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Show BLACK LETTERS AND WHITE Former Can Be Read at a Greater Distance Than the Latter, l Judgment of Experts. There Is a tendency on the part of railroads to adopt signs with white letters let-ters on a black background, not realizing realiz-ing thnt tho black letter on a white background is easier to read and can be seen at n grenter distance. Thle follows lit an Interesting way from the structure of the retina of the eye. The Impression of n letter nt tho limit of vision Is received on the ends of a small bundle of nerves which convey con-vey to tho brain a sort of mosaic Im pression. A nerve can only transmit to tho brain Information ns to whether or not n ray of light Is falling upon It, and when a nerve Is partly In tho light nnd partly In dnrkness tho sensation Is the same as though all of It was In the light. It follows, therefore, thnt nil nerves on tho dividing edge between any black and white area transmit the sensation sen-sation of light so that all whlto lines nnd whlto areas appear wider nnd all black lines nnd blnck areas oppenr narrower thnn they really nre. Illack letters grow thinner ut the limit of vision and are still recognizable, recogniz-able, while at tho same distance whlto letters grow thicker and cannot bo distinguished. dis-tinguished. Thero are circumstances when It Is necebsnry to use whlto let-' tors, but In such cases legibility will bo Improved If they are made with a I thin stroko and strongly lighted. Black i letters aro moro distinct if made with , a henvy stroke. Scientific American, - ! |