3|3 6.|
60 |5 2|4 6|3 8.|
-------------|-------------|-------------|-------------|
65 |5 4|4 8|3 10|
70 |5 7|4 10|4 .|
75 |5 9|5 0|4 2.|
80 |5 11|5 2|4 5|
-------------|-------------|-------------|-------------|
90 |6 4|5 6|4 7.|
100 |6 8|5 9|4 10|
120 |7 5|6 5|5 3|
150 |8 0|7 0|5 11|
-------------|-------------|-------------|-------------|
200 |9 6|8 0|6 9|
250 |10 6|9 2|7 8.|
300 |11 6|10 0|8 5|
350 |12 *6.|10 9|9 0|
400 |13 4|11 6|9 8|
-------------+-------------+-------------+-------------+

{57}

* * * * *

_Considerations of Monsieur _Auzout_ upon Mr. _Hook_'s New Instrument for
Grinding of _Optick-Glasses_._

In the above-mentioned _French_ Tract, there are, besides several other
particulars, to be represented in due place, contained some
_Considerations_ of Monsieur _Auzout_ upon Mr. _Hook_'s New _Engine_ for
grinding _Optick-Glasses_. Where he premises in _General_ his thoughts
touching the working of _Great_ Optick-Glasses, and that by the help of a
_Turn lathe_; affirming first of all, that not only the _Engin_ is to be
considered for giveing the _Figure_, but the _Matter_ also, which ought to
be brought to greater perfection, than it hath been hitherto. For, he finds
it not so easie (as least, _where he is_) to procure _Great_ pieces of
Glass without _Veins_, and other faults, nor to get such, as are thick
enough without _Blebbs_; which, if they be not, they will yield to the
pressure and weight, either when they are fitted to the _Cement_, or
wrought.

Secondly, He finds it difficult to work these _Great_ Glasses of the _same_
thickness, which yet is very necessary, because, that the least difference
in _Figures_ so little _convex_, can put the _Center_ out of the _Midle_, 2
or 3 _Inches_; and if they be wrought in _Moulds_, the length of time,
which is required to wear and to smooth th