RAILWAY ACCIDENTS 251 



merely require us to suppress the worse half of the present composite set 

 of block signals — the half, which relies on color — and to render uni- 

 versal its better portion which already signals by direction. The pres- 

 ent system would thus be simplified and fulfilled, rather that annulled, 

 and there would be no need of training engine drivers to an unfamiliar 

 code. And while the perception of the trend of a line of light requires 

 that the refractive power of the eye shall be normal or shall be cor- 

 rected by the use of glasses, the engineer's work even now demands 

 that his spatial vision shall be keen, and thus no innovation would be 

 made. 



But even were there many objections to the use of spatial signals, 

 they must be grave indeed to outbalance the fact that a line of light 

 not only frees us from the treachery of the color sense, but gives a 

 symbol that is distinct from the usual lights of the window or the street, 

 and at a stroke renders well-night impossible those accidents that come 

 from mistaking foreign lights for block signals. Moreover, we should 

 then have a system wherein danger would be indicated at all times as 

 clearly and as unmistakably as safety, whereas in the present code the 

 red danger signal can too readily remain unseen. An important ad- 

 vantage besides would be that signals of the kind here proposed could 

 hardly, by influence of smoke, or fog, or storm, be made to seem the 

 very contrary of what they really were. A green light may look 

 whitish, or a yellow light red, by mere conditions of the air. But a 

 vertical line can not well be made to appear horizontal, or a horizontal 

 diagonal, by smoke or fog. Its message might be cut off entirely, but 

 could not readily be distorted into its fatal opposite. In this, as in so 

 many other ways, a change of usage commends itself to the critical 

 sense. 



In urging that we no longer rely upon the color faculty for the 

 safety of our trains, I have spoken almost exclusively of those difficulties 

 which color offers to eyes that are entirely normal and sound. And 

 upon such facts the main objection to the present system may well be 

 based; for they are strong enough in themselves to condemn our usage 

 and to demand that it be changed. But the reasons so far given are 

 immeasurably strengthened by the existence of color-blindness and 

 other defects of the sense of color. There are some men, it is true, who 

 believe that the danger from this source is entirely averted by the cur- 

 rent examination of engineers. No one would wish needlessly to lessen 

 faith in such examinations. And yet it should be more widely known 

 that defects of color vision are not always easy for physicians to detect; 

 far less are they for laymen. And since many dangerous cases are 

 known to slip through the meshes of medical examiners elsewhere, it is 

 reasonably certain that the same is true with us. Dr. Stadfeldt, of 

 Copenhagen, in a recent examination of 295 pilots (who, like engine- 



