If the velocity with which the handle is moved be tripled, which it may be, without rendering the work too fatiguing; the quantity raised will be tripled, and nearly 1094 gallons will be raised 26 feet 10 inches, in an hour. This coincides very nearly with Desaguliers's estimate of the water which a man can raise by almost any hydraulic engine.

13. Having dwelt thus long upon the theory of Archimedes's screw, but little remains to complete our observations. It is obvious from what has been remarked, that this screw can never raise water when the angle which the central line of the spiral makes with the base of the cylinder is larger than the angle included between the base of the cylinder and the horizon; that is, it is always necessary that BAZ should be equal to, if not greater than, BED (fig. 6. pl. XXIV.) In practice, indeed, it is adviseable that CAL be between 40° and 60°, and BAZ - BED between 10° and 20°. The mean of both these is most to be recommended.

Sometimes Archimedes's screw, instead of being worked by men at a winch, is turned by means of float-boards fixed about the circumference of its lower end, upon which a stream of water acts if the water have a moderate fall, it will have sufficient efficacy to turn two screws, one above another; the top of the lower screw and the bottom of the upper screw may act the one upon the other, by means of a wheel upon each with an equal number of teeth-taking into each other: in this case the upper screw will turn in a contrary direction from the other, and consequently the spiral tube must be wound about the cylinder in an opposite direction. A solid wheel, or a light wheel with a heavy rim, turning upon the middle of the screw as an axis, will operate like a fly, and in some cases be very useful.

In the preceding investigations no notice has been taken of the effects of the air included in the spiral: yet if the spiral had been folded upon a cone instead of a cylinder, or if it had been formed of a flexible tube of varying diameter, these effects would have been important: some of them are considered in our account of the spiral pump. See HYDRAULIC Machines, No. 10.

M. Cagniard, formerly an élève of the Polytechnic School, has struck out a very ingenious application of Archimedes's screw. He employs it as bellows, in a machine which pro duces rotatory motion by means of a reservoir of hot water. When the screw is turned in the direction of the motion of the points which described the helices of which its threads are composed, the water which bathes the lower extremity of the screw does not rise in its threads, but still farther descends below the

screw, being replaced by the exterior air which escapes through the orifices of these threads. Thus M. Cagniard causes the air to descend to the bottom of a vessel full of water of the temperature of the atmosphere: another vessel filled with water to 180° or 200° (of Fahrenheit) contains a cylinder which is moveable on its axis, and is entirely immersed in the water: this cylinder is furnished with spouts in the direction of its length. The cold air passes from the bottom of the first vessel to that of the second, by means of a syphon; it enters the spouts of the cylinder, there becomes heated, and forces the cylinder to turn. The rotatory motion of the axis of the cylinder is transmitted to the axis of the Archimedean screw, and the motion of the cylinder is continued solely by the action of the hot water upon the atmospheric air.

For various purposes to which this improvement may be applied, see Hachette, Traité des Machines, p. 149-154.

SHIP Block Machinery. See BLOCK.

SHOEMAKERS' IMPLEMENT, to enable them to work in a standing posture. Such an instrument has been contrived by Mr. Thomas Holden of Fettleworth, Sussex; and its inventor rewarded with fifteen guineas by the Society of Arts. It resembles a stand, such as is used for reading-desks; at the top of which is a small block of wood, excavated so as to form a proper bed for the last, and the moulds or instruments used in making boots, which are kept firm upon it, by a stirrup or endless strap. The hollow block is joined into another piece (which connects it to the stand), so as to admit of a vertical motion; and it is retained, at any angle, in this motion, by a circular catch, with notches formed in its side, to fasten it on an iron catch projecting from the lower piece. This lower piece is shaped into a small cylinder beneath, which entering into a hole formed for it on the top of the pillar of the stand, permits the hollow block to be moved round about, without stirring the stand; so that, by the combination of these two motions, it may be placed in any position. Behind the hollow block, and on a level with it, an horizontal piece of board is supported by a small pillar, rising from one of the feet of the stand, and secured firmly by a brace to the stand itself; this board supports the tools and implements wanted, ready at hand for the workman's use.

The design of this invention is to obviate the necessity of using that very unwholesome posture in which shoemakers are accustomed to work; which compresses the lungs and bowels in such a manner, as to occasion consumption, inflammation of the bowels, and a variety of other frightful complaints.

The efficacy of the alteration of posture permitted by this

instrument, which enables the workman to stand at his work, is very well proved in the case of the inventor of it; who has produced a medical certificate, that he was, for many years, so afflicted with bowel complaints and piles, that he was under the necessity of leaving off his trade entirely, if he could not contrive to work standing; and that, since he has made use of this implement, his complaints are entirely removed, and he is so improved in flesh and countenance, that he " looks not like the same man;" and, for some years, has had no occasion for medicine. He has made many hundred pair of shoes on this stand, and recommends also its use, as "the quickest way of closing all the thread work.”

This implement might be made still more simple, by leaving out the part used to give the hollow block a circular motion, which does not appear always necessary, from the facility which the workman has, when standing at it, to place himself instantly at any side of the work he pleases; it would, as appears to us, be full as little, if not less, trouble to him to let the instrument remain unmoved, and turn himself round instead of it, as to stand still while he turned it about: though a small quantity of light confined to one direction may in some cases render the increased apparatus necessary.

A wooden vice of a proper height, fixed to a stake, and secured even by a wedge, if a screw should be deemed expensive, would also hold a last in any position required for the

workman.

Another contrivance for this purpose by Mr. J. King, has been lately recommended by the same society. The machine consists of an oblong frame of wood of two sides, with cross pieces. It may be conveniently fixed in a situation, and at a proper height for working, by screwing down to a window-cill, by means of two screws, such as are used for bedsteads. These, and an iron bracket, extending from the front of the machine, being screwed against the wainscot, support the machine very steadily; or a stand, consisting of proper legs, may be used, if preferred. The external parts of the machine are covered with leather, so as to become like cushions to support the last, and it is held down by a strap, which has a loop or treadle at the bottom, for the foot. The principal novelty of this invention consists in a lever, which is attached by an iron link to a wire, upon which it moves as a centre; and when that is down in its place, a small point or beak of iron enters into holes made in an iron plate; and the other end of the lever comes to rest on a stop, which has several holes in it. The end of the lever has, also, a little iron beak, which enters these holes. Thus, when the lever is down, it becomes an immoveable cross

bar of the frame, and the last may be held or wedged in between this, and either slide of the frame, and held down by the strap. But to adjust the width of the opening, on which the last lies, nothing more is necessary than to lift up the lever, so that the point clears the holes of the plate, then sliding the link along the wire, to the intended width, and shutting it down again, the beak or point enters some other hole of the plate, and holds the lever fast in the new position, so as to adapt it to the width of any last, or to hold it in any position, at pleasure.

Mr. King observes that, at other times, the last is held down by the foot-strap pressing the lever upon it-that the machine forms an universal vice, supporting and holding the last firmly down upon the cross-bar, in any required position. Two stiff pieces of sole-leather are also fixed in the frame, which, in certain positions, supports the last.

SIPHON. See CRANE.

SPIRAL-PUMP, at Zurich. See HYDRAULIC Engines. No. 10.

STEAM-ENGINE, an engine originally contrived for raising water by means of the expansive force of the steam or vapour produced from water or other liquids in a state of ebullition. This has been often called the Fire-engine, because of the fire used in boiling the liquid; but the latter term has, of late, been properly confined to machines for extinguishing fires. The steam-engine is justly deemed one of the most curious, important, and serviceable mechanical inventions, not only of modern, but of any, times; particularly when it is considered with regard to some of its late improvements, which render it applicable to all kinds of mill-work, to planing, sawing, boring, and rolling machines, and indeed to almost every purpose that requires a powerful first-mover, whose energy may be modified at the pleasure of the mechanist.

The principles and manner of operation of the steam-engines of Savery, Newcomen and Cawley, and of Watt, may be understood from the following brief explanations and remarks, which are meant as preparatory to the more detailed accounts of several engines with which we have been favoured.

1. Let there be a sucking pipe with a valve opening upwards at the top, communicating with a close vessel of water, no more than thirty-three feet above the level of the reservoir, and the steam of boiling water be thrown on the surface of the water in the vessel, it will force it to a height as much greater than thirty-three feet as the elastic force of the steam is greater than that of air; and if the steam be condensed by the injection of cold water, and a vacuum thus formed, the vessel will be filled from the reservoir by the pressure of the atmosphere; and the

steam being admitted as before, this water will also be forced up; and so on successively.

Such is the principle of the first steam-engine, said by the English to be invented by the marquis of Worcester; while the French ascribe it to Papin: though we believe the fact is that Brancas, an Italian, applied the force of steam ejected from a large œlopile as an impelling power for a stamping-engine so early as 1629. The hint so obscurely exhibited in the marquis of Worcester's Century of Inventions (see the word WORCESTER in this alphabetical arrangement) was carried into effect by captain Savery.

2. If the steam be admitted into the bottom of a hollow cylinder, to which a solid piston is adapted, the piston will be forced upwards by the difference between the elastic forces of steam and common air; and the steam being then condensed, the piston will descend by the pressure of the atmosphere, and so on successively. This is the principle of the steam-engine first contrived by Messieurs Newcomen and Cawley, of Dartmouth. This is sometimes called the atmospherical engine, and is commonly a forcing-pump, having its rod fixed to one end of a lever, which is worked by the weight of the atmosphere upon a piston at the other end, a temporary vacuum being made below it by suddenly condensing the steam, that had been admitted into the cylinder in which this piston works, by a jet of cold water thrown into it. A partial vacuum being thus made, the weight of the atmosphere presses down the piston, and raises the other end of the straight lever, together with the water, from the well. Then immediately a hole is uncovered in the bottom of the cylinder, by which a fresh quantity of hot steam rushes in from a boiler of water below it, which proving a counterbalance for the atmosphere above the piston, the weight of the pump-rods, at the other end of the lever, carries that end down, and raises the piston of the steam-cylinder. The steam hole is then immediately shut, and a cock opened for injecting the cold water into the cylinder of steam, which condenses it to water again, and thus making a vacuum below the piston, the atmosphere again presses it down and raises the pump-rods, as before; and so on continually.

3. The great features of improvement made by Mr. Watt upon the engine of Newcomen and Cawley are, as Mr. Nicholson remarks, first, that the elasticity of the steam itself is used as the active power in this engine; and secondly, that besides. various other judicious arrangements for the economy of heat, he condenses the steam, not in the cylinder, but in a separate vessel.