CHAPTER V.

Curiosities of Vision 165

LIST OF DIAGRAMS.

FIG. PAGE.

1. Image of Slit and Spectrum 12

2. Diagram of the Eye 24

3. Abney's Colour-patch Apparatus 45

4. Partially Intercepted Spectrum 49

5. Stencil Cards 52

6. Helmholtz's Curves of Colour Sensations 72

7. König's Curves 73

8. Stencil Card for Complementary Colours 77

9. Another form 79

10. Slide for Mixing any two Spectral Colours 80

11. Refraction of Monochromatic Light by Lens 87

12. Refraction of Dichromatic Light 89

13. Narrow Spectrum as seen from a Distance 97

14. Spectrum formed with V-shaped Slit 103

15. Bezold's Device for Demonstrating Non-achromatism of the Eye 108

16. Crossed Lines showing the Effect of Astigmatism 113

17. Another Design showing the same 114

18. Star-like Images of Luminous Points 116

19. Sutures of the Crystalline Lens 117

20. Multiple Images of a Luminous Point 120

21. The same, showing an increased number of Images 122

22. The same when a Slit is held before the Eye 123

23. Multiple Images of an Electric Lamp Filament 125

24. The same seen through a Slit 126-128

25. Illusion of Length 132

26. Another form 135

27. Another form 136

28. Another form 137

29. Another form 138

30. Illusion of Inclination 143

31. Zöllner's Lines 144

32. Slide for showing Illusions of Motions 147

33. Illusion of Motion 149

34. Illusion of Luminosity 152

35. Illusion of Colour 155

36. Recurrent Vision demonstrated with a Vacuum Tube 176

37. The same with a Rotating Disk 178

38. Apparatus for showing Recurrent Vision with Spectral Colours 181

39. Charpentier's "Dark Band" 187

40. Charpentier's Effect shown with the Hand 189

41. Multiple Dark Bands 192

42. Temporary Insensitiveness of the Eye after Illumination 194

43. Visual Sensations attending a Period of Illumination 199

44. Benham's Artificial Spectrum Top 200

45. Demonstration of Red Colour-borders 205

46. Black and White Screens for the same 209

47. Rotating Disk for the same 210

48. Demonstration of Blue Colour-borders 215

49. Disk for Experiments on the Origin of the Colour-borders 217

50. Disk for the Subjective Transformation of Colours 224