154 



APPENDICES 



5. Definition only superficial; no depth of 

 focus. 



6. Greneral "flatness" and lack of contrast 

 especially seen when photographing bacteria or 

 kindred objects. 



7. Curiously elongated appearance of objects 

 such as bacteria all in one direction. 



8. White-line effect around hairs or around 

 bacteria. 



9. Blackened effect and increase in area of 

 the shadows in diatoms. 



10. General poorness of definition, with lack 

 . of detail in diatoms. 



1 1 . A circular loss of light around periphery 

 of picture. 



12. Dots of circular appearance with rings 

 around them show on the negative, but cannot 

 be seen through the microscope without great 

 attention. 



5. This may arise in /oi^-power work from 

 too large a diaphragm being used. In medmni 

 and high power work from too thick a speci- 

 men, or too high angled an objective — one with 

 too great a numerical aperture. Shut Davis 

 diaphragm a trifle, or close substage iris a 

 little, or both. With very thick objects, photo- 

 graph first with a low power with high K A. — 

 such as with an inch apo. N. A. '3, and subse- 

 quently enlarge the negative (page 30). 



6. Wrong contrast screen employed. Under- 

 exposure or under-development, or both. Ab- 

 sence of critical light. Plate improperly sen- 

 sitised for the special colour of screen. 



7. This curious effect mostly arises from 

 using a too freshly made specimen. The 

 objects float in the Canada balsam, or the 

 cover-glass slowly slides over the slip. 



8. Always arises from closing the iris dia- 

 phragm too much — a modification of this effect 

 arises from not " backing " the plate. 



9. From iris being too closed — absence of 

 " backing " on the plate. 



10. The cover-glass adjustment may not be 

 correct for the thickness of the cover-glass. 

 This mostly occurs in high-power dry lenses — 

 \ for example. If no cover-glass corrector to 

 lens, draw out or push in the draw-tube (page 85), 



11. In /ow-power work this arises from too 

 small a condenser, or it is placed too far from 

 slip. In Mgh-'power work the light is not 

 actually critical, or the wrong condenser used. 



12. This arises from dirt in the eye-piece. 

 Turn the eye-piece round on its axis ; they will 

 move if it arises Irom this cause. Bubbles of a 

 minute nature in the cover-glass or in the 



