it's manifest that the Sun's Light is an heterogeneous Mixture of Rays,
some of which are constantly more refrangible than others, as was
proposed.
_PROP._ III. THEOR. III.
_The Sun's Light consists of Rays differing in Reflexibility, and those
Rays are more reflexible than others which are more refrangible._
This is manifest by the ninth and tenth Experiments: For in the ninth
Experiment, by turning the Prism about its Axis, until the Rays within
it which in going out into the Air were refracted by its Base, became so
oblique to that Base, as to begin to be totally reflected thereby; those
Rays became first of all totally reflected, which before at equal
Incidences with the rest had suffered the greatest Refraction. And the
same thing happens in the Reflexion made by the common Base of the two
Prisms in the tenth Experiment.
_PROP._ IV. PROB. I.
_To separate from one another the heterogeneous Rays of compound Light._
[Illustration: FIG. 23.]
The heterogeneous Rays are in some measure separated from one another by
the Refraction of the Prism in the third Experiment, and in the fifth
Experiment, by taking away the Penumbra from the rectilinear sides of
the coloured Image, that Separation in those very rectilinear sides or
straight edges of the Image becomes perfect. But in all places between
those rectilinear edges, those innumerable Circles there described,
which are severally illuminated by homogeneal Rays, by interfering with
one another, and being every where commix'd, do render the Light
sufficiently compound. But if these Circles, whilst their Centers keep
their Distances and Positions, could be made less in Diameter, their
interfering one with another, and by Consequence the Mixture of the
heterogeneous Rays would be proportionally diminish'd. In the twenty
third Figure let AG, BH, CJ, DK, EL, FM be the Circles which so many
sorts of Rays flowing from the same disque of the Sun, do in the third
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