CH. IX] 



PROJECT/ON MICROSCOPE 



259 



microscope for focusing and for the best position of the specimen in 

 relation to the other parts of the apparatus (§ 420.) The stage should 

 be very rigid. 



Fig. 210. 



Fig. 210. Mechanical Stage of Leitz. {Cut loaned by Wm. Krafft, N. Y.) 

 This has the advantage of having both milled heads at the side. It has the disad- 

 vantage of not being readily attached to the stage of a projection microscope. 



§ 415. Mechanical Stage. — For projection work this is almost a 

 necessity. While one is demonstrating there should be no time and no 

 energy wasted in finding the object. Preferably the milled heads of 

 the stage should be at the side, and the stage should be easy to remove 

 and put back into position. 



It should have sufficient range of motion to enable one to demon- 

 strate any section on a slide of serial sections. 



§ 416. Objective Carrier. — This like the stage should be on an 

 independent support. There should be both fine and coarse adjust- 

 ment. The tube should either be very short, or very large to avoid 

 restricting the field. For projection oculars there must be an adapter 

 for using them, and the adapter must be long enough to produce the 

 proper tube-length (160 mm.). As with the stage the objective car- 

 rier should be very substantial. 



§ 417. Objectives to Use in Micro-Projection. — One rarely 

 needs an objective lower than 100 mm. focus or higher than 3 mm. 

 The majority of the work with a screen distance of 5 to 8 meters will 

 be done with objectives of 60-75, 2 5 - 4°> J 6, 8, 6 or 3 mm. focus. For the 



