le.]

There are many ways of measuring distance across rivers, etc., without
crossing. The simplest, perhaps, is by the equilateral triangle. Cut
three poles of exactly equal length; peg them together into a
triangle. Lay {65} this on the bank of the river so one side points to
some point on the opposite bank. Drive in three pegs to mark the exact
points of this triangle (A,B,C). Then move it along the bank until you
find a place (F,E,G) where its base is on line with the two pegs,
where the base used to be, and one side in line with the point across
the river (D). The width of the river is seven eighths of the base of
this great triangle.

[Illustration: Measuring the width of a river by sighting with
a triangle. (tr)]

Another method is by the isosceles triangle. Make a right-angled
triangle as above, with sides six, eight, and ten feet (A,B,C); then,
after firmly fixing the right angle, cut down the eight-foot side to
six feet and saw off the ten-foot side to fit. Place this with the
side D B on the river bank in line with the sight object (X) across.
Put three pegs to mark the three {66} corner places. Then take the
triangle along the bank in the direction of C until C' D' are in line
with the sight object, while B' C' is in line with the pegs B C. Then
the length of the long base B C' will equal the distance from B to X.

[Illustration: Measuring height of tree.]

[Illustration: Measuring the distance between two distant objects.]

To measure the space between two distant objects, D and E. Line A B on
one, then move this right-angled triangle until F G is lined on the
other, with B G in line with G H. B G equals the space between D and E
then.

If the distance is considerable, it may be measured sometimes by
sound. Thus, when a gun is fired, a man is chopping, or a dog barking,
count the seconds between the sight and the hearing of the sound, and
multiply by eleven hundred feet, which is the distance sound travels
in a second.

[Illustration: To climb a tree that is too thick--Place small tree
against it.]

{67}

Occasionally, the distance of an upright bank, cliff, or building can
be measured by the echo. Half the seconds between shout and echo,
multiplied by eleven hundred gives the distance in feet.

The usual way to estimate long distances is by the time they take to
cover. Thus, a good canoe on dead water goes four to five miles an
hour. A man afoot walks three and a half miles an hour