V. The breadth of a river, or other short distance, may be taken
thus:—take two pickets of different lengths, drive the shortest into
the ground close to the edge of the bank; measure some paces back
from it, and drive in the other till you find, by looking over the
tops of both, that your sight cuts the opposite side.—Then pull up
the first picket, measure the same distance from the second, in any
direction the most horizontal, and drive it as deep in the ground as
before.—Consequently, if you look over them again, and observe where
the line of sight falls, you will have the distance required.