THE 



POPULAR SCIENCE 

 MONTHLY. 



FEBRUARY, 1885. 



THE SIGHT AND HEAEmG OF KAILWAY 



EMPLOYES.* 



By "WILLIAM THOMSON, M. D., 



PEOFESSOB OF OPHTHALMOLOGY, JEFFEESON MEDICAL COLLEGE. 



SHORTLY after the demonstrations of Professor Holmgren, in 

 Sweden, of the dangers in transportation to persons and property 

 on land and sea from color-blindness, the writer called the attention 

 of the officers of the Pennsylvania Railroad to the subject ; and, at 

 the request of the president, Mr. Thomas A. Scott, and the vice-presi- 

 dent, Mr. Frank Thomson, he undertook to solve the problem of elimi- 

 nating these dangerous men from their service. To his first state- 

 ment that there were probably four per cent of men incapable of 

 distinguishing unerringly between red and green flags by day, or lights 

 by night, it was responded that their signals alone would detect such 

 men, and force them from their places, since, as we all know, the most 

 imperative orders in railway administration are transmitted through 

 the visual organs, in the white of " Safety," the green of " Caution," 

 and the red of " Danger " ; and it was considered by the officers of the 

 road impossible for men color-blind to pass the thousands of signals in 

 daily use on their thousands of miles of road without detection. A 

 very slight search dispelled this idea, and a demonstration of the de- 

 fect before the Society of Transportation Officers of the Pennsylvania 

 Railway aroused the members of it to the dangers to be feared, and 

 led to the appointment of a special committee to aid the writer in 

 completing a system which would have practical value, with the Gen- 



* Read before Section B of the American Association for the Advancement of Science, 

 at Philadelphia, September 8, 1884. 

 VOL. XXVI. — 28 



