246 POPULAR SCIENCE MONTHLY 



to $3,500, a maiming and a death. On another occasion an engineman 

 runs past a signal which the station agent declares was set at " stop," 

 but which the engineer himself asserts was showing " clear." Im- 

 mediately after the passage of the train, the signal light was found to 

 have been extinguished, as it had been once before that evening; it is 

 not improbable, therefore, that the "clear" light which the engineer 

 saw was some neighboring light which he took to be his signal. His 

 mistake brought death to 18 persons, injury to 57 more and a loss of 

 $15,720. 



With this evidence of the danger which lies in using white for color 

 signaling, and before passing on to consider red, a word should be said 

 of green — a color which, partly by its strong contrast with red, its 

 companion in the system, has found most wide acceptance. Green 

 stands out distinct from the common lights of street and house; it 

 readily makes an impression upon the normal eye. But persons who 

 are not color blind are liable to be weak in their sense of this 

 very color. And smoke, one of the great disturbers of signals on the 

 railway, has a serious influence upon green. For smoke, which makes 

 white or yellow lights look red, does this by making ineffectual the very 

 rays that are so important for giving a green light its greenish cast. 

 The simple experiment of holding a smoked glass before a green rail- 

 way-light will easily show how hostile smoke is to the passage of green 

 rays. Now when, for this or any other reason, green comes dimly to 

 the eye, especially when sight has grown accustomed to the dark, it has 

 the misfortune of appearing, not green at all, but a pale and ambiguous 

 light that is indistinguishable from white. Under such circumstances, 

 especially upon those roads where both white and green are signal 

 colors, the danger of their confusion is not imaginary ; nor is the danger 

 of green's total obscuration slight. In the records of the Interstate 

 Commerce Commission occur more than one instance where the failure 

 to observe at night a " distant " or " caution " signal, which is often 

 green, has been an important part of the cause of fatal accidents. 



But after all, the core of the present system is red, and to this our 

 main attention should be given. The color is usually obtained by 

 bringing before the semaphore lamp a glass which, acting like a filter, 

 permits the passage of those rays that are red or reddish, and holds 

 back from the eye all other light. Such a ruby glass, by killing off in 

 this way all that portion of the flame's light which is green or blue or 

 violet, and often all that is yellow, does of necessity greatly reduce the 

 brightness of the signal, leaving it in many cases about one fifth as 

 intense as when, by the signal mechanism, the red glass is removed from 

 the front of the lamp. This readily explains — what any one can ob- 

 serve — that in a cluster of signal lights equally remote, the white 

 signals normally outshine to a marked degree the neighboring signals 



