One can conceive, says a learned antiquary, how a careful beating together of these materials had the effect of creating so binding a cement, since we know from our own practice, that puddling earth, fine gravel, and water together, form a lining for a canal, that becomes impervious to water when once settled, and it was probably from this puddling, and not from any secret as to the materials of the mortar, not now known, that this ancient cement owed its cohesive strength. When this square was set, the sides of the caisson were taken off, and another layer of bricks was then laid, and so Another caisson, and so on. The bricks used in this construction were one foot nine inches

PRELIMINARY ESSAY. 33

long, one foot broad, and one and a half inches thick ; the cement of one of the aqueducts at the bottom is six inches thick, and one and a half thick on the sides about two feet ;

above the floor of the canal were fixed, on each side, cramps of three lines square, at two and a half feet distance from each other. The utmost breadth of the piers of the aqueduct of Chaponost, which carried a canal of three feet broad, by six feet high, is not more than six feet, while the breadth of the aqueduct which passed over the river Baunan, arid which has no canal, is 24 feet broad, consisting of two piers, each five feet, supporting an arch 14 feet in diameter. M. Delorme,in his account, (Seance de 1'Academie, 1759,) traced three of the