ELECTRIC SIGNALS ON ENGLISH RAILROADS. 581 



more rapidly than that for blue or violet. In fact, as I said some time 

 ago, the violet nerves always lag behind. From this it happens that, 

 if we place side by side a quantity of blue and red light, arranging 

 matters meanwhile so that they appear to the eye to be of equal bright- 

 ness, then, upon adding considerably but equally to their actual lumi- 

 nosity, it will turn out that the red light will quite outstrip in apparent 

 brilliancy its rival. We have now two such squares of red and blue, 

 side by side on the screen, and it is difficult to say which is the 

 brighter ; but, when I greatly increase their illumination, it becomes 

 evident that the blue one has been beaten ; or, better still, when I re- 

 verse the experiment, starting with red and blue squares, of equal and 

 considerable brilliancy, then, upon turning down the light of the lan- 

 tern, and rendering them both dark, the blue square remains visible 

 after its red companion has vanished. As another example, I may 

 mention the blue color of the sky, which still continues plainly percep- 

 tible at night, when the illumination is so feeble that other colors have 

 disappeared. Dove has pointed out that, in picture-galleries, as the 

 light of day fades out, the blue colors in draperies and skies retain 

 their power longer than the reds and yellows. 



It is owing to this circumstance that, in actual landscapes, seen 

 under the comparatively feeble light of the moon, there is a prevailing 

 tendency to blueness. This also explains the circumstance that a 

 landscape, illuminated by bright white clouds, aj^pears more yellow in 

 general hue than when the clouds are not bright, though still retain- 

 ing their whiteness, the strong white light stimulating more power- 

 fully the sets of nerves concerned in the production of yellow. I think 

 we all know that, on dark, dull days, there seems to be a tendency to 

 blueness in the coloring, even though we may not have paid much 

 attention to the reverse phenomenon. All this is prettily illustrated 

 by a very simple experiment of Helmholtz's, who noticed that the im- 

 pression of a bright day was produced by merely holding a pale-yel- 

 low glass before his eyes, the tint of the glass being so faint as hardly 

 to disturb the natural colors of the objects ; the use of a very pale- 

 blue glass seemed, on the other hand, to darken up the landscape, as 

 though a cloud were passing over the scene. 



+«» 



ELECTEIO SIGNALING ON ENGLISH EAILKOADS. 



By C. E. PASCOE. 



I TAKE it for granted that most Americans who have traveled in 

 England know of, if they don't actually know, Clapham Junction. 

 It is a marvelous place is that Clapham Junction — a half-dozen or 

 more naked-looking graveled platforms, destitute of almost every con- 



