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After having one day examined a few locomotive engineers for visual power and the color sense in particular, I felt considerably dissatisfied and asked myself the question, what is the object of these examinations? The answer came immediately: To avoid accidents by the elimination of men with visual defects. Another question presented itself: But is this—the condition of the color sense and the visual power relative to form—all that can afford us information relative to the aptitude of the individual to perceive quickly and respond with judgment? Emphatically, no. There is another phenomenon, or rather several phenomena, the observation of which would add much greater certainty to our work and more personal satisfaction in its contemplation. These several phenomena consist of the time taken for the sensation to be carried from the retina through the optic nerve to the cortical substance of the brain; the time taken for comparison and
TILLEY R. THE PERSONAL EQUATION AMONG TRAINMEN OF EQUAL OR GREATER IMPORTANCE THAN VISUAL POWER OR COLOR SENSE.. JAMA. 1897;XXIX(5):229. doi:10.1001/jama.1897.02440310027001i