8I cannot here omit a brief explanation, as clearly as I can give it, of the principles on which hydraulic organs are constructed. A base of framed wood-work is prepared, on which is placed a brazen box. On the base, right and left, uprights are fixed, with cross pieces like those of a ladder, to keep them together; between which are enclosed brass barrels with moveable bottoms, perfectly round, having iron rods fixed in their centres, and covered with leather and woollen, attached by pins to the levers. There are also, on the upper surface, holes about three inches diameter, in which, near the pin-joint, are brazen dolphins with chains hanging from their mouths, which sustain the valves that descend below the holes of the barrels.
8With regard to water organs, however, I shall not fail with all possible brevity and precision to touch upon their principles, and to give a sufficient description of them. A wooden base is constructed, and on it is set an altar-shaped box made of bronze. Uprights, fastened together like ladders, are set up on the base, to the right and to the left (of the altar). They hold the bronze pump-cylinders, the moveable bottoms of which, carefully turned on a lathe, have iron elbows fastened to their centres and jointed to levers, and are wrapped in fleeces of wool. In the tops of the cylinders are openings, each about three digits in diameter. Close to these openings are bronze dolphins, mounted on joints and holding chains in their mouths, from which hang cymbal-shaped valves, let down under the openings in the cylinders.