(Κτησίβιος), celebrated for his mechanical inventions, was born at Alexandria, and lived probably about B. C. 250, in the reigns of Ptolemy Philadelphus and Euergetes, though Athenaeus (iv. p. 174) says, that he flourished in the time of the second Euergetes. His father was a barber, but his own taste led him to devote himself to mechanics. He is said to have invented a clepsydra or water-clock, a hydraulic organ (ὕδραυλις) and other machines, and to have been the first to discover the elastic force of air and apply it as a moving power. Vitruvius (lib. vii. praef.) mentions him as an author, but none of his works remain. He was the teacher, and has been supposed to have been the father, of Hero Alexandrinus, whose treatise called Βελοποιϊκά has also sometimes been attributed to him. (Vitr. 9.9, 10.12; Plin. Nat. 7.37; Athen. 4.174, xi. p. 497; Philo Byzant. (apud Vet. Math. pp. 56, 67, 72; Fabric. Bibl. Graec. vol. ii. p. 591.)