He promises withall, that he will explicate this way in his _Treatise of the usefulness of Telescopes_, where he intends to assign the Bigness of the _Diameter_ of all the _Planets_, and their proportion to that of the _Sun_; as also, that of the _Stars_, which he esteems yet much less, than all those have done, that have written of it hitherto; not believing, that the _Great Dog_, which appears to be the fairest Star of the _Firmament_, hath 2 _Seconds_ in _Diameter_, nor that those, which are counted of the sixth Magnitude, have 20 _thirds_; nor thinking, that all the Stars, that are in the _Firmament_, do enlighten the Earth as much as a Luminous Body of 20 _seconds_ in _Diameter_ would do, or, because there is but one half of them at the same time above our _Horizon_, as a Body of 14 _seconds_ in _Diameter_; and as the 18432^{th} part of the _Sun_ would enlighten us, or as the _Sun_ would do, if we were 14 times more distant from it, than _Saturn_, and 137 times further, than the Earth: Which, _he saith_, would not be credible, if he did not endeavor to evince it both by _Experience_ and _Reason_. And he doubts not, but that _Venus_, although she sends us no Light but what is reflected, does sometimes enlighten the _Earth_ more, than all the Stars together. Yet he would not have us imagine, from what he hath spoken of the smallness of the Stars, that _Telescopes_ do not magnifie them by reason of their great distance, as they do _Planets_; for this he judgeth a Vulgar Error, to be renounced. _Telescopes_ magnifie the _Stars_ (_saith he_) as much in proportion, as they do all other Bodies, seeing that the demonstration of their magnifying is made even upon _Parallel_ rays, which do suppose an infinite distance, though the Stars have none such: And if the _Telescopes_ did not magnifie the Stars, how could they make us see some of the _fiftieth_, and it may be some of the _hundreth_, and _twohundreth_ Magnitude, as they do, and as they would shew yet much lesser ones, if they did magnifie more? {64} * * * * * __M^r. Hook_'s Answer to Monsieur _Auzout_'s Considerations, in a Letter to the Publisher of these _Transactions_._ _SIR_,