290 optics. 



affected by the errors arising from the aberration of 

 rays, both from their different refrangibility and 

 the figure of the glasses. 



The solar, or camera obscura microscope, requires 

 the sunshine, and must be made use of in a 

 darkened chamber, as its name implies. 



It is composed of a tube, a looking-glass, a con- 

 vex lens, and Wilson's single pocket microscope, 

 before described, or any other similar one. 



The sun's rays being directed by the looking- 

 glass through the tube upon the object, the image 

 or picture of the object is thrown, distinctly and 

 beautifully, upon a screen of white paper, or a 

 white linen sheet, placed at some distance to re- 

 ceive the same; and may be magnified to an im- 

 mense size; for the farther off the screen is re- 

 moved, the larger will the object appear; insomuch, 

 that a mite may be magnified to the length of five 

 or six feet, or even a great deal more; but it is 

 indeed more distinct when not enlarged to above 

 half that size. 



The apparatus for this purpose, as represented 

 in the plate annexed, is as follows : A (Fig. 4.), a 

 square wooden frame, through which two long 

 screws pass, and assisted by a couple of nuts, 

 1 1, fasten it firmly to a window-shutter, wherein 

 a hole is made for its reception: the two 

 nuts being let into the shutter, and made fast 

 thereto. 



A circular hole is made in the middle of this 

 frame, to receive a piece of wood of a circular 

 figure B, whose edge, that projects a little beyond 

 the frame, composes a shallow groove, wherein runs 

 a catgut; which by twisting round, and then 

 crossing over a brass pulley 4, (the handle whereof, 

 5, passes through the frame,) affords an easy 



