CHAPTER II 



FOCUSING THE MICROSCOPE; WORKING DISTANCE; LIGHTING 

 WITHOUT AND WITH A CONDENSER; ARTIFICIAL DAY- 

 LIGHT; DARK GROUND ILLUMINATION 



§ 68. Apparatus and material for Chapter II. 



i. Microscope supplied with plane 7. Stage micrometer (fig. 80). 



and concave mirror, achromatic and 8. 10% solution salicylic acid in 



Abbe condensers, dry, adjustable 95% alcohol; cedar oil. 

 and immersion objectives, oculars, 9. Glass slides and cover-glasses 



triple nose-piece (fig. 25). (Ch. X). 



2. Lamp or lantern for microscopic 10. Preparation of stained bac- 

 work (fig. 37-38); opaque screen. teria. 



3. Homogeneous immersion liquid; 11. Vial of equal parts olive or 

 xylene; alcohol; distilled water. cottonseed oil, or liquid vaseline and 



4. Mounted preparation of fly's xylene. 



wing; lint; samples of starch. 12. Black and colored ink; pencils. 



5. Simple microscope; steel scale 13. Gum arabic mucilage, 

 ruled in \ mm. 14. Dark ground condenser 



6. Preparation of Pleurosigma (§ 125). 



(§ 98, 115); piece of black velvet. 15. Small arc lamp (fig. 49). 



Focusing 



§ 69. Focusing is mutually arranging an object and the microscope 

 so that a clear image may be seen. 



With a simple microscope either the object or the microscope or 

 both may be moved in order to see the image clearly, but with the 

 compound microscope the object more conveniently remains sta- 

 tionary on the stage, and the tube or body of the microscope is raised 

 or lowered (fig. 25). 



In general, the higher the power of the whole microscope, whether 

 simple or compound, the nearer together must the object and the 

 objective be brought. With the compound microscope, the higher 

 the objective, and the longer the tube of the microscope, the nearer 

 together must the object and the objective be brought. If the oculars 

 are not parfocal, the higher the magnification of the ocular, the nearer 

 must the object and objective be brought. 



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