Page:Popular Science Monthly Volume 72.djvu/253

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recognition of colors at night by any man, above all by a man who has many and most insistent duties besides.

That the color-sense is wholly unfit for the office it holds in rail-roading is hardly open to any doubt whatever. One must speak with less assurance, however, as to what should take its place. But even here the general principle that might guide the change is reasonably clear. Our eyesight detects two different features in objects—their color and their spatial character, such as shape, position and movement; and the sense of color is far less primitive and vital and masculine than is the rude sense of space. Nature seems to have held the sensitivity to color a cheap and slighted accomplishment, to be crowded out or postponed to the mere finishing school, like young ladies' French and dancing. But the rugged feeling for place and direction is early given and pressed deep until it becomes a central fact in self-preservation and advance.

Now if the eyesight of the engineer is to be depended upon at all, it is this more fundamental and stable portion of it that should be given responsible work. If the practical difficulties could easily be met, the power to distinguish between rest and rapid movement of some conspicuous object would be the best to call upon in signaling. For we, like the bird and beast in the woods, are alive to slight quick movements in the field of view, far more than to color or even to shape and size. When the arms are waved or a lantern swung by hand to attract attention, appeal is instinctively made to this deep and primal interest in moving things. But next to this, the simplest and least erring of our visual perceptions is of large differences like that between a vertical and a horizontal line or one aslant. Now these rough and simple elements are precisely those used for the day signals of most block systems, where there is an extended arm placed high beside the track, and its direction of pointing—up or down or at some angle intermediate to these—tells the engineer whether the track ahead is open to him or closed or to be entered only with caution. Such signals make no prime appeal whatever to the sense of hue, but only to the sober feeling for visual place. And there seems to be nothing to prevent that this same principle of signaling should be carried over into the night and be even more successful there. For the extended vane used for the day signal often is before some unpropitious background of buildings or of trees against which it stands out in no strong relief. But at night it would be possible to use some self-luminous line of light that would appear sharp and unmistakable against the dark.

The detailed mode of applying such a general principle belongs to mechanical art rather than to psychology. But lest the principle itself should be misjudged for want of some more definite form in the mind, it might be well to imagine a row of incandescent lights inserted in the signal-arm now used by day, but lengthened and otherwise modi-