These rubbers, in their revolution, pass directly over a series of eight tables, circularly arranged underneath them. The upper surfaces of the tables are all brought to one true horizontal plane, parallel to the plane described by the under surfaces of the rubbers in their revolution. The skins to be polished or grained, are placed on these tables, one on each, and if they were all perfectly equal in thickness, tenacity, and texture, very little more would be required to make such a machine work; but as the skins differ in every possible degree in those qualities, the tables are mounted upon elastic bearings, and are further supported by a lever to each, at the end of which lever is a step or treadle, whereon the workman stands, either with both feet or with one foot only, that he may temper the force according to circumstances, or the nature of the work under operation; and when he steps entirely off the lever, the table falls below the level of the range of the rubbers, and therefore out of action.
When the man is on the step, the surface of the table over which the rubbers act, approaches within the hundredth part of an inch of the plane described by the lower sides of the rubbers, so that when a skin is interposed, the thinnest parts are operated upon, and with a force as slight as the workman pleases, and the thick and tough parts with any greater pressure at the direction of the operator. For attaining and preserving a very true plane on that part of the table over which the polishers and grainers traverse, that portion of it is made of brass with adjusting screws underneath. The extremities of this metallic portion are gradually lowered a little from the true plane to prevent the rubbers striking the skin as they pass in rapid succession on to or off their work. A workman, who stands before each table, spreads the skin upon it, and keeps constantly shifting it after each rub it receives, till it has all been operated all over alike in parallel lines; he then turns the skin a little sideways, so that the grainers pass over the previous lines at an acute angle, as before mentioned in the hand work. The glazing and graining of leather may thus be performed in an equal, if not a superior manner to that of hand finishing, and at about one-tenth the cost.
Owing to the ground rubbers not being properly chamfered off towards their edges, and to the irregular movements of the skin over the table, by unpractised operators, the skins were at first occasionally scored, showing in a disadvantageous manner the curved lines upon its surface. These defects were soon remedied by attention to the points mentioned, and the work afterwards executed was upon the whole of a superior description; for it will be readily conceived, that with so great a radius as 4 feet (the wheel being 8 feet in diameter), the curvilinear form of the lines so close together, and crossing each other, so as to form minute lozenge-shaped projections, would appear to be straight; and that if a scratch be made across a skin, it would equally mar its beauty, whether it were in a straight or a curved line. However, a gentleman of great talent (Mr. Joseph Ellis) subsequently conceived the idea of a finishing machine that would groove the skin in straight lines; and it was constructed with great accuracy and beauty of workmanship by Mr. Alexander Galloway, who joined Mr. Ellis in a patent for it.
Whether this machine was ever brought to work to advantage the writer is not informed, or has no recollection, but it appears to him to be of a character deserving of notice in this place.