of the sun produces a light figure, which we call a white cross; the oblique reflection gives a dark figure, which we call a black cross. If we make the experiment all round the sky, we shall find that a fluctuation takes place in the intermediate regions."
We pass over a variety of observations on the modes of exhibiting this phenomenon, the natural transparent substances which exhibit it best, and the detail of the colours seen within136 them, and proceed to an instance where the author was enabled to distinguish the "direct" from the "oblique" reflection by means of the entoptic apparatus, in a painter's study.
40.
"An excellent artist, unfortunately too soon taken from us, Ferdinand Jagemann, who, with other qualifications, had a fine eye for light and shade, colour and keeping, had built himself a painting-room for large as well as small works. The single high window was to the north, facing the most open sky, and it was thought that all necessary requisites had been sufficiently attended to.