36 TH?] USE OF THE MICROSCOPE 



Practical Points 



1. Working aperture is more important practically tlian mere 

 objective aperture. 



2. It may be usually more convenient to have a separate low- 

 power microscope, than to have to remove the condenser from a 

 medium or high-power instrument. 



3. The source of light should be made equal to the source- 

 field by a diaphragm close to the source. 



4. The used aperture of the condenser should as nearly equal 

 the aperture of the objective as can be, without glare. 



5. The plane mirror can be employed with a large source of 

 light (without a condenser), for low powers. 



6. The concave mirror can be used when the source of light is 

 small, but only for low powers. 



7. A dry corrected condenser suffices for dry objectives. 



8. A water-immersion condenser should be used with high- 

 apertured objectives, for ultimate investigation. 



9. Putting a 3-millimeter diaphragm on the source of light 

 facilitates focusing immersion objectives of high aperture. 



10. Dry objectives are best used on objects in air. They can 

 be specially made and corrected for use without covers. 



11. Water-immersion objectives are best used for objects in 

 water. 



12. Oil-immersion objectives are best used on objects (in 

 balsam or) in immersion oil, or on objects in optical contact with 

 the cover-glass. They may be used without cover-glasses by 

 increasing the tube length. 



13. Frequent changing of eyepieces has disadvantages. The 

 objectives can be selected so that only one eyepiece is usually 

 necessary. 



J' 



