Microscopical Essays, 



97 



convenient to obtain the light, by forming this fpot before he puts 

 on either the opake box, or the tooth and pinion microfcope. 



* Now put in the opake box, and place the objeel: between the 

 plates at H ; open the door i k, and adjuft the mirror M, till you 

 have illuminated the object ftrongly. If you cannot effecl this by 

 the fcrew S, you muft move the fcrews O, R, in order to get the 

 light reflected ftrongly from the mirror N O P, oiithe mirror M, 

 without which the latter cannot illuminate the objeel:. 



The objeel; being ftrongly illuminated, fhut the door i k, and 

 a diftincl view of the objeel will foon be obtained on your fcreen, 

 by a dj lifting the tubes V X, which is effected by moving them 

 backwards or forwards, 



A round fpot of light Cannot always be procured in northern 

 latitudes, the altitude of the fun being often too low ; neither'can 

 it be obtained when the fun is directly perpendicular to the front 

 of the room. 



As the fun is continually changing it's place, it will be neceftary, 

 in order to keep his rays full upon the objeel, to keep them con- 

 tinually dire'&ed through the axis of the inftrument, by the two 

 fcrews Q and R. 



To view tranfparent objecls, remove the opake box, and infert 

 the tube Y of Fig. 2, Plate V. in it's place : put the flider, Fig. 3, 

 Plate V. into it's place at n, and the Aider, with the objects be- 

 tween the plates, at m ; then adjuft the mirror N O P, as before 

 direcled, by the fcrews Q, R, fo that the light may pafs through 

 , , ; 3 . N •**•*'' the 



