250 Public Lectures
color. What precisely is happening in the marble, in the eye,
in the mind, and also between these terms, to produce this
effect? Here is Locke’s answer:1 globules of light strike the
surface of the marble and rebound from it. The marble’s
surface has a texture which gives the rebounding light-par-
ticles two kinds of motion, rotational and progressive. The
progressive motion of certain of these light-particles carries
them forward to penetrate the lense of the eye and “to paint
the image”2 of the marble on the retina of the eye. Let us
for the moment construe this so-called “painting” not in the
literal sense but only in the sense of setting up a colorless
vibratory response among the material particles of the eye.
Now to this purely physical motion in the visual organ—
which may include parts of the brain—a “sensation is an-
nexed.” This is the white patch that is actually and directly
seen, and it is in the mind of the percipient. Of course, if the
sensing part of the mind is in the body, as it seems natural to
suppose, then it would appear that our patch of white should
be discoverable somewhere in the body of the observer, as
well as in his mind. And Locke is not at all loath to speak at
times as though colors are literally painted on the retina
and as though it is these retinal images that we directly see
in ordinary perception of bodies. In one disastrous place—∙
not in the Essay—after describing how a retinal image is
produced by the bombardment of particles, he states that
this image is seen. But Locke simply dare not mean that the
color white becomes a literal property of the retina, since
the retina is every bit as much a material object as the
marble, and Locke’s whole concern here is to show that colors
are never immediate qualities in bodies, but only in minds.
We therefore shall ignore this careless statement of his,
ɪ iv, 2, 11-13.
2Examination of Malebranche, Wks. Vol. IX, pp. 217-218.