1. 0n the principles of water organs, I cannot omit to touch as briefly and precisely as possible, and commit them to writing. A base is made of framed wood and a bronze vessel is placed upon it. On the base, uprights are set up right and left, with rungs like a ladder. Between these, bronze cylinders are enclosed. Pistons which move up and down are accurately wrought on a lathe, and with iron piston rods fixed in the middle. These rods are joined by pins to the levers, and the pistons are covered with leather and wool. Further, on the top surface of the cylinders are openings about three fingers (2 1/2 inches) broad. Adjoining the openings and placed on pins are bronze dolphins with valves hanging by chains from their mouths and secured below the openings of the cylinders.

    2. Within the chest where the water is stored there is an air-vessel, like a funnel inverted; beneath this, small blocks about three inches high are placed, and they keep even the lowest space between the lips of the air-vessel and the bottom of the chest. On the neck of the air-vessel a small box is constructed which carries the top of the instrument, which is called in Greek the canon musicus. Along this there are four channels, if the instrument is tetrachord; six if it is hexachord; eight if it is octochord.

    3. In the several channels are single stopcocks fitted with an iron handle. When the iron handle is turned, it opens an aperture from the chest into the channels. The canon has openings from the channels; and the openings are placed along the canon corresponding to the openings in the top board which, in Greek, is called the pinax Between the pinax above and the canon below, bars are fixed with openings corresponding to those of the canon and the pinax The bars are well oiled so that they easily pass backwards and forwards, closing and opening the holes in the channels. The bars are called plinthides.

    4. To these plinthides, iron springs are attached which connect with the keys of the organ, so that to touch the keys forthwith moves the plinthides. On the pinax, rings are fixed round the holes which allow the passage of the air from the channels. And these rings receive the feet of the organ pipes. Now from the cylinders, there run lengths of piping to the neck of the air-vessel and communicate with the openings in the chest. Over these openings there are placed valves wrought on the lathe. These valves, when the chest is supplied with air, close the openings and do not allow the air to escape.

    5. Thus when the levers are raised, the piston rods draw down the pistons towards the bottom of the cylinder, and the dolphins working on pivots, releasing the valves in the cylinders, fill the cavity of the cylinders with air. Thereupon the piston rods raise the pistons within the cylinders with rapid and violent strokes and close the openings above, with the valves; the air in the cylinders is forced by the pumping into the pipes. Through these it rushes into the air-vessel and by the neck into the chest. By a stronger motion of the levers, the air is further compressed, flows in by the openings of the stopcocks and fills the channels with air.

    6. Therefore when the keys are touched by the hands, they forthwith move the sliding bars backwards and forwards, closing some holes and opening others. By the art of music, the notes of the organ are struck with manifold and varied modulation

    I have striven to the best of my ability to describe clearly in writing a complicated machine. The task is not an easy one, nor accessible to the general understanding, except for those who have experience in matters of this kind. Yet if anyone grasps them imperfectly from my writings, a knowledge of the instrument will disclose the ingenuity and precision of its design.

translated from Latin by Frank Granger
Vitruvius, On Architecture, London, Boston 1962