8 + 1/12 + 1/12 + 2/27 to 1/27 + 1/18, that is, as 8/27 to 5/54, or
as 16 to 5. And therefore these differences will be 3/8A and 5/16A. Add
the first to 9A and subduct the last from 8A, and you will have the
Diameters of the Circles made by the least and most refrangible Rays
75/8A and ((61-1/2)/8)A. These diameters are therefore to one another as
75 to 61-1/2 or 50 to 41, and their Squares as 2500 to 1681, that is, as
3 to 2 very nearly. Which proportion differs not much from the
proportion of the Diameters of the Circles made by the outmost red and
outmost violet, in the 13th Observation of the first part of this Book.

_Obs._ 6. Placing my Eye where these Rings appear'd plainest, I saw the
Speculum tinged all over with Waves of Colours, (red, yellow, green,
blue;) like those which in the Observations of the first part of this
Book appeared between the Object-glasses, and upon Bubbles of Water, but
much larger. And after the manner of those, they were of various
magnitudes in various Positions of the Eye, swelling and shrinking as I
moved my Eye this way and that way. They were formed like Arcs of
concentrick Circles, as those were; and when my Eye was over against the
center of the concavity of the Speculum, (that is, 5 Feet and 10 Inches
distant from the Speculum,) their common center was in a right Line with
that center of concavity, and with the hole in the Window. But in other
postures of my Eye their center had other positions. They appear'd by
the Light of the Clouds propagated to the Speculum through the hole in
the Window; and when the Sun shone through that hole upon the Speculum,
his Light upon it was of the Colour of the Ring whereon it fell, but by
its splendor obscured the Rings made by the Light of the Clouds, unless
when the Speculum was removed to a great distance from the Window, so
that his Light upon it might be broad and faint. By varying the position
of my Eye, and moving it nearer to or farther from the direct beam of
the Sun's Light, the Colour of the Sun's reflected Light constantly
varied upon the Speculum, as it did upon my Eye, the same Colour always
appearing to a Bystander upon my Eye which to me appear'd upon the
Speculum. And thence I knew that the Rings of Colours upon the Chart
were made by these reflected Colours, propagated thither from the
Speculum in several Angles, and that their production depended not upon
the termination of Light and Shadow.

_Obs._ 7. By the Analogy of all th