a Greek physicist and inventor who is regarded as the first great figure of the ancient engineering tradition of Alexandria, Egypt. Ctesibius discovered the elasticity of air and invented several devices using compressed air, including force pumps and an air-powered catapult. He also improved the water clock, in which water dripping at a constant rate raised a float with a pointer; and a hydraulus (water organ), in which the weight of water forced air through the organ pipes.