It has been observed by the adversaries of the art, that exactly the same line will serve either for a road or a river, as it may be filled with gravel or with water. This ridicule may perhaps be deserved by those engineers who are in the habit of making navigable canals only, but the nice observer will see this material difference,- The banks of a natural river are never equidistant, the water in some places will spread to more than twice the breadth it does in others; this pleasing irregularity depends on the shape of the ground through which it flows: a river seldom proceeds far along the middle of a valley, but generally keeps on one side, or boldly stretches across to the other, as the high ground resists, or the low ground invites its course: these circumstances in natural rivers should be carefully imitated in those of art, and not only the effects, but even the causes, if possible, should be counterfeited, especially in the form of the shores: thus, the convex side of the river at A [in fig. 72], should have its shores convex, or steep; and the concave side of the river at B, should have its shores concave, or flat; because, by this means, the course of the river is accounted for.
