Fig. 74.
A little study of the figure (74) will explain its operation.
S, is the shaft; G G, the gutters; A, a trough to take away the water. The arrow indicates the direction in which the wheel turns; each gutter, as it revolves scoops up a portion of water and elevates it, till by the inclination to the axle, it flows towards the latter, and is discharged through one end of it.
The prominent defect of the tympanum arises from the water being always at the extremity of a radius of the wheel, by which its resistance increases as it ascends to a level with the axis, being raised at the end of levers which virtually lengthen till the water is discharged from them; this has been remedied by making the arms curving as shown in the Scoop Wheel (Fig. 75.) As this revolves in the direction of the arrow the extremities of the partitions dip into the water and scoop it up and as they ascend discharge it into a trough placed under one end of the shaft which is hollowed into as many compartments as there are partitions or scoops.
Fig. 75.
Fig. 76 represents a sectional view of an improved tympanum; this was invented by De La Faye; the illustration will be readily understood. As shown in Figs. 74 and 75 the wheel is driven by the current of a stream impinging upon what in later times came to be known as boards or floats on the circumference of the wheel.
Fig. 76.