individual reacts on optical stimuli.  If a playing child suddenly runs across the track of the electric railway, a difference of a tenth of a second in the reaction-time may decide his fate.  But I may say at once that I did not find characteristic differences in the rapidity of reaction of those motormen whom the company had found reliable and those who have frequent accidents.  It seems that the slow individuals do not remain in the service at all.  As a matter of course certain other indispensable single functions, like sharpness of vision are examined before the entrance into the service and so they cannot stand as characteristic conditions of good or bad service among the actual employees.

For this reason, in the case of the motormen I abstracted from the study of single elementary functions and turned my attention to that mental process which after some careful observations seemed to me the really central one for the problem of accidents.  I found this to be a particular complicated act of attention by which the manifoldness of objects, the pedestrians, the carriages, and the automobiles, are continuously observed with reference to their rapidity and direction in the quickly changing panorama of the street.  Moving figures come from the right and from the left toward and across the track, and are embedded in a stream of men and vehicles which moves parallel to the track.  In the face of such manifoldness there are men whose impulses are almost inhibited and who instinctively desire to wait for the movement of the nearest objects; they would evidently be unfit for the service, as they would drive the electric car far too slowly.  There are others who, even with the car at high speed, can adjust themselves for a time to the complex moving situation, but whose attention soon lapses, and while they are fixating a rather distant carriage, may overlook a pedestrian who carelessly crosses the track immediately in front of their car.  In short, we have a great variety of mental types of this characteristic unified activity, which may be understood as a particular combination of attention and imagination.

My effort was to transplant this activity of the motormen into laboratory processes.  And here I may include a remark on the methodology of psychological industrial experiments.  One might naturally think that the experience of a special industrial undertaking would be best reproduced for the experiment by repeating the external conditions in a kind of miniature form.  That would mean that we ought to test the motormen of the electric railway by experiments with small toy models of electric cars placed on the laboratory table.  But this would be decidedly inappropriate.  A reduced copy of an external apparatus may arouse ideas, feelings, and volitions which have little in common with the processes of actual life.  The presupposition would be that the man to be tested for any industrial achievement would have to think himself