r
and fresher from the stimuli of the day. It would seem not impossible
to undertake a systematic selection of various individuals under this
point of view, as different industrial tasks demand a different
distribution of efficiency between morning and night.

Such a selection and adjustment may be economically still more
important with reference to the fluctuations during the course of the
year. Economic inquiries, for instance, have suggested that younger
and older workingmen who ordinarily show the same efficiency become
unequal in their ability to do good work in the spring months, and the
economists have connected this inequality with sexual conditions. But
other factors as well, especially the blood circulation of the
organism and the resulting reactions to external temperature,
different gland activities, and so on, cause great personal
differences in efficiency during the various seasons of the year.
Inasmuch as we know many economic occupations in which the chief
demand is made in one or another period of the year, a systematic
study of these individual variations might be of high economic value,
where large numbers are involved, and might contribute much to the
individual comfort of the workers. But a constant relation to day and
year also seems to exist independent of all personal variations. When
the sun stands at its meridian, a minimum of efficiency is to be
expected and a similar minimum is to be found at the height of summer.
Correspondingly we have an increase of the total psychical efficiency
in winter-time. During the spring-time the behavior seems, as far as
the investigations go, to be different in the intellectual and in the
psychomotor activities. It is claimed that the efficiency of the
intellectual functions decreases as the winter recedes, but that the
efficiency of psychomotor impulses increases.[44]

The influences of the daily temperature, of the weather and of the
seasons may be classed among the physical conditions of efficiency. We
may group with them the effects of nourishment, of stimulants, of
sleep, and so on. As far as the relations between these external
factors and purely bodily muscle work are involved, the interests of
the psychologists are not engaged. But it is evident that every one of
these relations also has its psychological aspect, and that a really
scientific psychotechnical treatment of these problems can become
possible only through the agency of psychological experim