dependence is of the same kind with that which the Colours of thin
Plates have on the distance of the Surfaces of those Plates, because the
bigness of the Rings, and their Proportion to one another, and the
variation of their bigness arising from the variation of the thickness
of the Glass, and the Orders of their Colours, is such as ought to
result from the Propositions in the end of the third Part of this Book,
derived from the Ph nomena of the Colours of thin Plates set down in the
first Part.
There are yet other Ph nomena of these Rings of Colours, but such as
follow from the same Propositions, and therefore confirm both the Truth
of those Propositions, and the Analogy between these Rings and the Rings
of Colours made by very thin Plates. I shall subjoin some of them.
_Obs._ 10. When the beam of the Sun's Light was reflected back from the
Speculum not directly to the hole in the Window, but to a place a little
distant from it, the common center of that Spot, and of all the Rings of
Colours fell in the middle way between the beam of the incident Light,
and the beam of the reflected Light, and by consequence in the center of
the spherical concavity of the Speculum, whenever the Chart on which the
Rings of Colours fell was placed at that center. And as the beam of
reflected Light by inclining the Speculum receded more and more from the
beam of incident Light and from the common center of the colour'd Rings
between them, those Rings grew bigger and bigger, and so also did the
white round Spot, and new Rings of Colours emerged successively out of
their common center, and the white Spot became a white Ring
encompassing them; and the incident and reflected beams of Light always
fell upon the opposite parts of this white Ring, illuminating its
Perimeter like two mock Suns in the opposite parts of an Iris. So then
the Diameter of this Ring, measured from the middle of its Light on one
side to the middle of its Light on the other side, was always equal to
the distance between the middle of the incident beam of Light, and the
middle of the reflected beam measured at the Chart on which the Rings
appeared: And the Rays which form'd this Ring were reflected by the
Speculum in Angles equal to their Angles of Incidence, and by
consequence to their Angles of Refraction at their entrance into the
Glass, but yet their Angles of Reflexion were not in the same Planes
with their Angles of Incidence.
_Obs._ 11. The Colours of the new Rings were in a contrary order to
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