then he will observe, whether he can see them appear upon the Belt, as upon a darker ground, especially, the third of them, which is sensibly greater, and more Luminous, than the rest. He hopeth also, that in time, the shadow of Saturns Moon will be seen upon Saturn, although we are yet some years to stay for it, and to prepare also for better Glasses.
From this rare Observation, he inferrs the Proportion of the Diameter of the Satellites to that of Jupiter; and judgeth, that no longer doubt can be made of the turning of these 4. Satellites, or Moons about Jupiter, as our Moon turns about the Earth, and after the same way as the rest of the Celestial Bodies of our Systeme do move: whence also a strong conjecture may be made, that Saturns Moon turns likewise about Saturn.
Hence he also taketh occasion to intimate, that we need not scruple to conclude, that if these two Planets have Moons wheeling about them, as our Earth hath one that moves about it, the conformity of these Moons with our Moon, does prove the conformity of our Earth with those Planets, which carrying away their Moons with themselves, do turn about the Sun, and very probably make their Moons turn about them in turning themselves about their Axis; and also, that there is no cause to invent perplex'd and incredible Hypotheses, for the receding from this Analogie since (saith he) if this be truth, the Prohibitions of publishing this doctrine, which formerly were caused by the offence of Novelty, will be laid aside, as one of the most zealous Doctors of the contrary Opinion hath given cause to hope, witness Eustachius de Divinis, in his Tract against Monsieur Hugen's Systeme of Saturn, p. 49. where we are inform'd, that that learned Jesuit, P. Fabry, Penitentiary of S Peter in Rome, speaks to this purpose:
Whence this Author concludes, that the said Jesuite assuring us that the inquisition hath not absolutely declared, that those Scripture-places are to be understood literally, seeing that the Church may make a contrary declaration, no man ought to scruple to follow the Hypothesis of the Earths motion, but only forbear to maintain it in publick, till the prohibition be called in. But to return to the matter in hand, this Author, upon all these observations and relations of Cassini and Campani, doth find no reason to doubt any more of the excellency of the Glass used by them, above his; except this difference may be imputed to that of the Air, or of the Eys. But yet he is rather inclined to ascribe it to the goodness of their Glasses, and that the rather, because, he would not be thought to have the vanity of magnifying his own; of which, yet he intimates by the by, that he caused one to be wrought, of 150 Parisian feet; which though it proved none of the best, yet he despairs not to make good ones of that, and of far greater Length.
Signor Campani's Answer: and Monsieur Auzout's Animadversions thereon.
The other part of this French Tract, conteining Campani's Answer, and Mr. Auzout his Reflections thereon, begins with the pretended Shadows of the Ring upon Saturn, and of Saturn upon the Ring. Concerning which, the said Campani declareth, that he never believed them to be shadows, made by the Ring upon the Disk of Saturn, or by the body of Saturn upon the Ring, but the Rimms of these bodies, which being unequally Luminous, did shew these appearances. In which Explication, forasmuch as it represents, that the said Campani meant to note only the Inequality of the Light, which, he saith, his Glasses did discover, Mr. Auzout does
so far acquiesce, that he only wishes, that his own Glasses would shew him those differences. Next to the Objection, made by Monsieur Auzout, against Signor Campani, touching the Proportion of the Length of the Ring to its breadth, Campani replyeth, that the Glasses of Monsieur Auzout, shew not all the particulars, that his do, and therefore are unfit for determining the true Figure and breadth of the apparent Ellipsis of the Ring. To which M. Auzout rejoyns, that he is displeased at his being destitute of better Glasses, but that it will be very hard for the future to convince Campani touching the Proportion of the Ring, seing that the breadth of the Ellipsis is always diminishing, although, if the declination of the Ring remains always the same, one can at all times know, which may have been its greatest breadth. But he assures, that the breadth of the Ring is not the half of its length, and that it doth not spread out so much beyond Saturn's Body, as he hath alleged. And withal desirs to know, what can be answered by Sig. Campani to M. Hugens, who being persuaded, that the Declination of the Ring is not above 23 deg. 30′ having seen the Ring to spread out above the Body of Saturn, concludes, in a Letter to M. Auzout, that the length of the Ring is more than treble the Diameter of Saturn's body, which, according to Campani, is only as about 67 to 31. Which difference yet dos not appear to M. Auzout to be so great; but that M. Hugens perhaps will impute it to the Optical reason, which he (Auzout) hath alleged of the Advance of the light upon the obscure space; although he is of Opinion, he should not have concluded so great a Length, if he had not seen the Breadth spread out more, than he hath done: for (saith he) if the Length of the Ring be to the body of Saturn, 2½ to 1. and the Inclination be 23 deg. 30′ the Ring will be just as large, as the body, without spreading out; but if the Ring be bigger, it will a little spread out; and if it were treble, it must needs spread out the half of its breadth, which hath not so appeared to him.
Further, to M. Auzout's change of Opinion, and believing, that the Advance or Sally, seen by him in Jupiter, was the Shadow of one of his Moons, Campani declares, that he would not have him guilty of that change: Whereupon M. Auzout wonders, why Campani then hath not marked it in his Figure; and would