ATIONS AND OUR PERCEPTION OF THEM

[Sidenote: _Mind's Source of Supplies_]

Whatever you know or think you know, of the external world comes
to you through some one of your five primary senses, sight, hearing,
touch, taste and smell, or some one of the secondary senses, such
as the muscular sense and the sense of heat and cold.

The impressions you receive in this way may be true or they may be
false. They may constitute absolute knowledge or they may be merely
mistaken impressions. Yet, such as they are, they constitute all the
information you have or can have concerning the world about you.

[Sidenote: _Does Matter Exist?_]

Philosophers have been wrangling for some thousands of years as
to whether we have any real and absolute knowledge, as to whether
matter actually does or does not exist, as to the reliability or
unreliability of the impressions we receive through the senses.
But there is one thing that all scientific men are agreed upon,
and that is that such knowledge as we do possess comes to us by
way of perception through the organs of sense.

If you have never given much thought to this subject, you have
naturally assumed that you have direct knowledge of all the
material things that you _seem_ to perceive about you. It has
never occurred to you that there are intervening physical agencies
that you ought to take into account.

[Sidenote: _First-Hand Knowledge_]

When you look up at the clock, you instinctively feel that there is
nothing interposed between it and your mind that is conscious of it.
You seem to feel that your mind reaches out and envelops it.

As a matter of fact, your sense impression of that bit of furniture
must filter through a great number of intervening physical agencies
before you can become conscious of it.

Direct perception of an outside reality is impossible.

[Sidenote: _Second-Hand Knowledge_]

Before you can become aware of any object there must first arise
between it and your mind a chain of countless distinct physical
events.

Modern science tells us that light is due to undulations or
wave-like vibrations of the ether, sound to those of the air, etc.
These vibrations are transmitted from one particle of ether or air
to another, and so from the thing perceived to the body of man.

Think, then, what crisscross of air currents and confusion of ether
vibrations, what myriad of physical events, must intervene between
any distant object and your own body before sen