86 



Microscopical Essays. 



To USE THE IMPROVED DOUBLE MlCROSCOPE. 



Take the microfcope out of the box. Screw the body into the 

 round end of the upper part of the arm C D. 



Place the brafs Aiders, which contain the magnifiers, into the 

 dove-tailed flit which is on the under fide of the aforefaid arm, as 

 feen at E, Fig. 1, Plate IV. and Aide it forwards, until the mag- 

 nifier you mean to ufe is under the center of the body : oppoiite 

 to each magnifier in this Aide there is a notch, and in the dove- 

 tailed part of the arm C D there is a fpring, which falls into the 

 above-mentioned notch, and thus makes each magnifier coincide 

 with the center of the body. 



Pafs the ivory Aider you intend to ufe between the upper 

 plates of the Aider-holder K L, and then refleft as ftrong a light 

 as you can on .the object, by means of one of the mirrors ; after 

 this, adjuft the objeel to the focus of the magnifier and your eye, 

 by turning the milled fcrew M ; the motion of this raifes and 

 depreAes the Aage N I S. The degree of light necefiary for each 

 objeel, and the accuracy required in -the adjuftment of the lens 

 to their proper focal difiance from the objeel, will be eafily 

 attained by a little practice. 



When opake objects are to be examined, remove the Aider- 

 holder, and place the objeel: on a Aat glafs, or fix it to the nippers 

 L, Plate IX. the pin of thefc fit into the hole on the Aage; 

 H fcrew the concave fpeculum Plate IX. into the arm Q, Plate 



