5. _Perspective_ has been defined the art of delineating the outlines of objects on any given surface, as they would appear to the eye, if that surface were transparent, and the objects themselves were seen through it, from a fixed position. For example; when we look through a window at a mass of buildings, and observe that part of the glass to which each object, line, or point appears opposite, we find that their apparent position is very different from their real. A delineation of these objects on the glass, as they appear, would be termed a representation in perspective. 6. Correct perspective is the foundation of scientific painting; and, next in importance to this, is a proper distribution of light and shade. This branch of the art is called _chiaro obscuro_, or, when abridged, _chiaro-scuro_. The term is Italian in its origin, and its literal meaning is _clear_ and _obscure_. To the skilful management of light and shade, we are indebted for the strength and liveliness of pictures, and their relief, or the elevation which certain parts appear to assume above the plane upon which the objects are represented. 7. By the aid of perspective and chiaro-scuro, very good representations in one color are attained. Drawings in India-ink and crayons, as well as pictures taken from engraved plates and wood-cuts, are specimens of such productions. But a nearer approach to the appearance of nature, is made by the employment of colors analogous to those which are found to exist in the objects to be represented. 8. To produce various hues in painting, the artist employs coloring substances, which, either alone or by mixture, are analogous to them all; and, in their use, he is careful to apply them in such a manner, that the true colors remain distinct from the lights and shades necessary to produce the objects in relief. Artificial colors are divided into _warm_ and _cold_. The former are those in which red and yellow predominate; the latter are blue, gray, and others allied to them. 9. Before coloring substances can be applied in painting, they must be reduced to extreme fineness, and be mixed with some tenacious fluid, to cause them to adhere to the surface on which they are to be spread. The fluid employed for this purpose, and the mode of applying the colors, have given rise to the different kinds of painting, of which the following are the principal: _crayon_, _water-color_, _distemper_, _fresco_, and _oil-painting_. 10. The most simple mode of applying the colors is by means of crayons. They are made of black lead, a species of chalk, or of a mixture of coloring matter with gum, size, or clay. For painting in _water-colors_, the substances employed in communicating the tints are combined with gum, and formed into cakes or lozenges. When about to be used, they are dissolved in water, on glass or a glazed surface. The application in painting, is made by means of a camel's-hair pencil.