x CONTENTS. 



PAGE 



763. Variations in Colour Vision. Colour Blindness. The different kinds 

 of Colour Blindness ; red blind and green blind ; the Young- 



Helrnholtz explanation of them 1237 



764. The explanation of Colour Blindness on Hering's theory . . 1240 



765. The probable subjective condition of the Colour Blind . . . 1242 



766. Blue or Violet blindness ; absolute Colour Blindness . . . 1243 



767. Colour Blindness in the periphery of the retina .... 1244 



768. The influence of the yellow spot 1244 



769. Colour Sensations in relation to the intensity of the stimulus . . 1245 



SECTION IX. 

 ON THE DEVELOPMENT OF VISUAL IMPULSES. 



770. The Blind spot 1248 



771. Purkinje's figures ; their import 1249 



772. Possible theories as to the mode of origin of visual sensations . 1252 



773. Photochemistry of the retina ; visual purple 1253 



774. Hypothetical visual substances ; insufficiency of our present know- 

 ledge 1256 



775. The functions of the layer of rods and cones. The ophthalmoscope 1257 



776. Possible differences of function of rods and cones .... 1259 



777. Electric currents in the retina 1260 



SECTION X. 



ON SOME FEATURES OF VISUAL SENSATIONS ESPECIALLY IN RELATION 



TO VISUAL PERCEPTIONS. 



778. Simultaneous visual sensations ; the visual field .... 1261 

 779. The psychological and physiological methods ; sensations and per- 

 ceptions ; their want of agreement 1261 



780. Irradiation 1264 



781. Simultaneous contrast 1264 



782. After-images. Successive contrast 1265 



783. The phenomena of ' contrast ' in their bearing on the theories of 



colour vision 1266 



784. Eecurrent sensations. Ocular phantoms or hallucinations . . 1270 



SECTION XI. 

 BINOCULAR VISION. 



785. The movements of the eye-ball ; their limitations. Centre of rota- 

 tion, visual axis, visual plane 1272 



