is represented as driven by the endless rope O; 13 and 14 are two guide pullies, to conduct the rope in going on and coming off the large sheeve or grooved wheel P, round which that rope (driven by external machinery, and running from top to bottom of the rope-ground) passes, by which the first movement in the sledge is given. This sheeve, giving motion to the spindle or shaft Q, and being coupled with the shaft R, turns the pinion 1, which drives the pinion 2, upon whose shaft, S, is the small bevel-wheel 3, driving the large bevel-wheel 4, upon whose shaft again is the spur-wheel 5, driving the other wheel 6; which last wheel works in the rack-way. This wheel is not fast upon its shaft, being capable of sliding thereon, for the purpose of being put in and out of geer with the rack by means of the lever T. The machine travels on the ailway on four truck-wheels: the two shown in this figure are marked 7. The pinions 1 and 2 are changeable, to suit the different travelling speeds required.

So far as has been now described refers only to the backward movement of the machine; which movement, it must be understood, is in the direction along the rack-way, as from A towards B. The contrary, or forward, movement is of course in the direction from B towards A, and is effected by giving a reverse turn to the wheel 6, which works in the rack-way. The ne cessary machinery for this purpose is the small pinion 8, on the shaft Q, driving the wheel 9, on the shaft U; which last shaft, and the one coupled with it, W, lie parallel with, and extend to, the end of the shaft R, in order that the pinion 10, fixed on the end of W, may, when required, work in the pinion 2. The shaft S then becomes common to both the pinions 1 and 10, and may, as required, be driven by either the one or the other, the pinion 1 being for the backward movement, and the pinion 10 for the forward movement, one of them therefore must be out of geer while the other is in geer. The figure shows the pinion 10 as out of geer. But supposing it to be in geer with 2, and the pinion 1 out of geer with it, the effect is, that a contrary motion is given to the wheel 6, which works in the rack-way, by means of the intervening wheels 3, 4, and 5, before described. The twisting motions of this machine are produced by the shaft Q being continued to the front of the machine, where the wheel 11, on the end of the shaft, drives the counter-wheel 12, from whence the required degree of speed is given to the twisting hooks. From what has been before described, it will be seen, that the backward and forward motions of the machine are produced by means of the wheel 6 working in the rack-way either way about as required. As, therefore, any predetermined quantity of twist may be given by means of the change wheels 11 and 12, whilst at the same time the machine may be made to travel at any given predetermined speed, either backward or forward, by means of the change wheels 1, 2, and 10; and as the twisting as well as the travelling motions are driven by one and the same impulse, originating in the machine at the grooved wheel P; they must always preserve a relative speed to each other in such proportion as may be assigned to them. A forked lever, clasping on the catch-box 15, serves either to put in or out of geer all the motions of the machine, excepting that of the grooved wheel P. Fig. 488 is a view of the back end of the same machine, showing as much of the machinery as is necessary for understanding it. The same characters of reference used in fig. 1 denote the same parts in this.

Fig. 3 is a plan of part of the rack-way. A is the rack, and N N is the wood sleeper upon which it is fastened. The forward motion of the sledge is a remarkably slow movement; the speed of the wheel 6 therefore requires to be considerably reduced. The wheels shown in the figures will not reduce the motion sufficiently slow to suit every possible occasion; but enough is show to enable a mechanic readily to produce any degree of motion that may be required.

All or any part of the machinery which we have described may be driven by the power of steam, water, wind, or animals. In the course of describing the different machines, and their component parts, adapted for the various purposes of the invention, we have seldom taken notice either of their dimensions or of the materials of which they may be made, because no fixed rules can be given: but any competent mechanic, from what we have shown, will be enabled to apply such sizes, and use such materials, as may be suited and proportioned to the nature and design of each machine, and to the power which is to drive it, particularly when we add, that the figures in the plates marked "Tempering, and Backward and Forward Movements," are made out on a scale of an inch to a foot, and that the dimensions there given are such as Inay with effect be applied in practice.

SAW-MILLS.

SAW-MILLS, Constructed for the purpose of sawing either timber or stone, are moved by animals, by water, by wind, or by steam. They may be distinguished into two kinds; those in which the motion of the saw is reciprocating, and those in which the saws have a rotatory motion. In either case the researches of theorists have not yet turned to any account: instead therefore of giving any uncertain theory here, we shall proceed to the descriptive part, and refer those who wish to see some curious investigations on this subject to a Memoir on the Action of Saws, by Euler, en Mem. Acad. Roy. Berlin, 1756.

Reciprocating saw-mills, for cutting timber, and moved by water, do not exhibit much variety in their construction. The saw-mill represented in fig. 450 is taken from Gray's Ex.perienced Mill-wright; but it only differs in a few trifling particulars, from some which are described in Belidor's Architecture Hydraulique, and in Gallon's Collection of Machines approved by the French Academy.

The plate just referred to shows the elevation of the mill. A A the shaft or axle upon which is fixed the wheel B B, (of 174 or 18 feet diameter,) containing 40 buckets to receive the water which impels it round C C, a wheel upon the same shaft containing 96 teeth, to drive the pinion No. 2, having 22 teeth, which is fastened upon an iron axle or spindle, having a couplingbox on each end that turns the cranks, as D D, round; one end of the pole E is put on the crank, and its other end moves on a joint or iron bolt at F, in the lower end of the frame G G. The crank D D, being turned round in the pole E, moves the frames G G up and down, and those having saws in them, by this motion cut the wood. The pinion No. 2 may work two,

three, or more cranks, and thus move as many frames of saws. No. 3 an iron wheel having angular teeth, which one end of the iron K takes hold of, while its other end rolls on a bolt in the lever H H. One end of this lever moves on a bolt at I, the other end may lay in a notch in the frame G G so as to be pulled up and down by it. Thus the catch K pulls the wheel round, while the catch I falls into the teeth and prevents it from going backwards.

Upon the axle of No. 3 is also fixed the pinion No. 4 taking into the teeth in the under edge of the iron bar, that is fastened upon the frame TT, on which the wood to be cut is laid: by this means the frame T T is moved on its rollers S S, along the fixed frame U U; and of course the wood fastened upon it is brought forward to the saws as they are moved up and down by reason of the turning of the crank DD. VV the machine and handle to raise the sluice, when the water is to be let upon the wheel B B, to give it motion. By pulling the rope at the longer arm of the lever M, the pinion No. 2 is put into the hold or gripe of the wheel C C, which drives it; and by pulling the rope R, this pinion is cleared from the wheel. No. 5, a pinion containing 24 teeth, driven by the wheel C C, and having upon its axle a sheave, on which is the rope P P, passing to the sheave No. 6, to turn it round; and upon its axle is fixed the pinion No.7, acting on the teeth in an iron bar upon the frame TT, to roll that frame backwards when empty. By pulling the rope at the longer arm of the lever N, the pinion No. 5 is put into the hold of the wheel CC; and by pulling the rope Ò, it is taken off the hold. No. 8, a wheel fixed upon the axle No. 9, having upon its periphery angular teeth, into which the catch No. 10 takes, and being moved by the lever attached to the upper part of the frame G, it pushes the wheel No. 8 round; and the catch, No. 11, falls into the teeth of the wheel, to prevent it from going backward, while the rope rolls in its axle, and drags the logs or pieces of wood in at the door Y, to be laid upon the movable frames T T, and carried forward to the saws to be cut. The catches Nos. 10 and 11 are easily thrown out of play when they are not wanted. The gudgeons in the shafts, rounds of the cranks, spindles, and pivots, should all turn round in cods or bushes of brass. Z, a door in one end of the mill-house at which the wood is conveyed out when cut. W W, walls of the mill-house. QQ, the couples or framing of the roof. X X X, &c. windows to admit light to the house.

Saw-mills for cutting blocks of stone are generally, though not always, moved horizontally; the horizontal alternate motion may be communicated to one or more saws, by means of a rotatory motion, either by the use of cranks, &c. or in some such way as the following. Let the horizontal wheel A B D C, fig. 451, drive the pinion O N, this latter carrying a vertical pin P, at the distance of about one-third of the diameter from the centre. This pinion and pin are represented separately in No. 2 of fig. 451. Let the frame WS TV, carrying four saws, marked 1, 2, 3, 4, have wheels, V, T, W, W, each running in a groove or reel, whose direction is parallel to the proposed direction of the saws: and let a transverse groove PR, whose length is double the distance of the pin P from the centre of the pinion, be cut in the saw-frame to receive that pin. Then, as the great wheel revolves, it drives the pinion, and carries round the pin P; and this pin being compelled to slide in the straight groove PR, while by the rotation of the pinion on which it is fixed its distance from the great wheel is constantly varying, it causes the whole saw frame to approach and recede from the great wheel alternately, while the grooves in which the wheels run confine the frame, so as to move in the direction Tt, V v. Other blocks may be sawn at the same time by the motion of the great wheel, if other pinions and frames running off in the directions of the respective radii, E B, E A, E C, be

worked by the teeth at the quadrantal points B A and C. And the contrary efforts of these four frames and pinions, will tend to soften down the jolts, and equalize the whole motion.

The same contrivance, of a pin fixed at a suitable distance from the centre of a wheel, and sliding in a groove, may serve to convert a reciprocating into a rotatory motion; but it will not be preferable to the common conversion by means of a crank.

When saws are used to cut blocks of stone into pieces having cylindrical surfaces, a small addition is made to the apparatus. See figs. 452 and 453. The saw, instead of being allowed to fall in a vertical groove, as it cuts the block, is attached to a lever or beam F G, sufficiently strong; this lever has several holes pierced through it, and so has the vertical piece E D, which is likewise movable towards either side of the frame in grooves in the top and bottom pieces A L, D M. Thus the length K G of the radius can be varied at pleasure, to suit the curvature N O; and as the saw is moved backwards and forwards by proper machinery, in the direction C B, BC, it works lower and lower into the block, while, being confined by the beam FG, it cuts the cylindrical portion from the block P, as required.

When a complete cylindrical pillar is to be cut out of one block of stone, the first thing will be to ascertain in the block the position of the axis of the cylinder; then lay the block so that such axis shall be parallel to the horizon, and let a cylindrical hole of from one to three inches diameter be bored entirely through it. Let an iron-bar, whose diameter is rather less than that of the tube, be put through it, having just room to slide freely to and fro as occasion may require. Each end of this bar should terminate in a screw, on which a nut and frame may be fastened; the nut-frame should carry three flat pieces of wood or iron, each having a slit running along its middle nearly from one end to the other, and a screw and handle must be adapted to each slit: by these means the frame work at each end of the bars may readily be so adjusted as to form isosceles or equilateral triangles; the iron-bar will connect two corresponding angles of these triangles; the saw to be used, two other corresponding angles; and another box of iron or of wood, the two remaining angles; to give sufficient strength to the whole frame. This construction, it is obvious, will enable the workman to place the saw at any proposed distance from the hole drilled through the middle of the block; and then, by giving the alternating motion to the sawframe, the cylinder may at length be cut from the block as required. This method was first described in the Collection of Machines approved by the Paris Academy.

If it were proposed to saw a conic frustrum from such a block, then let two frames of wood or iron be fixed to those parallel ends of the block which are intended to coincide with the bases of the frustrum, circular grooves being previously cut in these frames to correspond with the circum

ferences of the two ends of the proposed frustrum; the saw being worked in these grooves, will manifestly cut the conic surface from the block. This, we believe, is the contrivance of Sir George Wright.

The best method of drilling the hole through the middle of the proposed cylinder seems to be this: on a carriage running upon four low wheels let two vertical pieces (each having a hole just large enough to admit the borer to play freely) be fixed, two or three feet asunder, and so contrived that the pieces and holes to receive the borer may, by screws, &c. be raised or lowered at pleasure, while the borer is prevented from sliding backwards and forwards by pieces upon its bar, which are larger than the holes in the vertical pieces, and which, as the borer revolves, press against these pieces: let a part of the boring bar between the two vertical pieces be square, and a grooved wheel with a square hole of a suitable size be placed upon this part of the bar; then the rotatory motion may be given to this bar by an endless-band, which shall pass over this grooved wheel and a wheel of much larger diameter in the same plane, the latter wheel being turned by a winch-handle in the usual way. As the boring proceeds, the carriage with the borer may be brought nearer and nearer the block, by levers and weights.

Circular saws, acting not by a reciprocating, but by a rotatory motion, have been long known in Holland, where they are used for cutting wood used for veneering. They were introduced into this country, we believe, by General Bentham, and are now used in the dock-yard at Portsmouth, and in a few other places; but they are not as yet so generally adopted as might be wished, considering how well they are calculated to abridge labour, and to accomplish, with expedition and accuracy, what is very tedious and irksome to perform in the usual way. Circular saws may be made to turn either in horizontal, vertical, or inclined planes; and the timber to be cut may be laid upon the plane in any direction; so that it may be sawed by lines making any angles whatever, or at any proposed distance from each other. When the saw is fixed at a certain angle and at a certain distance from the edge of the frame, all the pieces will be cut of the same size, without marking upon them by a chalked line, merely by causing them to be moved along, and keeping one side in contact with the side of the frame; for then as they are brought one by one to touch the saw revolving on its axle, and are pressed upon it, they are soon cut through.

Mr. Smart, of the Ordnance Wharf, Westminster Bridge, has several circular saws, all worked by a horse, in a moderate