14 CONTENTS. 



CHAPTEE II. 



What is Augnlar Aperture 93 



Angular Aperture ... .... 93 



How Shall we Measure Angular Aperture ... 95 



Object Glasses . , 97 



Something Further about Objectives .... 108 



Balsam Apertures 123 



Flatness of Field , 126 



Mounting of Objectives 129 



Nomenclature of Objectives 130 



Table of the Magnifying Power of Single Convex Lenses 134 



CHAPTER III. 



Objectives Continued 137 



Objectives of Lower Balsam Angle 144 



Adjustable Objectives ........ 148 



Eye-Pieces . 156 



CHAPTER IV. 



Manipulations Wenham's Reflex Illuminator . . 157 



The Woodward Illuminator ...... 163 



Tolles' Traverse Lens 179 



