there is the Primum mobile, that one would imagine, if we were in Jupiter, as we do here imagine Ours of 24. hours.

The Discovery is one of the best, that have been yet made in the Heavens; and those, that hold the Motion of the earth, find in it a full Analogy. For Jupiter turning about the Sun, does nevertheless turn about his Axis and although he be much bigger than the Earth, he does nevertheless turn much more swiftly than it, since he makes more than two Turns, and a third part, for its one; and carries with him 4. Moons, as the Earth does one.

This Observation ought to excite all Curious persons to endeavour the perfecting of Optick Glasses, to the end that it may be discovered, whether the other Planets, as Mars, Venus and Mercury, about whom no Moon hath as yet been discovered, do yet turn about their Axes, and in how much time they do so; especially Mars, in whom some Spot is discover'd, and Venus, wherein M. Burattini hath signified from Poland, he has observ'd Inequalities, as in the Moon.

It will be worth while, to watch for the seeing of Jupiter again this Spring, that this happy Observation may be confirmed in divers places, and endeavours used to make new ones.

1. Hydrostatical Paradoxes, made out by New Experiments (for the most part Physical, and Easie) by the Honourable Robert Boyle. This Treatise, promised in of these Papers, is now come forth: And was occasioned by the perusal of the Learned Monsieur Paschalls Tract, of the Æquilibrium of Liquors, and of the Weight of the Air: Of which two Subjects, the latter having been more clearly made out in England by Experiments, which could not be made by Monsieur Paschal and others, that wanted the advantage of such Engines and Instruments, as have here been frequently made use Rh