78 



ELEMENTARY CHEMICAL MICROSCOPY 



These reflectors are mounted upon small metal rods passing 

 through the adapters at right angles to the optic axis; a milled 

 head at the end of the rod permits changing the angle of incli- 

 nation of the reflecting surface. 



In several types the lateral opening for the incident light is 

 made variable in diameter either by means of an iris diaphragm 

 or a rotating collar provided with openings of different sizes. 



A typical prism illuminator is shown diagrammatically in Fig. 

 32. The reflecting device consists of a totally reflecting prism 

 P so mounted as to permit tipping slightly and thus changing 



FIG. 32. Prism Vertical Illuminator. FIG. 33 Disk Vertical Illuminator. 



the direction of the reflected ray R. Incident light I is projected 

 upon the prism through the horizontal opening O. A diaphragm 

 D extending not quite halfway across the aperture of the adapter 

 serves to screen the prism and to prevent interfering reflections 

 from blurring the image formed in the microscope. 



The construction of a disk illuminator is shown in Fig. 33. The 

 incident rays I, I strike a glass or mica disk G and are reflected 

 by it through the objective attached below. The rays I, I enter 

 through a circular opening O. The size of this opening may be 

 changed by turning the collar C which is provided with circular 

 openings of three different diameters. 



Adjustment of Vertical Illuminators. When the object to 

 be examined is small and is supported upon a glass object slide 



