In the above-mentioned French Tract there is also conteined M. Auzout's Opinion of what he had found New in the Treatise of Signor Campani, which was spoken of in the first Papers of these Transactions, concerning both the Effect of the Telescopes, contrived after a peculiar way by the said Campani at Rome, and
his New Observations of Saturn and Jupiter, made by means thereof.
First therefore, after that M Auzout had raised some scruple against the Contrivance of Signor Campani for making Great Optick-Glasses without Moulds, by the means of a Turn-lath, he examines the Observations, made with such Glasses: Where, having commended Campani's sincerity in relating what he thought to have seen in Saturn, without accomodating it to M. Hugens's Hypothesis, he affirms, that supposing, there be a Ring about Saturn, Signor Campani could not see in all those different times, that he observed it, the same Appearances, which he notes to have actually seen. For, having seen it sometimes in Trine Aspect with the Sun, and Oriental; sometimes, in the same Aspect, but Occidental; sometimes in Sextil Aspect, and Occidental; at another time, again in Trine, and Oriental, this Author cannot conceive, how Saturn could in all these different times have no difference in its Phasis, or keep always the same Shadow; seeing that, according to the Hypothesis of the Ring, when it was Oriental, it must cast the Shadow upon the left side of the Ring beneath, without casting any on the right side: and when it was Occidental, it could not but cast it on the right side beneath, and nothing of it on the other.
Concerning the Shadow above, which Campani affirms to be made by the Ring upon the Body of Saturn, M. Auzout judges, that there could be no such Phænomenon, by reason of its Northern Latitude at the times, wherein the Observations were made, vid. in April 1663; in the midst of August, and the beginning of October, next following, and in April 1664, except it were in October, and the Shadow strong enough to become visible.
But as to the Shadow below, he agrees with Campani, that it does appear, yet not as he notes it, seeing that it must be sometimes on the one side, sometimes on the other; and towards the Quadrat with the Sun it must appear biggest, as indeed he affirms to have seen it himself this year, insomuch that sometimes it seemed to him, that it covered the whole Ring, and that the Shadow, joyning with the obscure space between both, did interrupt the circumference of the Ring; but beholding it at other times in a cleer Sky, and when there was no Trepidation of the Air,
he thought, that he saw also the Light continued from without, although very slender. But he acknowledges, that he could never yet precisely determine, by how much the largeness of the Ring was bigger than the Diameter of Saturn's Body. As for the proportion of the Length to the Breadth, he affirms, to have alwaies estimated it to be two and a half, or very neer so; and to have found in his Observations, that in January last, one time, the length of Saturn was 12 Lines, and the breadth 5. Another time, the length was 12. Lines, and the breadth 4. and this by a peculiar method of his own. But yet he acknowleges also, that sometimes he hath estimated it as 7. to 3. and at other times as 13. to 5. and that if there do not happen a change in the magnitude of the Ring (as it is not likely there does) that must needs proceed from the Constitution of the air, or of the Glass's having more or less Aperture, or from the difficulty of making an exact estimate of their proportions. However it is not much wide (saith he) of two and a half, although Campani make the length of the Ring but double to its breadth.
Monsieur Auzout believes, that he was one of the first that have well observed this shadow of Saturn's Body upon its Rings which he affirms happened two years since; when, observing in July, for the first time, with a Telescope of 21. and then another of 27. foot, he perceived, that the Angle of the obscure space on the right side beneath, was bigger and wider, than the three other Angles, and that some interruption appear'd there, between the Ring, and the Body of Saturn; of which he saith to have given notice from that time to all his friends, and in particular, as soon as conveniently he could, to Monsieur Hugens.
He confesseth, that he hath not had the opportunity of observing Saturn in his Oriental Quadrat; yet he doubts not, but that the shadow appears on the Left-side, considering, that the Existence of the Ring can be no longer doubted of, after so many Observations of the shadow cast by Saturn's Body upon it, according as it must happen, following that Hypothesis; there being no reason, why it should cast the said shadow on one side, and not on the other.
Concerning the Observation of Jupiter and its satellites, the famous Astronomer of Bononia, Cassinus, having
published, that on the 30. day of July, 1664. at 2½ of the clock in the morning, he had observ'd, with Campani's Glasses, that there passed through the broad obscure Belt of Jupiter two obscurer spots, by him esteemed to be the shadows of the Satellites, moving between Jupiter & the Sun, and eclipsing him, and emerging from the Occidental Brim thereof: This Authour did first conceive, that they were not shadows, but some Sallies, or Prominencies in that Belt; which he was induced to believe, because he perceived not, that that Prominency, which he there saw, was so black, nor so round as Cassini had represented his spots; wherefore, seeing it but little differing in colour, from the Belt, and so not judging it round, because it did stand only about half its diameter out of the Belt, he persuaded himself, that it was rather a Sally, or Prominency of the Belt, than a round shadow, as that of a Satellite of Jupiter must have bin. But having been since informed of all the Observations made by Cassini and Campani, with the New Glasses, and seen his Figure, he candidly and publickly wisheth, that he had not spoken of that Sally, or Prominency; advowing that he can doubt no longer, but that it was the shadow of the Satellit between Jupiter and the Sun, having seen the other emerge, as soon as with a 20. foot Glass he made the Observation, and having not perceiv'd these shadows with a 12. foot Glass: But although he grants that they did ghess better than he, yet he doth it with this proviso, vid. in case they made that Observation on of July 30. not with their 36. but 12. or 17. foot Telescope. If it be wondred at, that Monsieur Auzout did not see this shadow move, he allegeth his indisposition for making long Observations, and addeth, that it may be much more wondred at, that neither Campani nor himself did see upon the obscure Belt the Bodies of the Satellites, as parts more Luminous than the Belt. For (saith he) although the Latitude was Meridional, it being no more than of 9. or 10. minutes, the Body of the Satellites should, thinks he, pass between us and the Belt, especially according to Campani, who maketh the Belt so large, and puts the shadows farr enough within the same. This maketh him conclude, that either they have not observed well enough, or that the motion of the Satellites doth not exactly follow the Belts, and is inclin'd unto them. Whereupon he resolves, that when he shall know that they are to pass between Jupiter and us, and to be over against the Belt, that