becomes comparatively neutralised in proportion to its distance from the edge of the darkest shade.
NOTE G.—Par. 98.
"The simplest case of the phenomenon, which Goethe calls a subjective halo, and one which at once explains its cause, is the following. Regard a red wafer on a sheet of white paper, keeping the eye stedfastly fixed on a point at its center. When the retina is fatigued, withdraw the head a little from the paper, and a green halo will appear to surround the wafer. By this slight increase of distance the image of the wafer itself on the retina becomes smaller, and the ocular spectrum which before coincided with the direct image, being now relatively larger, is seen as a surrounding ring."—S. F. Goethe mentions cases of this kind, but does not class them with subjective halos. See Par. 30.
NOTE H.—Par. 113.
"Cases of this kind are by no means uncommon. Several interesting ones are related in Sir John Herschell's article on Light in the Encyclopædia Metropolitana. Careful investigation has, however, shown that this defect of vision arises in most, if not in all cases, from an inability to perceive the red, not the blue rays. The terms are so confounded by the individuals thus affected, that the comparison of colours in their presence is the only criterion."—S. F.
NOTE I.—Par. 135.
The author more than once admits that this chapter on "Pathological Colours" is very incomplete, and expresses a wish (Par. 734) that some medical physiologists would investigate the subject further. This was afterwards