THE MICROSCOPE 33 



or 17 mm. If a nose-piece is attached, the width of 

 this must be deducted from the tube-length. 



The optical parts are the oculars, the objectives, the 

 substage condenser, and the mirror. The ocular is a 

 combination of lenses, which slips into the top of the 

 draw-tube and is nearest the eye. The objective is a 

 combination of lenses which is screwed into the nose- 

 piece and fits to the lower end of the draw-tube. The 

 substage condenser fits under the stage. It concentrates 

 the light on the object and is raised for high powers or 

 lowered for low powers. At the lower end of this con- 

 denser is the iris diaphragm, which is regulated by a 

 small lever with a milled head, and serves the purpose 

 of regulating the light supply. The mirror has two 

 sides, a concave and a flat. 



In the manipulation of the compound microscope the 

 following points should be strictly observed: 



1. Keep the instrument scrupulously clean. When 

 not in use, lock it in the case or cover it with a bell-jar. 



2. When carrying the instrument, grasp it by the 

 main pillar underneath the stage, not by the fine-adjust- 

 ment pillar. The fine adjustment consists of a very 

 delicate screw-thread, which is easily damaged. 



3. The lenses, condenser, and mirror, when needing, 

 should be wiped with Japanese lens-paper, never with 

 any coarse material. 



4. For cleaning use a damp cloth. For wiping the 

 lenses use water or xylol. Never use alcohol, as this 

 dissolves the cement holding the lenses in place and also 

 injures the lacquer. 



5. Do not take the instrument apart. The working 

 parts are of extremely delicate nature and easily injured. 



