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 b c d

is the square required.

[COROLLARY I.]

It is obvious that any rectangle in a horizontal plane may be drawn by this problem, merely making

a b′

, on the measuring-line, [Fig. 20.], equal to the sight-magnitude of one of its sides, and

a c′

the sight-magnitude of the other.

[p33]
][COROLLARY II.]

Let