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CTESIBIUS of Alexandria is mentioned by various writers as the teacher of Hero. Pliny speaks of him as the inventor of pumps for raising water, and as the author of studies on the expansive force of air and steam. Vitruvius gives a description of some of his inventions. The pump was almost identical with the forcing-pump in modern use. Water was drawn through an entrance-valve into an exhausted cylinder, and expelled from it through an exit-valve by the descent of a piston. Vitruvius describes also a very complicated water-clock invented by Ctesibius. The measurement of time was very imperfectly effected by the ancients, and was a great difficulty in their astronomical researches. Time, as we know from the speeches of Demosthenes, was rudely measured by the escape of water through a small opening in a vessel, like that of sand through an hour-glass. Obviously the escape was more rapid at the beginning when the pressure was the strongest. The water-clock of Ctesibius must have avoided these defects if, as Vitruvius asserts, it showed the hour, day, month, and sign of the sun. Presumably the vessel of water was kept constantly full, so as to ensure equal quantities being discharged in equal times.
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| This biography is
reprinted from The New Calendar of Great Men. Ed. Frederic
Harrison. London: Macmillan and Co., 1920. |
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