fervoir M, on the ground at the bottom of the wall. Then, while one man is fixing the ftone to the hook at the top of the wall, let another put water into the veffel D at the bottom till it nearly equals the weight of the ftone: after, which, leaving both to the free operation of gravity, or checking the motion a little if neceffary, the ftone will gradually descend to the ground, while the veffel D will be carried up to a funnel A, into which the water may be poured, and thence conveyed by a wooden or a leather pipe to the refervoir M. Then the veffel D may be fuffered to defcend, and the hook C will be raised to be fixed to another ftone: and thus the operation may be repeated as often as is necessary.

The fame method may likewise be adopted in lowering facks from a high granary, or packages from an upper warehouse, The velocity of the defcending weight may be fo regulated as to have any proportion to that which gravity imparts to bodies falling freely: thus, if W denote the weight to be lowered, V

that of the veffel of water, we shall have

I

W-V

W+v'

for the fraction

expreffing the ratio of the velocity to that freely imparted by gravity when denoted by unity. Thus, if V=W, the weight will fall through of 161⁄2, or about 5 feet in the firft fecond; if V=W, the weight will fall through of 16,2, or about 35 feet in the firft fecond: the friction of the pulley being in both instances difregarded.

I

FILES, machine for cutting of. There have been various contrivances for this purpofe; but the best we are acquainted with is described in the Tranfactions of the American Philofophical Society, and is as follows: AAAA fig. 6. pl. X. is a bench made of well-feafoned oak, the face of which is planed very fmooth. BBBBB the feet of the bench, which fhould be fubftantial. CCCC the carriage on which the files are laid, which moves along the face of the bench AAAA parallel to its fides, and carries the files gradually under the edge of the cutter or chifel HH, while the teeth are cut: this carriage is made to move by a contrivance fomewhat fimilar to that which carries the log against the saw of a faw-mill, as will be more particularly defcribed. DDD are three iron rods, inserted into the ends of the carriage CCCC, and paffing through holes in the ftuds EEE, which are screwed firmly against the ends of the bench AAAA, for directing the courfe of the carriage CCCC, parallel to the fides of the faid bench. FF two upright pillars, mortifed firmly into the bench AAAA nearly equidiftant from each end of it, near the edge, and directly oppofite to each

and

other. G the lever or arm which carries the cutter HH (fixed by the fciew I), 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 loofening these fcrews the arm which carries the chifel may be made to work more or less steadily. L is the regulating fcrew, by means of which the files may be made coarfer or finer; this screw works in a ftud M which is fcrewed firmly upon the top of the ftud 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 rife. Ñ is a steel fpring, one end of which is screwed to the other pillar F, the other end prees against the pillar O, which is fixed upon the arm G; by its preffure it forces the faid arm upwards, until it meets with the regulating fcrew 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 ítud or pillar O; and, by the motion of the arm G, is made to move the ratch-wheel Q. This ratch-wheel is fixed upon an axis, which carries a finall trundle-head or pinion R, on the opposite end; this takes into a piece SS, which is indented with teeth, and fcrewed firmly against one fide of the carriage CCCC: by means of this piece motion is communicated to the carriage. Tis a clamp for faftening 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 oppofite end, which works by a joint W, firmly fixed into the carriage CCCC. Y is a bridge, likewise fcrewed into the carriage, through which the fcrew X paffes, and preffes with its lower end against the upper fide of the clamp V; under which clamp the other end of the file ZZ is placed, and held firmly in its fituation while it is cutting, by the preffure of the faid clamp V. 7777 is a bed of lead, which is let into a cavity formed in the body of the carriage, fomething broader and longer than the largest fized files; the upper face of this bed of lead is formed variously, fo as to fit the different kinds of files which may be required. At the figures 22 are two catches which take into the teeth of the ratch-wheel Q, to prevent a recoil of its motion. 33 is a bridge to fupport one end 4 of the axis of the ratch-wheel Q. 5 a ftud to fupport the other end of the axis of that wheel..

When the file or files are laid in their place, the machine muft be regulated to cut them of the due degree of fineness, by means of the regulating fcrew L; which, by fcrewing further through the arm M, will make the files finer, and; vice verfa, by unfcrewing it a little, will make them coarfer; for the arm G will, by that means, have liberty to rife the higher, which will occafion the arm P, with the claw, to move further along the

periphery of the ratch-wheel, and confequently communicate a more extenfive motion to the carriage CCCC, and make the files coarfer.

When the machine is thus adjusted, a blind man may cut a file with more exactness than can be done in the ufual method with the keeneft fight: for by striking with a hammer on the head of the cutter or chifel HH, all the movements are fet at work; and, by repeating the ftroke with the hammer, the files on one fide will at length be cut: then they must be turned, and the operation repeated, for cutting the other fide. It is needlefs to enlarge much on the utility or extent of this machine; for, on an examination, it will appear to perfons 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 fmall files for watchmakers; as they may be executed by this machine with the greatest equality and nicety imaginable. As to the materials and dimenfions of the feveral parts of this machine, they are left to the judgment and skill of the-artift who may have occafion to make one; only obferving that the whole should be capable of bearing a good deal of violence.

FIRE-ESCAPE, a machine for removing perfons from the up per stories of houfes on fire. It confifts of a pole, a rope, and a basket. The pole is of fir, or a common fcaffold pole, of any convenient length from 36 to 46 feet. The diameter at bottom, or greateft end, about five inches; and at the top, or smallest end, about three inches. At three feet from the top is a mortife through the pole, and a pulley fixed to it of nearly the fame 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 mortife over the pulley, and then drawn tight on each fide to near the bottom of the pole, and made faft there till wanted. The basket fhould be of ftrong 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 ftrong iron curve or handle, with an eye or ring in the middle; and to one fide 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 fet against a house over the window from which any perfons are to escape, the manner of ufing it is fo plain and obvious, that it need not be defcribed. The moft convenient distance from the house for the foot of the pole to ftand, where practicable, is about 12 or 14 feet. If two strong

1

iron ftraps, about three feet long, riveted to a bár crofs, and spreading about 14 inches at the foot, were fixed at the bottom of the pole, this would prevent its turning round or flipping on the pavement: and if a strong iron hoop, or ferrule, riveted (or welded) to a femicircular piece of iron spreading about 12 inches, and pointed at the ends, were fixed on at the top of the pole, it would prevent its fliding against the wall.

When thefe two laft-mentioned irons are fixed on, they give the pole all the steadiness of a ladder; and because it is not eafy, except to perfons who have been used to it, to raise and fet upright a pole of 40 feet or more in length, it will be convenient to have two fmall poles or spars of about two inches diameter, fixed to the fides of the great pole at about two or three feet above the middle of it, by iron eyes riveted to two plates, fo 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 fliding on the pavement, when ufed occafionally to fupport the great pole like a tripod. There should be two strong afh trundles let through the pole, one at four feet and one at five feet from the bottom, to ftand out about eight inches on each fide, 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 perfon up to the affistance 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 fuch a pole as we have been speaking of can be raised from the ground, and two or three perfons taken out of the upper windows of a houfé, and fet down fafely in the street, in the space of 35 feconds, or a little more than half a minute. Sick and infirm perfons, women, children, and many others, who cannot make ufe of a ladder, may be fafely and eafily brought down from any of the windows of a houfe on fire by this machine, and, by putting a fhort pole, through the handles of the basket, may be removed to any diftance without being taken out of the bas ket. 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 fhade or gateway, and the basket fhould be kept at the watch-house. When the pole is laid up, the two spars fhould always be turned towards the head of it. The basket fhould be made of peeled rods, and the pole and fpars painted of a light ftone-colour, to render it more visible when used in the night.

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 purpofe at different times; the most effential particulars in a few of which we

fhall here defcribe.

The ufual conftruction of the fire-engine, after the great improvements were made in it by Mr. R. Newfham, was nearly that which is exhibited in fig. 2. pl. XV. where we have reprefented a vertical fection of the engine. The motion of the water in this machine is effected by the preffure of the atmofphere, the force of men acting upon the extremities H', H", of a lever, and thence giving motion to the pistons, and by the elafticity of condenfed air, in the following manner :-When the pifton Ris 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 rifes through the tube EF immerfed in the water of a vessel by the preffure of the atmosphere on its furface. The water of the barrel TU, by the fucceeding depreffion of the pifton R, fhuts the valve H, and is forced, through the superior canal ON, to enter by the valve I into the air-veffel a b c d; and the like being done alternately with respect to the other barrel WX, and its pifton S, the air-veffel is, by these means, continually filling with water, which greatly compreffes the air above the furface of the water in that veffel, and thereby proportionally augments its fpring; which at length is so far increased as to re-act with great force on the furface YZ of the fubjacent water, and compel it to ascend through the small tube e f to the ftop-cock e g, where upon turning the cock the water is fuffered to pass through a pipe h fixed to a ball and föcket; from the orifice of which it iffues in a continued ftream with a great velocity, to a confiderable height or distance; and it is ufually kept from diverging too foon in its progress by means of a long feries of flexible leather pipes, properly joined together, and known among the fire men by the name of the

hofe.

Defaguliers remarks (vol. I. p. 257.) that Mr. Newham contrived his engines in fuch 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 fucceffively thrown, on "the forcers 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 fame number of men he has generally thrown water further, higher, and in