Theory of Colours — trans. Charles Lock Eastlake (1840)

"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 within[4] 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 light appeared most unpleasantly grey and unsatisfactory; it became better, till at last, about an hour before noon, the objects had acquired a totally different appearance. Everything presented itself to the eye of the artist in its greatest perfection, as he would most wish to transfer it to canvas. In the afternoon this beautiful appearance vanished--the light became worse, even in the brightest day, without any change having taken place in the atmosphere.

"As soon as I heard of this circumstance, I at once connected it in my own mind with the phenomena which I had been so long observing, and hastened to prove, by a physical experiment, what a clear-sighted artist had discovered entirely of himself, to his own surprise and astonishment.

"I had the second[5] entoptic apparatus brought to the spot, and the effect on this was what might be conjectured from the above statement. At mid-day, when the artist saw his model best lighted, the north, direct reflection gave the white cross; in the morning and evening, on the other hand, when the unfavourable oblique light was so unpleasant to him, the cube showed the black cross; in the intermediate hours the state of transition was apparent."

The author proceeds to recall to his memory instances where works of art had struck him by the beauty of their appearance owing to the light coming from the quarter opposite the sun, in "direct reflection," and adds, "Since these decided effects are thus traceable to their cause, the friends of art, in looking at and exhibiting pictures, may enhance the enjoyment to themselves and others by attending to a fortunate reflection."

[1] The numbers, as usual, indicate the corresponding paragraphs in the original.

[2] In the historical part, Goethe has to speak of so many followers of Newton who begin their statements with "Si per foramen exiguum," that the term is a sort of by-word with him.

[3] At mid-day on the 24th of June the author observed the white cross reflected from every part of the horizon. At a certain distance from the sun, corresponding, he supposes, with the extent of halos, the black cross appeared.

[4] Whence the term _entoptic_.

[5] Before described: the author describes several others more or less complicated, and suggests a portable one. "Such plates, which need only be an inch and a quarter square, placed on each other to form a cube, might be set in a brass case, open above and below. At one end of this case a black mirror with a hinge, acting like a cover, might be fastened. We recommend this simple apparatus, with which the principal and original experiment may be readily made. With this we could, in the longest days, better define the circle round the sun where the black cross appears," &c.

NOTE T.--Par. 496.

"Since Goethe wrote, all the earths have been decomposed, and have been shown to be metallic bases united with oxygen; but this does not invalidate his statement."--S. F.

NOTE U.--Par. 502.