The water organ or hydraulic organ (early types are sometimes called hydraulis, hydraulos, hydraulus or hydraula) is a type of automatic 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. In addition to being the source of power to push air through the organ pipes, 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 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 above the camera aeolis in the organ grotto. This drop provides sufficient wind to power the restored six-stop instrument.
Among Renaissance writers on the water organ, Salomon de Caus was 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.
Water organs were described in the numerous writings of the famous Ctesibius (3rd century BC), Philo of Byzantium (3rd century BC) and Hero of Alexandria (c. 62 AD). Like the water clocks (clepsydra) of Plato's time, they were not regarded as playthings but might have had a particular significance in Greek philosophy, which made use of models and simulacra of this type. Hydraulically blown organ pipes were used to imitate birdsong, as well as to produce the awe-inspiring sound emitted by Memnon's statue at Thebes. For the latter, solar heat was used to syphon water from one closed tank into another, thereby producing compressed air for sounding the pipes.
Characteristics of the hydraulis have been inferred from mosaics, paintings, literary references, and partial remains. In 1931, the remains of a hydraulis were discovered in Hungary, with an inscription dating it to 228 AD. The leather and wood of the instrument had decomposed, but the surviving metal parts made it possible to reconstruct a working replica now in the Aquincum Museum in Budapest. The exact mechanism of wind production is debated, and almost nothing is known about the music played on the hydraulis, but the tone of the pipes can be studied.
Byzantine and Arab inventors developed, among other pieces, an automatic hydraulic organ (described by the Banu Musa in their 9th-century treatise Book of Ingenious Devices), a 'musical tree' at the palace of Khalif al-Muqtadir (ruled 908–32), and a long-distance hydraulic organ that could be heard from sixty miles away (described in the Arabic Sirr al-asrar and later translated into Latin by Roger Bacon). By the end of the 13th century hydraulic automata had reached Italy and the rest of Western Europe. During the Renaissance water organs again acquired magical and metaphysical connotations among followers of the hermetic and esoteric sciences. Organs were placed in gardens, grottoes and conservatories of royal palaces and the mansions of rich patricians to delight onlookers not only with music but also with displays of automata – dancing figurines, wing-flapping birds and hammering cyclopes – all operated by projections on the musical cylinder. Other types of water organ were played out of sight and were used to simulate musical instruments apparently being played by statues in mythological scenes such as 'Orpheus playing the viol', 'The contest between Apollo and Marsyas' and 'Apollo and the nine Muses'.
The most famous water organ of the 16th century was at the Villa d'Este in Tivoli. Built about 1569–72 by Lucha Clericho (Luc de Clerc; completed by Claude Venard), it stood about six metres high under an arch, and was fed by a magnificent waterfall; it was described by Mario Cartaro in 1575 as playing 'madrigals and many other things'. G. M. Zappi (Annalie memorie de Tivoli, 1576) wrote: 'When somebody gives the order to play, at first one hears trumpets which play a while and then there is a consonance …. Countless gentlemen could not believe that this organ played by itself, according to the registers, with water, but they rather thought that there was somebody inside'. Besides automatically playing at least three pieces of music, it is now known that the organ was also provided with a keyboard.
Other Italian gardens with water organs were at Pratolino, near Florence (c. 1575), Isola de Belvedere, Ferrara (before 1599), Palazzo del Quirinale, Rome (built by Luca Biagi in 1598, restored 1990), Villa Aldobrandini, Frascati (1620), one of the Royal Palaces at Naples (1746), Villa Doria Pamphili, Rome (1758–9). Of these only the one at the Palazzo del Quirinale has survived. Kircher's illustration in Musurgia universalis (1650), long thought to be a fanciful representation of a hypothetical possibility, has been found to be accurate in every detail when compared to the organ grotto at the Quirinale, except that it was reversed left to right. There are still traces of the instrument at the Villa d'Este but the mineral-rich water of the river which cascades through the organ grotto has caused accretions which have hidden most of the evidence from view.
In the early 17th century water organs were built in England; Cornelius Drebbel built one for King James I (see Harstoffer, 1651), and Salomon de Caus built several at Richmond while in the service of Prince Henry. There was one in Bagnigge Vale, London, the summer home of Nell Gwynn (1650–87), and Henry Winstanley (1644–1703), the designer of the Eddystone Lighthouse, is thought to have built one at his home in Saffron Walden, Essex. After the marriage of Princess Elizabeth to the Elector Palatine Prince Friedrich V, de Caus laid out for them the gardens at Heidelberg Castle which became famous for their beautiful and intricate waterworks. A water organ survives in the gardens at Heilbronn, Württemberg, and parts of one at the Wilhelmshöhe gardens in Kassel. The brothers Francini constructed waterworks and organs at Saint Germain-en-Laye and Versailles, which reached new heights of splendour and extravagance.
By the end of the 17th century, however, interest in water organs had waned. As their upkeep was costly they were left to decay and were soon forgotten; by 1920 not one survived (the so-called water organ at Hellbrunn Castle, Salzburg, is a pneumatic organ driven by hydraulically-operated bellows).
Their mechanism was subsequently misunderstood until the Dutch engineer Van Dijk pointed out in 1954 that air was supplied to the water organ by aspiration, which was the same method used in forges and smelting works in the 16th and 17th centuries. Aspiration is the process by which air is drawn into an opening into which water flows. For the water organ, a small pipe is arranged so that one end is open to the air and the other extends into a larger pipe that contains flowing water supplied by a stream, pond or stabilizing reservoir. The longer the vertical drop of the water, the more forceful the suction will be and the greater the volume of air sucked in.
Whereas the water organ uses water as a source of power to push air through organ pipes, the hydraulophone, a more recently invented instrument, uses water to make the sound, as well as for the user-interface. In the hydraulophone pipe organ, water typically flows into the organ pipes. The hydraulophone is played by blocking the flow of water jets with the fingers of the user. Typically the fingers are in direct physical contact with the same water that is used to make the sound, providing the user with a high degree of musical expression. In some hydraulophones the fluid user-interface (keyboard in which each key is a water jet) is separate from the sounding mechanism which is preferably also water-based.