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.

SURFACES OF SINGLE CURVATURE

127

Through F, the point in which O-D pierces the plane of the
base of the cylinder, draw a rectilinear tangent to the curve of
the base. This tangent will be vertically projected in f'-g', tangent to the vertical projection of the base, and horizontally projected in f,-g,-a,. F-G is by analysis a line of the required plane
and pierces H at 1, and pierces V at ml. S-s, drawn through d, and 1,

FIG. 123

is the required horizontal trace, and S-s' drawn through e' and m'
is the required vertical trace.
The element of tangency is that element determined by the
point G.
Since another straight line may be drawn through F tangent to
the curve of the base, another plane answering the conditions of the
problem may be constructed.
Check. Note whether the element of tangency, which is a line
of the required plane, pierces H and V in the traces now located.
CASE 3. When the cylinder is one of revolution with its axis parallel to G-L.