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 143
Tangent to the base of the convolute and parallel to U-u, draw
S-s,, the required horizontal trace. Through S and parallel to
U-u' draw S-s', the required vertical trace.
The element of tangency G-K may be determined by drawing
the element of the surface through the point of tangency G on
the base.
Since another plane may be drawn through M-N and tangent to
the cone, another plane may be constructed which will answer the
conditions of the problem.
Since the convolute is unlimited in extent, having its base in
the form of a spiral, an unlimited number of planes answering the
conditions of the problem may be constructed.
Check. Through any point, as K, on the element of tangency
draw a straight line K-L parallel to S-s,, and note whether it
pierces V in the vertical trace already located.