74 



Microscopical Essays. 



Place the focket, which is at the bottom of the opake ftage ? 

 on the bar QXT, fo that the concave mirror o may be next the 

 end D E of the wooden body. 



Screw the tubes P O into the end D E. The magnifier you in- 

 tend to ufe is to be fere wed on the end o of thefe tubes. 



The handle G b, or milled nut, Fig. 2, muft be placed on the 

 fquare end of the pinion a. 



Place the lamp lighted before the glafs lump n, and the' objecl 

 you intend to examine between the fpring plates of the ftage* 

 and the inftmment is ready for ufe. 



In all microfcopes, there are two circumftances which muft be 

 particularly attended to; the modification of the light, or the 

 proper quantity to illuminate the objea ; fecondly, the adjuft- 

 ment of the inftrument to the focus of the glaffes and the eye of 

 theobferver. In the ufe of the lucernai microfcope there is a 

 third circumftance, which is, the regulation of the guide for the 

 eye, each of which I {hall confider by itfeff. 



1 . To throw the light upon the objea. The flame of the lamp 

 is to be placed rather below the center of the glafs lump n, and 

 as near it as poffible ; the concave mirror o muft be fo inclined and 

 turned, as to receive the light from the glafs lump, and reflea it 

 thence upon the objea ; the beft fituation of the concave mirror, 



