modes of our own consciousness, which cannot
even be conceived to exist in the marble. But consider the redness, to
begin with. How does the sensation of redness arise? The waves of a
certain very attenuated matter, the particles of which are vibrating
with vast rapidity, but with very different velocities, strike upon the
marble, and those which vibrate with one particular velocity are thrown
off from its surface in all directions. The optical apparatus of the eye
gathers some of these together, and gives them such a course that they
impinge upon the surface of the retina, which is a singularly delicate
apparatus, connected with the termination of the fibres of the optic
nerve. The impulses of the attenuated matter, or ether, affect this
apparatus and the fibres of the optic nerve in a certain way; and the
change in the fibres of the optic nerve produces yet other changes in
the brain; and these, in some fashion unknown to us, give rise to the
feeling, or consciousness, of redness. If the marble could remain
unchanged, and either the rate of vibration of the ether, or the nature
of the retina, could be altered, the marble would seem not red, but some
other colour. There are many people who are what are called colourblind,
being unable to distinguish one colour from another. Such an one might
declare our marble to be green; and he would be quite as right in saying
that it is green, as we are in declaring it to be red. But then, as the
marble cannot, in itself, be both green and red, at the same time, this
shows that the quality "redness" must be in our consciousness and not in
the marble.

In like manner, it is easy to see that the roundness and the hardness
are forms of our consciousness, belonging to the groups which we call
sensations of sight and touch. If the surface of the cornea were
cylindrical, we should have a very different notion of a round body from
that which we possess now; and if the strength of the fabric, and the
force of the muscles, of the body were increased a hundredfold, our
marble would seem to be as soft as a pellet of bread crumbs.

Not only is it obvious that all these qualities are in us, but, if you
will make the attempt, you will find it quite impossible to conceive of
"blueness," "roundness," and "hardness" as existing without reference to
some such consciousness as our own. It may seem strange to say that even
the "singleness" of the marble is relative to us; but extremely simple
experim