such popular curiosity. In this sign experimental psychology has
conquered. The fundamental laws of the ideas and of the attention, of
the memory and of the will, of the feeling and of the emotions, have
been elaborated. Yet it slowly became evident that such one-sidedness,
however necessary it may have been at the beginning, would make any
practical application impossible. In practical life we never have to
do with what is common to all human beings, even when we are to
influence large masses; we have to deal with personalities whose
mental life is characterized by particular traits of nationality, or
race, or vocation, or sex, or age, or special interests, or other
features by which they differ from the average mind which the
theoretical psychologist may construct as a type. Still more
frequently we have to act with reference to smaller groups or to
single individuals whose mental physiognomy demands careful
consideration. As long as experimental psychology remained essentially
a science of the mental laws, common to all human beings, an
adjustment to the practical demands of daily life could hardly come in
question. With such general laws we could never have mastered the
concrete situations of society, because we should have had to leave
out of view the fact that there are gifted and ungifted, intelligent
and stupid, sensitive and obtuse, quick and slow, energetic and weak
individuals.

But in recent years a complete change can be traced in our science.
Experiments which refer to these individual differences themselves
have been carried on by means of the psychological laboratory, at
first reluctantly and in tentative forms, but within the last ten
years the movement has made rapid progress. To-day we have a
psychology of individual variations from the point of view of the
psychological laboratory.[1] This development of schemes to compare