The history of hydraulic engineering is enmeshed inextricably with the history of medicine and health, as well as with the welfare of society. Since the days of ancient Greece, the provision of safe, convenient, and reliable water has been central to the endeavors of engineers and doctors. The earliest hydraulic engineering for which records survive was that of the great aqueduct on the Greek island of Samos; and the first known hydraulic engineer was its builder, Eupalinus of Megara. The Greeks also invented the siphon to lift flowing water over intervening heights. During the second century BC, the Greek engineer Ctesibius was interested in the pressure differential so obtained. Roman engineers subsequently developed the skills of aqueduct construction and systems of distribution. The Aqua Appia, built in 312 BC and 16.5 km long, and the Aqua Anio Vetus, built in 272 BC, are the earliest known Roman aqueducts. The Aqua Marcia, which was built in 144 BC, was the first Roman aqueduct to be carried partly on bridges and in tunnels. These supplied saliens or street fountains , lacus or public basins , and balneae or public and private baths . The Roman military engineer Vitruvius Pollio ca. 20–26 BC 10-folio work, De Architectura, the eighth book of which concerned water supply. The next advance in hydraulic engineering was the construction of water-lifting machinery to replenish those reservoirs not fed naturally by gravity. The kinetic energy of flowing water to lift water itself was the first such force harnessed. These machines evolved from bucket-wheels operated by humans or by animals. The saqiya, or Persian wheel, first recorded in Mesopotamia, consisted of buckets attached to the circumference of a wheel that scooped, lifted, and then discarded water at a level higher than the primary stream. The waterwheel used a three-stage energy transfer—kinetic to mechanical to gravitational energy. More sophisticated water-lifting wheels and screws were recorded in the literature of Roman times, including water-lifting machines in Roman London. The dream of inventing an engine that would work continuously, without input from an intermediate waterwheel—or from heat, animal, or human power—had long been the holy grail of inventors, mathematicians, and engineers.
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