To measure the height of an accessible object.
[Plate, Surveying, and Reconnoitring, [Fig. 2].]
At an appropriate distance from the object, take its angular height and measure the distance to its base.
Construction—
Draw a line representing this distance, at one end of which draw another line at the angle found, and at the other erect a perpendicular; the intersection of these lines will determine the altitude of the object.
To measure the vertical height of a hill, or mountain.
[[Fig. 3], Plate, Surveying, and Reconnoitring.]
From a station a short distance from the hill, take, and note down its angular height; then select a rear position for a base line, using the tube of the protractor to insure a straight direction; proceed to the requisite distance on the base, and again note the altitude of the hill.
Construction—
The intersection of lines drawn from each end of the base line, at the angles found, will determine the altitude; the perpendicular height of which, added to that of the protractor above the ground, will give the altitude required.