Hydraulic ORGAN, denotes a musical machine that plays by means of water instead of wind. Of these there are several in Italy in the grottoes of vineyards. Ctesibes of Alexandria, who lived in the time of Ptolemy Euergetes, is said to have first invented organs that played by compressing the air with water, as is still practised. Archimedes and Vitruvius have left us descriptions of the hydraulic organ.