11. Painting in _distemper_ is used for the execution of works on a large scale, such as stage scenery, and the walls of apartments. The coloring substances are mixed with water, rendered tenacious by size or solutions of glue, or by skimmed milk, increased in tenacity by a small quantity of thyme. Linseed or poppy oil often serves as a vehicle for the colors, in this kind of painting. 12. Paintings in _fresco_ are executed on walls of plaster. The coloring matter mixed with water, being applied to the plaster while the latter is in a fresh state, sinks in, and incorporates itself with it, so as to become very durable. During the execution of the work, the plaster is applied to the wall in successive portions, no more being added at a time, than can be conveniently painted before it becomes dry. Works of this kind must be executed with great rapidity; and, on this account, patterns, called _cartoons_, are previously drawn on large paper, to guide the artist in his operations. 13. _Oil painting_ derives its name from the mixture of the colors in oil. The oils used for this purpose are extracted from vegetables; and, on account of the rapidity with which they dry, are denominated drying oils. For most purposes, this mode of painting is decidedly superior to all others. It admits of a higher finish, as it allows the artist to retouch his works with greater precision. The colors also blend together more agreeably, and produce a more delicate effect. Oil paintings are executed on canvas, wood, or copper. 14. Paintings are imitated with surprising elegance, by cementing together colored pieces of glass and marble, as well as those of wood. Representations by these means, are called _Mosaics_, or _Mosaic paintings_. The cause of their having received this appellation cannot be ascertained. Some, without much reason, attribute the origin and name of this branch of the art to Moses. Others suppose that works of this kind have been thus denominated, because they were first employed in grottoes dedicated to the _Muses_. 15. Drawings and paintings are divided into classes, according to the nature of the objects represented, the principal of which are _historical_, _architectural_, _landscape_, _marine_, _portrait_, _still life_, _grotesque_, _botanical_, and _animal_. The subordinate divisions of these branches are very numerous. 16. The propensity to imitation, so deeply rooted in the human mind, is the foundation of the arts of design; and there can scarcely be indicated a lengthened period in the history of man, in which it was entirely inactive. It may have first been accidentally exhibited in tracing the form of some object in the sand; or resemblances in sticks and stones, may have originally suggested the idea of imitations by means of lines and colors.