Page:Philosophical Transactions - Volume 001.djvu/60

This page has been validated.


the Reader, that he hath found, that the Apertures, which Optick Glasses can bear with distinctness, are in about a subduplicate proportion to their Lengths; whereof he tells us he intends to give the reason and demonstration in his Diopticks, which he is now writing, and intends to finish, as soon as his Health will permit. In the mean time, he presents the Reader with a Table of such Apertures; which is here exhibited to the Consideration of the ingenious, there being of this French Book but one Copy, that is known, in England.


A TABLE of the Apertures of Object-Glasses.
The points put to some of these Number denote Fractions.
Lengths of
Glasses.
For excellent
ones.
For good
ones.
For ordinary
ones.
Lengths of
Glasses.
For excellent
ones.
For good
ones.
For ordinary
ones.
Feet, Inches. Inch. Lines. Inch. Lines. Inch. Lines. Feet, Inches. Inch. Lines. Inch. Lines. Inch. Lines.
4 4. 4 3 25 3 4 2 10 2 4.
6 5. 5 4 30 3 8 3 2 2 7.
9 7 6. 5 35 4 0 3 4 2 10
1 0 8. 7 6 40 4 3 3 7 3 .
1 6 9 8. 7 45 4 6 3 10 3 2
2 0 11 10 8 50 4 9 4 0 3 4.
2 6 1 0 11 9 55 5 0 4 3 3 6.
3 0 1 1 1 0 10 60 5 2 4 6 3 8.
3 6 1 2 1 1 11 65 5 4 4 8 3 10
4 0 1 4 1 2 1 0 70 5 7 4 10 4 .
4 6 1 5 1 3 1 . 75 5 9 5 0 4 2.
5 0 1 6 1 4 1 1. 80 5 11 5 2 4 5
6 1 7. 1 5 1 2 90 6 4 5 6 4 7.
7 1 9 1 6 1 3 100 6 8 5 9 4 10
8 1 10 1 8 1 4 120 7 5 6 5 5 3
9 1 11 1 9 1 5 150 8 0 7 0 5 11
10 2 1 1 10 1 6 200 9 6 8 0 6 9
12 2 4 2 0 1 8 250 10 6 9 2 7 8.
14 2 6 2 2 1 9. 300 11 6 10 0 8 5
16 2 8 2 4 1 11. 350 12 6. 10 9 9 0
18 2 10 2 6 2 1 400 13 4 11 6 9 8
20 3 0 2 7 2 2.