of increasing the quantity of water which the machine will raise, unless it was in a considerable degree; and indeed the very best pumps will not raise a much greater proportion with the same power.

The only alteration which has been made on Mr. Cole's pump, since its first introduction, near thirty years ago, is, that they now omit the lower sprocket-wheel altogether, the ascending and descending pipes being so united by a curved metal tube, that the chain passes better than if a wheel was used. The cranks are made to take off, and apply, when wanted, that they may not be in the way; they are long enough for thirty men to work at once; of late it has been proposed to add fly-wheels to them. This would be attended with but slight advantage, and several inconveniences from occupying that room where the men should stand to work, it being an object to employ as many as possible; but if they are crowded, they only incommode each other instead of assisting.

14. The following simple and ingenious method of working a ship's pump, when the crew are either too few in number, or too much exhausted to attend to that duty when the performance is most necessary, namely, in a heavy gale, was put in practice with great success by Capt. Leslie, of the ship George and Susan, on a late voyage from Stockholm to North America. He fixed a spar aloft, one end of which was ten or twelve feet above the top of his pumps, and the other projected over the stern; to each end he affixed a block or pulley. He then fastened a rope to the spears of the pump, and after passing it through both pullies along the spar, dropped it into the sea astern. To the rope he fastened a cask of 110 gallons measurement, and containing 60 or 70 gallons of water. This cask answered as a balance-weight, and every motion of the ship from the roll of the sea made the machinery work. When the stern descended, or when a sea or any agitation of water raised the cask, the pumpspears descended; and the contrary motion of the ship raised the spears, when the water flowed out. The ship was cleared out in four hours, and the crew were of course greatly relieved.

15. Hand-pumps have been constructed in great variety for the use of ships; and as they are of great utility, we shall describe two or three of the best.

The ingenious Benjamin Martin invented a ship's pump with two barrels drawing from one suction-pump, so as to raise a constant stream.

This pump has so much merit, that we have given a section of it, fig. 256. Here A is the suction-pipe, conducting the water from the ship's hold up to the pump, where it is enlarged to communicate with both barrels D D, through the valves C C, in the bottom; E E are the pistons of the barrels, with double valves in them; they are not, like other pistons, fitted to slide in the barrels, but are simply brass rings, in which the valves are fitted, and being smaller than the barrels, have large circular pieces of leather fixed on them, the outside edges of which are attached to the insides of the pumpbarrels; hence, when the pistons are moved up and down, the leather folds sufficiently to admit the motion, as is shown in the figure; but being close all round, these pistons can have no leakage or friction, and only a small resistance from the stiffness of the leather.

To fasten the edges of the leather piston to the barrels, they are made in two lengths, an upper and a lower, and the leather is introduced in the joint between them, being half fast, and the pump kept together by bars II, fixed over the barrels, and bolts to press the upper length of the barrels down upon the lower. Both the barrels are included within a box or cistern B B, fixed upon the ship's deck, with trunks L L, which carry off the water as it runs over the tops of the barrels into the cistern. The pump is worked by piston-rods HH, being united by chains to a wheel K, the axle of which is supported by standards from the sides of the cistern B B, and is put in motion by the double lever M, at the end of which cross handles are fixed for several men to work at once. Mr. Martin's pump acts extremely well; the constant stream raised by the alternate action of two barrels upon one pipe, produces an advantage that was shown by experiment, for the water not only rises while the piston rises, but continues to do so even after the piston begins to descend; and therefore the pump was found to deliver more water than was expected from the calculation of the contents of the barrel, and the number of strokes made.

To account for this, it must be considered, that as this pump has both its large pistons working (alternately ascending and descending) at the same time, there must be produced a constant rising column of water in the pipe, whose velocity through a bore of five inches, to supply the barrels of twelve inches diameter each, must be so great, that it cannot be checked or stopped at once, or upon the first descent of the piston; and therefore a surplus of water is produced. Not withstanding these advantages of Mr. Martin's pump, it has objections, which are serious obstacles to its use on board ships, though in other situations it is a good machine: these are, the shortness of its stroke, which renders it very fatiguing for men to work for a long time; but another more serious objection is, that the leather would, in general, remain dry, and thus become liable to harden and grow stiff, so as to break into holes when used at first, before they become soaked, and to fill the cistern first with water would be very trouble

some.

16. The latest improvements in hand-pumps are by Capt. Jekyl, R. N. This gentleman has invented an addition to the pump of an air-vessel, and stuffing-box for the rod to pass

through, by which it will raise the water to a greater height than the head of the pump; and a hose being attached to the pump-spout, by very simple means, the water is conveyed to any part of the ship, and thrown in a jet through a hose-pipe with great force, to extinguish fire, if such a calamity should befall a ship; and thus the pump is rendered of twofold service. The idea of converting the pump to a fire-engine is not new, having been attempted in many different ways by forcingpumps; but these having pipes proceeding from the lower parts of the barrels and valves, which are not very accessible, are always liable to choke up by obstructions, and have not succeeded in general use. The air-vessel has always been in the way, if made of a sufficient size to answer the purpose of equalizing the stream. Capt. Jekyl has obviated these objections, and without altering the material parts of the handpump, has rendered it as complete a fire-engine as can be wished.

This is explained by figure 257, which is a section of the pump through its whole length. ABC is the iron brake or lever to work it; it is branched to the extreme end, and has a wooden pole C, fixed in it, for several men to hold at once; D is the iron stanchion or fulcrum of the brake; it is fixed to the pump-head by means of strong iron hoops at EE and FF, which at the same time strengthen the work of the pump. The centre-pin is to be at the height of two feet six inches above the ship's deck. I are the slings of the pump, united by a forelock or pin to the end of the brake, and suspending the pump-spear I, by means of the joint-piece g. IK is the pumpspear, made of copper in the upper part I, and the lower length K of iron; the latter has the bucket M attached to it. The valve of the bucket is made in a very simple and effective manner, the valve being merely a round plate of brass, with a hole through the centre, to receive the rod upon which it rises and falls, and covers the aperture in the bucket. The bucket is a ring of brass, with a cross bar to fix the rod in; it is made in two thicknesses, one above the other, and a cup of leather is held in between them, projecting all round the upper part of the bucket, and turning up, to make a tight fitting in the barrel. The two rings of the bucket are held together by the piston-rod passing through both, and a cross wedge beneath. L is the brass chamber in which the bucket works; it is well fitted into the wood of the pump-tree, so that the water cannot leak by it, and is bored smooth withinside.

N is the lower box, fitted into the lower part of the pump-tree, beneath the chamber; it has a groove round it, into which oakum is placed, and when it is put down, makes a tight joint; its valve is of the same construction as that of the bucket, with the addition of a ring or eye on the top of the pin, on which the valve rises and falls. By this eye the box can be drawn up when it needs repair, by first drawing up the bucket of the pump, and putting an iron down into this eye. OOP is the air-vessel; this is a cylinder of sheet-copper, soldered to a cover of brass; within the centre of it is a tube likewise soldered to the cover, through which the copper pumpspear passes, and is fitted round at top with a collar of leather and stuffing. To prevent the escape of the water, it is packed with hemp, and two rings of leather. R shows the place of two iron bars, fitted through the head 01