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

Now, therefore, if instead of

a m

in [Fig. 78.], we take the real length of A B, that real length will be to

a m

as A C to A B in [Fig. 79.]

And then, if the line drawn to the measuring-line P Q is still to cut

a

P in

b

, it is evident that the line P Q must be shortened in the same ratio that