having a tendency to chill and subdue the feelings, and to resolve all
things into atoms and numbers. For most men, an ignorant enjoyment is
better than an informed one, it is better to conceive the sky as a blue
dome than a dark cavity, and the cloud as a golden throne than a sleety
mist. I much question whether anyone who knows optics, however
religious he may be, can feel in equal degree the pleasure and
reverence an unlettered peasant may feel at the sight of a rainbow.'

What Ruskin did not guess was that the rudiments of the 'moral theory
of light' for which he craved, as this passage indicates, had been
established by Goethe long before.

*

In the section of his Farbenlehre dealing with 'physiological colours',
Goethe devotes by far the most space to the so-called 'afterimages'
which appear in the eye as the result of stimulation by external light,
and persist for some little time. To create such an afterimage in a
simple way, one need only gaze at a brightly lit window and then at a
faintly lit wall of the room. The picture of the window appears there,
but with the light-values reversed: the dark cross-bar appears as
light, and the bright panes as dark.

In describing this phenomenon Goethe first gives the usual explanation,
that the part of the retina which was exposed to the light from the
window-panes gets tired, and is therefore blunted for further
impressions, whereas the part on which the image of the dark frame fell
is rested, and so is more sensitive to the uniform impression of the
wall. Goethe, however, at once adds that although this explanation may
seem adequate for this special instance, there are other phenomena