a — c — b. The plane surface a b c equals the whole skin of the shield-body a b, and the straight lines within which the parallels of the straight surfaces are enclosed are the curved parallels that clothe the said body.

a b c — d f e. The irregular periphery a b c, being stretched out by motion, equals the straight line d e. Now, since the shield-body is divided into 5 parallels of equal width, both in themselves and among one another, I shall likewise divide that line d e, with the surface d e f, into five similar parallels of indefinite length; and then by circular motion I shall go turning each of its circles upon its indefinite straight line, which will be finished, at a determinate length, by the end of the circle that turns over it. When you straighten the curve a b c by its motion, mark the divisions on the curved line and on the indefinite straight line d e before you separate the curve from the straight; and so you will do in all the parallels one by one. It does not matter that they are of equal width among themselves, provided each of the curves is straightened over its own straight line, etc., and is terminated in its whole circular motion.