220 Chapter 14
Figure 14.3
Helmholtz ’ s opthalmotrope, a model used to study basic mechanisms of eye movements (built in 1857 by Chris-
tian Theodor Ruete).which his work was extremely important in clarifying so as to address pervasive confusion
about the exact meaning of these terms and the nuances between them. In brief, the linear
sequence of the Newtonian spectrum, arranged from red to violet, is perceived by the
human eye in a decidedly nonlinear way. Helmholtz ’ s diagram ( figure 14.4b ) shows that,
to mix colored lights to form white, a different amount of yellow must be mixed with
indigo, as compared with the relative amounts of orange and cyan-blue needed to produce
white. In this diagram, these differences show up in the asymmetric shape of the overall
curve, whose skew toward the red-orange side reflects the higher sensitivity of human
daytime vision to those colors, as compared with the blue-violet side.
In the course of this work, Helmholtz also devoted attention to the possibility of describ-
ing the perceived distances between colors “ on the principle of the musical scale, because
this seemed to be the best method for physiological reasons. Thus, colors whose