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4Each sort has half bricks made to suit it; so that when a wall is executed, the course on one of the faces of the wall shews sides of whole bricks, the other face of half bricks; and being worked to the line on each face, the bricks on each bed bond alternately over the course below. Besides the pleasant varied appearance which this method gives, it affords additional strength, by the middle of a brick, on a rising course, falling over the vertical joints of the course thereunder. The bricks of Calentum in Spain, Marseilles in France, and Pitane in Asia, are, when wrought and dried, specifically lighter than water, and hence swim thereon. This must arise from the porosity of the earth whereof they are made; the air contained in the pores, to which the water cannot penetrate, giving them a buoyant property. Earth of this sort being, therefore, of such a light and thin quality, and impervious to water, be a lump thereof of whatever size, it swims naturally like pumice-stone. Bricks of this sort are of great use for building purposes; for they are neither heavy nor liable to be injured by the rain.
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