232 



No. 3. 



E X 11 1) I U M *. 



By C. R. GORING, M.U. 



The discovery of a set of objects for ascertaining the 

 defining and penetrating powers of microscopes, has 

 founded a new era in the history of those instruments. 

 The thick aplanatic object-glass for diverging rays, and 

 the Amician reflecting microscope, have in consequence 

 been perfected. The substitution of diamond and sap- 

 phire lenses, for those made of glass, in the single micro- 

 scope, with the ingenious apparatus for illumination 

 contrived by Dr. Wollaston, may also in some measure 

 be attributed to the same source. It may surely be 

 affirmed that no improvements at all commensurate to 

 these in magnitude and importance are likely to be made 

 hereafter. Microscopes are now placed completely on 

 a level with telescopes, and, like them, must remain 

 stationary in their construction. 



In the present work I have endeavoured to establish 

 the mechanical part of the construction of microscopes, 



* From First Edition, with corrections. By C. R. G. 



