Caption: Mathematical Models by Arnold Emch - Series 1 (1920)
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7. Q2 with a system of hyperbolic sections. (C. N . Stokes) Cartesian equation: 16 (x2 + y2) (x2 + Ay2 - 4) + (x2 + Ay2) [7(x2 + Ay2) 16z2 - 28] = 0. Projective Generation of Surfaces 8. Cubic Surface (Cyclide) Generated by a pencil of planes, as 3 a x ~ xz = 0. and a projective pencil of spheres x2 + y2—(z~3a)2 - 2 x % = 0. This is a plaster cast model of a cubic cyclide and shows the circles as intersections of corresponding planes and spheres, and also the 7 real lines which are on the surface in this case. 9. Quartic ruled surface. Generated by the projectively related planes of two cones of the second class. The vertices of the two cones are at (0,0,0), and ( —2a, 0, 0) of a Cartesian system, and the tangent planes make angles of 45° with the xy — plane. The equation of the qaurtic is (a + x)2£2 - (a2 — z2) y2 = 0,
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