hes as narrow as possible.

It is somewhat more convenient for unskillful laborers to work in a wide
ditch than in a narrow one, and although the laborers frequently protest
that they cannot work so rapidly in narrow ditches, yet it is found
that, in contract work, by the rod, they usually open the ditches very
narrow.

Indeed, it will be found that, generally, the cost of excavation bears a
pretty constant proportion to the number of cubic feet of earth thrown
out.

It will surprise those unaccustomed to these estimates, to observe how
rapidly the quantity excavated, increases with the increased width of
the ditch.

To enable the reader accurately to compute the measurement of drains of
any dimensions likely to be adopted, a table and explanations, found in
the Report of the Board of Health, already quoted, are given below. The
dimensions, or contents of any drain, are found by multiplying together
the length, depth, and _mean_ width of the drain.

"Thus, if a drain is 300 yards long, and the cutting 3 feet deep,
20 inches wide at the top, and 4 inches wide at the bottom, the
mean width would be 12 inches (or the half of the sum of 20 and 4),
and if we multiply 300, the length, by 1, the depth in yards, and
by 1/3, the mean width in yards, and the product would be 100 cubic
yards. The following table will serve to facilitate such
calculations.

_Table showing the number of Cubic Yards of Earth in each Rod (5-1/2
Yards in length), in Drains or Ditches of various Dimensions._

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DEPTH. | MEAN WIDTH.
-------+------+------+------+------+------+------
Inches.|7 In. |8 In. |9 In. |10 In.|11 In.|12 In.
-------+------+------+------+------+------+------
30 |0.89 |1.02 |1.146 |1.27 |1.40 |1.53
33 |0.98 |1.12 |1.26 |1.40 |1.54 |1.68
36 |1.07 |1.22 |1.375 |1.53 |1.68 |1.83
39 |1.16 |1.324 |1.49 |1.655 |1.82 |1.986
42 |1.25 |1.426 |1.604 |1.78 |1.96 |2.14
45 |1.34 |1.53 |1.72 |1.91 |2.10 |2.29
48 |1.426 |1.63 |1.833 |2.04 |2.24 |2.444
51 |1.515 |1.73 |1.95 |2.164 |2.38 |2.60
54 |1.604 |1.83 |2.06 |2.29 |2.52 |2.75
57 |1.69 |1.935 |2.18 |2.42 |2.66 |2.90
60 |1.78 |2.036 |2.29 |2.546 |2.80 |3.056
=================================================