Tracing the working of any one of the human senses from a physical stimulus to its perception by man brings into play taxing problems which reach to the limits of knowledge in each of the sciences it touches. Vision—color vision—is a particularly complicated process to study. Physicists investigate light, how it is emitted, absorbed, reflected, and how it passes through space. Physicists and biologists study how it passes through the eye; biochemists, histologists, electrophysiologists, neurologists, and so forth, study how it is received by the nerve‐sensitive retina and then passed on to the brain. Somewhere along the line the psychologist enters the fray.