Page. 



thesis of Mairan and Du Tour. (123) Young's theory of diffraction ; 

 incomplete. (124) Fresnel's theory. (125, 126) Fringes produced 

 by a single edge explained, and their places computed. (127) Fringes 

 within the shadow of a narrow opaqne body explained. (128) Fringes 

 formed by a narrow rectilinear'aperture. (129) Diffraction by asmall 

 circular aperture. (1 30) Diffraction by an opaque circular disc. (131) 

 Diffracted rings produced by fibres irregularly disposed; Young's 

 eriometer. (132, 133) Diffraction by fine gratings. (134) Fixed 

 lines in the diffr-acted spectrum ; their intervals always proportional. 



(135) "Wave-lengths corresponding to the seven principal fixed lines. 



(136) Law of intensity of light in the diffracted spectrum. (137) Euled 

 and striated surfaces. (138) Colours of mother of pearl. (139) Dif- 

 fraction produced by diaphragms in telescopes, 98 



CHAPTER VIII. 



COLOURS OF THIN PLATES. 



(140, 141) Colours of thin plates exhibited under various circumstances. 

 (142) Newton's mode of observing them ; Newton's scale. (143) Laws 

 of the phenomena. (144-146) Laws of the rings, experimentally 

 proved. (147) Transmitted rings. (148) Iroscope. (149) Newton's 

 explanation of the colours of thin plates ; Jits of easy reflexion and trans- 

 mission. (150) Assumption of this theory disproved. (15,1) Specu- 

 lations of Hooke and Young the colours of thin plates produced by 

 interference. (152) Laws of the colours of thin plates mathematically 

 deduced. (153, 154) Point of contact a point of discordance of two 

 waves ; loss or gain of half an undulation. (155) Transmitted rings 

 explained. (156) Imperfection of Young's theory removed by Poisson ; 

 experimentum crucis of Fresnel. (157) Phenomena of interference 

 produced by two parallel plates. (158) Interference produced by two 

 plates slightly inclined. (159,160) Colours of thick plates Newton's 

 experiment ; explanation. (161) M. Babinet's variation of Newton's 

 experiment. (162) Colours of mixed plates. (163) Eeview of the two 

 theories in their application to the foregoing phenomena, 128 



CHAPTER IX. 



POLARIZATION OF LIGHT. 



(164) Polarization of light discovered by Huygens. (165) Polarization by 

 reflexion discovered by Malus. (166, 167) Distinctive characters of a 



