Water organ

The water organ or hydraulic organ (Greek: ὕδραυλις = ὕδωρ + αυλός / αυλη) (early types are sometimes called hydraulos, hydraulus or hydraula) is a type of pipe organ blown by air, where the power source pushing the air is derived by water from a natural source (e.g. by a waterfall) or by a manual pump. Consequently, the water organ lacks a bellows, blower, or compressor.

The hydraulic organ is often confused with the hydraulis. The hydraulis is the name of a Greek instrument created by Ctesibius of Alexandria. The hydraulis has a reservoir of air which is inserted into a cistern of water. The air is pushed into the reservoir with hand pumps, and exits the reservoir as pressurized air to blow through the pipes. The reservoir is open on the bottom, allowing water to maintain the pressure on the air as the air supply fluctuates from either the pumps pushing more air in, or the pipes letting air out.

On the water organ, since the 15th century, the water is also used as a source of power to drive a mechanism similar to that of the barrel organ, which has a pinned barrel that contains a specific song to be played. The hydraulis in ancient Greek is often imagined as an automatic organ, but there is no source evidence for it.

A hydraulis is an early type of pipe organ that operated by converting the dynamic energy of water (Ancient Greek: ὕδωρ, romanized: húdōr) into air pressure to drive the pipes (Ancient Greek: αὐλός, romanized: aulós). Hence its name hydraulis, literally "water (driven) pipe (instrument)". It is attributed to the Hellenistic scientist Ctesibius of Alexandria, an engineer of the 3rd century BCE. The hydraulis was the world's first keyboard instrument, and was the predecessor of the modern church organ. The ancient hydraulis was operated by pressing keys on the manual; the hydraulis' keys were well-balanced, and could be played with a light touch, as is clear from the Latin poem by Claudian (late 4th century), who uses that exact phrase to describe playing the keyboard:

Typically, water is supplied from some height above the instrument through a pipe, and air is introduced into the water stream by aspiration (using the Bernoulli effect) into the main pipe from a side-pipe holding its top above the water source. Both water and air arrive together in the camera aeolis (wind chamber). Here, water and air separate and the compressed air is driven into a wind-trunk on top of the camera aeolis, to blow the organ pipes. Two perforated ‘splash plates’ or ‘diaphragms’ prevent water spray from getting into the organ pipes.

The water, having been separated from the air, leaves the camera aeolis at the same rate as it enters. It then drives a water wheel, which in turn drives the musical cylinder and the movements attached. To start the organ, the tap above the entry pipe is turned on and, given a continuous flow of water, the organ plays until the tap is closed again.

Many water organs had simple water-pressure regulating devices. At the Palazzo del Quirinale, the water flows from a hilltop spring (once abundant, now only sufficient to play the organ for about 30 minutes at a time), coursing through the palace itself into a stabilizing ‘room’ some 18 metres (59 feet) above the camera aeolis in the organ grotto. This drop provides sufficient power to maintain air pressure to the restored six-stop instrument.

Among Renaissance writers on the water organ, Salomon de Caus is particularly informative. His book of 1615 includes a short treatise on making water organs, advice on tuning and registration, and many fine engravings showing the instruments, their mechanisms and scenes in which they were used. It also includes an example of suitable music for water organ, the madrigal Chi farà fed' al cielo by Alessandro Striggio, arranged by Peter Philips.