20 



ON THE CONSTRUCTION AND USE OF 



The machine, which is a simplification of Lord Itosse'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 vv/.v <ilir<it/x n/>/>< mio*/ n-1,',1, 

 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, , Fig. '21, carries at its 

 top a circular table l>, upon which the polisher c is screwed. Below a band-wheel (/ 

 is fixed. Above the table, at a distance of four inches, a hori/ontal bar c 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 I, the mirror in, and its iron back or chuck /.. The bar is 

 moved by a connecting rod /', attached to it at one end, and at the other to a pin // 



Fig. 22. 



The Foot Power. 



moving a slot. This slot is in a crank 7i, carried by a vertical shaft i, near the 

 former one a. The band-wheel k is connected with the foot power, Fig. 4 2'2. The 



