pass through a small passage, _obliquely_ out of a more difficult, into a
more easie _medium_.

Let us suppose therefore ABC in the second Figure to represent a large
_Chimical Glass-body_ about two foot long, filled with very fair Water as
high as AB, and inclin'd in a convenient posture with B towards the Sun:
Let us further suppose the top of it to be cover'd with an _opacous_ body,
all but the hole ab, through which the Sun-beams are suffer'd to pass into
the Water, and are thereby refracted to cdef, against which part, if a
Paper be expanded on the outside, there will appear all the colours of the
Rain-bow, that is, there will be generated the two principal colours,
_Scarlet_ and _Blue_, and all the _intermediate_ ones which arise from the
composition and dilutings of these two, that is, cd shall exhibit a
_Scarlet_, which toward d is diluted into a _Yellow_; this is the
refraction of the Ray, ik, which comes from the underside of the Sun; and
the Ray ef shall appear of a deep _Blue_, which is gradually towards e
diluted into a pale _Watchet-blue_. Between d and e the two _diluted_
colours. _Blue_ and _Yellow_ are mixt and compounded into a _Green_; and
this I imagine to be the reason why _Green_ is so acceptable a colour to
the eye, and that either of the two extremes are, if intense, rather a
little offensive, namely, the being plac'd in the middle between the two
extremes, and compounded out of both those, _diluted_ also, or somewhat
qualifi'd, for the _composition_, arising from the mixture of the two
extremes _undiluted_, makes a _Purple_, which though it be a lovely colour,
and pretty acceptable to the eye, yet is it nothing comparable to the
ravishing pleasure with which a curious and well tempered _Green_ affects
the eye. If removing the Paper, the eye be plac'd against cd, it will
perceive the lower side of the Sun (or a Candle at night which is much
better, because it offends not the eye, and is more easily manageable) to
be of a deep _Red_, and if against ef it will perceive the upper part of