MILLS, KILNS, MALT-HOUSES, ETC. 573 Tooin for the water to spread. In this case, the buckets at the top of the wlieel are not filled so completely as they otherwise would be, by which means less water is spilt when they first chanjre their position, and, consequently, there is less waste of power, as the water is lon<i;er retained in them. The cast-iron trough for the water is marked b, and the sluice, also of iron, c. The inclined boards of the buckets should be exactly in a line with the stream of water wlicn it issues from the spout, passing beneath it ; and, if the edges are made thin, there will be but little splash. The velocity of the perijjhery of the overshot wheel should he from 6 feet and a half to 8 feet and a half per second, and the higher the wheel is in proportion to the whole descent of water, the greater will be the effect ; provided the water, when it first impinges upon the wheel, has an equal or greater velocity than the bucket-boards ; otherwise it will cause a splash, which will, in a slight degree, retard the motion of the wheel. A fall of two or three inches, in most cases, will be sufficient for this. A greater impulse in the water will of course accelerate the speed of the wheel ; but the power will not be increased so much as if the diameter of the wheel were sufficiently enlarged for the water to act by its weight. In general, when the fall of water is between 4 feet and 10 feet, a breast wheel should be erected ; an imdershot should be used when the fall is below 4 feet, and an overshot wheel when the fall exceeds 10 feet." 1244. As an example of the kind of Building requisite for a Corn-Mill to be impelled by Water acting on a Breast JVheel, we shall give the following, erected at Unsted Lock. It is one of a ninnber of Designs that have been furnished us by John Perry, Esq., of Godalming, Surrey, which have been executed by him in that county and the adjoining one of Sussex. Fig. 1 104, to a scale of 9 feet to an inch, is an elevation of the up-stream end of the building, the down stream end being the same. In this figure the dotted line 1104
