INTJiODUCTION 



Causes of Injuhy. — (Continued) 



Cause 

 meter. 



31. Cover-glass too thin. 



32. Immersion oil 



smeared on cover- 

 glass. 



33. Wrong immersion 



oil. 



34. Bubbles in immer- 



sion oil. 



35. Bubbles with water- 



immersion objec- 

 tive with concave 

 front. 



36. Front lens of dry ob- 



jective soiled. 



37. Front lens of a 



water-immersion 

 objective greasy. 



38. Cemented lens com- 



ponents separat- 

 ing. 



39. Bubbles in balsam 



between compo- 

 nent lenses. 



40. Film on lens sur- 



faces inside objec- 

 tive, or fungi 

 growing on ex- 

 posed surfaces. 



41. Cloud of fine bub- 



l)les or flakes in 

 cement between 

 Ions {'ompoiiciits. 



Injury 

 water-immersion ob- 

 jectives (and to a 

 less extent of oil 

 immersions). 

 Spherical undercorrec- 

 tion. (This applies 

 also to oil-immersion 

 objectives.) 



Preventive 

 or slightly less, not 



Refractive errors with 

 dry searcher objec- 

 tive. 



Injury to corrections of 

 objective. 



Loss of light, and loss 



of aperture. 

 Loss of light, and loss 



of aperture. 



more. 



Use measured covers, 

 0.17 millimeter thick 

 (or no covers and 

 special objective), or 

 lengthen tube suffi- 

 ciently, or use objec- 

 tive with correction 

 collar. 



Use lowest oU-immer- 

 sion objective as a 

 searcher; or clean 

 cover every time. 



Use maker's oil. Espe- 

 cially avoid thick par- 

 affin oil. 



Put immersion oil on 

 front lens. 



Put water both on front 

 lens and on cover. 



Fog, more or less dense. Examine regularly with 



a magnifier. 



Fog, more or less dense. Clean regularly with 



xylol. 



Permanent fog. 

 Permanent fog. 

 Permanent fog. 



Permanent fog. 



Avoid dropping objec- 

 tives. 



Avoid heating of objec- 

 tives, by proximity to 

 lamp. 



Keep unused objectives 

 in dessicator, espe- 

 cially in tropical 

 climates. 



Return to maTcer, for 

 lenses to be rece- 

 mented. 



