_ and his Conclusion thereupon
(_videl. That we are not to expect Glasses of above 300 or 400 foot long at
most, and that neither _Matter_ nor _Art_ will go so far_) is, may be
judged from what I have newly told you of making any _Object-Glass_ of any
Length.

And for his good wishes, that those, who promise to make him see _Plants_
or _Animals_ in the _Moon_ (of which I know not any, that has done so,
though perhaps there may be some, notwithstanding his Objections, that do
not yet think it impossible to be done) had considered, what a Man is able
to see with his _bare_ Eye at 60 Leagues distance: I cannot but return him
my wishes, that he would consider the difference between seeing a thing
through the _Gross_ and _Vaporous_ Air neer the Earth, and through the Air
over our heads: Which, if he observe the Moon in the _Horizon_, and neer
the _Zenith_ with a _Telescope_, he will experimentally find; and, having
done so, he will perhaps not be so dissident in this matter.

Concerning his Advertisement to such, as publish _Theories_, I find not,
that he hath made use of it in his own case. For, in his _Theory_ about
_Apertures_ he seems to be very positive, not at all doubting to rely upon
it, _vid._ that the _Apertures_ must be _thus_ and _thus_ in _great_
Glasses, because he had found them _so_ or _so_ in some _small_ ones.

For his Proposal of amendments of some inconveniencies in this way, I
return him my thanks; but as to his first I believe, that the matter may be
conteined as wel in the _Concave_ Tool, as on the _convex_ Glass. And as to
that of 2 _Poppet-heads_ I do not well understand it, if differing from
mine; and the keeping of the Tool upon the Glass with a spring or weight,
must quickly spoyl the whole; since, if either of the _Mandrils_ will
easily yield backwards, the _regularity_ of _all_ will be spoiled: and as
to the wrigling and playing of the _Mandril_, I do not at all apprehend it.
{69}

His _Theory_ of _Apertures_, though he seems to think it very authentick,
yet to me it seems not so cleer. For, the same Glass will endure greater or
lesser _Apertures_, according to the lesser or greater Light of the
_Object_: If it be for the looking on the _Sun_ or _Venus_, or for seeing
the _Diameters_ of the _Fix'd Stars_, then smaller _Apertures_ do better;
if for the _Moon_ in the _daylight_, or on _Saturn_, or _Jupiter_, or
_Mars_, then the largest. Thus I have often made use of a 12 foot-Glass to
look on _