. Elements of technology :. lly applied to the circumference of wheels, which itcauses to revolve, either by its weight, by its lateral impulse, orby both conjointly. Water wheels are generally used inone of three forms. These are the overshot wheel, in whichthe water descends from the top of the wheel to the bot-tom ; the breast wheel, in which it is received at about half theheight of the wheel, and the undershot wheel, where it acts bythe impulse of a current flowing under the wheel. The over-shot wheel is the most powerful kind, and is always to be em-ployed where a sufficient fall of wate
. Elements of technology :. lly applied to the circumference of wheels, which itcauses to revolve, either by its weight, by its lateral impulse, orby both conjointly. Water wheels are generally used inone of three forms. These are the overshot wheel, in whichthe water descends from the top of the wheel to the bot-tom ; the breast wheel, in which it is received at about half theheight of the wheel, and the undershot wheel, where it acts bythe impulse of a current flowing under the wheel. The over-shot wheel is the most powerful kind, and is always to be em-ployed where a sufficient fall of water can be obtained. Overshot Wheel.—This is a wheel, or drum, the circumfer-ence of which is occupied by a series jp^^ ^of cavities, commonly called buckets,into which the water is delivered fromone or more spouts at the top of thewheel. By inspecting Fig. 1, it will beseen that the buckets on one side of thewheel are erect, and will consequentlybecome loaded with water ; while thoseon the other side are inverted, and of33. 258 OF THE MOVING FORCES USED IN THE ARTS. course empty. It follows that the loaded side will always pre-ponderate, and by descending will cause the wheel to revolve. If it were possible, says Dr Robison, * to construct thebuckets in such a manner, as to remain completely filled withwater till they came to the bottom of the wheel, the pressurewith which the water urges the wheel round its axis, would bethe same as if the extremity of the horizontal radius were con-tinually loaded with a quantity of water sufficient to fill a squarepipe, whose section is equal to that of the bucket, and whoselength is the diameter of the wheel. But such a state of thingsis impossible, and if a bucket be fall while at top, it will beginto lose water as soon as it turns into an oblique position, andmust continue to do so, till it reaches the bottom. The attention of engineers has been directed to giving thebuckets such a form as will enable them to retain the waterfor the long
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