dual differences of exhaustion, fatigue, exhaustibility, ability
to recover the lost energy, ability to learn from practice, and so on,
but they are still exclusively adjusted to the needs of the
school-teacher and of the nerve specialist and would hardly be
immediately useful to the manager of a factory. We shall need a long
careful series of investigations in order to determine how far those
manifold results from experiments with memory work, thought work,
writing work, and so on can be applied to the work which the
industrial laborer is expected to perform.

XVIII

PHYSICAL AND SOCIAL INFLUENCES ON THE WORKING POWER

The increase and decrease of the ability to do good work depends of
course not only upon the direct fatigue from labor and the pauses for
rest; a large variety of other factors may lead to fluctuations which
are economically important. The various hours of the day, the seasons
of the year, the atmospheric conditions of weather and climate, may
have such influence. Some elements of this interplay have been cleared
up in recent years. Just as the experiments of pedagogical psychology
have determined the exact curve of efficiency during the period of an
hour in school, so other investigations have traced the typical curve
of psychical efficiency throughout the day and the year. Sociological
and criminological statistics concerning the fluctuations in the
behavior of the masses, common-sense experience of practical life, and
finally, economic statistics concerning the quantity and quality of
industrial output in various parts of the day and of the year, have
supplemented one another. The systematic assistance of the
psychological laboratory, however, has been confined to the
educational aspect of the problem. Psychological experiments have
determined how the achievement of the youth in the schoolroom changes
with the months of the year and the hours of the day. It seems as if
it could not be difficult to secure here, too, a connection between
exact experiment and economic work. Much will have to be reduced to
individual variations. The laboratory has already confirmed the
experience of daily life that there are morning workers whose
strongest psychophysical efficiency comes immediately after the
night's rest, while the day's work fatigues them more and more; and
that there are evening workers who in the morning still remain under
the after effects of the night's sleep, and who slowly become freshe