Descriptive geometry . Fhi. 290. 202 DESCRIPTIVE GEOMETRY PCX, § 165. Fia. 290 (repeated). The meridian which forms the outline of a projection of thesurface, in Fig. 290 the F~-projection, is called the principalmeridian. The plane which contains thismeridian is called the principal meridianplane. The principal meridian plane is al-ways parallel to one of the coordinateplanes ; in Fig. 290 it is parallel to V. 166. Parallels. Let a double curved sur-face be formed by the revolution of itsmeridian section about the axis. Eachpoint of the generating meridian describesa circle lying in a plane p
Descriptive geometry . Fhi. 290. 202 DESCRIPTIVE GEOMETRY PCX, § 165. Fia. 290 (repeated). The meridian which forms the outline of a projection of thesurface, in Fig. 290 the F~-projection, is called the principalmeridian. The plane which contains thismeridian is called the principal meridianplane. The principal meridian plane is al-ways parallel to one of the coordinateplanes ; in Fig. 290 it is parallel to V. 166. Parallels. Let a double curved sur-face be formed by the revolution of itsmeridian section about the axis. Eachpoint of the generating meridian describesa circle lying in a plane perpendicular tothe axis (§ 74). These circles are calledparallels of the surface. The projection of a double curved sur-face of revolution on a plane perpendicularto its axis will consist of one or more cir-cles, which are the projections of particular parallels of thesurface (§§ 75, 84). For example, see the .ff-projection of thevase, Fig. 290. 167. Projections of a Point in a Double Curved Surface of Revo-lution. Through every point of a double curved surface
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