430 



Notes. 



nical, with rectangular motions performed by two racks and two pinions, 

 both pinions being at right angles to the stage, in which respect 

 Smith's Microscope was also similar. An achromatic condenser could 

 be fitted beneath the stage instead of the rotating diaphragm. The 

 compass joint was supplied with a screw clamp to fix the instrument 

 at any inclination. 



Fig. 118. 



Fig. 113 shows the next stage in the evolution of Ross's Micro- 

 scopes. Here the Lister limb is retained, but the cradle is dispensed 

 with, the limb itself being grooved and the rack attached to the body. 

 This capital form of mount was designed by Mr. Jackson, but it is 

 impossible to say who was «the first manufacturer to carry it out 

 practically. We know that both Powell and Smith adopted this plan 

 in 1841, and probably Ross made this Microscope in that year. The 



