PREFACE.
Reading edition
The following chapters are based upon notes of several unconnected lectures addressed to audiences of very different classes in the theatres of the Royal Institution, the London Institution, the Leeds Philosophical and Literary Society, and Caius House, Battersea.
In preparing the notes for publication the matter has been re-arranged with the object of presenting it, as far as might be, in methodical order; additions and omissions have been freely made, and numerous diagrams, illustrative of the apparatus and experiments described, have been provided.
I do not know that any apology is needed for offering the collection as thus re-modelled to a larger public. Though the essays are, for the most part, of a popular and informal character, they touch upon a number of curious matters of which no readily accessible account has yet appeared, while, even in the most elementary parts, an attempt has been made to handle the subject with some degree of freshness.
The interesting subjective phenomena which are associated with the sense of vision do not appear to have received in this country the attention they deserve. This little book may perhaps be of some slight service in suggesting to experimentalists, both professional and amateur, an attractive field of research which has hitherto been only partially explored.
CONTENTS.
PAGE.
Chapter I.
Light and the Eye 1
Chapter II.
Colour and its Perception 39
Chapter III.
Some Optical Defects of the Eye 84
Chapter IV.
Optical Illusions 130
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