runner keeps the stream always supplied to a certain degree, and when the lower hollow, which feeds the syphon runner F H, is filled up to OH, both the common runner and the syphon runner feed the stream together, until the lower hollow is drained.

.

In some places the most absurd tales are told and believed by ignorant people respecting such springs; their flowing and ceasing are ascribed to witchcraft; and designing men have sometimes taken advantage of the credulity of others, and gained credit for themselves, by fortelling the return of the spring after it had ceased, or pretending to stop it when it was running. Some notions connected with superstitions of this kind are adverted to in the account given of an intermitting, or rather a variable spring, at Laywell, near Torbay, in Devonshire, by Dr. Atwell, the first person who distinctly explained these appearances by a reference to the nature of the syphon. It is a long mile,' says he, distant from the sea, upon the north side of a ridge of hills lying between it and the sea, and making a turn or angle near this spring. It is situated in the side of those hills, near the bottom, and seems to have its course from the south-west towards the north-east. There is a constantly running stream which discharges itself near one corner into a basin, about eight feet in length, and four feet and a half in breadth, the outlet of which is at the farthest end from the entrance of the stream, about three feet wide and of a sufficient height. This I mention that a better judgment may be made of the perpendicular rise of the water in the basin at the time of the flux or increase of the stream. Upon the outside of the basin are three other springs which always run, but with streams subject to a like regular increase and decrease with the former: they seem indeed only branches of the former, or rather channels discharging some parts of the constantly running water, which could not empty itself all into the basin; and, therefore, when by means of the season or weather the springs are large and high, upon the flux or increase of this fountain, several other little springs are said to break forth, both at the bottom of the basin and without it, which disappear again upon the ebb or decrease of the fountain. All the constant running streams put together at the time I saw them, were, I believe, more than sufficient to drive an overshot mill, and the stream running into the basin might be one-half of the whole. I had made a journey, purposely to see it, in company with a friend; when we came to the fountain we were informed by a man working just by the basin, that the spring had flowed and ebbed about twenty times that morning, but had ceased doing so about half an hour before we came. I observed the stream running into the basin for more than an hour by my watch, without perceiving the least variation in it, or the least alteration in the height of the surface of the water in the basin; which we could observe with great nicety by means of a broad stone laid in a shelving position in the water. Thus disappointed, we were obliged to go and take some little refreshment at our inn; after which, we intended to come back and spend the rest of our time by the fountain,

before we returned home. They told us in the house that many had been disappointed in this manner, and the common people superstitiously imputed it to I know not what influence which the presence of some people had over the fountain; for which reason they advised, that, in case it did not flow and ebb when we were both present, one of us should absent himself, to try whether it would do so in the presence of the other. Upon our return to it, the man, who was still at work, told us that it had begun to flow and ebb about half an hour after we went away, and had done so ten or twelve times in less than a minute. We saw the stream coming into the basin, and likewise the others on the outside of the basin began to increase, and to flow with great violence, upon which the surface of the water in the basin rose an inch and a quarter perpendicularly, in nearly the space of two minutes; immediately after which the stream began to abate again to its ordinary course, and in nearly two minutes time the surface was sunk down to its usual height, where it remained two minutes more; then it began to flow again as before, and, in the space of twenty-six minutes, flowed and ebbed five times; so that an increase, decrease, and pause, taken together, were made in about five minutes, or a little more. I could observe by the mark upon the stones, that the surface of the water in the basin had risen, before we came, at least three quarters of an inch perpendicularly higher than we saw it; and I thought that I could perceive some very little abatement each turn, both in the height, and in the time of its sinking; but the time of the pause, or standing on the surface at its usual height, or equable running of the stream, was lengthened, yet so as to leave some abatement in the time of the rising, sinking, and pause al together.'

It should seem, that, in the hill from which this stream comes, there are three hollows, or reservoirs, of different sizes, and connected by syphons of different widths. The times of the increase and decrease lengthening, arises from the water sinking in one of the reservoirs, which makes it flow more slowly than when it is full.

Having already briefly adverted to the principle upon which the syphon acts, it will now be necessary for us to show in what manner this instrument may be employed as a prime mover. The apparatus to which we allude was contrived by Mr. C. A. Busby, the son of Dr. Busby, and termed the hydraulic orrery. The original apparatus, as described by Mr. Busby, in the fortieth volume of the Transactions of the Society of Arts, is exceedingly complicated; but the following arrangement, as constructed by Mr. Partington, and employed by him in his public lectures, will be found to possess much greater simplicity, and its construction will be easily understood. A, fig. 7, plate II., represents a tin water-tight vessel, placed in a circular trough C. The upper vessel of water is furnished with an upright stem of wire, supporting a ball S, which is intended to represent the sun. The smaller balls, E and m, revolve round the larger sphere in the same time that the earth and moon revolve round the sun, and as such, serve to convey a

tolerably accurate idea of the movements of those bodies. The syphon B may be considered as the prime mover; as the lateral apertures at D, by allowing the escape of a small portion of water from the lower extremity of the instrument, destroy the equilibrium within the tube, and give a preponderance of power to the side which is opposed to the jet, and by this simple process an equable rotatory motion is produced: the whole apparatus floating round the central wire that supports the sun.

The mode of constructing pumps must next be examined. The common sucking-pump consists of a pipe, open at both ends, in which is a moveable piston, bucket, or sucker, in which is situated the valve. The piston is leathered round, so as to move freely, but not to admit any air between it and the pump-barrel. When the pump is worked, the piston is raised, and causes a vacuum between itself and the valve below; the external pressure of the air upon the surface of the water in the well then forces it up through the lower valve to supply the vacuum, when the whole space between the valves is filled with water. At the next stroke of the pump, the piston is forced down, and the water rises through the upper valve; when the piston, on being again raised, in addition to its former operation, lifts up the water which had before passed through the upper valve, and discharges it from the spout of the pump; and this it continues to do as long as the pump is worked. Thus, every time the piston is raised, the lower valve rises, and the upper one falls; and every time it is depressed the upper valve opens, while the lower one shuts.

As it is the pressure of the atmosphere which causes the water to rise and follow the piston or bucket as it is drawn up; and since a column of water, about thirty-two feet high, is of the same weight as a column of air of equal area, from the earth to the utmost height of the atmosphere, therefore, the perpendicular height of the piston or bucket, from the surface of the water in the well, must always be less than thirty-two feet. For, independently of the inconvenience in most cases of having so long a stroke, if it were ever so much increased, the water would never rise higher than thirty-two feet (nor indeed so high, as it would have the weight of the valve to lift), and there would be an empty space between the surface of the water in the pumpbarrel and the sucker, and consequently a considerable loss of time and labor. But, when the water has once passed through the upper valve, it may be lifted by it to any height, if the pistonrod be made long enough, and a sufficient degree of strength employed, without ever lengthening the stroke.

The construction of pumps is usually explained to the student by glass models, in which the action both of the pistons and valves may be seen. In order to understand the arrangement of the common pump, we may refer to fig. 8, plate II. A is a vessel intended to contain water, which must be deep enough to rise at least as high as from B to C. The valve a on the moveable bucket D, and the valve b on the fixed box E (which box quite fills the bore of the pipe or barrel at E), will

each lie close, by its own weight, upon the hole in the bucket and box, until the engine begins to work. The valves are made of brass, and covered underneath with leather for closing the holes more exactly; and the bucket D is raised and depressed alternately by the handle F and rod G c, the bucket being supposed at H before the working begins.

Take hold of the handle F, and thereby draw up the bucket from H to I, which will make room for the air in the pump to dilate itself, by which its spring is weakened, and then its force is not equivalent to the weight or pressure of the outward air upon the water A: and, therefore, at the first stroke, the outward air will press up the water through the notched foot B, into the lower pipe, about as far as d: this will condense the rarefied air in the pipe between d and I to the same state it was in before; and then, as its spring within the pipe is equal to the force or pressure of the outward air, the water will rise no higher by the first stroke; and the valve b, which was raised a little by the dilatation of the air in the pipe, will fall, and stop the hole in the box E; and the surface of the water will stand at d. Then depress the piston or bucket from I to H, and, as the air in the part H cannot get back again through the valve b, it will (as the bucket descends), raise the valve a, and so make its way through the upper part of the barrel c, into the open air. But, upon raising the bucket D a second time, the air between it and the water in the lower pipe at d, will be again left at liberty to fill a larger space; and so, its spring being again weakened, the pressure of the outward air on the water A, will force more water up into the lower pipe from d to e; and when the bucket is at its greatest height I, the lower valve b, will fall, and stop the hole in the box E, as before. At the next stroke of the bucket or piston, the water will rise through the box E towards H, and then the valve b, which was raised by it, will fall when the bucket D is at its greatest height. Upon depressing the bucket again, the water cannot be pushed back through the valve b, which keeps close upon the hole whilst the piston descends. And, upon raising the piston again, the outward pressure of the air will force the water up through E, where it will raise the valve, and follow the bucket to I. Upon the next depression of the bucket D it will go down into the water in the barrel H; and, as the water cannot be driven back through the now close valve b, it will raise the valve a as the bucket descends, and will be lifted up by the bucket when it is next raised. And now, the whole space below the bucket being full, the water above it cannot sink when it is next depressed; but, upon its depression, the valve a will rise to let the bucket go down; and when it is quite down the valve a will fall by its weight, and stop the hole in the bucket. When the bucket is next raised, all the water above it will be lifted up and begin to run off by the pipe K. And thus, by raising and depressing the bucket alternately, there is still more water raised by it; which, getting above the pipe K, into the wide top L, will supply the pipe, and make it run with a continued stream.

will come in through the pipe h, and get into the barrel. It is evident, that a few repetitions wil at last fill the barrel on both sides of the piston with water. When this is accomplished, there is no difficulty in perceiving how, at every ise of the piston, the water of the cistern will come in by the valve n, and the water in the upper part of the barrel will be driven through the valve o; and, in every descent of the piston, the water of the cistern will come into the barrel by the valve p, and the water below the piston will be driven through the valve m; and thus there will be a continual influx into the barrel through the valves n and p, and a continual discharge along the rising-pipe I, through the valves m and o.

This machine is certainly equivalent to two forcing-pumps, although it has but one barrel and one piston; but it has no sort of superiority. It is not even more economical, in most cases; because, probably, the expense of the additional workmanship will equal that of the barrel and piston, which is saved. There is, indeed, a saving in the rest of the machinery, because one lever produces both motions. It therefore cannot be called inferior to two pumps; and there is undoubtedly some ingenuity in the contriv

ance.

The forcing-pump represented at fig. 1, plate III., consists of a barrel A B, and a piston or forcer C. It is also provided with an airvessel v.

When the forcer is first moved upwards in the barrel, the air between that and the water below, having room to dilate, by its natural spring, will of course be rarefied; the pressure of the atmosphere being intercepted by the force of the barrel A Bon one hand, and by the upper valve at S in the branching-pipe, on the other, the water will rise from the spring into A B, for the reason already given; and repeated strokes of the piston will fetch up the fluid to the forcer, and fill the cavity of the pipes between the fixed valves D and S. The water in this manner raised, being hindered from going down again by the lower valve, will be pressed by the forcer every time it descends, and be thereby obliged to make its way where there is least resistance, viz. through the upper valve at S. And whenever, on the rising of the forcer, this pressure intermits, the valve at S will immediately close under the weight of the upper water, and prevent its return that way, while the piston is rising with a fresh supply; and this is repeated at every stroke of the forcer.

It is evident that the operation of a pump is by starts, and that the water in the main remains at rest, pressing on the valve during the time that the piston is withdrawn from the bottom of the working-barrel. It is in most cases desirable to have this motion equable, and in some cases it is absolutely necessary. Thus, in the engine for extinguishing fires, the spout of water, going by jerks, could never be directed with a certain aim, and half of the water would be lost by the way; because a body at rest cannot in an instant be put in rapid motion; and the first portion of every jerk of water would have out a small velocity. A very ingenious contrivance has been fallen upon for obviating this inVOL. XI.

convenience, and procuring a stream nearly equable. At any convenient part of the rising pipe, beyond the valve S, there is annexed a strong and capacious vessel V, closed at top by a small pipe T fixed into it, which reaches nearly to the bottom of the vessel. When the water is forced along the rising-pipe, S, it gets into this vessel, and rises above the lower part of the pipe T. The air, which is above the water in the vessel, being now confined, and being condensed into a smaller space by the admission of more water at each action of the piston, presses by its elasticity upon the surface of the water, which cannot return by the valve S, and forces it up the pipe T in a continued stream. This air-vessel must be so large, that the change of bulk of the compressed air, during the inaction of the piston, may be inconsiderable, otherwise the stream will not continue until the next stroke. We must not imagine, that because the stream produced by the assistance of an air-vessel is almost perfectly equable, and because as much water runs out during the returning of the piston as during its active stroke, that it therefore doubles the quantity of water. No more water can run out than what is sent forward by the piston during its effective stroke. The continued stream is produced only by preventing the whole of this water from being discharged during this time, and by providing a propelling force to act during the piston's return. It is, however, a matter of fact, that a pump, furnished with an air-vessel, delivers a little more water than it would do without it.

In forcing-pumps it is of the utmost consequence to avoid all contractions in the pipes. The main, which leads from the forcing-pumps, should be equal to the working barrel. If it be only half the diameter, it has but onefourth of the area; the velocity in the main is four times greater than that of the piston; and the force necessary for discharging the same quantity of water is sixteen times greater. It is not, however, possible to avoid these contractions altogether, without making the main wider than the barrel; for if only so wide, with an entry of the same size, the valve makes a considerable obstruction. Unskilful engineers endeavour to obviate this, by making an enlargement in that part of the main which contains the valve. If this be not done with great judgment, it will increase the obstruction; for, if this enlargement be full of water, the water must move in the direction of its axis with a diminished velocity; and, when it comes to the main, it must again be accelerated. In short, any abrupt enlargement, which is to be afterwards contracted, does as much harm as a contraction, unless it be so short that the water in the axis keeps its velocity until it reach the contraction. All angular enlargements, all boxes into which the pipes, from different working-barrels, unite their water before it goes into a main, must therefore be avoided by an artist who would execute a good machine; and the different contractions, which are unavoidable at the seats of valves, and the perforations of pistons, &c., should be diminished, by giving the parts a trumpet shape. In the airvessel, for producing a constant stream, this is of 2 L

very great consequence. The throat, or the end of the tube throath which the water is forced by the expansion of the contined air, should be :lways form I'm this mamer. A neglect of this scemi ly tulling circunstance will diminish th performance at least one-fifth.

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Ta requisites of a valve are, that it be tight, and of sufficient strength to resist the pressure to which it is exposed; that it afford a free passage to the water; and that it do not allow much to go back whilst it is shutting. The clack-valve is of all others the most obvious and common. It conists merely of a leather flap, covering the perinac, and having a piece of metal on the upper sid, Loth to stion then and to make it heivier, that it may s ut of its lf. Sometimes the huge is of metal. The hinge being liable to oe worn by such incessant motion, and as it is troublesome, especially in deep mines and under water, to undo the joint of the pump, in order to put in a new valve, it is frequently annexed to a box like a piston, made a little conical on the outside, and dropt m'o a conical seat made for it in the pipe, where it sticks fast; and, to draw it up again, there is handle, like that of a basket, fixed to it, which can be laid hold of by a long grappling-iron. The only defect of this valve is, that, by opening very wide, when pushed up by the stream of water, it allows a good deal to go bak during its shutting again.

The butterly-valve is free from most of these inconveniences, and seems to be the most perfect of the clack-valves. It consists of two semicircul Paps reveiving round their diameters, which ar fixed to a bar placed across the opening through the cistern. Some engineers make their great valves of a pyramidal form, consisting of four clack, whose hinges are in the circumerence of the water-way, and which meet with their points in the middle, and are supported by for uls, which rise up from the sides, and This is a most excellent attan, affordin, te thojn spatioas Waxi-way, and A very readily.

T'..

vave, callel the nsists of a pate of as ex ctly ted pro

laid over the trunk, observing to break the joints. A third layer of boards, nailed firmly to the first and second layer, will complet the body of the pump, if of a common size Esty live inches); but, if the pu ap is larger, it may be strengthened by adding more layers of boards. The substitute for the upper box of the common pump consists of two isosceles triangular valves, the sides of which are double the length of the base, jointed with leather to two square pieces of wood (hard wood, if convenient). These two pieces of board, to which the valves are jointed, play diagonally in the pump. Between these two pieces of board is fastened, with nails, the pump rol, which is also made of deal board: the leather which forms the joint should be extended over the sides of the valves, so as to form the stuffing, as the valves lie obliquely in the angles of the pump. The inside of the valves may be loaded with sheet lead, if convenient; at any rate, they should be filled with as many nails as the valves will hold without weakening them. The upper valves are furnished with a check string, to prevent the fnction of the valves on the sides of the pump; this check, which may be made of small line, is very important to the ease of working the pump. It should be so adjusted as to prevent the valves from resting on the sides of the pump; the leather only should touch the pump. The lower valves, which are fixed to the bottom of the pump, are made similar to the upper valves, with the exception of the rod and check. Between the lower valves a piece of hard wood, for hooking up the valves, if no sheet iron or copper is at hand, should be fastened.

This pump works very easily, owing to the water-way by the valves being much greater than the water-way through common boxes. It is not liable to choke, in consequence of the water not being wire-drawn below the boxes or valves; for the water-way Lelow the valves may be so contracted as to draw up even iron; but, by enlangng the bottom of the pump, this will te

We may now notice the ingenious purap contrived by Mr. Aust, for winch he was rewarded by the Society of Arts. The advantages which it possesses over pumps of the ordinary construction depend on the curvilinear form of the barrel, which allows, and indeed obliges, the rod, the handle, and the lever, on which it works, to be all in one piece. Hence results, not only a much greater simplicity in the workmanship, and consequent cheapness, but a greater steadiness and precision of action, whereby more water is discharged, and the leathering of the valve will last a much longer time without wanting repair.

Plate II, fig. 3, is a view of the pump, aa, the bar. 1, forming a curve of a quaiter of a circle, ved at the upper end to the head ƒ, and at as lower to the pipe b: bb, the pi,e that cornets the water into the Lam1; it is made curvilinear, in order that as little ob