Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

50 ×	305
50 ×	1,257
50 ×	2,669
50 ×	1,755	Sum 299,300 ÷ 6 = 49,000,
and 56,200 – 49,000 = 7,200

cubic feet in favor of the method of end areas.

109. The prismoidal formula is algebraically

a + a′ + 4a″
6L = c,

when L = length,

c = cubic contents,

a = area of one end,

a′ = area of other end,

a″ = middle area;

or, verbally, to the sum of the end areas add four times the middle area, and multiply the result by one sixth of the length; the middle area being the area made upon the mean height of the two ends. Thus if the length is one hundred feet, and one end ten feet high, the other twenty feet high, and slopes one and a half to one, the cubic amount is, (the base being twenty-two feet,)