Note 21 — Chapter V · OPERATIONS OF 1839.
Reading edition
The plug (fig. 12, c c′), and feathers (fig. 12, d d′), are flat pieces of malleable iron, slightly tapered, and forming together a kind of compound wedge, the two feathers being first inserted into the hole, and the plug being driven between them by a series of gentle blows, from malls of the weight of from 30 lb. to 35 lb.