The Elements of Perspective / arranged for the use of schools and intended to be read in connection with the first three books of Euclid

by John Ruskin

Fig. 57.

Let A B D E, [Fig. 57.], be the square base of any pyramid.

Draw its diagonals, A E, B D, cutting each other in its center, C.

Bisect any side, A B, in F.

From F erect vertical F G.

Produce F B to H, and make F H equal to A C.

Now if the vertical altitude of the pyramid (C D in [Fig. 25.]) be given, make F G equal to this vertical altitude.

[p80]
]Join G B and G H.

Then G B and G H are the true magnitudes of G B and G H in [Fig. 56.]

If G B is given, and not the vertical altitude, with center B, and distance G B, describe circle cutting F G in G, and F G is the vertical altitude.