The attempt to express color relations by using merely two dimensions, or two definite characteristics, can never lead to a successful system. For this reason alone the system proposed by Mr. Munsell, with its three dimensions of hue, value, and chroma, is a decided step in advance over any previous proposition. By means of these three dimensions it is possible to completely express any particular color, and to differentiate it from colors ordinarily classed as of the same general character. The expression of the essential characteristics of a color is, however, not all that is necessary. There must be some accurate and not too complicated system for duplicating these characteristics, one which shall not alter with time or place, and which shall be susceptible of easy and accurate redetermination. From the teaching standpoint also a logical and sequential development is absolutely essential. This Mr. Munsell seems to have most successfully accomplished. In the determination of his relationships he has made use of distinctly scientific methods, and there seems no reason why his suggestions should not lead to an exact and definite system of color essentials. The Munsell photometer, which is briefly referred to, is an instrument of wide range, high precision, and great sensitiveness, and permits the valuations which are necessary in his system to be accurately made. We all appreciate the necessity for some improvement in our ideas of color, and the natural inference is that the training should be begun in early youth. The present system in its modified form possesses elements of simplicity and attractiveness which should appeal to children, and give them almost unconsciously a power of discrimination which would prove of immense value in later life. The possibilities in this system are very great, and it has been a privilege to be allowed during the past few years to keep in touch with its development. I cannot but feel that we have here not only a rational color nomenclature, but also a system of scientific importance and of practical value. H. E. CLIFFORD. MASSACHUSETTS INSTITUTE OF TECHNOLOGY, February, 1905. CONTENTS. Introduction By Professor Clifford. Part I. Chapter Paragraph I. COLOR NAMES: Red, Yellow, Green, Blue, Purple 1 Appendix I.--Misnomers for Color. II. COLOR QUALITIES: Hue, Value, Chroma 20 Appendix II.--Scales of Hue, Value, and Chroma. III. COLOR MIXTURE: A Tri-Dimensional Balance 54 Appendix III.--False Color Balance. IV. PRISMATIC COLORS 87 Appendix IV.--Children’s Color Studies. V. THE PIGMENT COLOR SPHERE: TRUE COLOR BALANCE 102 Appendix V.--Schemes based on Brewster’s Theory. VI. COLOR NOTATION: A Written Color System 132