regiments made much slower progress in training
than others; and a whole Division was delayed for months because of
the backwardness of a single regiment. When the psychological tests
were introduced, these slow-learning units were found to contain a
disproportionate number of men of low intelligence. From that time on,
it was possible by aid of the tests to equalize the intelligence of
different units when first formed, and thus insure equal {4} progress
in training. This was a good example of "control".

Most of us are attracted by the practical use of a science, and some
have no patience with any study that does not seem immediately
practical. But really any science, however much it is applied, must
remain fundamentally a pure science; that is, it must seek most of all
to know and understand. Practical scientific knowledge was usually
first obtained without any inkling of how it might be used. The
science of electricity is the most striking example of this. It began
as an attempt to understand certain curious phenomena, which seemed to
be nothing but curiosities; yet when the knowledge of these phenomena
had progressed to a certain point, abundant use was found for it. Much
the same is true of psychology, which began as a pure science and only
recently has found ways of applying its discoveries to practical
affairs. So the student beginning the science, though properly
desirous of making practical use of what he learns, should let himself
be governed for the present by the desire to know and understand,
confident that the more scientific (which is to say, the more
complete, systematic and reliable) his knowledge is, the more
available it will be for practical application.

General psychology.

Our science is not concerned entirely with differences between people,
but asks also in what ways people are alike, and this is indeed its
central problem. How do "we" observe, learn, remember, imagine, think?
What sensations and feelings do we have, what emotions, what
instincts, what natural and acquired impulses to action? How are our
natural powers and impulses developed and organized as we grow up?
Psychology is concerned with the child as well as the adult, and it is
even concerned with the animal. It is concerned with the abnormal as
well as the normal human being. So you will find books and {5} courses
on animal psychology, child psychology, abnormal psychology. Now
general psychology--or just plain "psychology"--h