_Example 3._—The spiral thread of a piece of twisted silk or wool held perpendicularly before the eye, appears in the part opposite to the light, of a much more decided colour than on the rest of the surface. _Example 4._—The folds of bright draperies present the same modification to an eye properly placed; the effect is particularly remarkable in yellow silk stuffs, and in sky-blue; for we can easily understand that it is less marked when the stuffs are less bright and of dark colours. _Example 5._—There are some stuffs which appear to be of two tones of the same scale of colour, and sometimes also of two tones of two contiguous scales, although the weft and the warp of these stuffs are of the same tone and the same colour. The cause of this appearance is very simple; the threads which, parallel to each other, form the designs, are in a different direction to the threads which constitute the ground of the stuff. Hence, whatever may be the position of the spectator with regard to the stuff, the threads of the design will always reflect coloured and white light in a different proportion to that reflected by the threads of the ground, and, according to the position of a spectator, the design will appear to be lighter or darker than the ground. _Third modification._—The colour complementary to that of a coloured object developed in one of its parts, in consequence of simultaneous contrast. 285. A natural consequence of the law of simultaneous contrast in general, and of the effect of a colour upon grey and black in particular, is, that since the same object presents some parts more or less dark, contiguous to some parts where we see the colour peculiar to the object, the first parts will appear tinted with the complementary to this colour. But to observe this effect, it is necessary that the grey part should reflect to the eye white light, and little or none of the coloured light which the object naturally reflects. _Fourth modification_, in a single coloured stuff. 286. For example, if the eye is directed towards a window which admits daylight, and a person clothed in a new blue coat, dyed with indigo or Prussian blue, be at the window, the eye will see one part of the coat will appear different from the other part, because the nap of the cloth is disposed in a contrary direction; one being of a fine blue, while the other is of an orange-grey, by the effect of contrast of the blue part with a part that reflects very little white light to the eye, without, or almost without, blue light. 287. But as the pile of the nap loses its regular position by wear, the cloth becoming dull and soiled, the coloured light is reflected irregularly from all points; and the effect is either absolutely destroyed or much weakened. If the garment be of a deep green, the grey part will appear reddish; if it be of a violet, maroon, or claret, the grey part will appear yellow.