120 



Microscopical Essays. 



exterior tube, being careful of the circular hole in the exterior 

 one. Nothing now remains to be done but to adjuft for the 

 focus, which is effected by pufhing down the tube T V till the 

 object appears diflinct. 



The inftrument may be ufed in two ways for tranfparent ob- 

 jects ; firft, in a vertical pofition, when the light is to be thrown 

 on the object by the mirror LM; or it may be examined by 

 looking up directly at the light ; in the latter cafe the mirror 

 rnuft be taken away. 



In viewing opake objects the mirror is of no ufe ; as much 

 light as poflible mull be let fall on them through the circular 

 holes of the tubes. 



Any object may be viewed by firfl pufhing the tube I R, and 

 then bringing the tube T to it's focal diflance from the object. 



A Description of those Parts of a Microscopical 

 Apparatus, which are delineated in Plate IX. 



A and B reprefent the brafs cells which contain the magni- 

 fiers belonging to the different kinds of compound microfcopes. 

 The magnifiers are fometimes contained in a Aider like that which 

 is delineated at Fig. 3, Plate V. The lenfes of A and B are con- 

 fined by a fmall cap ; on unfcrewing this, the fmall lens may be 

 taken out and cleaned. The magnifiers A of the lucernal micro- 

 fcope are fo contrived, that any two of them may be fcrewed 

 together, by which means a confiderable variety of magnifying 

 power is obtained. 



To 



