252 POPULAR SCIENCE MONTHLY 



men, 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. 



