Young, George, jr, Baxter, Hubert Eugene, joint author · New York, The Macmillan Co. · leaf 197
f the tangentis considered as extending in both directions from the curve,the surface which is genSrated is one of two nappes. If thetangents extend in but one direction, the surface is of a singlenappe. It is the surface that results from unwrapping a stringwound about a cylinder and following a… … One noppe. FiQ. 172 Two nappes. pitch of the helical directrix. The tangent at a is continuedto the limiting planes, giving the line be. From the mannerin which a helix is generated, it is known to be a curve of constantinclination. Hence the inclination of the tangent, i.e. the angleabd, is the…
Geometry, Descriptive
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