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 

 and concave mirror, achromatic and 

 Abbe condensers, dry, adjustable 

 and immersion objectives, oculars, 

 triple nose-piece (fig. 25). 



2. Lamp or lantern for microscopic 

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



3. Homogeneous immersion liquid; 

 xylene; alcohol; distilled water. 



4. Mounted preparation of fly's 

 wing; lint; samples of starch. 



5. Simple microscope; steel scale 

 ruled in \ mm. 



6. Preparation of Pleurosigma 

 (§ 98, 115); piece of black velvet. 



7. Stage micrometer (fig. 80). 



8. 10% solution salicylic acid in 

 95% alcohol; cedar oil. 



9. Glass slides and cover-glasses 

 (Ch. X). 



10. Preparation of stained bac- 

 teria. 



11. Vial of equal parts olive or 

 cottonseed oil, or liquid vaseline and 

 xylene. 



12. Black and colored ink; pencils. 



13. Gum arabic mucilage. 



14. Dark ground condenser 



(§ 125). 



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. 



36 



