The width of face is 2 feet, the number of buckets 160, and the power stated to be 30 horses. It is all of iron, and principally of wrought iron. It was sent to Italy, where it has been erected and set to work, but the useful effect has not been ascertained.

Attempts have been made to employ a high fall of water by placing one wheel above another; this was tried many years ago at Aberdare, in South Wales, where two wheels, each 40 feet in diameter, were so placed, like the figure of 8, and were connected by teeth on their respective rims-the lower wheel receiving the water after it left the upper one, and revolving in the opposite or reverse way. The result was not satisfactory; but in another case, a drawing of which lies before the writer, wherein Messrs. Charles Wood and Brothers, of Macclesfield, had two overshot waterwheels each of 26 feet in diameter, and 6 feet wide, placed over each other, they succeeded by a somewhat different arrangement of the toothed-wheel works. The two wheels were not connected immediately with each other, but by means of pinions, which worked into teeth upon the rims of the two water-wheels, causing them both to revolve in the same direction, so that the water, on leaving the buckets of the upper wheel, was more easily and readily received by the buckets of the lower wheel.

In either of these cases, however, the employment of the turbine, or the pressure engine, which will be described hereafter, would have been much less costly and more effective. The like may be said of all the contrivances to substitute endless chains with buckets applied to high falls instead of water-wheels. When the waterfall is too high for a wheel to be used conveniently, the turbine or the pressure engine should be resorted to, according to the kind of work required to be done by the machinery.

Where the quantity of water is large and variable, and the fall such as may be termed an intermediate height, but varying also with the supply, it is found advantageous not to lay the water upon the top of the wheel, so that it may work overshot, but to make the diameter of the wheel greater than the mean height of the fall, and to lay the water, as it were, on the shoulder" of the wheel, or at 45 degrees from the perpendicular, that is, half-way between the horizontal line and the perpendicular, or, as millwrights say, at nine o'clock." Very little mechanical effect is produced in the upper eighth of the circle as compared with

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the next quarter, on which the descent of the water is nearly perpendicular, and when the wheel is fitted with toothed segments at or near its circumference, acting on a pinion placed on a level with the axle, the weight of the water is brought to bear at once upon the pinion teeth, the stress is taken off the arms of the wheel, and the axle becomes, as it were, merely a pivot on which the wheel turns. By this arrangement, the late Messrs. Hughes and Wren, of Manchester, were enabled to make the arms of their wheels of simple tension rods of bar-iron, by which the rim of the wheel was tied and braced to the centre, a plan which, with some modifications and improvements, is still in use, and sometimes the segments have interior teeth, which renders the wheel-work more compact.

In the best constructed wheels, the water is laid on in a thin sheet of no greater depth than will give it a somewhat greater velocity than that of the wheel, the difference being just sufficient to pour into the succeeding buckets the proper supply of water. The buckets should be so capacious that they need not be full when the wheel carries its maximum load, in order that no water may be wasted, and that they may retain the water in them to the last moment that its weight on the wheel is effective, and yet empty themselves as soon as it ceases to be so. It is also expedient in prac

tice to make the sheet of water not so broad as the wheels: if the wheel be broad on the face, the stream may be 2 inches at each end short of the length of the buckets: the air escaping at the ends then blows out no water with it; and all these precautions, though small in themselves, tend to produce smoothness, regularity, and increased effect in the working of the machinery.

There is, however, one mode of using water-power-acting by its gravity-in buckets upon a chain, much used in South Wales, which is found very useful for raising ore from the pits. An endless chain is passed over a wheel of 16 feet in diameter placed between two pits. The chain passing down each pit, and through an opening at the bottom between the two: two large buckets, or rather shallow tubs, of wrought iron, are fixed upon the chain, so that the suspension is by the centre of the tubs, and they are so placed that when one tub is at the top of its pit, the other is at the bottom of its pit. Each tub or bucket is covered by a strong platform, which fills and closes the pit's mouth when hoisted up, and carries the small wagon or tram containing the ore upon

it; and each is also fitted with a valve at bottom to discharge the water. A branched pipe, communicating with an elevated reservoir, is laid to the pits' mouths, and fitted with stopcocks or valves. The tub at the pit's mouth being filled with water, over-balances the empty tub at bottom, and raises it, with its tram load of ore to the top. When the full bucket has descended the pit, the valve is opened and the water discharged; the other being filled in like manner, descends, and thus alternately each raises the other with its load of ore. The water finds its way out of the mine by a drift or adit into the valley; the long loop or bight of slack chain below the buckets, and hanging to the centre of each, equalises the weight of chain at all times; and a brake applied to the large wheel regulates the speed of the descending bucket. In some places, the two buckets work in one pit of an oblong form; the diameter of the wheel is reduced to 7 feet; it is fitted with toothed segments, working into a pinion, fixed upon a second axle, on which the brake-wheel is placed, in order to gain the requisite power to control the descending weight. Drawings of both these plans lie before the writer, but the principle and construction are so simple that description will probably suffice. It may be proper to mention that the buckets generally work in guides, that the discharging valves are opened by striking upon a point or projecting spike at the bottom of the pit, and that upon the platforms which cover the buckets there is a portion of the rail or tramway laid to match with the lines of way at the top and bottom of the pit, so that the tram or carriage may run from the platform to its destination.

CHAPTER X.

BREAST WHEELS, M. PONCELET'S WHEEL. LARGE STREAMS
AND LOW FALLS.

AT the time when Mr. Smeaton wrote the papers on undershot and overshot water-wheels, before referred to, the BREAST-WHEEL was but little known, and imperfectly understood; for it seems then to have been a kind of compromise between the two, in which it was attempted to combine the action of impulse and gravity. It had become evident that the impulse of a column of water did not produce the same effect as its weight; and the experiments of Mr. Smeaton showed what the difference was. Having investigated the other two modes of applying water power, he contents himself with saying, "We might naturally proceed to examine the effect where the impulse and weight are combined, as in the several kinds of breast-wheels, &c.; but the application of the same principles on these mixed cases will be easy, and reduce what I have to say on this head into a narrow compass; for all kinds of wheels where the water cannot descend through a given space, unless the wheel moves therewith, are to be considered of the nature of an overshot wheel, according to the perpendicular height that the water descends from; and all those that receive the impulse or shock of the water, whether in a horizontal, perpendicular, or oblique direction, are to be considered as undershots; and, therefore, a wheel, which the water strikes, at a certain point below the surface of the head, and, after that, descends in the arch of a circle, pressing, by its gravity, upon the wheel; the effect of such a wheel will be equal to the effect of an undershot, whose head is equal to the difference of level between the surface of the water in the reservoir and the point where it strikes the wheel, added to that of an overshot, whose height is equal to the difference of level between the point where it strikes the wheel and the level of the tail water."

It is here supposed that the wheel receives the shock of the water at right angles to its radii, and that the velocity of its circumference is properly adapted to receive the