3. The Relation between the Foveal and the Extra-Foveal Regions 13 4. The varying Sensibility of the Fovea 13 5. Chemical Analogy 14 6. Disappearance of Lights falling upon Fovea 15 7. Illusion of Moving Light 16 8. Purple After-Image 17 9. Currents seen in the Field of Vision not due to the Circulation 17 10. Pressure Figure 19 11. Macular Star 19 12. Entoptic Appearance of Cone Mosaic 20 13. Visual Acuity 21 THE EVOLUTION OF THE COLOUR-SENSE 26 THE FACTS OF COLOUR-BLINDNESS 34 1. Defects of Light-Perception 35 2. Defects of Colour-Perception 38 THE TWO MAIN VARIETIES OF COLOUR-BLINDNESS: 1. Dichromic Vision 40 2. Trichromic Vision 42 LECTURE II THE DETECTION OF COLOUR-BLINDNESS FROM A PRACTICAL POINT OF VIEW 1. Object of a Test for Colour-Blindness 44 2. The Requirements of a Test for Colour-Blindness 45 3. Persons to be Excluded 47 4. The Construction of a Test for Colour-Blindness 48 5. The Lantern Test 53 6. Other Tests for Colour-Blindness 66 LECTURE I _Delivered on February 1st_