CHAPTER III. 



ADJUNCTS TO THE MICROSCOPE. 



IN addition to the mirror, object-glasses, eye-glasses, and 

 the parts constituting the stand of a microscope, several acces- 

 sory instruments are needed by those who would devote atten- 

 tion to microscopic researches. The most necessary or useful 

 of these we proceed to describe. 



The Diaphragm, for cutting off extraneous light when 



Fig. 12. 



viewing minute transparent objects, consists of a plate of brass 

 perforated with several holes of different sizes. This revolves 

 on a pivot, so as to bring each hole in succession under the 

 object-glass. It is adapted under the stage of the instrument, 

 and is so essential in practice that few microscopes are made 

 without it. 



The Condenser. This is an arrangement under the stage 

 4* 



