d truly wrought
of that _Figure_, to make a _Telescope_, that with a single _Eye-glass_
should draw 300, 400, yea 1000 feet, _without_ at all _altering the
Convexity_: Monsieur _Auzout_ returns this consideration, and offer upon
it, which follows:

To perform (_saith he_) with a _lesser Object-glass_ the effect of a _great
Telescope_, we must find out a way to make such an _Object-glass_ to
receive as many Rayes as one will, without their being sensibly distant
from one another; to the end, that by applying to it a _stronger
Eye-glass_, there may be still Beams enough to see the Object, and to
obliterate the small specks and imperfections of the _Eye-glass_. And if
Mr. _Hook_ hath this Invention, I esteem it one of the greatest, that can
be found in the matter of _Telescopes_. If he please to impart it to us, we
shall be obliged to him; and {124} I wish, I had a secret in _Opticks_ to
encourage him to that communication. If I did believe, that this would be
esteemed one, To measure with a _great Telescope_ the _distance of Objects_
upon the _Earth_; which I have found long since, and proposed to some by
way of Paradox; _Locorum distantias ex unica statione, absque ullo
Instrumento Mathematico, metiri_; I doe here promise to discover it to him,
with the necessary Tables, as soon as He shall have imparted his to me;
which I will use, as he shall order me. For, although the _Practise_ doe
not altogether answer the _Theory_ of my Invention, because that the length
of the _Telescopes_ admits of some Latitude; yet one comes near enough, and
perhaps as Just, as by most of the wayes, ordinarily used with Instruments.
That, which I am proposing, I doubt not but M. _Hook_ will soon understand,
and see the determination of all Cases possible. I shall only say, that if
we look upon the sole _Theory_, we make use of an ordinary _Telescope_,
whereof the _Eye-glass_ is to be _Convexe_: for, by putting the Glasses at
a little greater distance, than they are, proportionably to the distance
for which it is to serve, and by adding to it a _new Eye-glass_, the Object
will be seen distinct, though obscure; and if the _Eye-glass_ be _Convexe_,
the Object will appear erect. They may be done two manner of ways; either
by leaving the _Telescope_ in its ordinary situation, the _Object-glass_
before the _Eye-glass_; or by inverting it, and putting _this_ before
_that_. But if any will make use of two _Object-glasses_, whereof the
_Focus's_ are kno