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upon its Poles: for we may perceive them to be perpetually shifting their Places from the Eastern to the Western Limb of the Sun; and in thus doing, their daily Stages and Motion exactly correspond to the Motion of a Globe ; that is, those Stages are shorter, and the Motion of the Spots seemingly flower towards the Sun's Limb, but near the Center of the Disk, larger and swifter; and all in exact Proportion to a double Line of Sines, or a Line of Sines on each Semidiameter of the Disk.
And farther yet, thefe Solar Spots, as they manifefly demonstrate the Sun to be a moving Globe, turning round once in somewhat above 25 Days, so they manifest them, selves to be something adhering unto, or nigh the Sun's globous Body, by means of the different Appearance they have in the different Parts and Positions of the Sun: As in the
middle of the Disk, if they are round, towards the Limb they become more and more oval or long, just as such a like Spot on a common Globe would appear when it is turned so as to be viewed by us fideways or going out of sight.
And lastly, another thing observable in and from these Spots is, that they describe various Paths or Lines over the Sun, sometimes strait, sometimes curved towards one Pole of the Sun, sometimes towards the other, exactly corresponding to the different Positions of the Earth in respect of the Sun, throughout all parts of the Year.
Thus in that vast Mass, the Sun, we have manifestly such a diurnal Motion as I spake of, or Circumvolution round its Axis ; a Motion constant and regular, and doubtless of as great use to some office or other, in some part or other of the Universe,
as the Motions of the Earth, are to the Inhabitants thereof: and a Motion therefore this is, demonstrating the concurrence of the Almighty.
Neither is it the Sun alone that undergoes a diurnal Rotation, but most, if not all the Erraticks about him. Saturn indeed, is at so great a distance from us, that we have not been able to perceive whether or no he hath such a Rotation ; but as the other Planets have it, and there is full as much occasion for it in Saturn as in them, so there is no great doubt to be made, but that he hath such a like Diurnal Motion, accommodated as well to his state, as it is in the Earth and the rest of the Planets.
So Jupiter is discovered to have manifestly a Motion round upon its Axis from East to West, in the space of gh. 56'; as Monf. Casini (g) by
(8) See his Observations in the Memoirs de Mathem. & Physique for Jan. 1692.
many repeated Observations in the year 1665, and other following years, first found, from the Spots observable on it; of which there are two kinds, which I my self have often seen as well as others before me; a short account of which (although it be a Digression) may not be unacceptable to many Readers. One kind of those Jovial Spots, is only the Shadow cast upon the Planet by the Satellites intercepting the Light of the Sun, when they are interposed between the Sun and Jupiter : the other are such as are really in the body of that Planet, after the manner of those we see in the Moon, but not permanent as they are. And by the motion of these latter Spots it is manifest, not only that Jupiter revolves round in the time mentioned, but that it is a moving Globe also, by reason (as was said of the Sun) those Spots move swifter, and in lar
ger Stages towards the middle, than towards the Limb of Jupiter's Disk. Also such Spots as are round about the middle, appear long or oval towards the Limb, or Edge of the Disk; as was before observed of the Sun's Spots.
As to Mars and Venus, they are both discovered to have Spots, or Parts lighter and darker, as well as Jupiter, and to have a motion also as he hath. Of those Spots in Mars, Dr. Hook had divers views in the year 1665, which he hath given us Figures of (b): and from thence concluded that Planet had a Motion, although he could not determine in what time it was performed. But Mr. Huygens exprefly faith (i) it is performed in the space of 24 h. 40'. But for the motion of Venus, Mons. Caffini could perceive the
(b) See Philof. Trans. No. 11, 14: