For neither of these purposes can the ordinary eyepiece 

 be used. It is provided with a mechanical means of 

 varying the distance between the eye and field lens for 

 the purpose of changing magnifying power. 



Micrometer Eyepiece. A micrometer is a strip 

 of glass upon which a series of regularly spaced lines 

 are ruled having definite values in fractions of an inch 

 or millimeter and is used to measure the size of an 

 object. When used with the 

 eyepiece it must be situated in 

 the focus of the eye lens and 

 rests either upon the diaphragm 

 or in slots provided on opposite 

 sides of the mounting. 



Another form is one in which 

 the micrometer is a permanent 

 part of the eyepiece and is pro- 

 vided with a screw adjustment to move it to different 

 points in the field of view, Fig. 45. 



Binocular Eyepiece is one constructed to bisect 

 the beam of light which comes from the objective, 

 thus rendering the image visible to both eyes and pro- 

 ducing a stereoscopic effect. It is applicable to the 

 monocular microscope. 



Erecting Eyepiece is composed of four systems 

 of lenses instead of two, some of which are sometimes 



Fig. 45. 



110 



