an instrument which serves to cut into pieces several solid matters, as wood, stone, ivory, and the like.

The best saws are of tempered steel ground bright and smooth; those of iron are only hammer-hardened. Hence the first, besides their being stiffer, are likewise found smoother than the last. They are known to be well hammered by the stiff bending of the blade; and to be well and evenly ground, by their bending equally in a bow.

The lapidaries, too, have their saw, as well as the workmen in mosaic; but of all mechanics, none have so many saws as the joiners, the chief of which are the following:

The pit-saw, which is a large two-handed saw, employed for sawing timber in pits, and chiefly used by the sawers.

The whip-saw, which has likewise two handles, used in sawing such large pieces as the hand-saw will not easily reach.

The hand-saw is made to be used by an individual, of which there are different kinds, as the frame-saw, which is furnished with cheeks. By the twisted cords which pass from the upper parts of these cheeks, and the tongue in the middle of them, the upper ends are drawn close together, and the lower set farther asunder. The tenon-saw, which being very thin, has a back to keep it from bending.

The compass-saw, which is very small, and its teeth usually not set.

Its use is to cut a round, or any other compass-kerb, on which account the edge is made broad, and the back thin, that it may have a compass to turn in.

At an early period, the trunks of trees were split with wedges into as many and as thin pieces as possible; and if it were necessary to have them still thinner, they were hewn on both sides to the proper size. This simple and wasteful manner of making boards has been still continued in some places to the present day. Peter the Great of Russia endeavoured to put a stop to it, by forbidding hewn dales to be transported on the river Neva. The saw, however, though so convenient and beneficial, has not been able to banish entirely the practice of splitting timber used in building, or in making furniture and utensils; and indeed it must be allowed that this method is attended with peculiar advantages which that of sawing can never possess. The wood-splitters perform their work more expeditiously than sawers, and split timber is much stronger than that which has been sawn; for the fissure follows the grain of the wood, and leaves it whole; whereas the saw, which proceeds in the line chalked out for it, divides the fibres, and by these means lessens its cohesion and solidity. Split timber, indeed, turns out often crooked and warped; but for many purposes to which it is applied this is not injurious, and these faults may sometimes be amended. As the fibres, however, retain their natural length and direction, thin SAW

were afterwards exported to Portugal. There was a saw-mill in the city of Breslau about the year 1427, producing a yearly rent of three merks; and in 1490, the magistrates of Erfurt purchased a forest, in which they erected a saw-mill, besides renting another in the neighbourhood. The first saw-mill in Norway was erected about the year 1530. In the year 1552 there was a saw-mill erected at Joachimsthal, the property of a mathematician called Jacob Geisen. In 1555, the Bishop of Ely, ambassador from Queen Mary of England to the court of Rome, having seen a saw-mill in the vicinity of Lyons, the writer of his travels gave a particular description of it. The first saw-mill was erected in Holland at Saardam in 1596, the invention of which is ascribed to Cornelius Cornelissen. The first mill of this kind in Sweden was erected in the year 1653.

In England, saw-mills had at first a similar effect with printing in Turkey, the ribbon-loom in the dominions of the church, and the crane at Strasbourg. When attempts were made to introduce them, they were violently opposed, because it was apprehended that the sawers would thus be deprived of the means of procuring subsistence. An opulent merchant in 1767 or 1768, by desire of the Society of Arts, caused a saw-mill to be erected at Limehouse, driven by wind; but it was demolished by the mob, and the damage was sustained by the nation, while some of the rioters were punished. This, however, was not the only mill of the kind then in Great Britain; for at Leith there was one driven by wind some years before. Saw-mills are very common in America, where the moving power is generally water. Some have been constructed on a very extensive plan.

The mechanism of a sawing-mill may be reduced to three principal things. The first is, that the saw is drawn up and down as long as is necessary, by a motion communicated to the wheel by water. The second is, that the piece of timber to be cut into boards is advanced by an uniform motion to receive the strokes of the saw; for here the wood is to meet the saw, and not the saw to follow the wood, therefore the motion of the wood and that of the saw ought immediately to depend the one on the other. The third is, that where the saw has cut through the whole length of the piece, the whole machine stops of itself, and remains immoveable; lest having no obstacle to surmount, the moving power should turn the wheel with too great velocity, and break some part of the machine.

When a completely 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 two inches diameter be bored entirely through it. Let an iron bar, whose diameter is rather less than that of this 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 from nearly 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 bar may readily be so adjusted as to form equal 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 bar of iron or wood the two remaining angles, to give sufficient strength to the whole frame. By this construction the workmen are enabled 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 saw-frame, the cylinder may at length be cut from the block, as required.

If it were proposed to saw a conic frustum 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 frustum, circular grooves being previously cut in these frames to correspond with the circumferences of the two ends of the proposed frustum; 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, be raised or lowered at pleasure, while the borer is prevented from sliding to and fro by shoulders upon its bar, which are larger than the holes in the vertical pieces, and which, as the borer revolves, press against those 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 the bar by an endless band which shall pass over this grooved wheel and a wheel of a much larger diameter in the same plane, the latter wheel being turned by a winch-handle in the usual way.

Circular saws, acting by a rotatory motion, have been long known in Holland, where they are used for cutting wood used in 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 a plane inclined in any direction; so that it may be sawn by lines making any angle 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.