panying them, if they perform no more, than shorter ones. Where, by the by, he takes notice, that he knows not yet, what Aperture Signor Campani gives to his Glasses, seeing he hath as yet signified nothing of it; but that the small one, sent by him to Cardinal Antonio, hath no more Aperture, than ordinary ones ought to have.
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 18432th 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 smallnes 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 two hundreth Magnitude, as they do, and as they would shew yet much lesser ones, if they. did magnifie more?