n constant rules, he keeps to a consistent method. So with the
physiologist; he has his microscope, his staining fluids, his means of
stimulating the tissues of the body, etc. The physicist also makes
much of his lenses, and membranes, and electrical batteries, and X-ray
apparatus. In like manner it is necessary that the psychologist should
have a recognised way of investigating the mind, which he can lay
before anybody saying: "There, you see my results, you can get them
for yourself by the same method that I used."

In fulfilling this requirement the psychologist resorts to two methods
of procedure. He is able to investigate the mind in two ways, which
are of such general application that anybody of sufficient training to
make scientific observations at all can repeat them and so confirm the
results. One of these is what is called Introspection. It consists in
taking note of one's own mind, as all sorts of changes are produced in
it, such as emotions, memories, associations of events now gone, etc.,
and describing everything that takes place. Other persons can repeat
the observations with their own minds, and see that what the first
reports is true. This results in a body of knowledge which is put
together and called "Introspective Psychology," and one chapter of the
story should be devoted to that.

Then the other way we have is that of experimenting on some one else's
mind. We can act on our friends and neighbours in various ways, making
them feel, think, accept, refuse this and that, and then observe how
they act. The differences in their action will show the differences in
the feelings, etc., which we have produced. In pursuing this method
the psychologist takes a person--called the "subject" or the
"re-agent"--into his laboratory, asks him to be willing to follow
certain directions carefully, such as holding an electric handle,
blowing into a tube, pushing a button, etc., when he feels, sees, or
hears certain things; this done with sufficient care, the results are
found recorded in certain ways which the psychologist has arranged
beforehand. This second way of proceeding gives results which are
gathered under the two headings "Experimental" and "Physiological
Psychology." They should also have chapters in our story.

3. There is besides another truth which the psychologist nowadays
finds very fruitful for his knowledge of the mind; this is the fact
that minds vary much in different individuals, or classes of
i