from twelve to sixteen are probably due to nervous conditions caused by functional changes. (3) The fact that at first the arm exceeds the hand in rate, is perhaps explained by the observation that in children of five the clasping tendency is still strong.
(1) INTRODUCTION. – § 1. Formulation of the Problem. We must reduce the manifold of color-sensations to as few as possible elementary sensations. (These are not in concept the "fundamental" colors of Donders, which represent a simple peripheral process.) In other words, we must reduce the spectral colors to such elementary sensations. Their curve has for abscissa a solar diffraction spectrum, for ordinates their own intensities in that spectrum. § 2. The color-mixer. § 3. Transformation of gaslight dispersion values into sunlight diffraction values. § 4. Monochromatic, dichromatic, and trichromatic systems (Donders) are to be investigated.
(2) MONOCHROMATIC COLOR SYSTEMS. – § 5. General properties of such systems. The literature of total color-blindness contains some 40 names. Characteristic are diminished keenness of vision and avoidance of light. § 6. The elementary-sensation curve. There is here only one elementary sensation. The maximum of intensity in the system examined lay in green. The form of the curve tallies fairly well with those obtained by Donders and Hering.
(3) DICHROMATIC SYSTEMS. – § 7. General properties of such systems. "Dichromates," in the sense of the present paper, are red-blind and green-blind persons. Characteristic are the terminal spectral distances, where only differences of intensity are present, and the mixture of which gives the intervening spectrum. Either these end-colors are the two elementary sensations, or these are excited within one or both of them in a constant relation. The neutral point of the spectrum corresponds to the sensation white. §§ 8, 9. Determination of the elementary-sensation curve. § 10. Deductions. If we denote the elementary sensations by W (warm) and C (cold), the C-curves show one type, the W-curves two distinct types. There are, therefore, two forms of dichromate systems. The position of the neutral point denoted by the wave-length of the abscissal spectral light at the point of intersection of the two ele-
