Reconstruction of a clepsydra water clock invented by Ctesibius of Alexandria c BC Ctesibius fl BC was an inventor and mathematician who initiated a tradition of great engineers in ancient Alexandria None of his writings have survived and his inventions are only known about from references to them made by others This clock worked by water dripping at a constant rate and raising a float with a pointer It was only superseded in terms of the accuracy of its timekeeping in the th century when Christiaan Huyghens showed how the pendulum could be applied to clocks
