Mr. Ferguson gives the following table for finding the dimenfions of a pump that fhall work with a given force, and draw water from a given depth, the handle being supposed to increase the power five times. It is alfo fupposed that one man can work a pump four inches diameter, and thirty feet high, and discharge 274 gallons of water in a minute; the measure being that called English wine-measure.

Now, to find the diameter of a pump that fhall raife water with the fame ease as a man can work a pump thirty feet high, with a four-inch bore, look for the height in the firft column, and over against it, in the fecond, you have the diameter or width of the pump, and in the third you find the quantity of water which a man of ordinary ftrength can difcharge in a minute,

OF THE FORCING PUMP, fig. 2, pl. 3.

It is fo called, because it not only raises the water into the barrel, like the foregoing, but it afterwards forces it up into a refervoir, in a lofty fituation. The operation and nature of this pump will be evident by attending to the working of this model, fig. 2, pl. 3. The pipe and barrel 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 Ba pipe M M is fixed, and at right-angles to this pipe a ciftern, or air-veffel, KK; at the bottom of the air-veffel there is a valve, b; from the top a fmall pipe, O'HI, is inferted fo as nearly to reach the bottom of the air-veffel, and at the fame time be air-tight at top.

I fhall now begin to work the model, that you may fee and comprehend the effects. The pipevalve, a, rifes when I draw the piston up; but falls down, and ftops the hole, the moment the pifton is at it's greateft 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-veffel, it is forced into this veffel by depreffing the pifton, and retained therein by it's valve b; which thuts the moment the piston begins to be raised, because the preffure

preffure of the water against the under fide thereof then ceases.

The water being thus forced into the air-veffel by repeated ftrokes of the pifton, has now got above the lower end, I, of the pipe, and begins to condense the air in the air-veffel; for the air has no way to get out of this veffel, but through the tube OHI of the pipe, and is prevented from escaping this way when the mouth of this tube is covered with water. It is also gradually more and more condensed as the water rifes in this veffel; till at last, as you fee, it preffes fo ftrongly upon the water as to force it up through the pipe OHI; from whence it fpouts at F in a jet to a great height, and is fupplied by alternately raifing and depreffing of the piston.

The higher the furface of the water is raised in the air-veffel, the smaller is the space into which the air is condenfed; and confequently it's fpring will be ftronger, and the preflure greater upon the water, which will be thereby driven with greater force through the pipe; and as the fpring of the air continues to act even while the pifton is rifing, the stream 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 clofed, to prevent the water, which is forced into the air-veffel, from running back by it's pipe into the air-veffel.

The effect of this kind of pump is not limited to raifing water to any particular altitude; fince the air's condenfation may be raised to any degree.

If the air's condenfation is double to that of the atmosphere, it's elaftic force will raise the water to about the height of thirty-four feet. If the condenfation be increased three-fold, the alti

tude

tude to which water may be raised by it will be about twice the former height, or fixty-eight feet; the altitude of the raised water being increased thirty-four feet for each addition of unity to the number which expreffes the air's condensation.

The engines ufed for extinguishing fire are upon this construction; confifting of 2 barrels, by which water is alternately driven into a clofe air-veffel. The forcing the water therein condenfes the air, which compreffes the water fo ftrongly, 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 condenfation of air upon it's furface,

OF DE LA HIRE'S PUMP, fig. 3, pl. 3.

The model before you is that of a pump invented by M. De la Hire, which is fo conftructed, as to raife water as faft by the defcent as the afcent of the pifton. As before, the trough in which the two pipes are placed reprefents the well: one of the pipes, B, is fitted to the lower end of the barrel in which the pifton works; the top of the other pipe, C, is fo connected with a smaller one, as to communicate 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 pifton. The valves e and s lie clofe and air-tight at the top of their refpective pipes E and F.

When the piston ftops at it's greatest height,

the

the valve at the bottom of the barrel closes, and prevents the water from being forced back. Hence, as the pifton is depreffed, it forces all the water in the barrel up through the lower crooked pipe F, and through it's valve, into the air-veffel.

The pifton-rod moves through what is called a collar of leather, which makes it air-tight.

During the defcent of the pifton, the valve upon the upper crooked pipe falls down, and the preffure of the air on the water in the trough raifes the water through this pipe, C, and the valve at the top of it, which is opened upwards by the power of the ascending water; and this water runs into the barrel of the pump, and fills all the space therein above the piston.

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 closes it, fo that no water can be forced back through it. As the pifton is raised, all this water is forced through the upper pipe E, and, after opening it's valve e, into the air-veffel P.

Thus, as the piston defcends, it forces all the water below it up the pipe F; and, as it rifes, it forces all the water above it up the pipe E; fo that there is as much water forced up into the airveffel by the afcent, as by the defcent of the pifton. The air is compreffed in the air-veffel as in the preceding cafe; and the water being equally forced in, rufhes out with a conftant and very nearly equal ftream. It is evident, from what we have already told you, that the top of the pipe that opens into the upper part of the barrel fhould never exceed thirty-two feet.

OF