PROPERTIES OF LENSES. 



23 



The compound microscope in its simplest form is 

 composed of two lenses the objective and eye lens ; 

 fig. 13, 1 and 2. It will be perceived that the real 

 image a b of the object A B formed by the objective 



FIG. 13. 



at a point just within the focus of the eye-glass is 

 changed into a virtual image at a b' by the latter, 

 both images being inverted as regards the object. 

 The principal of the more complex forms of the com- 

 pound microscope is similar, the number and arrange- 

 ment of the lenses being different both for objective 

 and eye-piece, the former has been already explained. 

 The eye-piece generally used is the Huygeian 

 named after its inventor Huygens, it consists of two 

 plano-convex lenses, 1 and 2 fig. 14, called respec- 



FIG. 14. 



tivcly eye and field lens, the former being one-third 



