270 THE USE OF THE MICROSCOPE 



25. When is a corrected immersion condenser required? 



26. In what way is a condenser to be focused? 



27. How can a high-power objective be focused quickly and without 

 risk of damage? 



28. Why are high dry objectives at their best with objects in air? 



29. When might dry objectives, corrected for uncovered objects, be of 

 advantage? 



30. Why are water-immersion objectives at their best for objects in 

 water? 



31. Why are oil-immersion objectives at their best with objects 

 mounted in immersion oil? 



32 What would be the advantage in having oil-immersion objectives 

 corrected for use without a coverglass? 



33. What are the disadvantages of too low eyepieces? 



34. How can much changing of eyepieces be avoided? 



35. What is the effect, in the binocular, of a wrong adjustment of the 

 distance between the eyepoints of the eyepieces? 



36. How can the correct distance between the eyepieces in a binocu- 

 lar be ascertained for any observer? 



37. Why should the eyepieces of the twin-objective binocular be 

 parfocal? 



38. How can the aperture of the twin objectives be readily estimated? 



39. How can a twin-objective binocular be best tested? 



40. What is orthomorphy? 



41. How can adjustment for different inter pupillary distances be 

 made in the monobjective binocular without altering the optical tube 

 length? 



42. What are the optical advantages of parallel tubes in a binocular? 



43. What advantage lies in good stereoscopic vision without loss of 

 definition, as in the Greenough binocular? 



44. What advantages does the twin-objective binocular possess over 

 the monobjective binocular used stereoscopically? 



45. What are the advantages of binocular vision without stereoscopic 

 effect, as compared with monocular vision? 



46. How can a usually sufficient stereoscopic effect be attained in the 

 monobjective binocular without loss of aperture or definition? 



47. How does the binocular act with regard to the floating motes of 

 the eyes? 



48. What effect may the blind spot of the eye have when using the 

 monocular with a large field? 



49. What advantages does the monocular have as compared with the 

 binocular? 



50. Why should the unoccupied eye be shaded with ground glass, and 

 not kept closed? 



51. ^^'hat is the use of a diaphragm in the drawtube? 



