116. I should observe that all these colours, at least to my eyes, did not undergo equally intense or equally continuous modifications. For instance, the modification produced by the successive view of yellow and violet, or of violet and yellow, is stronger and more durable than that produced by the successive view of blue and orange, and still more than that of orange and blue. The modification produced by the successive view of red and green, of green and red, is but slight, and not enduring. I may also add that the depth of tone exercises some influence on the modification; for, if after looking at orange, we look at dark-blue, the latter will appear greenish rather than violet, a result contrary to that afforded by a light blue. 117. I have thought it the more necessary to mention under a special name the phenomenon which I call _mixed contrast_, as it explains certain facts remarked by dealers in coloured fabrics, as well as the inconvenience felt by painters, who, wishing to produce an exact imitation of their models, look at them so long as to be unable to perceive their tones and modifications. I will mention two facts which have been communicated to me by manufacturers, referring the reader to Part II. for the application of the study of mixed contrast to painting. 118. First Fact. When a purchaser has looked a long time at a yellow cloth, and he is then shown an orange, orange-red, or scarlet one, he finds it dull, and judges it to be a dark or crimson-red; because the retina affected by the yellow has a tendency to see violet; and hence all the yellow of the orange colour disappears, and the eye sees it as a red, or a red inclining to violet. 119. Second Fact. If there be presented to a purchaser, one after another, fourteen pieces of a red fabric, he judges the six or seven last pieces to be less beautiful than the first, although they may be all identical. What is the reason of this false judgment? It is, that the eyes which have seen six or eight red pieces in succession, are in the same condition as if they had looked steadily for the same length of time at a single red stuff,—having a tendency to see the complementary of red, that is green. This tendency necessarily enfeebles the brilliancy of the red of the last pieces. The dealer, therefore, that he may not be a sufferer from the fatigued eyes of his customer, after showing him a few red pieces, should present some green ones, to restore the eyes to their normal state. If the view of the green were sufficiently prolonged to pass the normal state, the eyes would acquire a tendency to see red, and then the pieces seen last would appear more beautiful than the rest. PART THE SECOND. ON THE APPLICATION OF THE LAW OF SIMULTANEOUS CONTRAST OF COLOURS. INTRODUCTION.