. Elements of technology :. y thenecessity of discharging the water at a greater height from thebottom. * Chain Wheel,—^When there is a very small supply of waterfalling from a very great head, the double overshot wheel, witha chain of buckets, is a valuable machine. This wheel is re-presented in Fig. 4, where two rag wheels Fig. placed, one at top, and the other atbottom, and a series of buckets are fixed toan endless chain, the Hnks of which fall intonotches in the circumference of the ragwheels. The water issuing from the millcourse is introduced into the buckets on oneside at top. Th
. Elements of technology :. y thenecessity of discharging the water at a greater height from thebottom. * Chain Wheel,—^When there is a very small supply of waterfalling from a very great head, the double overshot wheel, witha chain of buckets, is a valuable machine. This wheel is re-presented in Fig. 4, where two rag wheels Fig. placed, one at top, and the other atbottom, and a series of buckets are fixed toan endless chain, the Hnks of which fall intonotches in the circumference of the ragwheels. The water issuing from the millcourse is introduced into the buckets on oneside at top. The descent of the loadedbuckets on this side puts the rag wheels inmotion, and the power is conveyed fromthe shaft of the upper wheel, to turn anykind of machinery. When the bucketsreach the bottom they allow the water to escape, and ascend-ing empty on the opposite side, they again return to the spoutto be filled as before. In this machine, the buckets have inevery part of their path the same mechanical effect to turn the. * Mechanical Philosophy, vol. ii. p. 600. On this subject Dr Brewster remarks, that if we employ a wheel thediameter of which is higher than the fall, we may take advantage of any cas-ual rise of the water above its usual level, and by a particular form of the de-livering sluice, introduce the water higher upon the wheel and thus actuallyincrease the height of the fall. OF THE MOVING FORCES USED IN THE ARTS. 261 wheels, and they do not allow the water to escape till they havereached almost the lowest part of the fall. This species of wheel possesses another advantage, namely,that by raising the lower wheel and taking out two or three ofthe buckets it may be made to work when there is such a quan-tity of back water as would otherwise prevent it from moving. Dr Robison, has described a machine of this kind, in whichplugs, or horizontal floatboards, are fixed to a chain. On thedescending side these plugs pass through a tube, alitde greaterin diameter than that
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