st Proposition of the first Part of this Book, and will
more fully appear hereafter. And the contrary happens in the posture of
the Paper [Greek: de], the more refrangible Rays being then predominant
which always tinge Light with blues and violets.

_Exper._ 4. The Colours of Bubbles with which Children play are various,
and change their Situation variously, without any respect to any Confine
or Shadow. If such a Bubble be cover'd with a concave Glass, to keep it
from being agitated by any Wind or Motion of the Air, the Colours will
slowly and regularly change their situation, even whilst the Eye and the
Bubble, and all Bodies which emit any Light, or cast any Shadow, remain
unmoved. And therefore their Colours arise from some regular Cause which
depends not on any Confine of Shadow. What this Cause is will be shewed
in the next Book.

To these Experiments may be added the tenth Experiment of the first Part
of this first Book, where the Sun's Light in a dark Room being
trajected through the parallel Superficies of two Prisms tied together
in the form of a Parallelopipede, became totally of one uniform yellow
or red Colour, at its emerging out of the Prisms. Here, in the
production of these Colours, the Confine of Shadow can have nothing to
do. For the Light changes from white to yellow, orange and red
successively, without any alteration of the Confine of Shadow: And at
both edges of the emerging Light where the contrary Confines of Shadow
ought to produce different Effects, the Colour is one and the same,
whether it be white, yellow, orange or red: And in the middle of the
emerging Light, where there is no Confine of Shadow at all, the Colour
is the very same as at the edges, the whole Light at its very first
Emergence being of one uniform Colour, whether white, yellow, orange or
red, and going on thence perpetually without any change of Colour, such
as the Confine of Shadow is vulgarly supposed to work in refracted Light
after its Emergence. Neither can these Colours arise from any new
Modifications of the Light by Refractions, because they change
successively from white to yellow, orange and red, while the Refractions
remain the same, and also because the Refractions are made contrary ways
by parallel Superficies which destroy one another's Effects. They arise
not therefore from any Modifications of Light made by Refractions and
Shadows, but have some other Cause. What that Cause is we shewed above
in this tenth Exp