to ascertain the height.
Place a staff (equal in length to the height of the observer’s eye) vertically at such a distance from the foot of the required altitude, that the observer, having laid himself upon his back, with his feet against the bottom of the stick, may see the top of the staff, and object in the same line. Then, by similar triangles, the height may be readily ascertained.
6.—BY MEANS OF THE TANGENT SCALE OF A GUN,
to ascertain the height of an object, the distance being known.
Lay the gun for the top of the object the height of which is required, then raise the tangent scale until the top of it, and the notch on the muzzle are in line with the bottom of the object: then, by similar triangles,
As the length of the gun
is to the length of the raised part of the tangent scale,
so is the distance from the gun to the object,
to the height required.
Plate 2.
Heights.
Fig. 1. Fig. 2.
Distances.
Fig. 3. Fig. 4. Fig. 5.