(5<S) 
the Reader 3 that he hath found, that the Apertures^ which Opticl ^ 
Glafjes can bear with diftin£tnefs , are in about a fubduplicate 
proportion to their Lengths ; whereof he tells us he intends to give 
the reafon and demonftration in his Viopticps, which he is now 
writing, and intends to finifh, as foon as his Health will permit. 
In the meantime, he prefents the Reader with a Table of fuch 
Apertures ; which is here exhibited to the Conlideration of the 
Ingenious, there being of this french Book but one Copy, that 
is known, in England. 
A T ABLE of the Apertures of ObjeB-Glaffes. 
The Points put to feme of thefe Numbers denote PraUions* 
Lengths 
of 
For e> 
■cellent 
For 
good 
For ordinary 
Lengths of 
For excellent 
For 
gosd 
ordinary 
Glafses. 
ones . 
ones. 
ones. 
Glafses. 
ones. 
1 ones. 
ones. 
Feet, Inches. 
Inch. 
Lines. 
Inch. 
Lines. 
Inch. 
Lines \ 
Feet, Inches. 
Inch, 
Lines. 
Inch. 
Ltnes. 
Inch. 
Lines. 
4 
4- 
4 
3 
25 
3 
4 
2 
IO 
2 
4. 
6 
7- 
I 
4 
3° 
3 
8 
3 
2 
2 
7 
9 
7 
6 
7 
37 
4 
0 
3 
4* 
2 
IO 
I 
o 
8, 
7 
d 
40 
4 • 
3 
3 ■ 
7 
3 
• 
I 
d 
9 
8. 
7 
47 
4 
6 
3 
IO 
3 
2. 
2 
o 
i i 
10 
8 
50 
4 
9 
4 
0 
3 
4- 
2 
6 
I 
Q 
II 
9 
55 
> 
0 
4 
3 
3 
d. 
3 
o 
I 
I 
r 
Q 
IO 
do 
7 
2 
4 
d 
3 
8. 
3 
6 
I 
, ' 
2 
i 
I 
ii 
d7 
7 
4 
4 
8 
3 
10 
4 
o 
1 
4 
I 
2 
I 
o 
70 
7 
7 
4 
10 
4 
• 
4 
6 
I 
7 
r 
3 
I 
• 
75 
7 
9 
5 
0 
4 
2. 
7 
o 
t 
6 
i 
4 
£ 
1 • 
80 
7 
x 1 
5 
2 
4 
7 
6 
I 
7* 
I 
7 
I 
2 
90 
d 
4 
7 
d 
4 
7. 
7 
I 
9 
1 
6 
I 
3 
ICO 
d 
8 
7 
9 
4 
10 
8 
( 
10 
I 
8 
I 
4 
1 20 
7 
7 
d 
7 
5 
3 
9 
I 
1 1. 
I 
9 
I 
5 
1 5*0 
8 
c 
7 
0 
5 
11 
IO 
2 
I 
I 
10 
I 
6 
200 
9 
6 
8 
0 
d 
9 
I 2 
2 
4 
2 
o 
I 
8 
250 
1 © 
6 
9 
2 
7 
8. 
r 4 
2 
d 
4 * 
2 
I 
9- 
300 
11 
6 
10 
O 
8 
5 
1 d 
2 
8 
2 
4 
I 
II. 
350 
12 
6. 
I© 
9 
9 
0 
1 8 
2 
I 0 
2 
6 
2 
i 
400 
x 3 
4 
11 
d 
9 
8 
120 
3 
0 
2 
7 
2 
2, 
1 
1 
