. Railroad construction. Theory and practice . ° curve it is 2865. {xi—Xr) is generally small. It may frequently beseen by inspection that the product V(xi—Xr) is roughly twiceor three times SR, or perhaps less than half of 37^, so that thecorrective term for that station may be written 2, 3; or 0 cubicyards, the fraction being disregarded. For much larger absoluteamounts the correction must be computed with a correspondinglycloser percentage of accuracy. The algebraic sign of the curvature correction is best deter-mined by noting that the center of gravity of the cross-section ison the right
. Railroad construction. Theory and practice . ° curve it is 2865. {xi—Xr) is generally small. It may frequently beseen by inspection that the product V(xi—Xr) is roughly twiceor three times SR, or perhaps less than half of 37^, so that thecorrective term for that station may be written 2, 3; or 0 cubicyards, the fraction being disregarded. For much larger absoluteamounts the correction must be computed with a correspondinglycloser percentage of accuracy. The algebraic sign of the curvature correction is best deter-mined by noting that the center of gravity of the cross-section ison the right or left side of the center according as Xr is greateror less than xi, and that the correction is positive if the center ofgravity is on the outside of the curve, and negative if on theinside. It is frequently found that xi is uniformly greater (or uni-formly less) than Xr throughout the length of the curve. Thenthe curvature correction for each station is uniformly positive ornegative. But in irregular ground the center of gravity is apt. Fia. 57. to be irregularly on the outside or on the inside of the curve,and the curvature correction will be correspondingly positive ornegative. If the curve is to the right, the correction will bepositive or negative according a,s (xi—Xr) is positive or negative:if the curve is to the left, the correction will be positive or nega- 108 RAILROAD CONSTRUCTION. § 92. tive according as (xr—xi) is positive or negative. Thereforewhen computing curves to the right use the form (xi—Xr) inEqs. 66 and 68; when computing curves to the left use the form(xr—xi) in these equations; the algebraic sign of the correctionwill then be strictly in accordance with the results thus Center of gravity of side-hill sections. In computing thecorrection for side-hill w^ork the cross-section would be treatedas triangular unless the error involved would evidently be toogreat to bedisregarded. The center of gravity of the trianglelies on the lin
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