A remarkable kind of _floating brick_, used by the ancients, has been made the subject of investigation in modern times, with a view to the suggestion of improvements in the making of bricks for particular purposes. Pliny states that at various places in Spain, in Asia Minor, and elsewhere, bricks were made which, besides possessing considerable strength and a remarkable power of enduring heat, were yet of such small specific gravity, that they floated on the surface of water. Like many of the arts of the ancients, the method of making these bricks, as well as the material of which they were made, were forgotten for many ages. About the year 1790, however, an Italian, named Fabbroni, turned his attention to the subject, and after various experiments on minerals of small specific gravity, he came to the conclusion that these bricks must have been composed of a substance called “mountain-meal;” or, at least, he found that he could make of this substance bricks which appeared to agree in every respect with those described by the ancients. This mountain-meal is an earth composed of flint, magnesia, clay, lime, iron, and water, in certain definite proportions. The bricks which Fabbroni formed of this material had the property of floating in water; they could not be fused by any ordinary degree of heat; and so low was their conducting power, that while one end of the brick was red-hot, the other could be held in the hand without the smallest inconvenience. It has been supposed that a peculiar kind of earth, found in some parts of Cornwall is the same as that with which Fabbroni experimented on in Italy, and that both are analogous to the kind of which the ancients made their floating bricks. Proceeding on this supposition, it has been proposed to make such bricks for the construction of _floating houses_ upon ornamental waters. At present such structures can be made only of timber; and, however the owner may decorate them, they have always a flimsy and unsubstantial appearance, and they are soon injured by the weather. If, however, a platform of good timber were employed as the base of the whole, and the weight so contrived as to keep this platform constantly under water, it would last a long time. The upper part of the structure formed of the floating bricks, might have all the appearance, and, indeed, all the stability of a brick house upon land; for this description of brick resists the influence of the atmosphere as well as the action of fire; and although it is not absolutely so strong as the heavy brick in common use, it is far more so in proportion to its specific gravity. We do not know whether these conjectures have yet been put to the test.