utmost solidity; wood framing is very commonly used, but masonry is preferable. Great care must be taken, by driving pile planking under the dam, to intercept all leakage of the water beneath the ground under the dani, as that loosens the earth, and destroys the foundation imperceptibly, when a violent flood may overthrow the whole. It is a common practice to place the dam obliquely across the river, with a view of obtaining a greater length of wall for the water to run over, and consequently prevent its rising to so great a height, in order to give vent to the water of a flood. But this is very objectionable, because the current of water constantly running over the dam, always acts upon the shore or bank of the river at one point, and will in time wear it away, if not prevented by expensive works. This difficulty is obviated by making the dam in two lengths which meet in an angle >, the vertex pointing up the stream. In this way the currents of water, coming from the two opposite parts of the dam, strike together, and spend their force upon each other, without injuring any part. A still better form is a segment of a circle, which has the additional advantage of strength, because if the abutments at the banks of the river are firm, the whole dam becomes like the arch of a bridge laid down horizontally. This was the form generally used by Mr. Smeaton.

The foot of the dam where the water runs down should be a regular slope with a curve, so as to lead the water down regularly; and this part should be evenly paved with stone, or planked, to prevent the water from tearing it up when it moves with a great velocity.

When the fall is considerable, it may be divided into more than one dam; and if the lower dam is made to pen the water upon the foot of the higher dam, then the water running over the higher dam, will strike into the water, and lose its force. There is nothing can so soon exhaust the force of rapid currents of water as to fall into other water, because its mechanical force is expended in changing the figure of the water; but when it falls upon stone or wood, its force is not taken away, but only reflected to some other part of the channel, and may be made to act upon such a great extent of surface as to do no very striking injury at any one time; but by degrees it wears away the banks, and requires constant repairs for it is demonstrable that, as much of the force of the water as is not carried away by the rapid motion with which it flows, after passing the dam, must be expended either in changing the figure of the water, or in washing

away the banks, or in the friction of the water running over the bottom..

The cotton-works of Messrs. Strutt, at Belper, in Derbyshire, are on a large scale, and the most complete we have ever seen, in their dams and water-works. The mills are turned by the water of the river Derwent, which is very subject to floods. The great wear is a semicircle, built of very substantial masonry, and provided with a pool of water below it, into which the water falls. On one side of the wear are three sluices, each 20 feet wide, which are drawn up in floods, and allow the water to pass sideways into the same pool; and on the opposite side is another such sluice, 22 feet wide. The water is retained in the lower pool by some obstruction which it experiences in running beneath the arches of a bridge; but the principal fall of the water is broken by falling into the water of the pool, beneath the great semicircular wear.

The water which is drawn off from the mill-dam above the wear, passes through three sluices, 20 feet wide each, and is then distributed by different channels to the mills, which are situated at the side of the river, and quite secure from all floods. There are six large water-wheels; one of them, which is 40 feet in breadth, we have mentioned, from the ingenuity of its construction; and another, which is made in two breadths of 15 feet each, we have also described. They are all breast-wheels. The iron-works of Messrs. Walker, at Rotherham, in Yorkshire, are very good specimens of water-works; as also the Carron-works in Scotland.-Dr. Rees's Cyclopædia and Dr. Brewster's Ferguson.

PENSTOCK.

THE following is a description of a pentrough and stock for equalizing the water falling on water-wheels, by Mr. Quayle. To ensure a regular supply of water on the wheel, and to obviate the inconveniencies arising from the usual mode of delivering it from the bottom of the pentrough, this method is devised of regulating the quantity delivered by a float, and taking the whole of the water from the surface.

Section of the pentrough. Fig. 99. A, the entrance of the water; B, the float, having a circular aperture in the centre, in which is suspended C, a cylinder, running down in the case E below the bottom of the pentrough. This is made watertight at the bottom of the pentrough at F, by a leather collar placed between two plates, and screwed down to the bottom. The cylinder is secured to the float so as to follow its rise

and fall; and the water is admitted into it through the opening in its sides, and there, passing through the box or case E, rises and issues at G on the wheel. By this means, a uniforın quantity of water is obtained at G; which quantity can be increased or diminished by the assistance of a small rack and pinion attached to the cylinder, which will raise or depress the cylinder above or under the water line of the float; and, by raising it up to the top, it stops the water entirely, and answers the purpose of the common shuttle. This pinion is turned by the handle H, similar to a winchhandle; and is secured from running down by a ratchetwheel at the opposite end of the pinion axis.

K and L are two upright rods to preserve the perpendicular rise and sinking of the float, running through the float, and secured at the top by brackets from the sides.

M, a board let down across the pentrough nearly to the bottom, to prevent the horizontal impulse of the water from disturbing the float.

Fig. 99*. A transverse section, showing the mode of fixing the rack and pinion, and their supports on the float. The rack is inserted into a piece of metal running across the cylinder near the top. That the water may pass more freely when nearly exhausted, the bottom of the cylinder is not a plane, but is cut away so as to leave two feet, as at C, fig. 99. The float is also kept from lying on the pentrough bottom by four small feet; so that the water gets under it regularly from the first.

Fig. 99**, An enlarged view of the cylinder, showing the rack and ratchet-wheel, with the clink, and one of the openings on the side of the cylinder; the winch or handle being on the opposite side, and the pinion, by which the rack is raised, enclosed in a box between them.

MR. SMEATON'S PENTROUGH.

FIG. 93*. G represents the pentrough through which the water flows, and FF strong cross-beams on which it is supported; the wheel is situated very close beneath the bottom of the trough, as the figure shows. EE are two arms of the wheel, which are put together, as shown in fig. 110. BD is the wooden rim of the wheel; the narrow circle beyond this is the section of the sole planking, and on the outside of this the bucket-boards are fixed as the figure shows; one of the bottomboards, b, of the trough at the end is inclined, and an opening is left between that end and the other boards of the bottom, to let the water pass through; this opening is closed by a sliding

shuttle, c, which is fitted to the bottom of the trough, and can be moved backwards and forwards by a rod d, and lever e, which is fixed into a strong axis f; this axis has a long lever on the end, which, being moved by the miller, draws the shuttle along the bottom of the trough, and increases or diminishes the aperture through which the water issues. The extreme edge of the shuttle is cut inclined, to make it correspond with the inclined part b, and by this means it opens a parallel passage for the water to run through, and this causes the water to be delivered in a regular and even sheet; and to contribute to this the edges of the aperture where the water quits it are rendered sharp by iron plates; the shuttle is made tight where it lies upon the bottom of the trough, by leather, so as to avoid any leakage when the shuttle is closed. When the wheel is of considerable breadth, the weight of the water might bend down the middle of the trough until it touched the wheel; to prevent this, a strong beam, O, is placed across the trough, and the trough is suspended from this by iron bolts which pass through grooves in the shuttle, so that they do not interfere with the motion of the shuttle.

Mr. Nouaille took out a patent, in October, 1812, for a new method of laying water upon an overshot-wheel, (see fig. 94,) which he thus describes:-"In my new method of applying water to water-wheels, I cause it to commence its action upon a point of the wheel's circumference, which is about 53 degrees distant from the vertex, or the highest point thereof, instead of applying it at the top of the wheel, as heretofore commonly practised for overshot-wheels. By these means I can have the advantages of a large wheel in situations where the fall would only allow of a smaller, if the water was applied at the top; thus, if there be a perpendicular of 12 feet, I cause a wheel of 15 feet diameter to be made, and of course the water must be made to act upon it at a height of 12 feet, which is three feet perpendicular below the top of the wheel, and at about 53 degrees from the top, measured round its circumference as above stated. I make the pentrough which brings the water to the wheel of such a form that it delivers the water from the bottom of it through the floor, and is directed at such an angle as to fall into the buckets nearly in the direction of the wheel's motion, which will be at an angle of 75 degrees with the horizon; the shuttle or gate slides upon the floor of the trough, so as to cover the aperture, and determine the quantity of water to be let out upon the wheel.

"The exact manner of carrying this principle into effect is particularly explained by the annexed draft, which is a vertical section of a water-wheel on my improved plan. In this the dotted line A A, fig. 116, represents the level of the water at its full head, and B the level of the tail-water; therefore A B is the extreme fall, A C is the depth of the water in the pentrough. Now, instead of the cominon practice of making a wheel of the diameter equal to BC, I make the wheel DEFG one-fourth larger than BC, then the water will be delivered upon it at the point E. The floor C of the pentrough C HL, does not come up to meet the end H thereof, but leaves a small space through which the water issues in the direction of the dotted line II, to the buckets of the wheel. The breadth of this space is determined by the shuttle K, which lays flat upon the floor of the pentrough, and slides over the aperture. It is regulated by means of a lever N, acted upon by a screw, rack, or other adjustment, at M, and the water is thus delivered in a very thin and reguiar sheet into the buckets."

Fig. 117 represents a method of laying on water which has for several years been in common use in Yorkshire and the north of England. In this the water is not applied quite at the top of the wheel, but nearly in the same position as the last described; but the advantages of this wheel over all others is, that the water can be delivered at a greater or less height, according to the height at which the water stands in the trough; but in all the preceding methods, if the water is subject to variations of height, as all rivers are, then the wheel must be diminished, so that in the lowest state of the water it will stand a sufficient depth above the orifice in the bottom of the trough to issue with a velocity rather greater than the motion of the wheel. In this case, when the water rises to its usual height, or above it, the increase of fall thus obtained is very little advantage to the wheel; the improved wheel can at all times take the utmost fall of the water, even when its height varies from three to four feet. A A is the pentrough made of cast-iron; the end of it is formed by a grating of broad flat iron bars, which are inclined in the proper position to direct the water through them into the buckets of the wheel. The spaces between the bars are shut up by a large sheet of leather, which is made fast to the bottom of the iron trough at a, and is applied against the bars; and the pressure of the water keeps it in close contact with the bars, so as to prevent any leakage. This is the real shuttle, and to open it so as to give the required stream