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

.

If one circle is above and another beneath the eye, neither the bottom nor top of the dish is seen,

d

. Unless the object be very large, the circles in this case will have little apparent curvature.

II. The preceding problem is simple, [p89] ]because the lines of the profile of the object (

a b

and

c d

, [Fig. 66.]) are straight. But if these lines of profile are curved, the problem becomes much more complex: once mastered, however, it leaves no farther difficulty in perspective.

Let it be required to draw a flattish circular cup or vase, with a given curve of profile.