Open main menu

Page:Popular Science Monthly Volume 72.djvu/250

This page has been proofread, but needs to be validated.
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." Immediately 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 railway-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 observe—that in a cluster of signal lights equally remote, the white signals normally outshine to a marked degree the neighboring signals