CHAPTER VI
SENSATION
We can best understand the problems of sensation and perception if we first
think of the existence of two great worlds—the world of physical nature without
and the world of mind within. On the one hand is our material environment, the
things we see and hear and touch and taste and handle; and on the other hand our
consciousness, the means by which we come to know this outer world and adjust
ourselves to it. These two worlds seem in a sense to belong to and require each
other. For what would be the meaning or use of the physical world with no mind
to know or use it; and what would be the use of a mind with nothing to be known
or thought about?
1. HOW WE COME TO KNOW THE EXTERNAL WORLD
There is a marvel about our coming to know the external world which we shall
never be able fully to understand. We have come by this knowledge so gradually
and unconsciously that it now appears to us as commonplace, and we take for
granted many things that it would puzzle us to explain.
Knowledge through the Senses.—For example, we say, "Of course I see
yonder green tree: it is about ten rods distant." But why "of course"? Why should
objects at a distance from us and with no evident connection between us and
them be known to us at all merely by turning our eyes in their direction when
there is light? Why not rather say with the blind son of Professor Puiseaux of
Paris, who, when asked if he would like to be restored to sight, answered: "If it
were not for curiosity I would rather have long arms. It seems to me that my
hands would teach me better what is passing in the moon than your eyes or
telescopes."
We listen and then say, "Yes, that is a certain bell ringing in the neighboring
village," as if this were the most simple thing in the world. But why should one
piece of metal striking against another a mile or two away make us aware that
there is a bell there at all, let alone that it is a certain bell whose tone we