se red at _t_, yellow
at _s_, green at _r_, blue at _q_, and violet at _p_; you may with an
Iron Wire, or any such like slender opake Body, whose breadth is about
the tenth part of an Inch, by intercepting the Rays at _k_, _l_, _m_,
_n_ or _o_, take away any one of the Colours at _t_, _s_, _r_, _q_ or
_p_, whilst the other Colours remain upon the Paper as before; or with
an Obstacle something bigger you may take away any two, or three, or
four Colours together, the rest remaining: So that any one of the
Colours as well as violet may become outmost in the Confine of the
Shadow towards _p_, and any one of them as well as red may become
outmost in the Confine of the Shadow towards _t_, and any one of them
may also border upon the Shadow made within the Colours by the Obstacle
R intercepting some intermediate part of the Light; and, lastly, any one
of them by being left alone, may border upon the Shadow on either hand.
All the Colours have themselves indifferently to any Confines of Shadow,
and therefore the differences of these Colours from one another, do not
arise from the different Confines of Shadow, whereby Light is variously
modified, as has hitherto been the Opinion of Philosophers. In trying
these things 'tis to be observed, that by how much the holes F and H are
narrower, and the Intervals between them and the Prism greater, and the
Chamber darker, by so much the better doth the Experiment succeed;
provided the Light be not so far diminished, but that the Colours at
_pt_ be sufficiently visible. To procure a Prism of solid Glass large
enough for this Experiment will be difficult, and therefore a prismatick
Vessel must be made of polish'd Glass Plates cemented together, and
filled with salt Water or clear Oil.

[Illustration: FIG. 1.]

_Exper._ 2. The Sun's Light let into a dark Chamber through the round
hole F, [in _Fig._ 2.] half an Inch wide, passed first through the Prism
ABC placed at the hole, and then through a Lens PT something more than
four Inches broad, and about eight Feet distant from the Prism, and
thence converged to O the Focus of the Lens distant from it about three
Feet, and there fell upon a white Paper DE. If that Paper was
perpendicular to that Light incident upon it, as 'tis represented in the
posture DE, all the Colours upon it at O appeared white. But if the
Paper being turned about an Axis parallel to the Prism, became very much
inclined to the Light, as 'tis represented in the Positions _