reason of their smalness I could not number. But in other Positions of
the Prisms, at which the Rings appeared of many Colours, I could not
distinguish above eight or nine of them, and the Exterior of those were
very confused and dilute.
In these two Observations to see the Rings distinct, and without any
other Colour than Black and white, I found it necessary to hold my Eye
at a good distance from them. For by approaching nearer, although in the
same inclination of my Eye to the Plane of the Rings, there emerged a
bluish Colour out of the white, which by dilating it self more and more
into the black, render'd the Circles less distinct, and left the white a
little tinged with red and yellow. I found also by looking through a
slit or oblong hole, which was narrower than the pupil of my Eye, and
held close to it parallel to the Prisms, I could see the Circles much
distincter and visible to a far greater number than otherwise.
_Obs._ 4. To observe more nicely the order of the Colours which arose
out of the white Circles as the Rays became less and less inclined to
the Plate of Air; I took two Object-glasses, the one a Plano-convex for
a fourteen Foot Telescope, and the other a large double Convex for one
of about fifty Foot; and upon this, laying the other with its plane side
downwards, I pressed them slowly together, to make the Colours
successively emerge in the middle of the Circles, and then slowly lifted
the upper Glass from the lower to make them successively vanish again in
the same place. The Colour, which by pressing the Glasses together,
emerged last in the middle of the other Colours, would upon its first
appearance look like a Circle of a Colour almost uniform from the
circumference to the center and by compressing the Glasses still more,
grow continually broader until a new Colour emerged in its center, and
thereby it became a Ring encompassing that new Colour. And by
compressing the Glasses still more, the diameter of this Ring would
increase, and the breadth of its Orbit or Perimeter decrease until
another new Colour emerged in the center of the last: And so on until a
third, a fourth, a fifth, and other following new Colours successively
emerged there, and became Rings encompassing the innermost Colour, the
last of which was the black Spot. And, on the contrary, by lifting up
the upper Glass from the lower, the diameter of the Rings would
decrease, and the breadth of their Orbit increase, until their Colours
reached successively to the center; and then they being of a
considerable breadth, I could more easily discern and distinguish their
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