Microscopical Essays. 



the places which correfpond to the two holes through which the 

 fcrew is to pals ; take away the microfcope, and bore two holes 

 at the marked places, fufficiently large to let the milled fcrews 

 pafs through them. 



Thefe fcrews are to pafs from the outfide of the mutter, to go 

 through it, and being then fcrewed into their refpeclive holes in 

 the i'quare plate, they will, when fcrewed home, hold it faff 

 again/i the iniide of the fhutter, and thus fupport the microfcope. 



Screw the conical tube A BCD to the circle a be, and then 

 Aide the tube G of the opake box into the cylindrical part C D 

 E F of the body; if opake objects are to be examined ; but if they 

 be tranfparent objects you mean to fhew, then place the tube Y 

 within the tube C D E F. 



The room is to be darkened as much as poflible, that no light 

 may enter but what paries through the body of the microfcope ; 

 for, on this circumflance, together with the brightnefs of the fun- 

 mine, the perfection and difunctxiefs of the image in a great mea- 

 fure depend. 



I fhall firft confider the microfcope as going to be used for 

 opake objects, l. Adjufl the mirror N O P, fo as to receive the 

 folar rays, by means of the two finger fcrews or nuts, O, R ; the 

 firft, O, turns the mirror to the right or left ; the fecond, R, raifes 

 or depreffes it : this you are to do till you have reflected the fun's 

 light through the lens at A B, ftrongly upon afcreen of white pa- 

 per, placed at fome diftance from the window, and formed thereon 

 a round fpot of light. An unexperienced obferver will find it more 



conve- 



