Descriptive geometry . Km. 323. 274 DESCRIPTIVE GEOMETRY [XXV, § 194 Thus, in Fig. 324, which shows the F-projection only, theplane X, parallel to the left-hand contour element of the conewhose vertex is a, cuts a parabola from this cone. A cone. Fig. 324. whose vertex is b can evidently be placed so as to contain thesame parabola, which thus becomes the line of intersection ofthe two cones. In this case the cones intersect again in aclosed curve, an ellipse or circle E. If two cones arc identical in form, and placed so that theircorresponding elements are parallel (Eig. 325), the intersec-

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