XVI.

DECREASE OF THE APPEARANCE OF COLOUR.

243.

We need only take the five conditions (210) under which the appearance of colour increases in the contrary order, to produce the contrary or decreasing state; it may be as well, however, briefly to describe and review the corresponding modifications which are presented to the eye.

244.

At the highest point of complete junction of the opposite edges, the colours appear as follows (216):--

Yellow-red. Blue. Green. Red. Blue-red. Yellow.

245.

Where the junction is less complete, the appearance is as follows (214, 215):--

Yellow-red. Blue. Yellow. Blue-red. Green. Red. Blue. Yellow-red. Blue-red. Yellow.

Here, therefore, the surface still appears completely coloured, but neither series is to be considered as an elementary series, always developing itself in the same manner and in the same degrees; on the contrary, they can and should be resolved into their elements; and, in doing this, we become better acquainted with their nature and character.

246.

These elements then are (199, 200, 201)--

Yellow-red. Blue. Yellow. Blue-red. White. Black. Blue. Yellow-red. Blue-red. Yellow.

Here the surface itself, the original object, which has been hitherto completely covered, and as it were lost, again appears in the centre of the colours, asserts its right, and enables us fully to recognise the secondary nature of the accessory images which exhibit themselves as "edges" and "borders."--Note N.

247.

We can make these edges and borders as narrow as we please; nay, we can still have refraction in reserve after having done away with all appearance of colour at the boundary of the object.

Having now sufficiently investigated the exhibition of colour in this phenomenon, we repeat that we cannot admit it to be an elementary phenomenon. On the contrary, we have traced it to an antecedent and a simpler one; we have derived it, in connexion with the theory of secondary images, from the primordial phenomenon of light and darkness, as affected or acted upon by semi-transparent mediums. Thus prepared, we proceed to describe the appearances which refraction produces on grey and coloured objects, and this will complete the section of subjective phenomena.