Page:Journal of the Optical Society of America, volume 30, number 12.pdf/29

 connecting the experimental data with the lines of dominant wave-length, designated by crosses in, were determined on the basis of the psychophysical system described below and are taken from of the Tyler-Hardy paper.

The 1926 data of are plotted in different form in  in order to discover whether such variations as there may be in the relation between hue and dominant wave-length are random differences, or whether there may be some regularity in the pattern of variation. Each arrow point, at the value plotted, indicates the direction and magnitude of the difference between the dominant wave-length of that sample and the average dominant wave-length of all the samples of that hue designation, the length of arrow indicating the proportional part of the whole A interval. These average dominant wave-lengths were computed from Tables and.

From an examination of Figs. and and reference to Tables,  and , we may conclude that there are many deviations from dominant wave-length constancy among the samples for a single hue and its complementary. Some of the deviations are obvious from inspection of the samples, others are not. The hue which has the most constant dominant wave-length is yellow; the hue exhibiting the least constant dominant wave-length is blue-green, the deviation for this hue being nearly enough to extend to the average dominant wavelength of Munsell blue. In addition there is a very definite trend in some of the hues for the dominant wave-lengths of the samples of high Munsell value to be greater than those for the lower values. For example, with the blue-green samples, from values 8/ to 2/, dominant wavelength progresses from 506 through 500, 492, 496, 490 to 485 and 487 mμ. A reverse progression holds for the red series, the samples of high Munsell value being shorter in wave-length than those of low value, the progression being from a dominant wave-length of 599 mμ at value 8/ to 615 (or 640) m&mu; at value 2/. Such progressions are suggestive of the Bezold-Br&uuml;cke phenomenon (12), the change in hue produced by an increase in luminance, but it must be recalled that the samples of each Munsell hue represented by differ in purity as well as in luminous apparent reflectance. So the more or less regular departures from constant dominant wave-length shown in for all but the yellow and green-yellow hues may exemplify the hue change by admixture of achromatic light (19) as well as the Bezold-Br&uuml;cke phenomenon, and indeed the latter phenomenon would seem to be secondary for Munsell red and yellow-red because the