The machine, which is a simplification of Lord Rosse’s, was intended to give spiral strokes. It differed from the original, however, in demanding a changeable stroke, and in the absence of the lateral motion. In another most essential feature it varied from both that and Mr. Lassell’s, the mirror was always uppermost while polishing, and being uncounterpoised escaped to as great an extent as possible from the effects of irregular pressure. To any one who has studied the deformations of a reflecting surface, and knows how troublesome it is to support a mirror properly, the advantage is apparent.
Fig. 21.
Polishing Machine.
The construction is as follows: A stout vertical shaft, a, Fig. 21, carries at its top a circular table b, upon which the polisher c is screwed. Below a band-wheel d is fixed. Above the table, at a distance of four inches, a horizontal bar e is arranged, so as to move back and forward in the direction of its length, and to carry with it by means of a screw l, the mirror m, and its iron back or chuck n. The bar is moved by a connecting rod f, attached to it at one end, and at the other to a pin g moving a slot. This slot is in a crank h, carried by a vertical shaft i, near the former one a. The band-wheel k is connected with the foot power, Fig. 22. The machine, except those parts liable to wear by friction, is made of wood. The ends o o′ of the horizontal bar e, are defended by brass tubes working in mahogany, and have even now but little shake, though many hundred thousands of reciprocations have been made.
Fig. 22.
The Foot Power.
The foot power consists of an endless band with wooden treads a a′, passing at one end of the apparatus over iron wheels b b′, which carry the band-wheel c upon their axle. At the other end it goes over the rollers d d′. Two pairs of intermediate wheels e e′, serve to sustain the weight of the man or animal working in it. The treads are so arranged that they interlock, and form a platform, which will not yield downwards. Owing to its inclination when a weight is put on the platform a′, it immediately moves from b toward d and the band-wheel turns. By a moderate exertion, equivalent to walking up a slight incline at a slow rate, a power more than sufficient to polish a 15 1/2 inch mirror is obtained. This machine, in which very little force is lost in overcoming friction, is frequently employed for dairy use, and is moved commonly in the State of New York by a sheep. I have generally myself walked in the one used by me, and have travelled some days, during five hours, more than ten miles.