the yellow Circle in each Ring will be more dilated than the red; and
the Excess of its Dilatation will be so much the greater, by how much
the greater is the obliquity of the Rays, until at last it become of
equal extent with the red of the same Ring. And for the same reason the
green, blue and violet, will be also so much dilated by the still
greater obliquity of their Rays, as to become all very nearly of equal
extent with the red, that is, equally distant from the center of the
Rings. And then all the Colours of the same Ring must be co-incident,
and by their mixture exhibit a white Ring. And these white Rings must
have black and dark Rings between them, because they do not spread and
interfere with one another, as before. And for that reason also they
must become distincter, and visible to far greater numbers. But yet the
violet being obliquest will be something more dilated, in proportion to
its extent, than the other Colours, and so very apt to appear at the
exterior Verges of the white.
Afterwards, by a greater obliquity of the Rays, the violet and blue
become more sensibly dilated than the red and yellow, and so being
farther removed from the center of the Rings, the Colours must emerge
out of the white in an order contrary to that which they had before; the
violet and blue at the exterior Limbs of each Ring, and the red and
yellow at the interior. And the violet, by reason of the greatest
obliquity of its Rays, being in proportion most of all expanded, will
soonest appear at the exterior Limb of each white Ring, and become more
conspicuous than the rest. And the several Series of Colours belonging
to the several Rings, will, by their unfolding and spreading, begin
again to interfere, and thereby render the Rings less distinct, and not
visible to so great numbers.
If instead of the Prisms the Object-glasses be made use of, the Rings
which they exhibit become not white and distinct by the obliquity of the
Eye, by reason that the Rays in their passage through that Air which
intercedes the Glasses are very nearly parallel to those Lines in which
they were first incident on the Glasses, and consequently the Rays
endued with several Colours are not inclined one more than another to
that Air, as it happens in the Prisms.
There is yet another circumstance of these Experiments to be consider'd,
and that is why the black and white Rings which when view'd at a
distance appear distinct, should not only become confused by viewing
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