turbances which come from without. Here again the
chief interest ought to be attached to those interferences which the
workman himself no longer feels as such. In a great printing-shop a
woman who was occupied with work which demanded her fullest attention
was seated at her task in an aisle where trucking was done. Removing
this operator to a quiet corner caused an increase of 25 per cent in
her work.[40] To be sure there are many such disturbances in factory
life which can hardly be eliminated with the technical means of
to-day. For instance, the noise of the machines, which in many
factories makes it impossible to communicate except by shouting, must
be classed among the real psychological interferences in spite of the
fact that the laborers themselves usually feel convinced that they no
longer notice it at all. Still more disturbing are strong rhythmical
sounds, such as heavy hammer blows which dominate the continuous
noises, as they force on every individual consciousness a
psychophysical rhythm of reaction which may stand in strong contrast
to that of a man's own work. From the incessant inner struggle of the
two rhythms, the one suggested by the labor, the other by the external
intrusion, quick exhaustion becomes unavoidable.

If it were our purpose to elaborate a real system of psychological
economics, we should have to proceed here to a careful study of the
influences of fatigue on the industrial achievement. We should have to
discuss the various kinds of fatigue and exhaustion, the conditions of
restoration, and the whole group of related problems of psychophysics.
But this is the one field which has been thoroughly ploughed over by
science and by practical life in the course of the last decades. No
new suggestion and no new hint of the importance of the problem is
needed here. Our short discussion was planned to be confined to those
regions which have not been worked up in systematic investigations
and for which new devices seemed desirable. Hence we do not reproduce
here the rich material of facts which the physiologists and
psychophysicists have brought together in the last half-century, the
importance of which for industrial labor is perfectly evident.
Moreover, the practical applications and the insight into the social
needs have transformed the factories themselves into one big
laboratory in which the problem of fatigue has been studied by
practical experiments. The problem of the dependence of fatigue an