12 



PRACTICAL TBEATISE ON 



the end, C, a convex glass, and on its outside a male screw. 

 Three thin plates of brass, E, are made to slide easily in the 

 inside of the body to form the stage, one of these plates, 

 F, is bent semi-circularly ia the middle, for the reception of 

 a tube of glass, for viewing the circulation of the blood in 

 small fish, whilst the other tw6 are flat, and between these 

 last all the object sliders are introduced ; between the stage 

 and that end of the body into which the magnifier screws 

 is a bent spring of wire, H, this answers the purposes of 

 keeping the objects fixed between the plates of the stage, 

 and of pressing the stage firmly against the screw-tube. 

 The magnifiers suppUed with this microscope were eight in 

 number, and the objects were adjusted to their focus by 

 the screw-tube, D, for which purpose the screw was made 

 of nearly the same length as the body. This instrument 

 was held in the hand in such a position, that the direct hght 

 from a candle or lamp might pass directly into the condensing 

 glass; it was subsequently much improved by the addition 



of a spiral spring, instead 

 of the curved one, and of 

 a handle which screwed 

 into the body at right an- 

 gles to its length, and 

 served the purpose of keep- 

 ing the body in the hori- 

 zontal position, 



Mr. "Wilson was also the 

 inventor of a microscope for 

 opaque objects, represented 

 by fig. 9; this consisted of 

 a thin piece of flat brass, B, 

 about six inches long and 

 half-an-inch wide, one end 

 of which served as a handle, 

 and to the other. A, the mag- 

 nifier was screwed; con- 

 nected with the middle of 

 this piece of brass by a hinge was a jointed arm, PP, 



Fig. 9. 



