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If it be assumed that the base of the triangle represents a line 1,000 feet long and that the first sloping line represents a road having a rise that brings it 50 feet above the starting point, this is figured as 50 feet in a thousand, or 5 per cent. In other words, one foot of rise for every 20 feet, but the latter instance does not mean distance actually traveled by a car in ascending such a slope, but distance measured horizontally with reference to that slope. The grade is measured by the tangent of the angle of inclination and not by its sine, so that a grade which represents 100 per cent. cortesponds to an angle of inclination of but 45 degrees, and not go degrees, or perpendicular, as is commonly supposed. At the upper end of the next sloping line the elevation would amount to 661 feet, which is equivalent to a rise of one foot for every 6f feet traveled horizontally. So one in three cortesponds to a 33 1-3 per cent. grade, one in two to a 50 per cent. grade, and so on until a 100 per cent. grade is reached, which, as noted, is the equivalent of a 45 degree angle.
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