102 Mr, SAMUEL HUNTER, 

Fig. 3. 
to the lever at D, and kept pressed by springs at K and Lagamst 
the ratchet ring, D K ending in a hook, so that when the lever 
A B is pushed towards the speculum this hook seizes the ratchet 
ring and causes the speculum to turn a little, because the motion 
at D is less than at C; for the same reason, when the motion is 
reversed D L pushes against the ratchet ring and causes another 
little turn. . 
I N isa similar arm, causing at each pull the ratchet wheel 
M N to turn; this wheel carries an arm, O M, attached to the 
lever Q H, H being attached to the projection G; Q H pivots on 
F. By regulating the length of O M or F H or both, the amount 
of side motion is adjusted. The arms attached to the lever at 
E caused the polisher to revolve when a circular one was used. 
But Sir John Herschel states, that with a speculum of 183 inches 
diameter by using a fixed oval polisher of 1:12 and 0:97 diameters 
(the speculum being 1), with grooves at an angle of 45° to the 
stroke, he obtained most satisfactory results without using any 
side motion, H being then fixed in position and the arm I N 
detached. When the speculum and polisher are caused to 
revolve, with the side motion in action, the speculum will describe 
curves somewhat similar to those of Lord Rosse’s polisher, but 
the shock given to the speculum at the commencement of each 
push and pull must be injurious. In Lord Rosse’s machine this 
shock is not felt, the stroke being given by a crank motion. The 
length of stroke used on a round polisher without side motion 
was 0°47, and with side motion 0°29, the total side motion being 
0:19, the speculum as before being 1. | 
