cave eye lens by means of which magnifications from 

 5 to 100 diameters are obtained. Change in magnify- 

 ing power is conveniently made either by changing 

 the object lenses or by varying the position of the eye 

 lens. The field of this lens is necessarily small but it 

 is the only form yet devised by which a long working 

 distance combined with high magnifying power can be 

 obtained. 



Holders, Stands and Dissecting Micro- 

 scopes. There is a great variety of mechanical contri- 

 vances for holding magnifiers, to give steadiness as 

 well as to leave the hands free for moving and working 



on the object and adjusting 

 for focus. When provision 

 is made to hold and adjust 

 the lens the apparatus may 

 be called a lens holder or 

 stand, but when a platform 

 called a stage, upon which 

 the object can be placed, 

 Fig- 20. and a mirror for illuminating 



the object properly, are added, it is called a dissecting 

 microscope. 



There are two forms of magnifiers which contain 

 within themselves some properties of stands. One, the 

 Tripod Magnifier, Fig. 20, rests upon three legs and 

 has a screw for adjustment of focus. Its optical parts 



18 



