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66 THE FOURFOLD ROOT. [CHAP. IV.
blind, acquire a sufficiently complete knowledge of the rela
tions of Space, to enable them to replace their want of eye
sight by it to a considerable degree, and to perform astonish
ing feats. A hundred years ago Saunderson, for instance,
who was blind from his birth, lectured on Optics, Mathe
matics, and Astronomy at Cambridge. 1
This, too, is the
only way to explain the exactly opposite case of Eva Lauk,
who was born without arms or legs, yet acquired an accurate
perception of the outer world by means of sight alone as
rapidly as other children.2 All this therefore proves that
Time, Space, and Causality are not conveyed into us by
touch or by sight, or indeed at all from outside, but that
they have an internal, consequently not empirical, but
intellectual origin. From this again follows, that the per
ception of the bodily world is an essentially intellectual
process, a work of the Understanding, to which sensation
merely gives the opportunity and the data for application
in individual cases.
I shall now prove the same with regard to the sense of
sight. Here the only immediate datum is the sensation
experienced by the retina, which, though admitting of great
variety, may still be reduced to the impression of light and
dark with their intermediate gradations and to that of
colours proper. This sensation is entirely subjective: that
is to say, it only exists within the organism and under the
skin. Without the Understanding, indeed, we should never
even become conscious of these gradations, excepting as of
peculiar, varied modifications of the feeling in our eye,
which would bear no resemblance to the shape, situation,
proximity, or distance of objects outside us. For sensation,
in seeing, supplies nothing more than a varied affection of
the retina, exactly like the spectacle of a painter s palette
1
Diderot, in his
of Saunderson.
2 See
"
Lettre sur les Aveugles," gives a detailed account
"
Die Welt a. W. u. V." vol. ii. chap. 4.