n this case the thickness
of the Water, at which they arrived when viewed most obliquely, was to
that thickness which exhibited them by perpendicular Rays, something
less than as 8 to 5. By the best of my Observations it was between 15
and 15-1/2 to 10; an increase about 24 times less than in the other
case.

Sometimes the Bubble would become of an uniform thickness all over,
except at the top of it near the black Spot, as I knew, because it would
exhibit the same appearance of Colours in all Positions of the Eye. And
then the Colours which were seen at its apparent circumference by the
obliquest Rays, would be different from those that were seen in other
places, by Rays less oblique to it. And divers Spectators might see the
same part of it of differing Colours, by viewing it at very differing
Obliquities. Now observing how much the Colours at the same places of
the Bubble, or at divers places of equal thickness, were varied by the
several Obliquities of the Rays; by the assistance of the 4th, 14th,
16th and 18th Observations, as they are hereafter explain'd, I collect
the thickness of the Water requisite to exhibit any one and the same
Colour, at several Obliquities, to be very nearly in the Proportion
expressed in this Table.

-----------------+------------------+----------------
Incidence on | Refraction into | Thickness of
the Water. | the Water. | the Water.
-----------------+------------------+----------------
Deg. Min. | Deg. Min. |
| |
00 00 | 00 00 | 10
| |
15 00 | 11 11 | 10-1/4
| |
30 00 | 22 1 | 10-4/5
| |
45 00 | 32 2 | 11-4/5
| |
60 00 | 40 30 | 13
| |
75 00 | 46 25 | 14-1/2
| |
90 00 | 48 35 | 15-1/5
-----------------+------------------+----------------

In the two first Columns are express'd the Obliquities of the Rays to
the Superficies of the Water, that is, their Angles of Incidence and
Refraction. Where I suppose, that the Sines which measure them are in
round Numbers, as 3 to 4, though probably the Dissolution of Soap in the
Water, may a little alte