98 



ELEMENTARY CHEMICAL MICROSCOPY 



The pillar ?2 carries an illuminating tube V, provided with 

 a condensing lens movable forward and back by the knob p. 

 A glass cell w serves to hold water for cooling, or colored liquids 

 for ray filters. Strips of black glass g are inserted in a slot for 

 modifying the light during visual observations or Wratten Ray 

 Filters may be inserted for photography. A shutter s at the 

 end of the tube is provided for making photographic exposures; 

 at the opposite end of V a movable disk D with one large and 

 three small openings serves to regulate the amount of light 

 entering the vertical illuminators; and to further assist in prop- 



FIG. 45. Path of Light Rays in the Reichert Metallurgical Microscope. 



erly illuminating the object, an iris diaphragm is mounted in 

 the tube V just back of the shutter s. 



The vertical illuminators are two in number, separately 

 mounted in tubes which may be each in turn swung in place 

 by moving a lever; one tube carries a prism, the other a plane 

 glass disk. In the illustration the prism is shown in place; 

 since the horizontal displacement of the prism (P in Fig. 45) 

 must vary with each objective, Reichert has provided an ingeni- 

 ous method of indicating the proper position; an indicating 

 finger i in the form of a Y actuated by a milled-headed screw 

 moves over a scale whose graduations are marked with the focal 

 lengths of the different objectives; a tapered knob attached to 



