ON HYDRAULIC POWER-NEW HYDRAULIC MACHINE.

Sir,-The overshot water-wheel is the only machine in general use, upon which streams of water operate by their gravity, in the course of their descent; and it is only the power exerted by a stream during its descent from a very limited elevation, that can possibly be made available through the medium of this machine; because, in the first place, an overshot water-wheel requires a perpendicular fall, which can seldom be obtained from a very considerable altitude, by artificial means; and, in the second place, because in the few instances in which a very elevated fall is attainable, it is found practically impossible to construct a wheel of a corresponding dia

meter.

The overshot water-wheel is therefore a very inefficient machine when applied to streams of rapid descent, and the consequence is, not only that such streams are very imperfectly employed, in cases where a water-wheel is used, but whereever the quantity of water is insufficient to turn a wheel with effect, the stream lies wholly neglected, although in a theoretical point of view, its great descent may be much more than equivalent to the deficiency in the quantity of water.

Hilly and undulating districts abound with little rivulets, which flow down the sides of declivities from elevations of from one to three hundred feet, and which, on account of their diminutive size, are at present entirely disregarded. Such streams as these, however, would become most efficient sources of mechanical power, if they were made to operate by their gravity throughout the whole, or the greater part of their descent, instead of the very limited portion of it which a water-wheel is capable of employing. Streams of this description are to be met with on the banks of many of our navigable rivers, and in a multitude of other situations well suited for mills and manufactories, where hydraulic power would prove of the utmost value.

With the view, therefore, both of increasing the efficiency of many streams which are already in actual use, and of bringing into valuable employment an immense number of others, of which at present no use can be made, it is of the utmost importance that some method

should be devised, of concentrating the power developed by rapid streams during their descent from very elevated situations, and of applying such power to the purpose of propelling machinery.

The first step towards accomplishing this object, must be to get quit of the necessity of having a perpendicular fall, and the only conceivable way in which this can be done, is by conducting the stream in a pipe from the commencement to the foot of the descent, and bringing the column of water contained in the pipe, to bear upon machinery at the bottom. But still the question remains, in what manner is the pressure of the water to be made to act on the machinery?

Before proceeding, however, with this consideration, it is proper to observe, that in whatever way we may apply the pressure of the water, it would be extremely important that the motion of the water through the pipe should be slow, otherwise much of the force of gravity would be expended in the production of motion, and the power exerted on the machinery, would, in consequence, be greatly diminished. To make this perfectly intelligible, suppose the lower part of the pipe to be fitted with a piston, and conceive the piston to move forward in the pipe as rapidly as the water could possibly follow it; in this case it is plain, that the whole action of gravity would be expended in producing the mere motion of the water, and no force whatever would be exerted on the piston; but if the velocity of the piston were such, as to retard the course of the water through the pipe, then a part only of the force of gravity would be required to generate the motion of the water, and the remainder would operate on the piston; and the slower the motion of the water were rendered by the resistance of the piston, the less in a very rapidly decreasing ratio, would be the quantity of force expended in the production of motion, and the greater, in consequence, would be the amount of the power which would remain to act upon the piston. But the less rapid the motion of the water through the pipe, the larger would the pipe require to be made, in order to carry off the same quantity of water. Hence, therefore, the pipe for the conveyance of the stream would have to be very capacious, as compared with

what would be requisite, merely to draw off the whole of the water, if its escape from the lower extremity of the pipe were perfectly free.

It is scarcely necessary to remark, that the diminution of effect, consequent on the expenditure of power in producing the motion of the water, would not be peculiar to a machine propelled by a pressure to be thus obtained by means of a pipe, for it is very well known, that in the case of an overshot wheel, considerable power is lost in generating the motion of the water, during its descent in the buckets of the wheel.

And now, with respect to the manner of applying the pressure of the water to the machinery at the foot of the pipe: the mode which most naturally suggests itself is by means of a cylinder and piston, the same as in the steam-engine, and this method I understand has been recently put in practice at some lead mines in the north of England, but with what success I am not particularly informed. It is easy, however, to perceive that this system of employing the pressure must be subject to very serious objections, for unless the passages for the admission and escape of the water into and out of the cylinder, were many times larger than the corresponding passages in the steam-engine, either the motion of the piston would be excessively slow, or the water would acquire such an accelerated velocity on entering and escaping from the cylinder, as would neutralize a very great part of the pressure; and if, on the other hand, the passages were made sufficiently spacious to obviate these disadvantages, the valves would have to be enlarged to such an extent, as would render the difficulty of working them very considerable. Another objection to this mode of employing the pressure is, that the column of water contained in the pipe would be brought to a state of rest at the termination of every stroke of the piston, and considerable power would be expended in renewing the motion of the water at the commencement of each succeeding stroke.

We ought, therefore, to endeavour to effect the object in view, by some contrivance which would be free from contracted passages, and in which valves might be dispensed with, for without contracted passages, valves could not be employed without inducing great loss of

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The pipe for the conveyance of a stream from some considerable elevation, communicates with the upper end of the tube A B CD, which is of somewhat larger diameter than the pipe, and of a shape which will be best understood by reference to the drawing. In the upper side of this tube there is a slit or opening, extending from the point B to the mouth of the tube, by means of which slit, the rim of the wheel, E F G, is admitted into the interior of the tube. The breadth of the rim being somewhat greater than the diameter of the tube, the inner edge of the rim, or that which is nearest the centre of the wheel, remains outside of the slit, while the outer edge of the rim extends to the opposite side of the interior of the tube, and there falls into a groove adapted to receive it. The thickness of the rim is exactly equal to the width of the slit, so that that slit is accurately filled up by the insertion of the rim. Under these circumstances it is evident that the wheel would be capable of revolving with part of its rim constantly immersed in the tube, while no opening would be left through which the water could escape except the mouth of the tube.

The rim of the wheel contains four equidistant circular apertures, three only of which are seen in the drawing, the remaining one being situated in that part of the rim which is concealed in the tube. The diameter of each of these apertures is exactly equal to the interior diameter of the tube, and a circular plate or disk, of the same thickness as the rim, turns upon an axle in each aperture, so as to be capable of assuming a position either at right angles to the rim, as represented at E, or in the same plane with it, as represented at F and G, in which latter position the disks would accurately close up the apertures, and form, as it were, part of the rim.

Now suppose the disk belonging to

the aperture which is concealed in the tube, to be at right angles to the rim, the same as the disk which is represented at E; in this position the disk in question would intercept the passage through the tube, and form a piston, which would sustain upon its upper surface the whole pressure of the superincumbent water, and the consequence would be, that the disk would be pushed forward in the tube, and the wheel would be put in motion. The pressure, however, upon the disk would of course only continue until it reached the mouth of the tube; but in the mean time the disk which occupies the aperture at G, would have entered the tube, and if as soon as it were admitted, it were caused to turn upon its axis, so as likewise to assume a position at right angles to the rim, it also would constitute a piston, upon which the water would begin to operate, the instant it ceased to act upon the other. All then that would be requisite to maintain the constant rotation of the wheel, would be, to cause the disks, or pistons, as I shall now call them, to shut up into the apertures after quitting the tube, and again to open out and assume the requisite position as soon as they are admitted within it.

Many ways may be conceived of changing the positions of the pistons in the order required, but the method which is represented in the drawing, and which I shall now proceed to explain, would probably be as simple and efficacious as any other.

The axles upon which the pistons are fixed are prolonged to the centre of the wheel, and upon each prolonged axle two cross-levers are fixed, one at right angles to the piston attached to the axle, and the other in the same plane with it. The levers and the pistons being thus fixed upon axles common to both, the pistons would necessarily obey any change of position to which the levers might be subject. In order, therefore, to reverse the position of each piston when it has entered the tube, we have only to reverse the direction of the levers with which the piston is connected, and this would be effected by the following contrivance.

h, i, k, is a slide which may be fixed to the frame in which the wheel revolves, or to any other stationary object, and which slide is so adjusted that when the wheel is in motion, the levers which are

at right angles to the pistons may strike in rotation with one end against the head of the slide, as they arrive at the point at which the pistons are to be turned. By this arrangement the position of each lever would be changed from a direction perpendicular to the slide, into a direction parallel with the slide, in which latter direction the lever would be retained by the subsequent action of the slide, until the piston in counection with it reached the mouth of the tube. Thus each piston would be turned into the requisite position, exactly at the moment required, and in that position would be maintained so long as it remained in the tube.

A similar slide would have to be fixed on the opposite side of the wheel, in the situation indicated by dotted lines, so as to operate on the other set of levers, and by a similar process, to shut back the pistons into the apertures, preparatory to again entering the tube.

In order to render the pistons capable of turning round in the tube, it would be necessary to make their edges of a spherical and not of a cylindrical form, and the sides of the apertures would require to be similarly shaped to make them correspond with the edges of the pistons. It will be perceived, however, that in consequence of so shaping the edges of the pistons, it would only be a single line round each piston, that could be in contact with the sides of the tube, on which account the pistons could not be made to fit perfectly water-tight. If the machine were propelled by the pressure of steam, the leakage which would be thus occasioned would constitute a serious defect, but in a machine propelled by the pressure of water leakage would be, comparatively, of very slight importance, because the quantity of water which would escape through a crevice, under a given pressure, would be extremely insignificant, as compared with the quantity of steam which would escape under similar circumstances.

The mouth of the tube should be turned upwards, sufficiently to render every part of the opening higher than that part of the tube which is situated at C, in order that by the action of the air, the tube might be kept constantly full, below as well as above the piston, which for the time being would be in operation. The advantage of this would be, that on the principle of suction, the water con