288. The complementary is only developed upon cloths of dark and sombre colours; thus red, scarlet, orange, yellow, and light blue garments do not exhibit it, because they have always too much of the essential colour which is reflected. The modification occurs only when one of the parts is more strongly illuminated than the other by diffused light (279). 289. There is also one circumstance where the fourth modification will appear evident; it is when we look at a series of light tones—blues, rose, &c. (belonging to the same scale)—of a skein of silk or wool, placed upon an easel, that one-half of the same skein presents to the eye the threads disposed in a contrary direction to those of the other half. The half of the skein which does not reflect coloured light to the eye, appears tinted with the complementary of the other half which does reflect it. 290. Fourth modification in a stuff presenting a dark and a light tone belonging to the same scale. If we place in juxtaposition a dark tone and a light tone of the same scale, well assorted, the light tone will appear of the colour complementary to the scale to which it belongs. This modification is too important to allow me to pass it over hastily. 291. When we look for several seconds on a fabric dyed with a coloured ground, and on which therefore patterns intended to be white, but which, owing to the imperfection of the process employed, have received a light tone of the colour of the ground, the patterns will appear of the colour complementary to the latter. Thus, upon a ground of yellow-chromate of lead, they will appear violet; upon a ground of orange-chrome, they will appear blue; upon a green ground, rose, &c. To dispel the illusion, and to recognise the true tint of the pattern, it is only necessary to cover the ground with a white paper so perforated as to leave visible only the pattern coloured like the ground. The influence of a dark tone upon a feeble tone is such, that not only is the latter neutralized, but the place it occupies upon the cloth appears also tinted with its complementary colour. 292. From the preceding observations it follows that there may be a printed cotton, the design of which, although coloured, will appear to most eyes white, and not of the complementary of the ground. For those eyes which see it thus, the perception of the phenomenon of contrast will correct the imperfection of the art of the calico-printer. 293. In the Lectures upon Contrast, which I delivered in 1836, at the Gobelins, I remarked, that in applying paper (cut for the purpose) upon the lights of a blue drapery of the Virgin in a tapestry representing the Holy Family, after Raphael, they appeared of a light blue, although, when they were seen surrounded with darker tones, they appeared of an orange tint.