Thickness of the Air at the darkest Part of the first dark Ring made by
perpendicular Rays; and half this Thickness multiplied by the
Progression, 1, 3, 5, 7, 9, 11, &c. gives the Thicknesses of the Air at
the most luminous Parts of all the brightest Rings, _viz._ 1/178000,
3/178000, 5/178000, 7/178000, &c. their arithmetical Means 2/178000,
4/178000, 6/178000, &c. being its Thicknesses at the darkest Parts of
all the dark ones.
_Obs._ 7. The Rings were least, when my Eye was placed perpendicularly
over the Glasses in the Axis of the Rings: And when I view'd them
obliquely they became bigger, continually swelling as I removed my Eye
farther from the Axis. And partly by measuring the Diameter of the same
Circle at several Obliquities of my Eye, partly by other Means, as also
by making use of the two Prisms for very great Obliquities, I found its
Diameter, and consequently the Thickness of the Air at its Perimeter in
all those Obliquities to be very nearly in the Proportions express'd in
this Table.
-------------------+--------------------+----------+----------
Angle of Incidence |Angle of Refraction |Diameter |Thickness
on | into | of the | of the
the Air. | the Air. | Ring. | Air.
-------------------+--------------------+----------+----------
Deg. Min. | | |
| | |
00 00 | 00 00 | 10 | 10
| | |
06 26 | 10 00 | 10-1/13 | 10-2/13
| | |
12 45 | 20 00 | 10-1/3 | 10-2/3
| | |
18 49 | 30 00 | 10-3/4 | 11-1/2
| | |
24 30 | 40 00 | 11-2/5 | 13
| | |
29 37 | 50 00 | 12-1/2 | 15-1/2
| | |
33 58 | 60 00 | 14 | 20
| | |
35 47 | 65 00 | 15-1/4 | 23-1/4
113