S. THE SLIDING HATCH. 87 utmost advantage of both these powers; otherwise a reduction must be made on that account. Here Mr. Smeaton leaves the subject; his remarks having suggested considerable improvements on the common practice of his day, and dispelled many popular errors. The principles he developed, and the rules he deduced from them, were productive of great practical benefit; and his papers may still be studied with much advantage. The late Mr. Rennie may be said to have continued these researches; and, in 1784, he erected a large breast-wheel, worked by the weight of the water alone. To this wheel he first applied the sliding hatch, over which the water flowed upon the wheel, instead of issuing under the hatch or sluice, as formerly; and by this means the whole height of the fall is realised. In this case, the sluice or hatch is to be drawn up, in order to stop the flow of water, which runs over it; whereas, before this time, it was let down to shut off the water running out below. The water ran over the top of the sliding hatch, as over a dam, in a thin sheet, and was laid upon the breast of the wheel, or below the level of the axle, where it acted, by its gravity, upon the float boards; being held up to the breast. by masonry cut to a circular arc, drawn from the centre, fitting the wheels' circumference, and confining the water on all sides, so that none of it could escape without doing its part in the work; for the float-boards filled the channel, and there were sole-boards upon the rim of the wheel. Here let it be observed, that these sole-boards, which form an obtuse angle with the floats, are notched upon the oak starts to which the float-boards are fixed; but they do not completely close the wheel rim; a long narrow slit or opening is left across the face of the water-wheel, between the starts, permitting the air to escape, and the water freely to enter, as each bucket or float presents itself to receive its load; and should the river be flooded, and rise against the wheel, so that it". runs in backwater," the ready admission of air from above prevents a partial vacuum from being formed between the floats, which would tend to retard the escape of the water, and thus reduce the useful effects. Although in this wheel, which is without "shrouding" or sides, there is but little cavity or depth to cause such retention, yet in large wheels, with well-buckets and deep shrouding, the loss of power would be important. It has always been the author's practice, even in over-shot w to make provision for ventilating the buckets, and pr "the suction," as workmen say, from the tail water. however, there is sometimes a little water lost by means, and the orifice so left is more effectual when larger, especially when buckets of much capacity are instead of floats, as they now frequently are, in br wheels, an ingenious method of ventilating the buckets been proposed by Mr. Fairbairn, which is well worth little extra cost it may occasion in the first outlay of ca required for the erection of a large wheel. In order to lay the water upon these wheels with th velocity required, and, at the same time, to keep the strea in a thin sheet, Mr. Rennie next adopted a double hatch, sluice adding, as it were, another hatch, fixed above th first ; so that, by an adjustment of the two, a narro opening might be left between them, capable of nice regu lation to every variation of power required for the quantit of work to be done in the mill. The upper hatch dippe just so much below the water's surface as to give th needful head above the orifice to produce a jet flowing with the desired speed; and the under hatch being raised or lowered by racks and pinions, the thickness of the stream delivered upon the wheel, was diminished or increased at pleasure, while it continued to drive the mill at an uniform rate, by varying the load or quantity of water. The next improvement was the application of the governor, or regulator, to adjust the supply of water to the wheel, without the attention of the miller; so that the slightest variation in the demand for power in the mill or factory might be met by a corresponding expenditure on the prime mover. The double revolving pendulum, adopted, as a regulator for the steam-engine, by Mr. Watt, is generally used; and as the governor-balls fly out or collapse, the one or other of a pair of bevilled wheels is engaged and disengaged, so as to turn the pinion spindle, or endless screw, in opposite directions, and so moving the racks to raise or lower the sluice. Some of the French mechanicians use a strong circular bellows, weighted on the upper boards and having a small opening for the escape of the air, so adjusted that when the wheel is working at the proper speed the upper board of the bellows is maintained at a certain level, but when the wheel goes a little too fast, the air accumulates in the bellows and raises the upper board, when a projecting iron finger fixed upon it "strikes into gear one of the bevilled wheels, and disengages the other. The machinery so put in motion diminishes the supply of water, and the speed of the whole is reduced. On the contrary, when the water-wheel goes too slow, and the bellows are not fully inflated, the upper board sinks, and the iron finger reversing the motion of the pinion spindle opens the sluice, and increases the supply of water; but powerful bellows may act directly on the sluice itself. Sometimes when applied to overshot wheels, the governor moves a slide, with many long narrow openings in it, which coincide with similar openings in a metal plate in the bottom of the pentrough, or spout, which is closed at the end, so that the water must pass through these openings to the wheel; and, as they enlarge or contract with every movement of the vigilant governor, the speed of the wheel is kept uniform and steady. When the water is laid on the shoulder of the wheel, a curved slide, or a broad band of leather, rolled on or off a cylinder or roller, of small diameter, is substituted for a sluice. The leather is fastened at the lower end to a curved grating, adapted to the form of the wheel; and, at the other end, to the roller, which descends as the leather rolls upon it; and the water flows over the roller as it does over Mr. Rennie's hatch. Latterly the curved slide, or sluice, the segment of a circle, fitting the periphery of the wheel, has been preferred to the leather band and roller, as being more durable; and the sluice is now better fitted, since improved tools have been introduced in the manufacture of machinery. There are several other modes of applying governors; these will, perhaps, be considered sufficient. but Breast-wheels are often made wide across the face, and of considerable power. One of the widest was erected many years ago, by Messrs. Strutt, at their Belper cotton-mills. It was 40 feet wide, but only 12 feet 6 inches diameter; the shaft was made hollow, like a cask, and so large as to form the body of the wheel, the float-boards being fixed immediately upon it. This hollow axis was 48 feet long, composed of thirty-two staves, 6 inches thick, bound together by iron hoops; the diameter in the middle was 7 feet 2 inches, tapering to 5 feet at one end, and 6 feet at the other, upon which a toothed wheel, 14 feet in diameter, was placed. The ends of this barrel were made solid for 3 feet at the small end, and 4 feet at the larger, to receive the gudgeons or pivots on which it turned. The float-boards, twenty-four in number, did not come in immediate contact with the barrel, but a space of 2 inches was left for the air to escape. The length of the float-board was divided into ten parts, and these were supported_by rings fixed upon the hollow axis, placed 4 feet apart. The divisions of the float-boards were not placed in line with each other, but every one in advance of the next, by equal steps, so that the water might not strike the whole length of 40 feet at once, but act in a rapid succession of intervals, and thus make the stroke imperceptible. A pair of very powerful wheels were erected about twenty-five years ago, at the Catrine Works in Ayrshire, by Messrs. Fairbairn and Lillie. It was originally intended to have four of these wheels, and provision was made for receiving them, should the factory be extended and require more power; but at present two wheels are sufficiently powerful, except in very dry seasons, to turn the whole work of the mills. These wheels are each 50 feet in diameter; 10 feet 6 inches wide inside the buckets; and 15 inches deep in the shroud; they are fitted with internal toothed segments forming a circle of 48 feet 6 inches diameter; the teeth are 3 inches pitch, and the breadth is 15 inches. The fall of |