Page:Journal of the Optical Society of America, volume 33, number 7.pdf/63



wave-length. Reference to Fig. 13 shows that the loci representing the same hue at different values are in some regions much more closely grouped than in others. The 10Y line, for example, is nearly the same at all value levels. This agrees with findings of Purdy (32) and of Exner (7) in their investigations of the Bezold-Brücke effect. Figure 13 also suggests invariables of this type at