Production of the Colours of the Spectrum -- Effect of Light upon Colours -- Definition of Terms -- Complementary Colours -- As Produced by Light and by Pigments -- The After-Image in Consecutive Contrast -- Simultaneous Contrast -- All Colours Impart about them Tints of their Complementaries -- Principles Determining Use together of Two Colours -- Of Three Colours -- Of Four Colours -- Consecutive and Simultaneous Contrast Due to Physiological Action of the Eye -- Correspondences between Ratios of Harmonic Colours and Tones -- Owing to Minuteness of Colour-Waves Nothing in Colours Corresponds to the Different Scales in Music -- The Ratios of the Two Notes of a Single Musical Scale Forming the Most Perfect Consonance -- This Ratio as Represented among the Colours -- Colour Harmony as Actually Developed -- Not from Ratios Occasioning Vibrations, but from Analysis of Light -- The Field-Theory of Colour-Harmony -- Theory Based on Psychological Effects -- On Physiological Effects -- Tone, or the Predominant Use of One Colour in a Painting -- Why this May Fulfil the Same Principle of Harmony as the Use of Great Variety of Colour -- Colour Harmony Results from an Application to Colour of All the Principles Unfolded in Chapters XIV. and XV. -- Beauty in Art -- And Suggestion -- Conclusion.
IT is now more than two centuries since Newton, analysing the rays of the sun, detected that all the different colours, except, perhaps, extreme purple are contained in light. Most of us know how to reproduce his analysis. By means of a mirror, the sun's rays are reflected in a small band through a narrow opening in a window-shade or blind, and sent into an otherwise darkened room. When they enter this room, they are made to pass through a glass prism. The prism turns the band of rays aside from its direction, and, at the same time, separates