CONTENTS xxxv 



SECTION VI. 

 On Colour Sensations. 



PAGE 



§ 558. The existence of many kinds of colour sensations . . . 891 



§ 559. The mixing of colour sensations 892 



§ 560. The several usual colour sensations result from the mixture of 



simpler, primary sensations 893 



§ 561. The conditions which determine the characters of colour sensations 895 



§ 562. Complementary colours 896 



§ 563. Any colour sensation produced by the suitable mixture of three 



colour sensations .......... 897 



§ 564. The Young- Helmholtz theory of colour sensations .... 898 



§ 565. Hering's theory of colour sensations. A comparison of the two 



theories 900 



§ 566. Variations in colour vision. Colour blindness. The different 



kinds of colour blindness ; red blind and green blind ; the 



Young-Helmholtz explanation of them 

 § 567. The explanation of colour blindness on Hering's theory 

 § 568. The probable subjective condition of the colour blind 

 § 569. Blue or violet blindness ; absolute colour blindness . 

 § 570. Colour blindness in the periphery of the retina 

 § 571. The influence of the yellow spot .... 



906 

 909 

 911 

 912 

 913 

 913 



§ 572. Colour sensations in relation to the intensity of the stimulus . .913 



SECTION VII. 

 On the Development of Visual Impulses. 



§ 573. The blind spot 916 



§ 574. Purkinje's figures ; their import 917 



§ 575. Possible theories as to the mode of origin of visual sensations . . 920 

 § 576. Photochemistry of the retina ; visual purple ; the pigment epi- 

 thelium 922 



§ 577. The functions of the layer of rods and cones. The ophthalmoscope 926 



§ 578. Possible differences of function of rods and cones .... 927 



§ 579. Electric currents in the retina 928 



SECTION VIII. 



On Some Features of Visual Sensations especially in Relation 



to Visual Perceptions. 



§ 580. Simultaneous visual sensations ; the visual field .... 929 

 § 581. The psychological and physiological methods ; sensations and per- 

 ceptions ; their want of agreement 929 



§ 582. Irradiation 932 



§ 583. Simultaneous contrast 932 



§ 584. After-images. Successive contrast 933 



