XXVI CONTENTS. 



FA6B 



Notes on Aperture, Microscopical Vision, and the Value of 

 wide-angled Immersion Objectives : — 



I. The Aperture Theories. — Apertures exceeding 180° 



angular in Air. — The true Notation for Aperture Part 2 303 



1. The Two Theories of Aperture „ 304 



2. '■'■Dry" and'''' Immersion" Objectives. {Fig. 50^) „ 3l)5 



3. Definition of " Aperture." (Figs. 51-53) .. „ 807 



4. Increase of Aperture with the Incre ise in the 



Densitij of the Medium. — Apertures exceed- 

 ing 180° angular in Air. {Figs. 54 and 55) „ 308 



5. The Photometrical Test. — Supposed Identity 



of the Hemispheres in different Media. 



(%s. 56-62) „ 311 



6. The " Resolution " Test „ 316 



7. The " Angular Grip " „ 318 



8. Numerical Aperture. {Figs. GS and 6i) .. „ 321 



II. Angular-Aperture Fallacies „ 326 



1. The Hemisphere Puzzles „ 326 



(a) Tlie Convex Hemisphere. {Figs. 65-67) „ 326 



(b) Tlie Concave Hemisphere. {Fig. 68) „ 328 



(c) The Hemisphere as a Condenser. {Figs. 



6d and 70) „ 329 



2. Illumination Fallacies, {Figs. 71-73) .. „ 330 



3. Power of the Plane Surface of a Zens. 



{Fig-m , 332 



4. The Diagram Fallacy. {The Stokes Immer- 



sion and the Shadbolt Dry Objectives.) 



{Figs. 75 and 76) „ 333 



5. Fallacies in Practical Construction .. .. „ 337 



6. " Not Image-forming Rays " {Fig. 77) . . „ 338 



7. " Only a Question of Nomenclature" .. „ 340 



III. Photometrical Questions connected with Aperture . . „ 341 



1. Difference of Radiation in the same Medium. 



{Figs.78-S2) „ 341 



2. Increase of Radiation in Glass, Oil, ^-c. 



{Figs. 83-^0) „ 343 



IV. Microscopical Vision and the Delineating Power of 



Objectives „ 347 



1. The Abbe Theory of Microscopical Vision. 



{Figs. Ql-l(i7) „ 348 



2. The Delineating Power of Objectives and 



Aperture. {Figs. 108 and 109) . . . , „ 356 



V. The Value of Wide-angled Immersion Objectives . , „ 359 



"■ Opaque '" Illumination by the Vertical Illuminator . . .. „ 362 



Amphipleura pellucida by Rejiected and Transmitted Light „ 363 



Fluid for Homogeneous Immersion „ 366 



Further Remarks on t/ie Apertures of Microscope Objectives. 



(Fig. WO) „ 376-7 



On the Estimation of Aperture in the Microscope. {Figs. 



111-113) Part 3 388 



