the screw r), and works on the centres of two screws KK, which are fixed into the two pillars FF in a direction right across the bench AAAA. By tightening or loosening these screws the arm which carries the chisel may be made to work more or less steadily. L is the regulating screw, by means of which the files may be made coarser or finer; this screw works in a stud м which is screwed firmly upon the top of the stud F: the lower end of the screw L bears against the upper part of the arm G, and limits the height to which it can rise. N is a steel spring, one end of which is screwed to the other pillar F, and the other end presses against the pillar o, which is fixed upon the arm G; by its pressure it forces the said arm upwards, until it meets with the regulating screw L. P is an arm with a claw at one end marked 6, the other end is fixed by a joint into the end of the stud or pillar o; and, by the motion of the arm G, is made to move the ratch-wheel g. This ratch-wheel is fixed upon an axis, which carries a small trundle-head or pinion R, on the opposite end; this takes into a piece ss, which is indented with teeth, and screwed firmly against one side of the carriage cccc: by means of this piece motion is communicated to the carriage. T is a clamp for fastening one end of the file zz in the place or bed on which it is to be cut. v is another clamp or dog, at the opposite end, which works by a joint w, firmly fixed into the carriage cccc. y is a bridge, likewise screwed into the carriage, through which the screw x passes, and presses with its lower end against the upper side of the clamp v; under which clamp the other end of the file zz is placed, and held firmly in its situation while it is cutting, by the pressure of the said clamp v. 7777 is a bed of lead, which is let into a cavity formed in the body of the carriage, something broader and longer than the largest fixed files; the upper face of this bed of lead is formed variously, so as to fit the different kind of files which may be required. At the figures 22 are two catches which take into the teeth of the ratch-wheel o, to prevent a recoil of its motion. 33 is a bridge to support one end 4 of the axis of the ratch-wheel g. 5 a stud to support the other end of the axis of that wheel.

When the file or files are laid in their place, the machine must be regulated to cut them of the due degree of fineness, by means of the regulating screw L; which, by screwing further through the arm M, will make the files finer, and, vice versa, by unscrewing it a little, will make them coarser; for the arm & will, by that means, have liberty to rise the higher, which will occasion the arm P, with the claw, to move further along the periphery of the ratch-wheel, and consequently communicate a extensive motion to the carriage cccc, and make the files

coarser.

When the machine is thus adjusted, a blind man may cut a file with more exactness than can be done in the usual method with the keenest sight: for by striking with a hammer on the head of the cutter or chisel HH, all the movements are set at work; and, by repeating the stroke with the hammer, the files on one side will at length be cut: then they must be turned, and the operation repeated, for cutting the other side. It is needless to enlarge much on the utility or extent of this machine; for, on an examination, it will appear to persons of but indifferent mechanical skill, that it may be made to work by water as readily as by hand, to cut coarse or fine, large or small, files, or any number at a time; but it may be more particularly useful for cutting very fine small files for watchmakers: as they may be executed by this machine with the greatest equality and nicety imaginable. As to the materials and dimensions of the several parts of this machine, they are left to the judgment and skill of the artist who may have occasion to make one; only observing that the whole should be capable of bearing a good deal of violence.

FIRE-ESCAPE, a machine for removing persons from the upper stories of houses on fire. It consists of a pole, a rope, and a basket. The pole is of fir, or a common scaffold pole, of any convenient length from 36 to 46 feet. The diameter at bottom, or greatest end, about five inches: and at the top, or smallest end, about three inches. At three feet from the top is a mortise through the pole, and a pulley fixed to it of nearly the same diameter with the pole in that part. The rope is about three quarters of an inch diameter, and twice the length of the pole, with a spring hook at one end, to pass through the ring in the handle of the basket when used: it is put through the mortise over the pulley, and then drawn tight on each side to near the bottom of the pole, and made fast there till wanted. The basket should be of strong wicker-work, three feet and a half long, two feet and a half wide, rounded off at the corners, and four feet deep, rounding every way at the bottom. To the top of the basket is fixed a strong iron curve or handle, with an eye or ring in the middle; and to one side of the basket, near the top, is fixed a small cord, or guide-rope, of about the length of the pole. When the pole is raised, and set against a house over the window from which any persons are to escape, the manner of using it is so plain and obvious, that it need not be described. The most convenient distance from the house for the foot of the pole to stand, where practicable, is about 12 or 14 feet. If two strong iron straps, about three feet long, riveted to a bar cross, and spreading about 14 inches at the foot, were fixed at the bottom of the pole, this would prevent ts turning

round or slipping on the pavement: and if a strong iron hoop, or ferrule, riveted (or welded) to a semicircular piece of iron spreading about twelve inches, and pointed at the ends, were fixed on at the top of the pole, it would prevent its sliding against the wall.

When these two last-mentioned irons are fixed on, they give the pole all the steadiness of a ladder; and because it is not easy, except to persons who have been used to it, to raise and set upright a pole of 40 feet or more in length, it will be convenient to have two small poles or spars of about two inches diameter, fixed to the sides of the great pole at about two or three feet above the middle of it, by iron eyes riveted to two plates, so as to turn every way; the lower end of these spars to reach within a foot of the bottom of the great pole, and to have ferules and short spikes to prevent sliding on the pavement, when used occasionally to support the great pole like a tripod. There should be two strong ash trundles let through the pole, one at four feet and one at five feet from the bottom, to stand out about eight inches on each side, and to serve as handles, or to twist the rope round in lowering a very heavy weight. If a block and pulley were fixed at about the middle of the rope, above the other pulley, and the other part of the rope made to run double, it would diminish any weight in the basket nearly one-half, and be very useful in drawing any person up to the assistance of those in the chambers, or for removing any effects out of a chamber, which it might be dangerous to attempt by

the stairs.

It has been proved, by repeated trials, that such a pole as we have been speaking of can be raised from the ground, and two or three persons taken out of the upper windows of a house, and set down safely in the street, in the space of 35 seconds, or a little more than half a minute. Sick and infirm persons, women, children, aud many others, who cannot make use of a ladder, may be safely and easily brought down from any of the windows of the house on fire by this machine, and by putting a short pole through the handles of the basket, may be removed to any distance without being taken out of the basket. The pole must always have the rope ready fixed to it, and may be conveniently laid up upon two or three iron hooks under any shade or gateway, and the basket should be kept at the watchhouse. When the pole is laid up, the two spars should always be turned towards the head of it. The basket should be made of peeled rods, and the pole and spars painted of a light stonecolour, to render it more visible when used in the night.

Other ingenious contrivances for this purpose are described in Mr. Bosworth's "Accidents of Human Life."

FIRE-ENGINE, the name now commonly given to a machine by which water is thrown upon fires in order to extinguish them. Various machines have been contrived for that purpose at different times; the most essential particulars in a few of which we shall here describe.

The usual construction of the fire-engine, after the great improvements were made in it by Mr. R. Newsham, was nearly that which is exhibited in fig. 2. pl. XV. where we have represented a vertical section of the engine. The motion of the water in this machine is effected by the pressure of the atmosphere, the force of men acting upon the extremities H', H", of a lever, and thence giving motion to the pistons, and by the elasticity of condensed air, in the following manner:-When the piston R is raised a vacuum would be made in the barrel TU if the water did not follow it from the inferior canal EM (through the valve H), which rises through the tube EF immersed in the water of a vessel by the pressure of the atmosphere on its surface. The water of the barrel TU, by the succeeding depression of the piston R, shuts the valve H, and is forced, through the superior canal ON, to enter by the valve I into the airvessel abcd; and the like being done alternately with respect to the other barrel wx, and its piston s, the air vessel is, by these means, continually filling with water, which greatly compresses the air above the surface of the water in that vessel, and thereby proportionally augments its spring: which at length is so far increased as to re-act with great force on the surface yz of the subjacent water, aud compel it to ascend through the small tube ef to the stop-cock eg, where upon turning the cock the water is suffered to pass through a pipe h fixed to a ball and socket; from the orifice of which it issues in a continued stream with a great velocity, to a considerable height or distance; and it is usually kept from diverging too soon in its progress by means of a long series of flexible leather pipes, properly joined together, and known among the fire-men by the name of the hose.

Desaguliers remarks (vol. I. p. 257.) that Mr. Newsham contrived his engines in such a manner, "that part of the men who work them exert their force by treading, which is more effectual than any other way that men can work at such engines; the whole weight of the body being sufficiently thrown on the forces of the pumps: and even part of a man's strength may be added to the weight by means of horizontal pieces to which he can apply his hands when he is treading; whereas, by applying the hands to move levers or turn winches, the power must act very unequally. This is the reason why with the same number of men he has generally thrown water further, higher, and in greater quantities, with the same sized engines, than other

engineers who have tried their engines against his." Notwithstanding the truth of this remark, we are not aware that the combination of human weight and strength here recommended has been practised in any subsequent fire-engines, or indeed in any machines whatever, except the ingenious walking crane of Mr. Hardie..

The greatest artifice in the engine according to the construction just described is the contrivance to produce a continual stream, which is done by the compression and proportional elasticity of air in the barrel abcd, called the air-vessel. For the air, being an elastic fluid, will be susceptible of compression in any degree by the water forced in through the valves at IK; and, since the force of the air's spring will always be inversely as the space it possesses (art. 489. vol. I.), it follows that when the air-vessel is half full of water the air will be compressed into half the space it possessed at first, and therefore its spring will be twice as great as at first.

But this spring at first was equal to the pressure of the atmosphere on the same surface: for if it were not it could not have sustained or resisted the pressure of the atmosphere which stood over it, and consequently could not have filled the vessel before the water was driven in; which yet we find it did, and maintained an equilibrium with the common air. The vessel then being half filled with water, or the air compressed into half the first space, its spring will in this case be equal to twice the pressure of the atmosphere; and therefore when the stop-cock at p is turned, the air within, pressing on the subjacent water with twice the force it meets with from the external air in the pipe ef, will cause the water to spout out of the engine to the height of 32 or 33 feet, if the friction is not too great.

When the air-vessel is full of water, the air takes up + part; whence its spring will be three times as great as that of the common air, and it will project the water with twice the common atmospheric pressure; consequently, it will rise to the height of 62 or 64 feet. When the air-vessel is full of water the air will be compressed into its part, and so will protrude the water with three times the atmospheric pressure, and carry it to the height of 96 or 99 feet. Hence it will be easy to state the law by which the spring of the air will act on the surface of the water below it, as in the following table.