The colours of the rainbow are not produced by the sun, for they
occur in many ways without the sunshine; as may be seen by holding a
glass of water up to the eye; when, in the glass--where there are
those minute bubbles always seen in coarse glass--each bubble, even
though the sun does not fall on it, will produce on one side all the
colours of the rainbow; as you may see by placing the glass between
the day light and your eye in such a way as that it is close to the
eye, while on one side the glass admits the [diffused] light of the
atmosphere, and on the other side the shadow of the wall on one side
of the window; either left or right, it matters not which. Then, by
turning the glass round you will see these colours all round the
bubbles in the glass &c. And the rest shall be said in its place.