Concerning the Observation of _Jupiter_ and its _satellites_, the famous _Astronomer_ of _Bononia_, _Cassinus_, having {73} published, that on the 30. day of _July_, 1664. at 21/2 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 {74} 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