APPENDICES 



155 



13. Unequal illumination in the background, 

 although the light is central and all other 

 defects remedied. 



14. Minute points known to exist in speci- 

 men cannot be well seen in photograph when 

 using a given lens. 



15. ISTegative generally thin. 



16. Negative black looking and high lights 

 choked. 



17. When using "oblique light" too long an 

 exposure becomes necessary. 



18. Definition at fault when using oblique 

 light and immersion condenser, which becomes 

 worse and worse the greater the obliquity. 



19. Unsatisfactory effect in definition with 

 high-power work which cannot be accounted 

 for by any of the previous remarks, especially 

 noticeable as accompanied with roundness of 

 field. 



20. General fogginess of image on the 

 ground glass. 



Canada balsam. Clean the eye-piece with 

 spirits of wdne. Avoid touching the lacquer. 



13. Unequal colouring of the Canada bal- 

 sam. Place slide on white paper, and see if 

 one part is not of a deeper yellow than another. 

 Expose deeply and develop highly. Then, in 

 printing, hold two feet from light, giving four 

 times the exposure sufficient at one foot, shad- 

 ing the too thin portions whilst so doing with 

 a card. Be careful when selecting specimens 

 to avoid this nuisance. 



14. The objective is probably of too low a 

 N. A. The field is flooded, perhaps, with too 

 much light. Close the substage iris a trifle. 

 Too violent a contrast screen used. Plate not 

 sufficiently " backed." 



15. Under-exposure or under-development. 

 If not too pronounced, intensify (page 126). 



16. Too much developed — thin (page 124). 



17. See if the beam from auxiliary con- 

 denser plays directly into the limited aperture 

 in the iris. Shift the condenser until it does, 

 and the light also if necessary. If using a 

 mirror, try the concave side. 



18. See that the oil connecting substage con- 

 denser has not dried up and " run ofi'." This 

 is nearly always the cause. 



19. See that the substage condenser is 

 central. Close iris to a pinhole, and lower the 

 whole substage, and note if pinhole is central 

 with the eye-piece employed. Occasionally this 

 may be central with one eye-piece and not with 

 another. 



20. See if eye-piece is not " steaming " from 

 condensed moisture on the front lens or the 

 back one. 



