Microscopical Essays. 



87 



IX. and thenpafs the pin of this arm through the focket D, Fig. 1, 

 PL IV. the light is now to be reflected from the concave mirror to 

 the filver fpeculum, and from this down on the object. No ex aft 

 rule can be given for reflecting the light on the object ; we muft 

 therefore refer the reader to the mother of all aptnefs, practice. 

 The fpeculum muft be moved lower or higher, to fuit the focus 

 of the different magnifiers, and the nature of the objecl. 



The preceding directions apply equally to the ufmg of this in- 

 ftrument as a single microscope, with this difference only, 

 that the body A B is then removed, and the eye is applied to the 

 upper furface of the arm C D, exactly over the magnifiers. 



A List of the Apparatus of the improved Compound 



Microscope, 



The Aider, with the magnifiers. 



The body of the microfcope, 



The flider-holder. 



The tube, with the condenfing lens 3 



The pin and arm for the filver fpeculum. 



The filver fpeculum. 



A brafs box for the filver fpeculum, 



A brafs 



