256. There are two systems of Painting—the one consists in representing as accurately as possible upon a flat surface an object in relief in such a way that the image makes an impression upon the eye of the spectator similar to that which the object itself would produce. This is termed the _Art of Chiaro-’scuro_. 257. There is a means of imitating coloured objects much simpler in its facility of execution than the preceding. It consists in tracing the outline of the different parts of the model, and in colouring them uniformly with their peculiar colours. There is no relief, no projection; it is the plane image of the object, since all the parts receive a uniform tint: this system of imitating is _Painting in Flat Tints_. PAINTING ON THE SYSTEM OF CHIARO-’SCURO. 258. Are the modifications perceived in a single coloured object, for example, in a blue or red stuff, &c., indeterminable, when these draperies are seen as draperies of a vestment or furniture, with more or less distinct folds, or are they determinable, in given circumstances? This is a question of which I am about to attempt a solution. 259. Firstly, let us distinguish three circumstances in which modifications of colours may be observed:— 1. Modifications produced by coloured lights falling upon the model. 2. Modifications produced by two different lights—as, for example, the light of the sun and diffused daylight—each illuminating different parts of the same object. 3. Modifications produced by diffused daylight. 260. We will suppose that in the two first cases the lighted surfaces are plane, and that all their superficial parts are homogeneous, and in the same conditions, except that of light. In the third case, we shall consider the position of the spectator viewing an object lighted by diffused daylight, the surface of which is not so disposed as to act equally in all its parts upon the light which it reflects to the eye of the spectator. 261. Modifications produced by coloured lights. Red rays falling on Black make it appear Purple-black. ” White ” Red. ” Red ” Redder. ” Orange ” Redder. ” Yellow ” Orange. ” Deep Green ” Red-black. ” Light Green ” Reddish-grey. ” Light Blue ” Violet. ” Violet ” Purple. 262. Modifications produced by Orange light.