The name of a very efficient instrument, extensively used by carpenters, and other mechanics, for boring holes in wood. There are several varieties adapted to their peculiar offices, or to the prejudices of workmen. The oldest, or common auger, has a long iron shaft, with a large cross handle at right angles to it, at the top, for enabling the workman to apply both his hands with a considerable leverage, in turning round the shaft, into which is welded a semi-cylindrical piece of steel, from 3 to 6 inches in length, which varies with the size or diameter of the hole made by the instrument; the extremity of this piece is furnished with a sharp tooth, and a cutting edge, which is a small portion of a spiral, and inclined so as to cut as a chisel, the edge operating upon a radical line proceeding from the centre of the hole; and, as it is being constantly turned in a circular direction, the chips of wood are turned out in spiral pieces, and are received into the semi-cylinder above, which has usually one of its longitudinal edges a little sharp to keep the sides of the perforator clean.

The upper portion of the shaft is made smaller than the lower, or steel part, for facilitating the escape of the chips, and to enable the instrument to pass the bore freely.

Another instrument, differing from the foregoing, is provided at its extremity with a conical screw, like a gimlet, for piercing the wood the more readily and truly. We have, indeed, frequently noticed in well-made augers of this kind, that no pushing, or rectilineal force whatever is required, the screw keeping them always up to their work.

In a third instrument, chiefly used by shipwrights, that portion of steel, already described, as of a semi-cylindrical form in the common auger, is altogether in this made of a spiral figure, and is found to facilitate the boring materially, besides preventing all liability of the chips becoming jammed or clogged in the tool, which pass freely through the spiral channels, and are discharged externally as the perforation is continued.

A patent for an improvement upon the last-mentioned auger was taken out about ten years ago, by Dr. Church, of Birmingham; but the originality of his invention has been the subject of dispute. In the specification of the patent, the principle of the inventor is stated to consist in forming an instrument of a helical figure, by winding a bar of steel of a " mixtilinear trapezoid" shape, round a cylindrical mandrel, by which a circular hole is formed throughout its length, for the insertion of a movable central guide-pin; the upper end of this central pin is screwed into the shank of the auger, and the lower, or working part, is furnished with a wood screw; the office of the latter is to draw the auger into the wood as it is turned, the cutting edges on the helical part at the same time clearing the wood as this auger deepens in the perforation. In grinding and sharpening the edges of the auger, the central pin is, of course, removed for the purpose; and it is obvious that the edges may be ground and sharpened as long as any of the spiral steel bar remains, which renders the instrument extremely valuable, as one, with proper care, may be made to last a man's life-time.

This auger, besides, far surpasses all others by the rapidity and facility of its operation.