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

a line parallel to the given line, bearing the proportion to it that T S bears to T D.

[p15]
][COROLLARY II.]

If the line A B is in a horizontal plane, the vertical distance of one of its extremities must be the same as that of the other.

Therefore, in that case, A C equals B C′ ([Fig. 6.]).

And the construction is as in [Fig. 8.]

Fig. 8.

In [Fig. 8.] produce

a b

to the sight-line, cutting the sight-line in V; the point V, thus determined, is called the Vanishing-Point of the line A B.