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 was Sextus Julius Frontinus, water commissioner in Rome during the reigns of Nerva and Trajan. He possessed a shrewd knowledge of the flow of fluids, but hardly more than that which any observing man may pick up by working around a water works system to-day. In 1628 Castelli published a small pamphlet on the flow of fluids, followed in 1643 by a pamphlet giving more important discoveries. In 1828 Fourneyron invented the turbine and from that time to this important discoveries on the flow of water have been announced at intervals. The past twenty-five years have seen the knowledge respecting the flow of water placed on nearly as satisfactory a basis as a knowledge of the stresses in structures, although for fifty years prior enough was known to enable engineers to carry out great hydraulic works with reasonable certainty and economy.

Hydraulic engineers were formerly employed in large numbers on the design and construction of power plants operated by water wheels. After the introduction of the steam engine the water wheel declined in importance and many mills replaced their hydraulic plant with steam plants. To-day the hydraulic engineer is again in demand to design and erect water power installations in which the wheel picks up the power from falling water and carries it to huge electric generators, to be converted into electricity which is easily transmitted for long distances. The term