. The railroad and engineering journal . ight-box of this vessel on beam of a vessel, C the point of intersection of the rayswith the midship line, after leaving the properly placedscreening-board, and C the point of intersection due toadditional error. The secant BC cutting the two parallels,B O and A C , the angle at C represents the total devia-tion from a direct line ahead ; or the constant angle (8°)at C, plus the additional angular error of the light screensfrom a fore-and-aft the triangle A B C, tangent C = A B -^ A C A C - A B X cotangent C. By this it will be seen that an addi
. The railroad and engineering journal . ight-box of this vessel on beam of a vessel, C the point of intersection of the rayswith the midship line, after leaving the properly placedscreening-board, and C the point of intersection due toadditional error. The secant BC cutting the two parallels,B O and A C , the angle at C represents the total devia-tion from a direct line ahead ; or the constant angle (8°)at C, plus the additional angular error of the light screensfrom a fore-and-aft the triangle A B C, tangent C = A B -^ A C A C - A B X cotangent C. By this it will be seen that an additional error of onepoint (Hi) will cause the rays from the outer part of thelens to intersect the midship line of a vessel of 15 , at a distance of only ft., and with a vessel of30 ft. beam, at a distance of only 42 6 ft., ahead of thethe screening boards. There is, then, beyond this point, a constantly wideningangle, in which an observer is liable to be deceived, sup-posing that by seeing two lights at once he can estimate. *KLp. ?^ a scale of i in. to the foot. This shows the angle overwhich the Yorktowti s lights must necessarily show, al-though they actually show much further—both across thebows and abaft the beam. In the other diagrams the lines have been drawn at arbi-trary angles, but will suffice to illustrate the effect of addi-tional error in the placing of the side-lights. It is evidentthat, from the causes mentioned by Commander Chadwick,there will be a constant error, even when the light-screensare placed in an exact fore-and-aft line. This, for theordinary lantern, will be an error of about 8. In fig. 2, in the small triangle X VZ, representing the within the customary J of a point the course upon whichthe vessel is approaching. The foregoing are the principal sources from which col-lisions arise ; and the only way to prevent their occurrenceis to endeavor, by close inspections and heavy penalties,to obtain strict observance of the existing laws
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectrailroa, bookyear1887
