Page:Journal of the Optical Society of America, volume 30, number 12.pdf/26

 data being made for both the diffuse-normal and the 45°-normal conditions. These computations were made on the basis of the 1931 I.C.I. standard observer and coordinate system and for I.C.I. Illuminant C. The weighted ordinate method was used, summations being taken at every 10 mu. Values of dominant wave-length (A) and excitation purity (P.) have been read from the charts of the Hardy Handbook of Colorimetry (7). Values of X, Y, Z, of x, y, of A, and of P, are given in Tables, and.

It will be recalled that the values of Y represent the luminous apparent reflectances relative to MgO. gives the average values of Y for the respective Munsell samples in Tables, and , and for the neutral samples given in the 1919 report (2).

A. H. Munsell left two representations of his system, first, the charts of his Atlas, and second, statements concerning the method by which they might be tested. Without doubt he intended the charts to exemplify the laws of color sensation by illustrations of equally stepped scales of hue, value, and chroma. Also without doubt he intended these as “measured scales”, and described them as having been measured, value by the photometer, and chroma by matches made on Maxwell spinning disks. The rule used for measuring chroma is that colors of complementary or opposite hue balance to gray in areas that are in inverse proportion to the products of their values and chromas.

The Munsell color system was based upon five color standards so chosen as to appear to be of the same lightness, the same saturation, and equally separated in hue. From these five standards chosen to fulfill the purely psychological requirement of appearance, it is possible by application of the psychophysical rules given in the Atlas of the Munsell Color System to derive a whole system of color standards. This aspect of the original Munsell color system has been analyzed by Tyler and Hardy (11). It is probable that Mr. Munsell believed that a color system derived by these psychophysical rules would also conform to psychological requirements analogous to those met by the five basic standards, but we now know that the conformity is not exact. We propose therefore to inquire whether the papers measured in 1919 and 1926 represent more nearly the psychological system