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 alter its refractive Virtue. In the third Column,
the Thickness of the Bubble, at which any one Colour is exhibited in
those several Obliquities, is express'd in Parts, of which ten
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