s to obscure one or two of the innermost
Rings. And therefore I usually placed the Speculum at about six Feet
from the Window; so that its Focus might there fall in with the center
of its concavity at the Rings upon the Chart. And this Posture is always
to be understood in the following Observations where no other is
express'd.

_Obs._ 2. The Colours of these Rain-bows succeeded one another from the
center outwards, in the same form and order with those which were made
in the ninth Observation of the first Part of this Book by Light not
reflected, but transmitted through the two Object-glasses. For, first,
there was in their common center a white round Spot of faint Light,
something broader than the reflected beam of Light, which beam sometimes
fell upon the middle of the Spot, and sometimes by a little inclination
of the Speculum receded from the middle, and left the Spot white to the
center.

This white Spot was immediately encompassed with a dark grey or russet,
and that dark grey with the Colours of the first Iris; which Colours on
the inside next the dark grey were a little violet and indigo, and next
to that a blue, which on the outside grew pale, and then succeeded a
little greenish yellow, and after that a brighter yellow, and then on
the outward edge of the Iris a red which on the outside inclined to
purple.

This Iris was immediately encompassed with a second, whose Colours were
in order from the inside outwards, purple, blue, green, yellow, light
red, a red mix'd with purple.

Then immediately follow'd the Colours of the third Iris, which were in
order outwards a green inclining to purple, a good green, and a red more
bright than that of the former Iris.

The fourth and fifth Iris seem'd of a bluish green within, and red
without, but so faintly that it was difficult to discern the Colours.

_Obs._ 3. Measuring the Diameters of these Rings upon the Chart as
accurately as I could, I found them also in the same proportion to one
another with the Rings made by Light transmitted through the two
Object-glasses. For the Diameters of the four first of the bright Rings
measured between the brightest parts of their Orbits, at the distance of
six Feet from the Speculum were 1-11/16, 2-3/8, 2-11/12, 3-3/8 Inches,
whose Squares are in arithmetical progression of the numbers 1, 2, 3, 4.
If the white circular Spot in the middle be reckon'd amongst the Rings,
and its central Light, where it seems to be most luminous,