Law of Falling Bodies
may be cited as an example. By this law, the physicist means that in
observing falling bodies in the past, he has noticed that they fall
about sixteen feet in the first second and acquire in this time a
velocity of thirty-two feet. He has noted that, taking into account the
specific gravity of the object and the resistance of the air, this way
of falling holds true of all objects at about the level of the sea.

The more we carefully study the events of the world, the more strongly
we come to feel that definite causes, under the same circumstances,
always produce precisely the same result. The scientist has faith that
events will continue to happen during all the future in the same order
of cause and effect in which they have been happening during all the
past.

The astronomer, knowing the relations of the members of the solar
system--the sun and planets--can successfully predict the occurrence of
lunar and solar eclipses. In other fields, too, the scientist can
predict with as much certainty as does the astronomer, provided his
knowledge of the factors concerned is as complete as is the knowledge
which the astronomer has of the solar system. Even in the case of human
beings, uncertain as their actions seem to be, we can predict their
actions when our knowledge of the factors is sufficiently complete. In a
great many instances we do make such predictions. For example, if we
call a person by name, we expect him to turn, or make some other
movement in response. Our usual inability to make such predictions in
the case of human beings is not because human beings are not subject to
the law of cause and effect, it is not that their acts are due to
chance, but that the factors involved are usually many, and it is
difficult for us to find out all of them.

=The Science of Psychology.= Now, let us ask, what is the science of
psychology? What kind of problems does it try to solve? What aspect of
the world has it taken for its field of investigation?

We have said that each science undertakes to describe some particular
aspect of the world. Human psychology is the science of human nature.
But human nature has many aspects. To some extent, our bodies are the
subject matter for physiology, anatomy, zooelogy, physics, and chemistry.
Our bodies may be studied in the same way that a rock or a table might
be studied. But a human being presents certain problems that a rock or
table does not present. If we conside