hydraulis - greek water organ - reconstruction by Rob van Haarlem
An animation of the first organ in history In 275 BC a Greek engineer called Ktesibios invents in Alexandria a machine for playing bronze flutes. This machine fits a series of “automata”, often complicated mechanisms, able to do things independently like opening doors, imitating bird sounds and making fountains work. Alexandria at that time as well as its famous library attracted many scientists, describing and reporting their inventions. This included technical engineers like Ktesibios and the later Heron of Alexandria. The invention of Ktesibios was a complicated machine, consisting of three mechanical parts. First a hand-operated pump, build as a bronze cylinder with an inlet valve, exhaust valve and a piston. The second part was a bronze vessel partially filled with water and capable to contain compressed air. The third part was an airtight metal box, distributing pressurized air to the flutes by means of air ducts closed and opened by sliders. Every slider was perforated with holes according to the position of the flutes above it. The instrument sounded by moving the sliders. The invention was called  “organon hydraulikon”  or short  “hydraulis”,  also known as water organ”. popular and expensive The hydraulis became very popular in its time, despite being expensive and as a consequence reserved for the rich and mighty. The powerful sound made it particularly suitable for public places like amphitheaters en the halls of palaces. The high costs for possessing a  hydraulis were not only caused by the production, but even so by the necessity of continuous maintenance. For exemple, it is not wise to keep motionless water for a longer period of time in a bronze vessel, especially not in the warm climate of the Mediterranean. The pistons were covered with textiles for an airtight seal, probably in combination with oil for both air tightness and friction. The many bronze sliders had to be oiled in order to move easily and smoothly. Maintenance of a hydraulis required the attention and care of specialized people, as it still is with pipe organs. Of course the instruments also had to be tuned. Vitruvius mentions organs with two, four, six and eight rows of pipes. Assuming the hydraulis was made with pipes en keyboard according to the  Greek scale, the  “Systema Teleion Ametabolon”,  it means a number of  21 x 8 = 168 pipes. Besides the bronze Hydraulis a smaller and wooden organ later existed, having its air supplied by two folding bellows, called the “Pneumatikon”. the end and the beginning The production of the hydraulis ends abruptly in the 9th century by a ban on production and use of the instrument by the Byzantine emperor. Considering the fact that the hydraulis was constructed only and exclusivly in the imperial workshops in Constantinopel, this meant ultimately the end off all instruments outside Byzantium. Since that time the use of the hydraulis was only permitted to the imperial court in Constantinopel. The quantity of precious bronze metal made the melting down of the silenced instruments a sensible solution and an explanation for the complete disappearing of the greek hydraulis. The wooden pneumatikon was not banned and arrived at the Karolingian court at Aachen in the 8th and 9th century as a diplomatic offering of the Byzantine emperor. This gift had to be a pneumatikon because giving a hydraulis would have been a recognition of the king of the Franks being emperor of the West-Roman Empire. Doing something like that was impossible for the ruler of the Eastern Roman Empire, considering himself the legitimate ruler of the undivided Roman Empire. King Pepin the Short in 757 as well as Charlemagne in 812 did receive little organs with bellows from the envoys from Byzantium. The third instrument however,  intended for Louis the Pious, would not only finish the Byzantine monopoly on organ building, but above all start the evolution of West European pipe organs, ultimately leading to new keyboard instruments such as the clavichord, the harpsichord en the pianoforte,  followed in the 20th century by new electrical en digital keyboard instruments. The technical operation of the hydraulis is complex and not easy to explain with  only words. And some reconstructions of the hydraulis on the internet are not entirely right: especially the inlet and exhaust valves are sometimes missing or the way the air is going is unclear. The following animation is the result of a number of drawings made for personal use to clarify the operation of the organ. The animation first shows the operation within the cylinder. The air is sucked inside through the inlet valve and compressed by the upcoming piston. The compressed air opens the exhaust valve and flows into the vessel. The exhaust valve closes and the downward motion of the piston creates a lower air pressure within the cylinder forcing the inlet valve to open. The figures shown are mainly symbolic. Only the standard air pressure of 76 cmHg is correct. The remaining figures just indicate “more” or “less”. The pressure for instance of the compressed air within the cylinder (105) has to be higher than the hypothetical “100” in the exhaust tube in order to open the exhaust valve. Before playing the organ there has to be a buildup of water pressure by the cylinders. As soon as the air starts escaping to the water surface - called “the boiling” of the organ -  the optimal wind pressure is reached. As long as the organ is played the pumping of air by the cylinders has to continue because the air pressure for the pipes will drop as soon as the water level goes down and the organ will immediately be out of tune. So organ playing without someone to manage the cylinders is impossible.   In the animations the wooden supports for the cylinders are left out. The second animation shows the continuous operation of the Ktesibios cylinder with and without figures. In time this article will be supplemented with new information and additions to the existing text. Topics will be the playing mechanism, the shape of the bronze vessel and the air pressure. Version 01                                                                                                                                                  page top