Since an analysis like the present requires to be confirmed by ocular demonstration, we beg every reader to make himself acquainted with the experiments hitherto adduced, not in a superficial manner, but fairly and thoroughly. We have not placed arbitrary signs before him instead of the appearances themselves; no modes of expression are here proposed for his adoption which may be repeated for ever without the exercise of thought and without leading any one to think; but we invite him to examine intelligible appearances, which must be present to the eye and mind, in order to enable him clearly to trace these appearances to their origin, and to explain them to himself and to others.
[1] The date of the publication, 1810, is sometimes to be remembered.—T.
[2] The forms in fig. 2, [plate 1], when seen through a prism, are again intended to exemplify this. In the plates to the original work curvilinear figures are added, but the circles, fig. 1, in the same plate, may answer the same end.—T.
[3] The author has before observed that colour is a degree of darkness, and he here means that increase of darkness, produced by transparent mediums, is, to a certain extent, increase of colour.—T.
[XVI.]
DECREASE OF THE APPEARANCE OF COLOUR.
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.