Page:Popular Science Monthly Volume 72.djvu/256

, must distinguish colored signals), found 17 who were defective in their color sense. And Professor Nagel, of the University of Berlin, one of the great authorities in this department of research, and who has been called upon to assist the Royal Prussian Railways, has lately found in responsible positions like those of engine driver, fireman, switch tender, no fewer than twelve typical instances of red-green blindness among men whose sense of color had been officially tested and approved four or five times. Of about 300 employees of all branches of the service, all of whom had been tested at least once—and almost all of them more than once, by physicians and not by mere laymen—Nagel reports five per cent. to be typically color-blind; not color-weak merely, but actually color-blind. It is, therefore, difficult to partake of that happy confidence expressed by one of our leading railway journals, that "the railroads have long since done away with the dangers of color-blindness, by taking color-blind men off from their engines." We must, on the contrary, believe that the undiscovered presence of color-blind and color-weak men upon our engines adds to the many reasons for refusing longer to intrust the safety and life of thousands to one of the most fickle of our human faculties.