Def. 22. The axis of the cylinder is the straight line which remains fixed and about which the parallelogram is turned.
Def. 23. And the bases are the circles described by the two sides opposite to one another which are carried round.
| Rectangle ABEC is rotated around the side AC to produce a cylinder. Its axis is AC and it has two circles for bases.
The concept of cylinder has been generalized since Euclid's time as have so many ancient mathematical concepts. Euclid's cylinders are right, circular cylinders since their axes are at right angles to their bases and their bases are circles. |
Book XI Introduction - Definitions 18 through 20 - Definition 24.