the jug from the side, and gradually clouding the water by the
admixture of suitable substances. Whilst the brightness appearing in
the direction of the light goes over from yellow and orange to an
increasingly red shade, the darkness of the black background brightens
to blue, which increases and passes over to a milky white.

It had already become clear to Goethe in Italy that all
colour-experience is based on a polarity, which he found expressed by
painters as the contrast between 'cold' and 'warm' colours. Now that
the coming-into-being of the blue of the sky and of the yellow of the
sun had shown themselves to him as two processes of opposite character,
he recognized in them the objective reason why both colours are
subjectively experienced by us as opposites. 'Blue is illumined
darkness - yellow is darkened light' - thus could he assert the
urphenomenon, while he expressed the relation to Light of colours in
their totality by saying: 'Colours are Deeds and Sufferings of Light.'

With this, Goethe had taken the first decisive step towards his goal -
the tracing of man's aesthetic experience to objective facts of nature.

If we use the expressions of preceding chapters, we can say that
Goethe, in observing the coloured ur-phenomenon, had succeeded in
finding how from the primary polarity, Light-Dark, the opposition of
the yellow and blue colours arises as a secondary polarity. For such an
interplay of light and darkness, the existence of the air was seen to
be a necessary condition, representing in the one case a lightening, in
the other, a darkening element. That it was able to play this double
role arose from its being on the one hand pervious to light, while yet
possessing a certain substantial density. For a medium of such a nature
Goethe coined the expression trübes Medium.