ABSTRACT
This chapter describes cylinder and cone rolling, where the cylinder describes straight lines in the plane while the cone describes circles, because the circles in the cone are unequal, and of things moving about one and the same centre the larger always travels the quicker. Now, when all the circles in the cone travel together but at unequal speeds, the effect is that the outermost circles move over the most ground, that is describe the longest line, in the same time; hence they all move in a circle. The chapter explores the difference between the trace on a plane made by an oblique section when the cylinder rolls on the plane and that made by a right section. It also explains the idea of a centre of gravity, which is that of the perpendicular that divides the impinging object into two equal parts in weight, and the extremity of which is supposed to impinge on the plane.
