10. In many places, the clay is mixed or prepared for the moulder by driving round upon it a yoke of oxen, or by means of a simple machine, consisting of a beam, into which has been driven a great number of spokes. One end of this beam is confined in a central position, while the other is moved round in a sweep by animal power. 11. Machines have also been invented by the aid of which the clay may be both mixed and moulded; but these have been very little used. A machine, however, is often employed in pressing bricks which have been formed in the usual manner. The pressing is done after the bricks have become partially dry. Such bricks are employed in facing the walls of the better kinds of structures. 12. _Tiles._--Tiles are plates used for covering roofs. They resemble bricks in their composition and mode of manufacture, and are shaped in such a manner that when placed upon a building, the edge of one tile receives that next to it, so that water cannot percolate between them. Tiles, both of burnt clay and marble, were used by the ancients; and the former continue to be employed in various parts of Europe. Flat tiles are used for floors in many countries, and especially in Italy. THE BRICKLAYER. 1. The particular business of the bricklayer is to lay bricks in mortar or some other cement, so as to form one solid body; but he frequently constructs the foundations of buildings in rough stones, and, in some cities, he sets hewn stone in the superstructure. In the country, plastering is likewise connected with this business. 2. Bricklaying consists in placing one brick upon another in mortar, chiefly in the construction of walls, chimneys, and ovens. In connecting these materials, especially in walls, two methods are employed, one of which is called the _English bond_, and the other, the _Flemish bond_. In the former method, the bricks are most commonly of one quality, and are laid crosswise and lengthwise in alternate rows. The bricks which are laid across the wall are called _headers_, and those which are laid in the other direction are called _stretchers_. The brick-work of the Romans was of this kind, and so are the partition-walls of many modern brick edifices. 3. The bricks employed in the walls constructed according to the Flemish method, are of two, and frequently of three, qualities. Those placed in the front, or on the external surface, are manufactured with greater care, and, in some cases, are formed in a larger mould. A wall put up on this principle may be said to consist of two thin walls composed of stretchers, with occasional headers, to unite them together. The space between them, when the wall is thick, is filled in with the inferior bricks.