CONTENTS Xix 



Page 

 REFLECTION FROM CONVEX MIRRORS 410 



REFRACTION . 410 



REFRACTION BY PRISMS 413 



Construction of the path of a ray passing through a prism. 



REFRACTION BY CONVEX LENSES 416 



Principal focus Estimation of principal focal distance 



Conjugate foci Virtual image Construction of image 



obtained with 'convex lens. 



REFRACTION BY CONCAVE LENSES 422 



REFRACTION BY SEGMENTS OF CYLINDERS 422 



REFRACTION THROUGH COMBINED CONVEX AND CYLIN- 

 DRICAL LENSES 424 



ABERRATION . . . 426 



Spherical aberration by reflection Spherical aberration 

 by refraction Dispersion circles Myopia Hyper- 

 metropia Chromatic aberration Aberration avoided 

 by a diaphragm. 



NUMBERING OF PRISMS AND LENSES 435 



Numbering of prisms Numbering of lenses. 



IX 

 REFRACTION IN THE EYE 



REFRACTION IN THE EYE .......... 487 



The eye as a camera obscura. 

 THE SCHEMATIC EYE 438 



CARDINAL POINTS OF THE CORNEA (SYSTEM A) ... 440 

 Construction drawing of System A Principal focal dis- 

 tances Construction of image Calculation of position 

 to cbnjngate foci-. 



CARDINAL POINTS OF THE 'CRYSTALLINE LENS (SYSTEM B) 445 

 Construction drawing of System B Optical centre Nodal 

 points Principal surfaces The point s Principal 

 points Principal focal distances. 



CARDINAL POINTS OF THE EYE (SYSTEM C) . . . . 451 

 Principal surfaces Nodal points Principal foci. 



