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

"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 in a great degree accomplished by Dr. Johannes Müller, in his memoir "Über die Phantastischen Gesichtserscheinungen." Coblentz, 1826. Similar phenomena have been also investigated with great labour and success by Purkinje. For a collection of extraordinary facts of the kind recorded by these writers, the reader may consult Scott's Letters on Demonology and Witchcraft.[1] The instances adduced by Müller and others are, however, intended to prove the inherent capacity of the organ of vision to produce light and colours. In some maladies of the eye, the patient, it seems, suffers the constant presence of light without external light. The exciting principle in this case is thus proved to be within, and the conclusion of the physiologists is that external light is only one of the causes which produce luminous and coloured impressions. That this view was anticipated by Newton may be gathered from the concluding "query" in the third book of his Optics.

[1] See also a curious passage on the beatific vision of the monks of
Mount Athos, in Gibbon, chap. 63.

NOTE K.--Par. 140.

"Catoptrical colours. The colours included under this head are principally those of fibres and grooved surfaces; they can be produced artificially by cutting parallel grooves on a surface of metal from 2000 to 10,000 in the inch. See 'Brewster's Optics,' p. 120. The colours called by Goethe _paroptical_, correspond with those produced by the diffraction or inflection of light in the received theory.--See Brewster, p. 95. The phenomena included under the title 'Epoptical Colours,' are generally known as the colours of thin plates. They vary with the thickness of the film, and the colour seen by reflection always differs from that seen by transmission. The laws of these phenomena have been thoroughly investigated. See Nobili, and Brewster, p. 100."--S. F.

The colours produced by the transmission of polarised light through chrystalised mediums, were described by Goethe, in his mode, subsequently to the publication of his general theory, under the name of Entoptic Colours. See note to Par. 485.

NOTE L.--Par. 150.

We have in this and the next paragraph the outline of Goethe's system. The examples that follow seem to establish the doctrine here laid down, but there are many cases which it appears cannot be explained on such principles: hence, philosophers generally prefer the theory of absorption, according to which it appears that certain mediums "have the property of absorbing some of the component rays of white light, while they allow the passage of others."[1]