When the mill is fed too fast, the corn bears up the stone and is ground too fast, and besides it clogs the mill so as to make it go too slow ; when the mill is too slow. ly fed, it goes too fast ; and the stones by their attrition, are apt to strike fire : both these inconveniences are avoided by turning the pin backward or forward, which draws up or lets down the shoe, and thus regulates the feeding as the miller sees convenient.
It affords us pleasure in being able to lay before the reader reduced copies of two designs for water.wheels, by the late Mr. John Smeaton, and which we have obtained from Sir Joseph Banks, K B. who has permitted our draughtsmen to make copies of Mr. Smeaton 's original drawings, which are in his possession. The first is an undershot water-wheel. See fig 1. Plate 11. Mill-work.
A is the main shaft, or axis, upon which the wheel turns, and which communi cates its power; to the interior mechanism of the mill : a a a a are six arms mor ticed into this shaft, and supporting the rim, b b of the wheel; into this rim the starts, e e, are morticed; these arc short pieces of wood, to which the float boards,ff, are nailed; it is by the action of the water upon these that the wheel is turned : g g are boards fixed obliquely, and extending from one float to the next ; they are to prevent the water passing through the wheel without acting upon it. B B is a circular breasting or sweep, which is made to fit to the wheel as close as possible without touching, so that very little water may escape ; the ends of the boards also fit the aides of the wheel-race, or trough, in the same man ner. D D is the crown of the breasting, which is a segment of a circle. And d is the shuttle, by which the quantity of water going to the wheel is regulated, and consequently its power. There are two of the rims, b b, (though only one is seen, the other being behind it) with separate sets of arms and starts, to sup port the float-boards at each end ; and in some very broad wheels three rings are employed.
Figure 2. is an overshot water-wheel, as designed by Mr. Smeaton, and gene rally recommended by him in the latter years of his business.
A is the main shaft, with two seta of clasp arms embracing it, and supporting two rings (one only of which, a a, is seen, the other being behind it) parallel to each other, and at the distance apart of the breadth of the wheel: b b are a number of boards nailed down to the rings at their ends, i n the same manner as flooring boards are nailed upon the joists, and forming, upon the wheel, a complete cylinder: on each of the ends of these boards a circular ring, d d, is fixed, and between these the boards, forming the buckets are fastened, by having their ends let into grooves made in the inside of the rings d d; the bucket-boards are each composed of two pieces, as is suffi ciently explained in the figure. The
pen-trough, which brings the water to the wheel, is next to be described ; it is a long square trough, B B, with a hole in its bottom at one end, through which it delivers its water upon the wheel : e is a board called the shuttle, covering this hole, and made to fit water-tight up on the bottom of the trough by leather ; it is drawn backwards or forwards by a rod connecting it with a lever, f, by which the miller can draw it : his a beam across the pen-trough: and k, an iron bolt to support the bottom of the trough; the edge of the hole over which the wa ter runs, is the distance of one bucket beyond the perpendicular line going through the centre of the wheel; and it is formed of iron plate, with a sharp edge, to avoid dropping ; the edge of the shut tle is also covered with iron plate, that the water may be delivered clean, and in one entire sheet. The first-men tioned iron plate is bent so as to deliver the water nearly horizontally. The wheel is inclosed in a close breasting of stone, D D.
Attempts have been made to construct water-wheels which receive the impulse obliquely, like the sails of a common wind-mill. By this means a slow but deep river could be made to drive our mills; though much power would be lost by the obliquity. Dr Robison describes one that was very powerful ; it was a very long cylindrical frame, having a plate standing out from it, about a foot broad, and surrounding it with a very ob lique spiral, like a corkscrew. This was immersed nearly a quarter of its diame ter (which was 12 feet), having its axis in the direction of the stream. By the work performed, it seemed more power ful than a common wheel that occupied the same breadth of the river. Its length was not less than 20 feet : had it been twice as long, it would have nearly dou bled its power, without occupying more of the water-way. Perhaps such a spiral continued quite to the axis, and moving in a am:table canal, wholly filled by the stream, might be an advantageous way of employing a deep and slow current.