Young, George, jr, Baxter, Hubert Eugene, joint author · New York, The Macmillan Co. · leaf 282
el of the surface. Theactual slope of such a plane, with respect to H, may be shownby passing a cutting plane, Z, perpendicular to the lines oflevel. This plane intersects X in the line a^f. Now let Z berotated into H, on ZZ* as an axis. The point a is in the axisof rotation, and does not move, but… … Fig. 246 A cut by any other vertical plane, as Y, can be found in thesame way. The line cd shows such a section, rotated into H.The angle <t> is the angle between the line c°d and H. Lines of level may be used also to describe planes intersectingin various ways, as shown by the roof plan in…
Geometry, Descriptive
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