. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . next chapter, the whole grade may be operated as if equalto the average grade, AF, which is better than BCj althoughmuch worse than AN. The process of compensation con-sists in reducing the grade on every curve by such an amountthat the actual resistance on each curve, due to both curvatureand grade, shall precisely equal the resistance on the practical effect of such reduction is that the virtual gradeis kept constant, while the nominal grade fluctuates. One effect
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . next chapter, the whole grade may be operated as if equalto the average grade, AF, which is better than BCj althoughmuch worse than AN. The process of compensation con-sists in reducing the grade on every curve by such an amountthat the actual resistance on each curve, due to both curvatureand grade, shall precisely equal the resistance on the practical effect of such reduction is that the virtual gradeis kept constant, while the nominal grade fluctuates. One effect of this is that (see Fig. 212) instead of accomplish-ing the vertical rise from A to G (, HG) in the horizontaldistance AH, it requires the horizontal distance AK, Such anaddition to the horizontal distance can usually be obtained byproper development, and it should always be done on a ruling 562 RAILROAD CONSTRUCTION. § 511 grade. Of course it is possible that it will cost more to accom-plish this than it is worth, but the engineer should be sure ofthis before allowing this virtual increase of the Fig. 212. European engineers early realized the significance of unre-duced curvature and the folly of laying out a uniform rulinggrade regardless of the curvature encountered. Curve compen-sation is now quite generally allowed for in this country, butthousands of miles have been laid out without any compensa-tion. A very common limitation of curvature and grade hasbeen the alliterative figures 6° curvature and 60 feet per mileof grade, either singly or in combination. Assuming that theresistance on a 6° curve is equivalent to a grade ( feetper mile), then a 6° curve occurring on a 60-foot grade woulddevelop more resistance than a 75-foot grade on a *mountain cut-off of the Lehigh Valley Railroad nearWilkesbarre is a fine example of a heavy grade compensatedfor curvature, and yet so laid out that the virtual grade is uni-form from bottom to top,
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