102 



Mb, Samuel Hunter, 



Fig, 3. 



to the lever at D, and kept pressed by springs at K and L against 

 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 is a similar arm, causing at each pull the ratchet wheel 

 M N to turn ; this wheel carries an arm, M, attached to the 

 lever Q H, H being attached to the projection G; QH pivots on 

 F. By regulating the length of 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 18| 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 

 019, the speculum as before being 1. 



