Descriptive geometry . e plan as the part infront of IIY and outside of circle D. A point like 6, for ex-ample, although in front of the principal meridian plane T,is nevertheless invisible in ^-projection, being hidden In aportion of the, surface still further in front. Beginning atthe left, the visible portion of the F-projection begins at point13, lying in the principal meridian plane P, extends through9, 11, 10, 8, 1, and ends at point 2 in the highest parallel, J). 252 DESCRIPTIVE GEOMETRY [XXIII, § 182 C. A Line Tangent to the Intersection. A tangentline is drawn at the point 10. This li
Descriptive geometry . e plan as the part infront of IIY and outside of circle D. A point like 6, for ex-ample, although in front of the principal meridian plane T,is nevertheless invisible in ^-projection, being hidden In aportion of the, surface still further in front. Beginning atthe left, the visible portion of the F-projection begins at point13, lying in the principal meridian plane P, extends through9, 11, 10, 8, 1, and ends at point 2 in the highest parallel, J). 252 DESCRIPTIVE GEOMETRY [XXIII, § 182 C. A Line Tangent to the Intersection. A tangentline is drawn at the point 10. This line is the intersection ofthe given plane Q with the plane S, tangent to the surface atpoint 10 (§ 178). Find the tangent plane S by any conven-ient method (Prob. 38, § 170). Here only the H-tra,ce, HS, isfound. The intersection of HS and IIQ locates one point, .s,of the tangent line T. A second point is the given point 10of the intersection, which is here used instead of finding theF-trace, VS, of the tangent Fig. 313. 183. Points in Meridian Planes. Attention has already beencalled, in the preceding constructions, to certain properties of XXIII, § 184] PLANE AND TORUS 253 the points which lie in the principal meridian plane and themeridian plane of symmetry. These points are of sufficientimportance to warrant a further discussion. In an actual con-struction, instead of finding these points last, as was done inexplaining the preceding problem, it is better to find them atthe outset. This is shown in Fig. 313, in which are found
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