OP THE MICROSCOPE. 31 



other. If well made they give excellent definition and a large 

 field, and, when mounted on a stand, are very serviceable as 

 dissecting microscopes, especially in working upon coarse objects, 

 and picking out shells, the larger foraminifera, etc. Their 

 form enables us to support them by means of a small wire 

 ring, arranged as in a retort stand, and the large bell-mouth of 

 the frame prevents any light from entering the eye. except that 

 which has passed through the lens. They are very cheap, and 

 any intelligent boy can make a tolerable stand for one. The 

 same stand will answer for several glasses of different powers. 



Fig. 4. WATCH-MAKERS' GLASS. Fig. 5. 



The eye-glass shown in Figure 4 is a doublet, the front lens 

 of which is set in a separate piece, shown in Figure 5. When 

 the latter is removed, the remaining part forms a very service- 

 able low-power glass ; when both are used together, the com- 

 bination forms an excellent high-power magnifier. This form 

 is one made by the Bausch & Lomb Optical Co. 



Engravers' Glasses. These are mounted in frames, 

 similar to that of the watch-makers' eye-glass, but as they are 

 larger, and are therefore not so readily held in the eye, after the 

 fashion of the latter, they are always used with a stand of some 

 kind. Those of the best quality are, in general, doublets, con- 

 sisting of two plano-convex lenses, and as they give a large 

 field of view, with very good definition, they are altogether the 



