INDEX 



B1<J 



of sub-stage condensers, 46, 49, 

 52 ; relation to aplanatic 

 cone, 47, 53 ; means of 

 reducing, 49, 50, to increase 

 penetration, 22, 296, 299, to 

 give contrast, 297 ; effective 

 working value, 52, 167, relative 

 to N.A. of objective, 161; 

 in dark-ground illumination, 



55, H j _; 



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OBJECTIVE-CHANGERS, nose-piece, 34, 

 36, 37, 163 ; sliding, 32, (Zeiss), 36, 

 151, 163; Watson & Sons', 38; 

 centration with, 32, 36, 38, 163; 

 effect on tube-length, 37, 151 

 Objectives, choice of, 18, 21, 26, 27 ; 

 tests for, 28-32, 285 ; selected 

 list, 33 ; comparison of types, 

 284 



achromatic, meaning of, 18, 21 ; 

 description of, 26, 193 ; with 

 projection-ocular, 40, 152, 

 without ocular, 41, with com- 

 pensating ocular 42 ; correc- 

 tion-collar on, 155 ; colour- 

 screens with, 205, vide 

 Colour-screens ; exact focus- 

 sing for photography, 152, 

 153 ; magnifying power of, 

 35, 193 ; tests for defining 

 power, 28, 300, for correction, 

 29-32 



apochromatic, meaning of, 18, 

 21 ; description of, 27, 195 ; 

 Zeiss, 26, 30, 33, 284; with 

 ordinary ocular, 40, with pro- 

 jection-ocular, 40, 152, with 

 compensating ocular, 42, 152 ; 

 correction-collar on, 33, 165 ; 

 focussing with, 192 ; magni- 

 fying power of, 35, 195 ; tests 

 for defining power, 28, 29, 

 for correction, 29-32 



monochromats for ultra-violet 

 light, 27, 251, 253 



semi-apochromatic, 20, with com- 

 pensating ocular, 42 



dry-lens, 19 ; advantage of, 

 156; tests for, 28-30; in- 

 fluence of cover-glass thick- 

 ness, 160 ; for metallography, 

 163 



immersion-lens, advantage of, 

 19; tests for, 29, 30 ; focussing 

 with, 150, correction for cover- 

 glass thickness, 156 ; in metal- 



lurgical work, 24 ; with verti- 

 cal illuminators, 68 

 care of, 151 ; centration of, 32, 

 36-38, 163 ; combination with 

 ocular, 40-43, 152, 194; cor- 

 rection for chromatic and 

 spherical aberration, 21, tests 

 for, 29-30, 300; correction 

 . for cover-glass thickness, or 

 L tube length, vide Cover-glass 

 thickness ; focal length of, 

 26, 193 ; flatness of field, 25, 

 tests for, 29 ; magnifying 

 power of, 26, 34, 35, 193, vide 

 also Magnification ; numerical 

 aperture, vide Numerical aper- 

 ture ; penetration of, 21-24, 

 286, vide also Penetration ; 

 relation to tube-length, 151 ; 

 resolving power of, 26, 28, 60, 

 [_J as depending on N.A., 31, 

 vide also Resolving power ; 

 stopping down to increase 

 T | penetration, 22-24, 59 ; for 

 bacteriological work, 33, 162 ; 

 for metallography, 263 

 Object-slide thickness, 58 

 Oblique illumination, to test objec- 

 tives, 28, 30; of bacteria, 268, 

 290 ; of diatoms, 302, 303 ; of 

 metal surfaces, 61, 63 ; of opaque 

 objects, 285, 286 ; by decentreing 

 sub-stage iris, 302 



Oculars, ordinary, 38, 42 ; compen- 

 sating, 38, 40, 42, 152 ; Huy- 

 ghenian, 38, 40 ; Ramsden, 38, 



40, 186 



with achromatic objectives, 35, 

 38, 42 ; with apochromatic 

 objectives, 40, 152; with 

 either achromatic or apochro- 

 matic, the Universal (Swift), 

 42, the Holoscopic (Watson), 

 42 ; projection, 32, 38, 40, 



41, 152, Zeiss, 44 ; quartz for 

 ultra-violet light, 251 



combination with objective, 34, 

 41, 42, 152, 194 ; dust on, 153 ; 

 focussing, vide Focussing eye- 

 pieces ; magnification of, 34, 

 35, 40, 195 ; selection of, 152 

 Oil, for immersion lenses and con- 

 densers, cedar- wood, 19 ; how to 

 apply, 24, 56, 150 ; for lamps, 77 

 Oil -immersion condensers, 49, 55, 

 56, Swift, 50, Leitz, 50; lenses, 

 vide Objectives, immersion 

 Oil lamps, 76, 166, 169 ; heat from, 

 77 ; actinic value of, 226 



