Plane trigonometry, by S.L. Loney.

CHAPTER XIV.

HEIGHTS AND DISTANCES.
191. IN the present chapter we shall consider some
questions of the kind which occur in land-surveying.
Simple questions of this kind have already been considered
in Chapter III.
192. To find the height of an inaccessible tower by
means of observations made at distant points.
Suppose PQ to be the tower and that the ground
passing through the foot Q of the
tower is horizontal. At a point A
on this ground measure the angle
of elevation a of the top of the /I/
tower.
Measure off a distance AB(=a) A-a B Q
from A directly toward the foot of
the tower, and at B measure the angle of elevation /.
To find the unknown height x of the tower, we have
to connect it with the measured length a. This is best
done as follows:

L. T.

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