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 906 



567. The explanation of colour blindness on Hering's theory . . . 909 

 568. The probable subjective condition of the colour blind . . .911 



569. Blue or violet blindness ; absolute colour blindness .... 912 



570. Colour blindness in the periphery of the retina .... 913 



571. The influence of the yellow spot 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 



