INDEX 



287 



N.A. (See Numerical Aperture) 

 Napthalene mono-bromide immersion 



fluid, 67 

 Narcotic for living organisms, 249 



fluid, 268 



Natural History objects, Opaque, 191 

 Navicula, crabro, 255 

 - lyra, 255 



rhomboides, 178 

 Negatives, Contrast in, 225 



Improvement of, 226 

 Nelson's condenser, 105 



dark ground condenser, 183 



definition of critical light, 114 

 Nernst lamp, 19, 91 



Zeiss', 92 



Nosepiece, Centring, 29 



Diaphragm, 181 



Rotating, 30 



Sliding objective changer, 30 

 Notebook for exposures, 170 

 Numerical Aperture, Abbe's defini- 

 tion of, 60 



- bacteria, for, 241 



condensers, of, 103 



- and depth of focus, 64, 122 



- diatoms, for, 254 



- diffraction, and, 121, 255 



dry lenses, 255 

 "f" ratio, 79 



- flat field, and, 65, 255 



living micro-organisms, for, 

 244 



maximum useful, 121 



objects various, for, 121 



oil immersion objectives, 67 



- penetration and, 64, 122, 255 



- powers, for various, 66 



- resolution, 60, 67, 255 



spherical error, and, 50 

 working distance, and, 66 



Objectives, Achromatic, 52 



Apochromatic, 53 

 Brilliance of, 55 



compared to Achromats, 56 



Objectives, Achromatic, N.A. of, 55 



Round field of, 55 



Superiority of, 55 



Under-correction of, 55 



Brightness of image of, 63 



- Changers for, 30, 31 



- Combination of, with eyepieces, 

 74 



condensers, as, 113 



corrected for photography, 52 



Correction Collars for, 70 



cover-glass thickness, and, 69 



Definition of, 65 



Equivalent focal length of, 59 



- Flatness of field of, 65 



- Fluorite, 54 



- Focal length and power of, 59 



Focal planes of, 59 



Holoscopic, 54 



Improved achromatic, 54 



- Initial magnifications of, 59, 76, 

 78 



- Table of, 81 



Mono-chromatic, 52 



Numerical Aperture of, 60 



Oil immersion (q.v. ), 67 



- Penetration of (q.v.), 63 



Resolving power of (q.v.), 61 



Semi-apochromatic, 54 



Sets of, 58, 80 



Short, for metallography, 196 



- Testing, 56 



- Under-correction of high-power, 

 54 



Working distance of (q.v.), 65 

 Objects, Preliminary examination of, 



143 



Oblique illumination, 176 

 Amphipleura and, 177, 257 



- Condenser for, 179 



Continental Substage, and, 177 



- false images, and, 176, 254 

 resolution, and, 176, 178 



- for Surirella, 256 

 Stops for, 177 



Oil immersion condensers, 109 



