to
measure, but that of the first seemed to be about five or six Degrees,
and that of the third about twelve. The like Crowns appear sometimes
about the Moon; for in the beginning of the Year 1664, _Febr._ 19th at
Night, I saw two such Crowns about her. The Diameter of the first or
innermost was about three Degrees, and that of the second about five
Degrees and an half. Next about the Moon was a Circle of white, and next
about that the inner Crown, which was of a bluish green within next the
white, and of a yellow and red without, and next about these Colours
were blue and green on the inside of the outward Crown, and red on the
outside of it. At the same time there appear'd a Halo about 22 Degrees
35' distant from the center of the Moon. It was elliptical, and its long
Diameter was perpendicular to the Horizon, verging below farthest from
the Moon. I am told that the Moon has sometimes three or more
concentrick Crowns of Colours encompassing one another next about her
Body. The more equal the globules of Water or Ice are to one another,
the more Crowns of Colours will appear, and the Colours will be the more
lively. The Halo at the distance of 22-1/2 Degrees from the Moon is of
another sort. By its being oval and remoter from the Moon below than
above, I conclude, that it was made by Refraction in some sort of Hail
or Snow floating in the Air in an horizontal posture, the refracting
Angle being about 58 or 60 Degrees.

THE

THIRD BOOK

OF

OPTICKS

_PART I._

_Observations concerning the Inflexions of the Rays of Light, and the
Colours made thereby._

Grimaldo has inform'd us, that if a beam of the Sun's Light be let into
a dark Room through a very small hole, the Shadows of things in this
Light will be larger than they ought to be if the Rays went on by the
Bodies in straight Lines, and that these Shadows have three parallel
Fringes, Bands or Ranks of colour'd Light adjacent to them. But if the
Hole be enlarged the Fringes grow broad and run into one another, so
that they cannot be distinguish'd. These broad Shadows and Fringes have
been reckon'd by some to proceed from the ordinary refraction of the
Air, but without due examination of the Matter. For the circumstances of
the Phaenomenon, so far as I have observed them, are as follows.

_Obs._ 1. I made in a piece of Lead a small Hole with a Pin, whose
breadth was the 42d part of an Inch. For 21 of those Pins laid together
took up the breadth of ha