hich either the
Phaenomenon might be render'd more conspicuous, or a Novice might more
easily try them, or by which I did try them only. The same Thing, I have
often done in the following Experiments: Concerning all which, this one
Admonition may suffice. Now from these Experiments it follows not, that
all the Light of the blue is more refrangible than all the Light of the
red: For both Lights are mixed of Rays differently refrangible, so that
in the red there are some Rays not less refrangible than those of the
blue, and in the blue there are some Rays not more refrangible than
those of the red: But these Rays, in proportion to the whole Light, are
but few, and serve to diminish the Event of the Experiment, but are not
able to destroy it. For, if the red and blue Colours were more dilute
and weak, the distance of the Images would be less than an Inch and a
half; and if they were more intense and full, that distance would be
greater, as will appear hereafter. These Experiments may suffice for the
Colours of Natural Bodies. For in the Colours made by the Refraction of
Prisms, this Proposition will appear by the Experiments which are now to
follow in the next Proposition.

_PROP._ II. THEOR. II.

_The Light of the Sun consists of Rays differently Refrangible._

The PROOF by Experiments.

[Illustration: FIG. 12.]

[Illustration: FIG. 13.]

_Exper._ 3.

In a very dark Chamber, at a round Hole, about one third Part of an Inch
broad, made in the Shut of a Window, I placed a Glass Prism, whereby the
Beam of the Sun's Light, which came in at that Hole, might be refracted
upwards toward the opposite Wall of the Chamber, and there form a
colour'd Image of the Sun. The Axis of the Prism (that is, the Line
passing through the middle of the Prism from one end of it to the other
end parallel to the edge of the Refracting Angle) was in this and the
following Experiments perpendicular to the incident Rays. About this
Axis I turned the Prism slowly, and saw the refracted Light on the Wall,
or coloured Image of the Sun, first to descend, and then to ascend.
Between the Descent and Ascent, when the Image seemed Stationary, I
stopp'd the Prism, and fix'd it in that Posture, that it should be moved
no more. For in that Posture the Refractions of the Light at the two
Sides of the refracting Angle, that is, at the Entrance of the Rays into
the Prism, and at their going out of it, were equal to one another.[C]
So also in other Exper