the white cross appears on the side of the sun also.135
"We thus conclude that the direct reflection 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.
"But after our friend had worked for some time, it appeared to him, in painting portraits, that the faces he copied were not equally well lighted at all hours of the day, and yet his sitters always occupied the same place, and the serenity of the atmosphere was unaltered.
"The variations of the favourable and unfavourable light had their periods during the day. Early in the morning the