Railway and Locomotive Engineering . is meansthat an object presenting a certain magni-tude at say a distance of 50 yards willappear to be only half as large at 100yards. At 150 jards it will appear one-third the size it was at the first is the reason why the rails in atrack appear to run together in the dis-tance. As a matter of fact, they are 4 ins. apart all over the line, yet on amile or two of tangent they seem to havemet or to have but a small space betweenthem. This is very marked, of course;but the fact that men or horses appearsmaller to us at a distance from the c
Railway and Locomotive Engineering . is meansthat an object presenting a certain magni-tude at say a distance of 50 yards willappear to be only half as large at 100yards. At 150 jards it will appear one-third the size it was at the first is the reason why the rails in atrack appear to run together in the dis-tance. As a matter of fact, they are 4 ins. apart all over the line, yet on amile or two of tangent they seem to havemet or to have but a small space betweenthem. This is very marked, of course;but the fact that men or horses appearsmaller to us at a distance from the cabwindows of a locomotive is not so pro-nounced because they are surroundedwith familiar objects which have grownapparently smaller with them while main-taining a strict proportion between themall. In our December, 1910, issue, page 498,we alluded to the diffusion of light asfollowing what is called the law of theinverse square. That is, as the distancefrom the source of light increased, theintensity of the light became less in pro-. ERIE ENGINE N.\MED .OiFTER \CK BRlNER. the observer nears the object it appar-ently increases in size. This growing and diminishing of theobject as the distance from the observerto it is increased or lessened follows alaw of nature. This can be proved in avery simple way. For example, the diskof the full moon is a circle with a diam-eter of about 2,160 miles and hangs inthe heavens at an average distance of240,000 miles from the earth, yet its portion to the square of the of a certain intensity at SO yardsbecame only one-quarter as strong at 100yards or at twice the distance. Weshowed that one object of the parabolicreflector of a locomotive headlight was toconcentrate all the reflected rays of lightand pour them forth in as nearly as pos-sible a parallel cylinder of solid light andso prevent diffusion and defeat the lawof the inverse square. February, 1911. RAILWAY AND LOCOMOTIVE ENGINEERING. 63 It is rather a curious thing that
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