The operation consists in taking from these tables " of level sections '" and " of side triangles," (by simple inspection and addition) the contents, . in cut)ic yards, of four prisms, each 100 feet long, and each of uniform cross section throughout ; the several cross sections being, respectively, that at one station, that at tile other station, that of the imaginary prism to the right of the center plane, and tl/~t of the corresponding prism to tile left of said plane. These lbur contents are then added together, and their sum divided by 3, the quotient giving tile contents of the 100 feet station, in cubic yards.
The " distances out '~ are not required to be given ; nor are any drawings of the end or middle crosa sections, or calculations of ti~eir areas, required to be made. The author assures us, speaking no doubt from experience, that '~ with a little t)raetiee this method will be found rapid." That this should be the ease will be readily understood when it is remembered, that, as already stated, tile entire process consists ill inspection of tables, addition, and division by 3. The simplicity of the operation tends, also, of course, to iYeedom from liability to error.
In its application, tile method appears to be limited to "three level sections." For five level sections, and for side hill work, etc., it would have to be supplemented by some of the methods already in use.
J. C. T., JIยข.