upon its Poles: for we may perceive them to be perpetually fhifting their Places from the Eaftern to the Weftern Limb of the Sun; and in thus doing, their daily Stages and Motion exactly correfpond to the Motion of a Globe; that is, thofe Stages are fhorter, and the Motion of the Spots feemingly flower towards the Sun's Limb, but near the Center of the Disk, larger and fwifter; 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 manifeftly demonftrate the Sun to be a moving Globe, turning round once in somewhat above 25 Days, fo they manifeft themfelves to be fomething adhering unto, or nigh the Sun's globous Body, by means of the different Appearance they have in the different Parts and Pofitions 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 fuch a like Spot on a common Globe would appear when it is turned fo as to be viewed by us fideways or going out of fight. And lastly, another thing obfervable in and from thefe Spots is, that they describe various Paths or Lines over the Sun, fometimes ftrait, fometimes curved towards one Pole of the Sun, fometimes towards the other, exactly corresponding to the different Pofitions of the Earth in respect of the Sun, throughout all parts of the Year. Thus in that vaft Mafs, the Sun, we have manifeftly fuch a diurnal Motion as I fpake of, or Circumvolution round its Axis; a Motion conftant and regular, and doubtless of as great use to fome office or other, in some part or other of the Universe, as as the Motions of the Earth, are to the Inhabitants thereof: and a Motion therefore this is, demonftrating the concurrence of the Almighty. Neither is it the Sun alone that undergoes a diurnal Rotation, but moft, if not all the Erraticks about him. Saturn indeed, is at fo great a diftance from us, that we have not been able to perceive whether or no he hath fuch a Rotation; but as the other Planets have it, and there is full as much occafion for it in Saturn as in them, fo there is no great doubt to be made, but that he hath fuch a like Diurnal Motion, accommodated as well to his ftate, as it is in the Earth and the reft of the Planets. So Jupiter is discovered to have manifeftly a Motion round upon its Axis from East to Weft, in the space of 9h. 56', as Monf. Caffini (g) by (g) See his Obfervations in the Memoirs de Mathem. & Phyfique for Jan. 1692. G many many repeated Observations in the year 1665, and other following years, first found, from the Spots obfervable on it; of which there are two kinds, which I my self have often feen as well as others before me ; a short account of which (although it be a Digreffion) may not be unacceptable to many Readers. One kind of thofe Jovial Spots, is only the Shadow caft upon the Planet by the Satellites intercepting the Light of the Sun, when they are interpofed between the Sun and Jupiter: the other are fuch as are really in the body of that Planet, after the manner of those we fee in the Moon, but not permanent as they are. And by the motion of these latter Spots it is manifeft, not only that Jupiter revolves round in the time mentioned, but that it is a moving Globe alfo, by reafon (as was faid of the Sun) thofe Spots move swifter, and in lar 2 ger ger Stages towards the middle, than towards the Limb of Jupiter's Disk. Alfo fuch Spots as are round about the middle, appear long or oval towards the Limb, or Edge of the Disk; as was before obferved 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 alfo 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, Monf. Caffini could perceive the (b) See Philof. Trans. No. 11, 14. (i) Cofmotheor. p. 24. Spots |