CH. IX] 



DO AND DO NOT IN MICRO-PROJECTION 



313 



441. Summary of Chapter IX: 



Do 



1. Use actual objects in lec- 

 tures and discussions as well as 

 diagrams (352). 



2. Employ a projection micro- 

 scope with equipment for speci- 

 mens ranging from 60 mm. to 

 less than i mm. in diameter 



(354). 



3 . In demonstrating with the 

 projection microscope use first a 

 low power and show the rela- 

 tions of parts, then use higher 

 powers to show details. 



4. Use objectives without 

 oculars from 125 mm. to 4 mm. 

 focus (355)- 



5 . Oculars or amplifiers can be 

 used with all the objectives on 

 the microscope (fig. 138), but 

 preferably with those not higher 

 than 8 mm. focus. 



6. Use a screen distance from 

 5 to 10 meters (16 to 33 feet). 



7. It is better to use a micro- 

 scope in the usual manner if 

 very high powers, like the oil 

 immersion, are to be used (355). 



8. If possible use a triple- 

 lens condenser ( 363). 



Do NOT 



1 . Do not stop with diagrams 

 where actual specimens can be 

 shown. Diagrams alone are 

 liable to give false impressions. 



2. Do not use projection 

 apparatus with a narrow range 

 of field or of powers. 



3. Do not show minute de- 

 tails without first showing the 

 object as a whole, so that rela- 

 tions can be clearly recognized. 



4. Do not use oculars for 

 projecting for large, class demon- 

 strations. Oculars restrict the 

 field too much. 



5. Do not use oculars or 

 amplifiers unless for special 

 reasons. 



6. Do not have the screen 

 distance too great. 



7 . Do not try to make out the 

 finest details by projection, but 

 use a microscope in the ordinary 

 way. 



8. Do not use a poor con- 

 denser for micro-projection, the 

 triple form, meniscus next the 

 radiant, is best. 



