E. M. NELSON ON HISTORIC MICROSCOPY. 229 



fastened to the arm, with rack and pinion focussing, like the tail- 

 piece of a telescope, eye-piece screwed into draw tube. There were 

 draw tube steadying rods fixed to the tripod feet like a telescope, 

 a mechanical stage, an elementary substage, and a mirror. 



The last microscope I am going to describe is one of the 

 earliest of Andrew Ross in 1831. Stand was non -inclining, 

 vertical rod on tripod foot, rack and pinion, triangular bar, 

 coarse adjustment, direct acting screw, fine adjustment, with 

 milled head at the bottom of the pillar underneath the tripod 

 foot. The mirror was fixed to one leg of the foot. A mechanical 

 stage with rectangular movements, also mechanical movements 

 to body to move it over the object. There was no tail-piece, but a 

 condensing lens was placed in a tube fitting to the underneath part 

 of the stage. 



I have now brought the history of the microscope to a date so 

 near the present time that the further advances in the construction 

 of the instrument will be well known to you all. 



