OPTICS. ^79 



H, a spiral spring of steel, between the end G, 

 and the plates of brass ; intended to keep the 

 plates in a right position, and act against the long 

 screw C. 



I, a small turned handle, for the better hold of 

 the instrument, to screw on or off at pleasure. 



To this microscope belong seven different mag- 

 nifying glasses ; six of them are set in silver, brass, 

 or ivory, and marked 1, 2, 3, 4, 5, 6, the lowest 

 numbers being the greatest magnifiers. 



L (Fig. 6.) is the seventh magnifier, set in the 

 manner of a little barrel, to be held in the hand for 

 the viewing any larger object. 



This may be of further use : by applying a thin 

 cap, with a hole in it, a quarter of an inch square, 

 exactly in the focus of the lens, when a piece 

 of linen cloth is applied upon the brass, and 

 viewed through the other end, the threads will 

 appear greatly magnified, so that they may be 

 counted, and thereby the quality of the cloth may 

 be ascertained by calculation. 



M (Fig. 7.), is a flat slip of ivory, called a slider, 

 with four round holes through it, in which are placed 

 objects between two glasses, or pieces of mica. 



Eight such ivory sliders, and one of brass, are 

 usually sold with this microscope ; some with 

 objects placed in them, and others empty, for 

 viewing any thing that may offer, but whoever 

 wishes to make a large collection of objects, may 

 have as many as he desires. 



The brass slider is to confine any small object, 

 that it may be viewed without crushing or destroy- 

 ing it. 



Fig. 8. is a forceps, or pair of pliers, for taking 

 up insects, or other objects, and adjusting them to 

 the glasses. 



t 4- 



