Descriptive geometry . Fig. 206. Fig. 207. In this new position, the plane will be perpendicular to the F-trace, VS, will be an edge view of the plane, andmust therefore pass directly through c. A plane may be revolved until perpendicular to H by using XIV, § 135] THE REVOLUTION OF PLANES 131 an axis perpendicular to V. This is done in Fig. 207, wherethe plane Q is revolved about the line A, perpendicular to V,until the P-trace of the plane, in its new position VR, isperpendicular to the ground line. Then HR is an edgeview of the plane, and passes through c\ In this figure, theaxis A,

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Descriptive geometry . Fig. 206. Fig. 207. In this new position, the plane will be perpendicular to the F-trace, VS, will be an edge view of the plane, andmust therefore pass directly through c. A plane may be revolved until perpendicular to H by using XIV, § 135] THE REVOLUTION OF PLANES 131 an axis perpendicular to V. This is done in Fig. 207, wherethe plane Q is revolved about the line A, perpendicular to V,until the P-trace of the plane, in its new position VR, isperpendicular to the ground line. Then HR is an edgeview of the plane, and passes through c\ In this figure, theaxis A, besides being perpendicular to V, is taken lyingin H} which simplifies the hnding of the point c, in which Aintersects Q. As in the revolution of a straight line (§§ 78, 79), a plane,when revolved about an axis perpendicular to H, maintainsalways its original angle with H. If the axis is perpendicularto V, the angle between the revolving plane and V does notchange. 135. The Distance between Two Parallel Planes. As a

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