those who fly at great heights it is a familiar experience to see the
sky assume a deep indigo hue. There can be no doubt that at still
higher altitudes the colour of the sky passes over into violet and
ultimately into pure black. Thus in the case of blue the field of
vision owes its darkening to a decrease in the resistance by which our
visual ray is met in the optical medium. It is precisely the opposite
with yellow. For here, as the density of the medium increases, the
colour-effect grows darker by yellow darkening first to orange and then
to red, until finally it passes over into complete darkness.

This shows that our visual ray is subject to entirely different dynamic
effects at the two poles of the colour-scale. At the blue pole, the
lightness-effect springs from the resistant medium through which we
gaze, a medium under the influence of gravity, while the darkness is
provided by the anti-gravity quality of cosmic space, which as a
'negative' resistance exercises a suction on the eye's inner light. At
the yellow pole it is just the reverse. Here, the resistant medium
brings about a darkening of our field of vision, while the
lightness-effect springs from a direct meeting of the eye with light,
and so with the suctional effect of negative density.

Our pursuit of the dynamic causes underlying our apperception of the
two poles of the colour-scale has led us to a point where it becomes
necessary to introduce certain new terms to enable us to go beyond
Goethe's general distinction between Finsternis (darkness) and Licht
(light). Following Goethe, we have so far used these two terms for what
appears both in blue and yellow as the respective light and dark
ingredients. This distinction cannot satisfy us any more. For through
our last observations it has become clear that the Finsternis in blue
and the Licht in yellow are opposites only in appearance, because they