with a hole at W, into which the water fpouting SECT. V. Of the MOTION of WATER in CONDUIT IN conducting water from one place to another, the conduit pipes must be longer in proportion as the places to which it is to be conveyed are more diftant from each other. In the additional tubes above mentioned, SECT. IV. we took no notice of FRICTION, as in the cafes then under confideration it was scarcely perceptible. In long tubes, however, it is different; for the friction of thefe leffens confiderably the velocity of the water. On this part of our fubject, we need only to relate the refult of the various experiments that have been made. In thofe of M. Boffut, the tubes were straight; one of them was 16 lines infide diameter, the other two inches; and the tubes were fucceffively lengthened from 30 to 180 feet. The conftant altitude of the water in the refervoir, above the axis of each tube, was in fome cafes one foot, in others two feet. This is a branch of hydrostatics, in which theory is neceffarily imperfect, and the only means of arriving at truth muft be from experiment. INCHES of inches of wa Constant al- Distance to No. of CUBIC No. of cubic ft. meter in a which the water was WATER dis ter dischar conveyed, ex- charged by the tube of ged by the tube of two 16 lines di inches dia ameter in a minute. minute. By comparing this with the table in SECT. IV. it appears that the discharges of water there are much greater than the corresponding ones in the prefent table, and that the difcharge is leffened as the tube is lengthened, because there is a greater furface for friction. The diminution alfo in the discharge is not in proportion to the length of the tube; for the first 30 feet diminishes the discharge much more than the fecond 30 feet, and the third length of 30 feet diminishes ftill less in the dif charge, and so on. From these experiments it appears, that great accuracy is not neceflary in practice; and perhaps we may adopt for a general rule," that the difcharges made in equal times by an horizontal tube, with the fame altitude of refervoir, but at different distances from the first aperture of the tubes, are to each other nearly in the inverse ratio of the fquare roots of the distances." The difcharge is more in proportion from the there is lefs rubbing furface in proportion in the larger tube than from the fmaller one; because larger tube. If the tubes are curved inftead of being ftraight, the discharge will be somewhat diminifhed. This diminution in the discharge appears to arife from the impact of the water against the angular parts of the tube, whereby its velocity is diminished. This diminution will therefore vary with the degree of curvature. When the plane of the curvature of the tube is in a vertical direction, there will be portions of the tube where the air will fix itself, so as to leffen the velocity, or even stop the courfe of the water. Let ABCDE, fig. 13, pl. CLXXXVI. be a tube, whose upper end A is joined to the refervoir that furnishes the water, G the end by which the fountain is fupplied. When the communication at A is opened, the tube is filled with air; the water will fill the tube AB, drive out the air, and rife to C. Here experience has fhewn, that the water runs down the lower part of the curvature, and fills up the neck D, leaving behind it the column of air CD; which will remain there, notwithstanding the preffure of the common air AB, The The water continuing to flow, runs down the lower part of EF, and fills the neck F, leaving the 2d column of the air at EE; fo that the water will be only raised to I, and will not run out at G. SECT. VI. Of the CHAIN PUMP. AFTER what has been faid concerning conduit pipes, the efflux of water from different apertures, &c. we are led to confider the nature and action of pumps. Their general principles will be found explained under PNEUMATICS and PUMP. We fhall here notice the different kinds, and remark fome varieties in their construction. One of the most valuable mechanical inventions of this kind is the CHAIN PUMP. It is generally made from 12 to 24 feet long; confifts of two collateral fquare barrels, and a chain of piftons of the fame form, fixed at proper distances thereon, The chain is moved round a coarse kind of wheel work, fixed at one end of the machine. The teeth of this are so contrived as to receive one half of the flat pistons, and let them fold in, and they take hold of the links as they rife. A whole row of the piftons (which go free of the fides of the barrel by near a quarter of an inch) are always lifting when the pump is at work; and as this machine is generally worked with brifknefs, they bring up a full bore of water in the pump. It is wrought either by one or two handles, according to the labour required. This pump is fo contrived, that, by the continual folding in of the pistons, ftones, dirt, and whatever may happen to come in the way, may alfo be cleared: it is therefore used to drain ponds, fewers, and remove foul water, in which no other pump could be employed. A fection of this machine, as fixed in a frigate of war, is exhibited in pl. CLXXXVII. where A is the keel, V the floor timber, X the kelfon, a, a, a the several links of the chain, bb the valves, C the upper wheels, D the lower wheels, ce the cavities upon the furface of the wheels to receive the valves, as they pass round thereon, dd the bolts fixed across the surface of the wheels, to fall in the interval between every two links, to prevent the chain from fliding back. SECT. VII. Of the COMMON or SUCKING PUMP. THIS PUMP, as well as the FORCING PUMP, and all others which act by the preffure of the atmosphere, are pneumatic as well as hydraulic machines, and are therefore styled by fome hydraulico-pneumatical engines. Their nature, action, and operation, are beft explained by glafs models; in which the motion of the piftons and the play of the valves may be diftinctly seen. We shall however attempt to describe them. The COMMON or SUCKING PUMP is delineated on pl. CLXXXVII. fig. 3. A tub or trough filled with water may reprefent the well from which water is to be raised. There are two valves in this pump: the one (6) at the upper end of the small tube; the other (a) on the moveable pifton. When the pump is not worked, their weight makes them lie close upon the holes over which they are placed. The PISTON is raifed or depreffed by means of the pifton-rod, which is connected with the pump. handle. The pifton being placed at the bottom of the barrel, before we begin to work, we fhould raife it from the bottom to the top of the barrel; which makes room for the air in the pump, be low the pifton, to expand itself. The air in the pipe being thus dilated, preffes lefs on the surface of the water within the pipe, than the atmosphere does without on that in the trough; and confequently the water rifes in the tube till the preffures are equal; that is, till the air within is juft as denfe as that without; and it will there remain at rest between the two equal preffures. The valve at the bottom, which rofe a little to let fome of the rarefied air into the barrel, falls down again, and clofes the hole at the top of the pipe. We now deprefs the pifton; and as the air in the barrel cannot get back again through the valve ¿, at the top of the pipe, it will raise the valve in the pifton, and fo make its way through the upper part of, the barrel into the open air. Upon raifing the pifton again, the air between it and the water in the lower pipe will again be left at liberty to fill a larger fpace; and fo its fpring being again awakened, the preffure of the atmosphere will force more water into the pipe; and when the pifton is at the top of the barrel, the lower valve falls, and stops the hole at the top of the pipe, as before. The fame effect is produced by every ftroke, till at last the water in the pipe reaches the bottom of the barrel. Now, upon depreffing the pifton, as the water cannot be forced back again through the lower valve, it will raise the upper valve as the piston defcends, and will be lifted up by the pifton when raised again. The whole space below the piston being now full of water, as the water cannot escape by the lower valve, it will, on depreffing the piston, raise the valve, in order to let the pifton down. When this is quite at the bottom, the valve will fall by its own weight, and stop the hole in the piston. When the pifton is next raised, all the water above it will be lifted up, and run out of the spout; and thus, by alternately raifing and depreffing the pifton, ftill more water will be raised; which, getting above the Pipe into the wide part at top, will fupply the fpout, and make it run with a continual ftream. Thus, every time the piston is elevated, the lower valve rifes, and the upper valve falls; but every time we deprefs the pifton, the lower valve falls, and the upper one rifes. As it is the preffure of the air in the atmosphere which caufes the water to rife, and follow the piston when drawn up; and as a column of water, 33 feet high, is of equal weight with as thick a column of air, from the earth to the very top of the atmosphere; therefore the perpendicular height of the pifton from the furface of the water in the well muft always be less than 33 feet, otherwife the water will never rife above the piston. But when the height is lefs, the preffure of the atmosphere will be greater than the weight of the water in the pump, and will therefore raise it above the pifton; and when the water has once got above the pifton, it may be thereby lifted to any any height, if the rod be made long enough, and a fufficient degree of ftrength be employed to raise it with the weight of water above the piston. The force required to work a pump is as the altitude of the water to be raised, and as the fquare of the diameter in that part where the pifton works. Hence, if two pumps be of equal height, and the one be twice the bore of the other, the largest will raise four times as much water as the narroweft, and will therefore require to be worked with four times as much strength. The wide nefs or narrowness of the pump in any other part befides that where the piston works, does not render the pump either more or lefs difficult to work, except what difference may arife from the friction of the water in the bore, which is always greater in a narrow bore than a wide one. The pump rod is generally raised by means of a lever, whofe longer arm, where the power is applied, is generally 5 or 6 times the length of the fhorter arm; by which means it gives five or fix times as much advantage to the power. Mr FERGUSON gives the following table for finding the dimenfions of a pump that shall work with a given force, and draw water from a given depth, the handle being fuppofed to increase the power five times. It is alfo fuppofed that one man can work a pump four inches diameter, and 30 feet high, and discharge 274 gallons of water, English wine measure, in a minute: Height of the pumps above the furface of the well. Feet. 10 Diamet. of the | Water difcharbore where the ged in a mi. pifton works. nute. 5966 20 4'90 40 25 4'38 32 30 4'00 27 35 3'70 23 40 3°46 20 3 45 3'37 To find the diameter of a pump that fhall raife water with the fame eafe as a man can work a pump 30 feet high, with a four-inch bore, look for the height in the first column, and over against it, in the 2d, is fhewn the diameter or width of the pump, and in the 3d the quantity of water which a man of ordinary strength can difcharge in a minute. SECT. VIII. IMPROVEMENTS of the COMMON PUMP. IN 1766 it was announced in the public papers, VOL. XI. PART II. that at SEVILLE in Spain, a fimple fucking pump had been conftructed, which raised water 60 feet; and they concluded from thence, that those were ftrangely deceived who had afferted that the preffure. of the atmosphere would not support a higher column than 32 feet. On examination it was found, that an ignorant tin-man at Seville had made a common fucking pipe with its lower valve 60 feet from the furface of the water; but finding he could raise no water by it, either through impatience or paffion, with a ftroke of a hatchet he made a fmall opening about ten feet above the furface of the water, and which forced a small quantity of water above the lower valve; the reafon of which we fhall explain by a diagram. See fig. 3, plate CLXXXVII. Suppofe PF the fucking tube, d the furface of the water, from d to F 60 feet; and that after a certain number of strokes of the piston, the water was raised 32 feet in the tube, or to e; and that then a fmall hole was made at ten feet from the furface of the water. The air which enters this preffing equally every way, makes the water which is below b fall down into the well; while the pref fure upwards forces the water up 32 feet through the valve into the body of the pump. But this is not all, for it would have carried it to a much greater height; for the air near the earth is above 800 times rarer than water; and fuppofing the denfity of a column thereof to be uniform (which is not the cafe), ten feet of water taken away would be equivalent to a column of 8000 feet of air; so that the remaining 22 feet would be in equilibrium with the air, after being raised 8000 feet. To have a fecond portion of wafer, the hole b must be stopped up, and the piston worked till the water rifes to e, and then re-open the hole. In the first place we see, that this pretended discovety is fo far from invalidating the principle of the preffure of the air, that it is a direct consequence thereof; 2d, that even to make it answer at all, it is neceflary that the pipe be very small, or the column of water would be broken to pieces, the air would pass through, and very little would rife. But a real improvement of the common pump has been made by Mr TODD of Hull. This invention in fome particulars bears a resemblance to the ordinary one, but he has contrived to double its powers by the following means: Having prepared the pifton cylinder, which may be 12 feet high, he cuts from the bottom thereof about three feet; at the end of the great cylinder he places an atmofpheric valve, and to the top of the small cylinder a ferving valve. In the bottom of the small cylin der, which contains the ferving valve, is inferted an oblong elliptical curved tube, of equal calibre with the principal cylinder, and the other end is again inferted in the top of the great cylinder. This tube is divided in the fame manner as the firft cylinder, with atmospheric and ferving valves, exactly parallel with the valves of the first cylin der. The pump, thus having double valves, produces double effects, which effects may be still farther increased by extending the dimenfions. tube forew, which projects from the fide of a reThe cylinder is fcrewed for service on a male fervoir or water ciftern, and is worked by the hand. The pifton-plunger ist worked by a toothed feg ! ment-wheel, fimilar to the principle of the one ufed in working the chain-pumps of fhips belonging to the royal navy plate CLXXXVII. fig. 2.); and the wheel receives motion from a hand winch, which is confiderably accelerated by a fly-wheel of variable dimenfions, at the oppofite end.'. This pump, in addition to its increased powers, poffeffes another very great advantage. By ferew ing to it the long leather tube and fire-pipe of the common engine, it is in a few minutes converted into an effective fire-engine. Hence, whoever poffelles one, may be faid to have a convenient do mestic apparatus against fire. Three men can work it; one to turn the winch, another to direct the fire-pipe, and a third to supply the wa ter. SECT. IX. Of the FORCING PUMP. THE FORCING PUMP is so called, because it not only raises the water into the barrel, like the former, but afterwards forces it up into a refervoir in a lofty fituation. The nature and operation of this pump will be evident, by attending to the working of the model, fig. 4. The pipe and bar rel are the fame as in the other pump, but the pifton G is folid, having no valve, fo that no water can get above it. At the bottom of the barrel B a pipe MM is fixed, and at right angles to this pipe a ciftern or air veffel KK; at the bot tom of the air veffel there is a valve b; from the top à fmall pipe OHI is inférted, fo as nearly to reach the bottom of the air veffel, and at the fame time be air-tight at top. In working this pump, the pipe valve a rifes when we draw the pifton up; but falls down, and ftops the hole, the moment the pifton is at its greatest height. Now as the water, which has been raised above this valve, cannot get back again into the pipe, but has a free paffage by the pipe M M, that opens into the air veffet, it is forced into this veffel by depreffing the pifton, and retained therein by its valve b; which huts the moment the pifton begins to be raised, because the preffure of the water against the under fide exifts no longer. -The water, being thus forced into the air veffel by repeated strokes of the piston, we fuppofe to have now got above the lower end, I of the pipe, and that it begins to condense the air in the airveffel; for the air has no way to get out of this veffel, but through the tube O HJ of the pipe, and is prevented from efcaping this way when the mouth of this tube is covered with water. It is al fo gradually more and more condensed as the water rifes in this veffei; till at laft it preffes fo ftrongly upon the water as to force it up through the pipe O HI; whence it spouts at F in a jet to a great height, and is fupplied by alternately raising and depreffing the pifton. The higher the furface of the water is raised in, the air veffel, the smaller is the space into which the air is condensed; and confequently its fpring will be ftronger, and the preffure greater upon the water, which will be thereby driven with the greater force through the pipe; and as the spring of the air continues to act even while the pifton is rifing, the ftream will be uniform as long as the pifton is worked. The valve of the pipe opens to let the water follow the pifton in rifing. Whilft this valve is open, that of the air veffel is closed, to prevent the water, which is forced out of the air-veffel, from running back by its pipe into the air-veffel. The effect of this kind of pump is not limited to raifing water to any particular altitude; face the condensation of the air may be raised to any degree. If the condensation of the air is double to that of the atmosphere, its elaftic force will raife the water to about the height of 34 feet. If the condenfation be increased threefold, the altitude to which water may be raised by it will be about twice the former height, or 68 feet; the altitude of the raised water, being increased 34 feet for each addition of unity to the number which expreffes the condenfation of the air... The engines used for EXTINGUISHING FIRE are made upon this conftruction; and confift of two barrels, by which water is alternately driven into a close air-veffel. The forcing the water therein condenfes the air, which compresses the water fo strongly, that it rushes out with great impetuofity and force through a pipe that comes down into it, and makes a continued uniform ftream by the con. densation of air upon its furface. See SECT. XI. SECT. X. OF OTHER PUMPS which a& by the PRESSURE of the ATMOSPHERE. M. De la HirE'S PUMP is calculated to raise water as faft by the defcent as the afcent of the pifton. The trough in which the two pipes are placed reprefents the. well; one of the pipes, B, fig. 5. is fitted to the lower end of the barrels, in which the pifton works; the top of the other pipe, C, is fo connected with a smaller one, as to com. municate with the upper part of the barrel. There is a valve on the top of the pipes B, C, and alfo on the two pipes E, F, which proceed from the pump-barrel into the air-veffel P. The pifton is folid, or without any valve or opening. As the pifton rifes, the air, preffing on the furface of the water in the trough, forces it up the pipe B, at the bottom of the barrel, and fills it with water up to the piston. The valves e and S lie clofe and air-tight at the top of their respective pipes E and F. When the pifton ftops at its greatest height, the valve at the bottom of the barrel clofes, and prevents the water from being forced back. Hence, as the piston is depreffed, it forces all the water in the barrel up through the lower crooked pipe F, and through its valve into the air-veffel. The pifton rod moves through what is called a collar of leather, which makes it air-tight. During the descent of the piston, the valve upon the upper crooked pipe falls down, and the prefsure of the air on the water in the trough railes the water through this pipe C, and the valve at the top of it, which is opened upwards by the power of the afcending water; and this water runs into the barrel of the pump, and fills all the space therein above the pifton. As foon as the pifton is as low as it can go, the valve at the end of the upper pipe, D. falls down and clofes it, fo that no water can be forced back through it. Aș the pifton is raised, all this water is forced through the upper pipe E. and after opening its valve, f, into the air-veffel P. Thus, as the piston descends, it forces all the water |