e trouble {63} accompanying 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 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 M