Elements of descriptive geometry, with applications to isometric projection and othe forms of one-plane projection; a text-book for colleges and ingineering schools by O. E. Randall.

CHAPTER X

REPRESENTATION OF SINGLE CURVED SURFACES
231. Cylindrical Surfaces and the Cylinder. The cylindrical surface is a single curved surface which may be generated by a
moving straight line which during the movement touches a given
curved line and always remains parallel to its first position (see
Section 222).
The generating line is called the generatrix, the curved line is
called the directrix, and the various positions occupied by the
generatrix are called the rectilinear elements of the surface.
The intersection of a cylindrical surface by any plane which is
not parallel to the elements is called a section, or base, of the surface. When this plane is taken perpendicular to the elements, the
section is called a right section, and according to the nature of
this section cylindrical surfaces are classified as circular, elliptical,
parabolic, hyperbolic, etc.
The section of a cylindrical surface made by the plane H will
often serve as a convenient base.
A plane parallel to the elements of a cylindrical surface and
cutting the surface will cut the surface in elements, since all the
elements of such surfaces are parallel.
If the base of a cylindrical surface is a closed curve, like a circle
or an ellipse, the space inclosed by the cylindrical surface is called
a cylinder.
The straight line through the center of the base and parallel to
the elements of the surface is called the axis of the cylinder.
If one of two parallel straight lines is revolved about the other
as an axis, the surface so generated is cylindrical, and the cylinder
so generated is a cylinder of revolution whose right section is a
circle.
232. To represent the Cylinder. The cylinder is usually represented by projecting one of its bases, which may be assumed
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