Plate I. Newton’s Theory. The Indigo line is erroneously placed between the Violet and the Red; it should be between the Blue and the Violet. Page 40.--_Fifth line from the bottom, for_ Fraunhoper _read_ Fraunhofer. _To face p. vi., Lovibond, Light and Colour Theories._] [P.R. 1317 LIST OF PLATES TO FACE PAGE Plate I. Six Colour Theories 4 " II. Circles Illustrating Absorption of White Light 11 " III. Diagram Illustrating Analysis of White Light 13 " IV. First System of Charting Colour 31 " V. Second System of Charting Colour 33 " VI. Six Tintometrical Colour Charts 39 " VII. Two Circles 40 " VIII. Absorption Curves of Dyes 76 " IX. Fading Curves of Dyes 78 " X. Comparison Curves of Healthy and Diseased Blood 80 " XI. Specific Colour Curves of Healthy and Diseased Human Blood 82 PURPOSE The purpose of this work is to demonstrate that colour is a determinable property of matter, and to make generally known methods of colour analysis and synthesis which have proved of great practical value in establishing standards of purity in some industries. The purpose is also to show that the methods are thoroughly scientific in theory and practice, and that the results are not likely to be changed by further discoveries. Also that out of the work done a new law has been developed, which the writer calls the Law of Specific Colour Development, meaning that every substance has its own rate of colour development for regularly increasing thicknesses. THE THEORY. Of the six colours in white light--red, orange, yellow, green, blue and violet; Red, Yellow and Blue are regarded as dominants, because they visually hold the associated colours orange, green and violet in subjection. An equivalent unit of pure red, pure yellow and pure blue is adopted, and incorporated into glass. The unit is multiplied to obtain greater intensities, and divided to obtain lesser intensities. The coloured glasses are called absorbents. The red absorbent transmits violet, red and orange, but the red ray alone is visible as colour, until the other absorbents are superimposed, and the character of the group of rays changed. In the same way yellow transmits orange and green, and blue transmits green and violet, whilst the yellow and blue alone are visible as colour. Orange, green and violet are here called subordinates, which may be developed as follows:-- Or. = R. + Y. Gr. = Y. + B. Vi. = B. + R.