CONTENTS. Vll 



CHAPTEE V. 



DOUBLE REFRACTION. 



Page. 



(81) Double refraction discovered by Bartbolinus. (82, 83) Bodies pos- 

 sessing double refraction ; Iceland spar. (84) Ordinary and extraor- 

 dinary rays. (85, 86) Optic axis; phenomena of double refraction 

 symmetrical around it. (87) Construction ofHuygens for the direc- 

 tions of the two refracted rays. (88) Case in which both rays are 

 refracted according to the ordinary law. (89) Eefractive indices in 

 Iceland spar for the principal rays of the spectrum. (90) Case in 

 which the refracting surface, and the plane of incidence, contain the 

 optic axis. (91) Attractive and repuhice crystals. (92) Biaxal crys- 

 tals. (93) Connexion between the optical characters and the crystal- 

 line forms, discovered by Brewster. (94) Double refraction in biaxal 

 crystals. (95) Effects of double refraction ; two images. (96, 97) 

 Double-refracting prism. Double image micrometer, 63 



CHAPTER VI. 



INTERFERENCE OP LIGHT. 



(98) Effect of co-existing vibrations. Law of superposition of small motions. 

 (99) Union of two waves ; interference of light. (100) Analogous phe- 

 nomena in water, and in air. (101, 102) Grimaldi's experiment of in- 

 terference ; Young's experiment. (103) Phenomena of interference 

 of aqueous waves. (104, 105) Explanation of Young's experiment; 

 positions of the bands calculated. (106) Fresnel's experiment of in- 

 terference ; positions of the fringes. (107) Interference of direct 

 arid obliquely-reflected lights. (108) Interference produced by an 

 obtuse prism. (109) Arago's experimentum crucis displacement of the 

 fringes produced by interposed plate. (110, 111) Laws of the com- 

 position of co-existing vibrations. (112) Rectilinear propagation of 

 light explained on the principles of the wave-theory, 78 



CHAPTER VII. 



DIFFRACTIO N. 



(113) Diffracted fringes observed by Grimaldi. (114-116) Diffraction 

 by a single edge ; form of the fringes. (117) Diffraction by fine wire. 

 (118, 119) Diffraction by a narrow rectilinear aperture. (120) New- 

 ton's explanation of the phenomena. (121) Newtonian theory refuted ; 

 effects independent of the nature and form of the body. (122) Hypo- 



