optics. H77 



look through it. On the back of this speculum a 

 male screw L is made to fit the brass ring 1, to 

 screw into the said ring at pleasure. 



There are four of these concave specula, of dif- 

 ferent magnifying powers, to be used as objects to 

 be examined may require. The greatest magni- 

 fiers must always have the least apertures. 



M (Fig. 3.), a round object-plate, one side white, 

 and the other black, intended to render objects the 

 more visible, by placing them, if black, on the 

 white, and if white, on the black side. A steel 

 spring, N, turns down on each side, to make any 

 object fast; and issuing from the object-plate, is a 

 hollow pipe to screw it on the needle's point G. 



O (Fig. 4.), is a small box of brass, with a glass 

 on each side, contrived to confine any living 

 object, in order to examine it: this, also, has a 

 pipe to screw upon the end of the needle G. 



A soft hair-brush is necessary to clean the 

 glasses, or specula ; and a drop of any liquid may 

 be applied to the isinglass of the box O, in order 

 to view animalcules. 



When you would view any object, screw the 

 speculum with the magnifier you would think best 

 to use, into the brass ring I. Place the object 

 either on the needle G, in the pliers, H, on the 

 object-plate M, or in the brass hollow box, O, as 

 may be most convenient, according to the nature 

 and condition of it : then holding up the instru- 

 ment by the handle P, look against the light 

 through the magnifying lens ; and by means of 

 the nut D, together with the motion of the needle, 

 by managing its lower end, the object may be 

 turned about, raised, or depressed, brought nearer 

 the glass, or put farther from it, till you hit the 



t 3 



