x CONTENTS. 



PAGE 



7G3. Variations iii Colour Vision. Colour Blindness. The different Kinds 

 of Colour Blindness ; lied Blind and Green Blind ; the Young- 



Helmholtz Explanation of them 99 



761. The Explanation of Colour Blindness on Hering's Theory ... 102 



705. The probable Subjective Condition of the Colour Blind .... 104 



766. Blue or Violent Blindness ; Absolute Colour Blindness .... 105 



767. Colour Blindness in the Periphery of the Retina 10G 



768. The Influence of the Yellow Spot 106 



769. Colour Sensations in Relation to the Intensity of the Stimulus . 107 



SECTION IX. 

 Ox THE DEVELOPMENT OF VISUAL IMPULSES. 



770. The Blind Spot 110 



771. Purkinje's Figures ; their Import Ill 



$ 772. Possible Theories as to the Mode of Origin of Visual Sensations . 114 



773. Photochemistry of the Retina ; Visual Purple 115 



774. Hypothetical Visual Substances ; Insufficiency of our Present 



'Knowledge .' 118 



775. The Functions of the Layer of Rods and Cones. The Ophthalmoscope 119 



776. Possible Differences of Function of Rods and Cones 121 



777. Electric Currents in the Retina 122 



SECTION X. 



ON SOME FEATURES OF VISUAL SENSATIONS ESPECIALLY IN RELATION 

 TO VISUAL PERCEPTIONS. 



778. Simultaneous Visual Sensations ; the Visual Field 123 



779. The Psychological and Physiological Methods ; Sensations and 



Perceptions ; their Want of Agreement 123 



780. Irradiation 126 



781. Simultaneous Contrast 126 



782. After-Images. Successive Contrast 127 



733. The Phenomena of ' Contrast ' in their Bearing on the Theories of 



Colour Vision 128 



784. Recurrent Sensations. Ocular Phantoms or Hallucinations . . 132 



SECTION XI. 

 BINOCULAR VISION. 



785. The Movements of the Eye-Ball ; their Limitations. Centre of 



Rotation, Visual Axis, Visual Plane . . 134 



