RAILWAY ACCIDENTS 247 



that are red. This, of itself, is an undesirable condition, since the 

 sign of danger should of all be most outspoken. 



The disadvantage under which the red danger signal labors is, how- 

 ever, quite insufficiently expressed by saying that the ruby glass often 

 virtually destroys fully four fifths of the light from a lantern flame 

 already none too bright, and to this extent increases the liability that 

 the most momentous of the signals will at some crisis be seen too late or 

 not at all. Even the remaining portion is often far less effectual upon 

 the eye than its physical quantity would lead us to expect. The im- 

 portance of the matter for signaling will perhaps justify some further 

 account. 



If, by reliable devices of the laboratory, a semaphore light showing 

 " white " be gradually reduced in brightness, a point can easily be 

 found where the eye, grown accustomed to the dark, can just perceive 

 the light. And when for comparison a railway ruby glass, or 

 " roundel," is placed before the lamp, the observer now obtains no con- 

 scious impression at all. But instead of having to increase fivefold 

 the brightness coming through the glass (as one might expect, know- 

 ing that the red glass is pervious, say, to but one fifth of the light of 

 the flame), it is necessary to increase it no less than fourteenfold. 

 Such an increase is the least I have found necessary when experiment- 

 ing at night over a stretch of more than four thousand feet and when 

 smoke gave a relative advantage to the red. Within the laboratory the 

 red has never been perceptible until the light was increased eighteen 

 times the brightness required for white. Such, however, are the most 

 favorable experiments, and are by no means average ones. On the 

 average it is necessary to increase the light as much as thirty times 

 before any conscious impression at all is made by the light through the 

 red glass. One of the subjects of this experiment — a man who would 

 pass the usual tests for color-blindness — has still remained insensible 

 to the red when the light is increased to seventy times what is needed 

 for the white ! Such facts as these show clearly that by merely looking 

 at a cluster of railway signals, or even by taking the usual tests of 

 their relative intensity or visibility when shining bright, we get no 

 adequate idea whatever of the difficulty which the eye has with very 

 feeble reds. And feeble reds are no great rarity in the actual conduct 

 of trains. The many influences which render signal lights obscure 

 thus act with a peculiarly fatal force upon the very color which is 

 our chief reliance for the protection of life. 



And the doubt thus raised regarding red is not allayed by the 

 reports of railway accidents. For in these reports the frequency with 

 which engineers fail to observe red signals at night is a most im- 

 pressive fact. It is often impossible to tell assuredly why men at such 

 times are unconscious of the danger sign; but even when allowance is 



