98 
ELEMENTARY CHEMICAL MICROSCOPY 
The pillar P2 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 5 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 
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 
