The most durable of fences are those formed of small oaks, split lengthwise by the wedge into thin boards.
In the case of a wedge with parallel ends the ratio x2/h2 is replaced by x/h.
This formula holds for the general case in which the base is a trapezium; the wedge being thus formed by cutting a triangular prism by any two planes.
(ii) Let R be one edge of a wedge with parallel ends, and S the face containing the other two edges.
On the other hand, if he struck straight at Charleroi - the allied junction point - he would drive the "Armee du Nord" like an armoured wedge between the allies, if only he caught them unsuspicious and unready.