Waves. The edges also of the Prism and Lens, so far as they may make any
irregular Refraction, must be covered with a black Paper glewed on. And
all the Light of the Sun's Beam let into the Chamber, which is useless
and unprofitable to the Experiment, ought to be intercepted with black
Paper, or other black Obstacles. For otherwise the useless Light being
reflected every way in the Chamber, will mix with the oblong Spectrum,
and help to disturb it. In trying these Things, so much diligence is not
altogether necessary, but it will promote the Success of the
Experiments, and by a very scrupulous Examiner of Things deserves to be
apply'd. It's difficult to get Glass Prisms fit for this Purpose, and
therefore I used sometimes prismatick Vessels made with pieces of broken
Looking-glasses, and filled with Rain Water. And to increase the
Refraction, I sometimes impregnated the Water strongly with _Saccharum
Saturni_.
_PROP._ V. THEOR. IV.
_Homogeneal Light is refracted regularly without any Dilatation
splitting or shattering of the Rays, and the confused Vision of Objects
seen through refracting Bodies by heterogeneal Light arises from the
different Refrangibility of several sorts of Rays._
The first Part of this Proposition has been already sufficiently proved
in the fifth Experiment, and will farther appear by the Experiments
which follow.
_Exper._ 12. In the middle of a black Paper I made a round Hole about a
fifth or sixth Part of an Inch in diameter. Upon this Paper I caused the
Spectrum of homogeneal Light described in the former Proposition, so to
fall, that some part of the Light might pass through the Hole of the
Paper. This transmitted part of the Light I refracted with a Prism
placed behind the Paper, and letting this refracted Light fall
perpendicularly upon a white Paper two or three Feet distant from the
Prism, I found that the Spectrum formed on the Paper by this Light was
not oblong, as when 'tis made (in the third Experiment) by refracting
the Sun's compound Light, but was (so far as I could judge by my Eye)
perfectly circular, the Length being no greater than the Breadth. Which
shews, that this Light is refracted regularly without any Dilatation of
the Rays.
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