It is obvious that the first use of water for mechanical purposes involved leading the water from a stream or other source, for use at another place. A primitive mechanism for raising water from a stream was •the noria, consisting of a large upright framework like a wheel, placed over a stream or river so that the flow of the current turned it around on its axis. To the periphery of the wheel were at tached hinged buckets. which were often earthen jars tied on the frame, and which were partly filled as they dipped in the stream, and being carried to the top were emptied by a tripping device into a trough, which led the water away on the higher level.
When men began to use machinery, as for grinding wheat, a better mechanism than the noria was necessary, and they learned to dam a stream and secure a fall of water to drive the wheel, which was provided with cross boards, so as to give the water a surface to push against. When the water struck the wheel on top, pushing with both its weight and velocity, it was an overshot wheel; if it passed under it was an undershot wheel; if the water struck the wheel just below the level of the shaft it was a breast wheel; when the wheel was mounted on its side rotating on an upright shaft, with spiral or curved flanges for buckets, it was a tub-wheel, which form is the progenitor of the turbine. Overshot and undershot wheels were used for hundreds of years to drive flour mills, and a few are still in use, but such wheels are very wasteful of water, as compared with modern constructions.
Flow of Water Through A large and important section of the science of hydraulics is that which treats of the study of the flow of water through orifices of varying shapes and sizes and under varying heads. From these studies has come the knowledge which guides the mechanic in the proper forma tion of a nozzle suitable to the economical and efficient delivery of a certain amount of water under the pressure of any given head. Experi ments in this direction are carried on by passing the water through an opening in a thin plate. Careful measurements of the spouting jet give a very close idea of its natural form. In this way the observed contraction of thejet just after issuing from the opening has led to the use by water-supply engineers of an entrance tube, or amouthpiecep of modified funnel-shape placed within the reservoir, in the case of the supply pipe leading out of a reservoir. Out side of this mouthpiece the pipe is gradually expanded into an elongated funnel or ladju tage?' The effect of these modifications has been to increase the velocity and consequently the discharge from the reservoir into the pipe to, in some cases, twice the volume to be theo retically expected from the existing head of water in Ate reservoir.
Another economic result from the study of the jet from an orifice is in the formation of hose nozzles for fire service, where the aim is to produce a jet of the largest possible volume and velocity with the smallest amount of fric tion.
Flow of Water in In the prac tical applications of hydraulics, water is con veyed to a place where it is to do work, in open channels or in pipes. In the case of the former the velocity or speed of the current depends solely on the grade of the bottom of the chan nel. The water simply l'runs down hill," and the steeper the grade the swifter the current. The material in which the channel is formed will control the grade it is possible to give the canal or ditch, as too high a velocity for the water will tend to destroy the channel. So where the channel is simply cut in the natural earth the grade is perforce made safe for the material. A water velocity of three inches per second will carry off fine clay; at six inches per second, ordinary soil will be carried away; at one foot per second, coarse sand will run off; at two feet per second, gravel washes away; at six feet per second, large stones will be rolled along. It is customary, therefore, to line a channel with some enduring material, such as concrete, or even masonry if it is to be permanent. The flow of water in these channels will obviously be affected by the fric tion at the bottom and sides of the channel. This is technically known as the "wetted per imetero and is measured on the cross-section of the stream. All along these edges of the flow ing body of water the stream is held back, the normal speed of the current being found only toward the centre and near the surface. The action of wind may serve to retard or advance the surface velocity. So it becomes a matter of considerable intricacy to determine just how much water will be delivered and at what velocity, by a given stream flowing down a given grade. A great number of formulas have been proposed by different engineers to aid in making such calculations, and these are to be found in the technical textbooks on hydraulics.