account of a quicksilver pump, which has been recently invented by Mr. Thomas Clark of Edinburgh, and which works almost without friction. It has great power in drawing and forcing water to any height, and is extremely simple in its construction.

a a is the main pipe inserted into the well b; a valve is situated at c, and another at d, both opening upwards; a piece of iron tube is then bent into a circular form, as at f, again turned off at g in an angular direction, so as to pass through a stuffing box at h, and from thence bent outwards as at i, connecting itself with the ring. A quantity of quicksilver is then put into the ring filling it from q to q, and the ring being made to vibrate upon its axis h, a vacuum is soon effected in the main pipe by the recession of the mercury

from g to q, thereby causing the water to rise and fill the vacuum: upon the motion being reversed, the quicksilver slides back to g, forces up the water and expels it at the spout e.

"Mr. Clark calculates that a pump of this description with a ring twelve feet in diameter, will raise water the same height as the common lifting pump, and force it one hundred and fifty feet higher without any friction." (Mechanics' Register, and Jamieson's Edinburgh Journal.)

31. It is usual to class with pumps, the machine known by the name of Archimedes' screw or the water-snail. This consists either of a pipe wound spirally round a cylinder, or of one or more spiral excavations formed by means of spiral projections from an internal cylinder, covered by an external cylindrical case, so as to be water tight. The cylinder which carries the spiral is placed aslant, so as to be inclined to the horizon in an angle of from 30° to 45°, and capable of turning upon pivots in the direction of its axis posited at each extremity. The lower end of the spiral canal being immersed in the river or reservoir from which water is to be raised, the water descends at first in the said canal solely by its gravity; but the cylinder being turned, by human or other energy, the water moves on in the canal, and at length it issues at the upper extremity of the tube.

Several circumstances tend to make this fect and inefficacious in its operation.

instrument imperThe adjustments

necessary to ensure a maximum of effectual work are often difficult to accomplish. It seldom happens, therefore, that the measure of the work done exceeds a third of the power employed so that this apparatus, notwithstanding its apparent ingenuity and simplicity, is very sparingly introduced by our civil engineers.

32. Spiral Pump. This machine is formed by a spiral pipe of several convolutions, arranged either in a single plane, as in the marginal diagram, or upon a

cylindrical or conical surface, and revolving round an axis. The curved. pipe is connected at its inner end, by a central water-tight joint, to an ascending pipe, r P, while the other end, s, receives, during each revolution, nearly equal quantities of air and water. This apparatus is usually called the Zurich machine, because it was invented, about 1746, by Andrew Wirtz, an inhabitant of Zurich. It has been employed with great success at Florence, and in Russia; and the late Dr. Thomas Young states, that he employed it advantageously for raising water to a height of forty feet. The outer end of the pipe is furnished with a spoon s, which contains as much water as will half fill one of its coils. The water enters the pipe a little before the spoon has reached its highest position, the other half remaining full of air. This air communicates the pressure of the column of water to the preceding portion; and in this manner the effect of nearly all the water in the wheel is united, and becomes capable of supporting the column of water, or of water mixed with air, in the ascending pipe. The air nearest the joint is compressed into a space much smaller than that which it occupied at its entrance; so that, when the height is considerable, it becomes advisable to admit a larger portion of air than would naturally fill half the coil. This, while it lessens the quantity of water raised, lessens also the force requisite to turn the machine. The loss of power, supposing the machine well constructed, arises only from the friction of water on the pipes, and that of the wheel on its axis and where a large quantity is to be raised to a moderate height, both of these sources of resistance may be rendered very inconsiderable.

33. Schemnitz Vessels, or the Hungarian Machine. The mediation of a portion of air is employed for raising water, not only in the spiral pump, but also in the air vessels of

B

D

Schemnitz, as shown in the annexed diagram. A column of water, descending through a pipe, c, into a closed reservoir, B, containing air, obliges the air to act, by means of a pipe, D, leading from the upper part of the air vessel, or reservoir, on the water in a second reservoir, A, at any distance either above it or below it, and forces this water to ascend through a third pipe, E, to any height, less than that of the first column. The air vessel is then emptied, the second reservoir filled, and the whole operation repeated. The air, however, must acquire a density equivalent to the requisite pressure before it can begin to act so that, if the height of the columns were 34 feet, it must be reduced to half its natural space before any water could be raised, and thus half of the force would be lost. But, where the height is small, the height lost in this manner is not greater than what is usually spent in overcoming friction, and other imperfections of the machinery employed. The force of the tide, or of a river rising and falling with the tide, might easily be applied to the purpose of raising water by a machine of this kind. Thus, if at low tide the vessel A were filled with air; then, at high tide, the water flowing down the tube E, would cause the water in the vessel B to ascend in the pipe c.

34. The Hydraulic Ram. In this hydraulic arrangement, the momentum of a stream of water flowing through a long pipe is employed to raise a small quantity of water to a considerable height. The passage of the pipe being stopped by a valve which is raised by the stream, as soon as its motion becomes sufficiently rapid, the whole column of fluid must necessarily concentrate its action almost instantaneously upon the valve. In these circumstances it may be regarded as losing the characteristic property of hydraulic pressure, and to act almost as though it were a single solid so that, supposing the pipe to be perfectly elastic and inextensible, the impulse may overcome almost any pressure that may be opposed to it. If another valve opens into a pipe leading to an air vessel, a certain quantity of the water will be forced in, so as to condense the air, more or less rapidly, to the degree that may be required for raising a portion of the water contained in it to a given height.

The late Mr. Whitehurst appears to have been the first who employed this method: it was afterwards improved by

Mr. Boulton. But, like many English inventions, it never was adequately estimated, until it was brought into public notice by a Frenchman. M. Montgolfier, its re-inventor, gave to it the name which it now bears of the Hydraulic Ram, in allusion to the battering ram.

The essential parts of this machine are represented in the annexed diagram. When the water in the pipe A B (moving

in the direction of the arrows) has acquired sufficient velocity, it raises the valve B, which immediately stops its farther passage. The momentum which the water has acquired then forces a portion of it through the valve, c, into the air vessel, D. The condensed air in the upper part of D causes the water to rise into the pipe E, as long as the effect of the horizontal column continues. When the water becomes quiescent, the valve в will open again by its own weight, and the current along A B will be renewed, until it acquires force enough to shut the said valve в, open c, and repeat the operation.

The motion in the horizontal tube arises from the acceleration of the velocity of a liquid mass falling down another tube, and communicating with this.

In an experiment made upon an hydraulic ram, at Avilly, near Senlis, by M. Turquet, bleacher, the expense of power was found to be to the produce, as 100 to 62. In another, as 100 to 55 in two others, as 100 to 57. So that a hydraulic ram, placed not in unfavourable circumstances, may be reckoned to employ usefully rather more than half its force..

**For more full accounts of the three last contrivances, the reader may consult the 2d volume of my Mechanics.

SECTION III.-Wind and Windmills.

1. Air, when in continuous motion in one direction, becomes a very useful agent of machinery, of greater or less energy, according to the velocity with which it moves. Were

it not for its variability in direction and force, and the consequent fluctuations in its supply, scarcely any more appropriate first mover could generally be wished for. And even with all its irregularity, it is still so useful as to require a separate consideration.

2. The force with which air strikes against a moving surface, or with which the wind strikes against a quiescent surface, is nearly as the square of the velocity: or, more correctly, the exponent of the velocity determined according to the rule given at pa. 103, varies between 2-03 and 2.05; so that in most practical cases, the exponent 2, or that of the square, may be employed without fear of error. If i be the angle of incidence, s the surface struck in feet, and v the velocity of the wind, in feet, per second; then for the force in avoirdupois pounds, either of the two following approximations vs sin2 I

may be used: viz. f = 440

or ƒ = .002288 v2 s2 sin3 1.

Of these, the first is usually the easiest in operation, requiring only two lines of short division, viz. by 40 and by 11. If the incidence be perpendicular, sin2 1 = 1, and these be

come,

f=

=

v2 52
440

=002288 va s2.

3. The table in the margin exhibits the force of the wind when blowing perpendicularly upon a surface of one foot square, at the several velocities announced. The velocity of 80 miles per hour is that by which the aeronaut Garnerin was carried in his balloon from Ranelagh to Colchester, in June, 1802. It was a strong and boisterous wind; but did not assume the character of a hurricane, although a wind with that velocity is so characterized in Rouse's table. In Mr. Green's aerial voyage from Leeds, in September, 1823, he travelled 43 miles in 18 minutes, although his balloon rose to the height of more than 4000 yards.

Borda found by experiment in the year 1762, that the force of the wind is very nearly as the square of the velocity, but