CHAPTER XVI.

Contrast Colours--Measurement of Contrast Colours--Fatigue of the Eye--After-Images p. 196

LIST OF ILLUSTRATIONS.

FIG. PAGE

Colour-patch apparatus _Frontispiece_

1. Spectrum of sunlight 18

2. Carbon poles of an electric light 20

3. Curve for converting prismatic spectrum into wave-lengths 28

4. The thermopile 35

5. Heating effect of different sources of radiation 38

6. Colour-patch apparatus 42

7. Rotating sectors 45

8. Spectrum of Carbon Sodium and Lithium 48

9. Interference bands 60

10. Absorption of rays by the atmosphere 68

11. Luminosity curve of spectrum of the positive pole of the electric light 79

12. Rectangles of white and vermilion 82

13. Arrangement for measuring the luminosities of pigments 83

14. Measurement of the intensity of rays reflected from white and coloured surfaces 88

15. Intensity of rays reflected from vermilion, emerald green, and French ultramarine 92

16. Method of obtaining two patches of identical colour 95

17. Absorption by red, blue, and green glasses 99

18. Light reflected from metallic surfaces 100

19. Intensities of vermilion, carmine, mercuric iodide, and Indian red 101

20. Intensities of gamboge, Indian yellow, cadmium yellow, and yellow ochre 101

21. Intensities of emerald green, chromous oxide, and terre verte 103

22. Intensities of indigo, Antwerp blue, cobalt, and French ultramarine 104

23. Method of obtaining a colour template 104

24. Template of carmine 106

25. Template of luminosity of white light 108

26. Absorption of transmitted and reflected light by Prussian blue and carmine 107

27. Collimator for comparing the intensity of two sources of light 109

28. Spectrum intensities of sunlight, gaslight, and blue sky 109

29. Comparison of sun and sky lights 111

30. Slide with slits to be used in the spectrum 113

31. Screen on which to match gamboge 116

32. Diaphragm in front of prism 128

33. Curve of sensitiveness of silver bromo-iodide 136

34. Curves of colour sensations 139

35. K[oe]nig's curves of colour sensations 151

36. Maxwell's colour-box 152

37. Maxwell's curves of colour sensations 154

38. Chromatic circle 168

39. Disc to cause alternate opening and closing of two slits 179

40. Disc painted blue and red 181

41. Electro-motor with discs attached 183

42. Method of cutting disc to allow an overlap of a second disc 184

43. Arrangement to find value of gamboge in terms of emerald green and vermilion 188

44. Disc arranged to give approximately all the spectrum colours 192

45. Method of showing contrast colours 196

COLOUR MEASUREMENT AND MIXTURE.