102 



E. M. NELSON ON EVOLUTION OF THE MICKOSCOPE. 



The next microscope is of the simple kind, invented by M. 

 Joblot, Professor of Mathematics at the French Academy of Fine 

 Arts. The ornamented plate, seen in Fig. 13, holds the lens, the 

 focus being adjusted by the nut and screw ; the plate next to the 

 ornamental one is a concentric rotary stage. The mechanical 

 details of this stage are well thought out, and it is properly sprung 



Fig. 13. 



(see Fig. 14). The tube A, Fig. 13, called by the inventor "the 

 canon," which is lined with black cloth or velvet, has a diaphragm 

 at each end ; these diaphragms are held in position by movable 

 caps, which allow the diaphragms to be changed. This microscope 

 is a decided advance on any of the simple microscopes that pre- 

 ceded it, not only on account of the mechanical contrivance of the 



