such a border depends on the position of light and darkness in relation
to the base of the prism. If the lighter part is nearer to the base,
then blue and violet tints are seen at the border, and with the reverse
position tints of yellow and red (Plate B, Fig. i). Along this path of
study Goethe found no reason for regarding the spectrum-phenomenon as
complete only when both kinds of border-phenomena appear simultaneously
(let alone when - as a result of the smallness of the aperture through
which the light meets the prism - the two edges lie so close that a
continuous band of colour arises). Hence we find Goethe - unlike Newton
- treating the two ends of the spectrum as two separate phenomena.

In this way, the spectrum phenomenon gave Goethe confirmation that he
had succeeded in expressing in a generally valid form the law of the
origin of the blue and the yellow colours, as he had read it from the
heavens. For in the spectrum, too, where the colour blue appears, there
he saw darkness being lightened by a shifting of the image of the
border between light and dark in the direction of darkness; where
yellow appears, he saw light being darkened by a shifting of the image
in the direction of light. (See the arrow in Fig. i.)

In the colours adjoining these - indigo and violet on the blue side,
orange and red on the yellow side - Goethe recognized 'heightened'
modifications of blue and yellow. Thus he had learnt from the
macro-telluric realm that with decreasing density of the corporeal
medium, the blue sky takes on ever deeper tones, while with increasing
density of the medium, the yellow of the sunlight passes over into
orange and finally red. Prismatic phenomenon and macrotelluric
phenomenon were seen to correspond in this direction, too.

Faithful to his question, 'How does colour arise?' Goethe now proceeded