The lapidary works by means of wheels. These wheels are instruments for sawing and filing the stones which come under his hand: he has nothing to add to them, but a good deal to take away from them. When any one divides an orange with a sharp knife _equatorially_, he treats it as a choanite is treated in the simplest case: but the principle is somewhat different. The knife may cut the first as smooth as cheese, owing to the superior hardness of the steel and the compressibility of the fruit: but no instrument that man can invent will ever do this with a substance like flint or jasper. All that the wheel can do is to act like a saw, and to take out from the centre of the pebble, in the shape of saw-dust, a section equal in thickness to the wheel itself. If this be effected, and no more, then that part of the work is perfectly done: and this is not effected, without some fault, once in a dozen times, unless the workman be both skilful and attentive. The usual fault is, that the plane of section is not kept perfectly horizontal. But let us now see how the wheels act. There must always be two of them: one which is to cut by its edge, and another which is to polish by its surface. But the lapidary is generally provided with several of both kinds; partly in case of accident, partly on account of variety in the texture of the pebbles brought to him. Each wheel is fixed upon an axis of its own, of perhaps a cubit’s length. And this portable axis is bevelled as a screw, for some inches, at the other end, so that it can be screwed at pleasure into a solid revolving spindle planted upright in the floor of the workshop. The spindle itself may either be worked by a leathern strap and a treddle; or, as is more usual, by a winch-handle acting at a mechanical advantage. The horizontal wheel being made to spin round by turning the winch with one hand, the workman grasps the pebble firmly in the other, and presses it against the edge of the disk, which revolving in a horizontal plane acts like a saw. A pencil-line may first be drawn on the stone, to mark out the intended section.