_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_, 21/2 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 {77} gladly know, whether that _Sally_ be more easie to discover, than the _Shadows_ of the _Satellites_, which _Campani_ believs, _Auzout_ hath not seen; and whether he be assured, that those obscure parts, which he there distinguishes, do not change: for if they should not change, then _Jupiter_ would not turn about his _Axis_, which yet, he saith, it doth, according to the _Observation_ made by Mr. _Hook_, _May_ 9 1664. inserted in the first papers of these _Transactions_. The full Discovery of which particular also he makes to be a part of _Cassini's_ and _Campani_'s work, seeing that they so distinctly see the inequalities in the _Belts_, and see also sometimes other _Spots_ besides the _Shadows_ of the _Satellites_: where he exhorts all the Curious, that have the conveniency of observing, to endeavor the discovery of a matter of that importance, which would prove one of the greatest _Analogies_ for the _Earth's Motion_. * * * * * _An Account of Mr. _Richard Lower_'s newly published _Vindication_ of Doctor _Willis_'s _Diatriba_ de _Febribus_._