194 THE USE OF THE MICROSCOPE 



oil, from too thick a cover, from paraffin wax on the cover, 

 or from cleaning with alcohol. 



13. If the high oil-immersion objective presses on the 

 cover-glass before the object, or the image of the 3-miUi- 

 meter diaphragm, is seen, the cover is too thick, probably 

 over 0.20 millimeter. 



14. If the defining power of an oil-immersion objective 

 is imperfect, it may arise from dry immersion oil on the 

 front lens. 



15. If the condenser aperture circle at the back of the 

 objective is smaller than it should be, the source dia- 

 phragm may be too far from the ground glass. 



16. If the rotating nosepiece gives trouble, it may come 

 from not turning it in the right direction, usually clockwise, 

 seen from below\ 



17. In using acetocarmine, dry objectives may be clouded 

 by a film of carmine on the front lens. 



18. If the condenser does not give enough light, it may be 

 that immersion oil or water has got between the lenses. 



19. A common cause of poor images with low and medium 

 dry objectives, is immersion oil on the front lens. 



20. If the properly corrected condenser fails to give a 

 full cone, it is probable that the slide is too thick or too 

 thin. A partial correction of this may be made by moving 

 the lamp nearer or farther, respectively. 



MANIPULATION OF HIGH POWERS 



When starting work, see that the lamp distance is correct 

 with the microscope slanted to the correct degree. Make 

 the interocular distance on the binocular correct. Insert 

 the slide, and water immerse the condenser. Get the light 

 centered by pulling out an eyepiece and looking down the 

 tube. Focus down the low-power objective on the edge 

 of this light circle which you shift so as to make the edge 

 cross the field. Put the object in the spot of light. 

 Reduce condenser aperture to suit low-power objective 

 while looking at eyepoint with 10 magnifier. Apply 



