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

is the inclined line required.

Fig. 42.

If the line is inclined in the opposite direction, as D C in [Fig. 42.], we have only to join

d c

instead of

a b

in Fig. 41., and

d c