With a careful time-measurement of the motions, it can often be directly traced how purely technical processes in the machine itself influence and control the whole psychical system of impulses in the man.  I observed, in a factory, for instance, the work at a machine which performed most of its functions automatically.  It had to hammer fine grooves into small metal plates.  A young laborer stood before every such machine, took from a pile, alternately from the right and from the left, the little plates to be serrated, placed them in the machine, turned a lever to bring the hammer into motion, and then removed the serrated plates.  The speed of the work was dependent upon the operative, as he determined by his lever movement the instant at which the automatic serrating hammer should be released.  The man’s activity demanded 9 independent movements.  I found that those who worked the most quickly were able to carry out this labor for hours at a uniform rapidity of 4 to 4-1/2 second for those 9 movements.  But the time-measurement showed that even these fastest workers were relatively slow in the first 5 movements which they made while the machine stood quiet, and that they reached an astonishing quickness of movement in the 4 last actions during which at the same time the serrating hammer in bewildering rapidity was beating on the plate with sharp loud cracks.  The hammer reinforced the energy of the young laborers to an effectiveness which could never have been attained by mere voluntary effort.

Often the simplicity or complication of the stimulus may be decisive in importance, and this also holds true where the most elementary reactions are involved, for instance, the mere act of counting which enters into many industrial functions.  Experiments carried on in my laboratory[31] have shown that the time needed to count a certain number of units becomes longer as soon as the units themselves become more complicated.  Their inner manifoldness exerts a retarding influence on the eye as it moves from one figure to another.  A certain psychical inhibition arises; the mind is held back by the complexity of the impression and cannot proceed quickly enough to the next.  Psychologically no less important is the demand that the external technical conditions so far as they influence consciousness, should remain as far as possible the same, if the same psychical effect is desired, because then only can a perfectly firm connection between stimulus and movement be formed.  In technical life this demand is much sinned against.  A typical case is that of the signals for which the engineer on the locomotive has to watch.  In the daytime the movable arms of the semaphore indicate by their horizontal, oblique, or vertical position whether the tracks are clear.  At night-time, on the other hand, the same information reaches him by the different colors of the signal lanterns.  From a psychical point of view it is probable that the safety of the service would be increased if an unchangeable connection between signal and movement were formed.  It would be sufficient for that purpose if the color signals at night were given up and were replaced by horizontal, oblique, or vertical lines of white light or rows of points.  Successful experiments of this kind have been carried on by psychologists in the service of this railroad problem.[32]