41. A parabola spun about this axis in three dimensions traces out a shape known as a paraboloid of revolution. 42. According to a contemporary publication, " the construction of the twin hyperbolic paraboloid main roofs is unique ". 43. The mirrors have spherical shape with a curvature corresponding to the position of the plate in the paraboloid reflector. 44. The density of the liquid, for example, has no effect on the focal length of the paraboloid . 45. The market is especially noteworthy for its roof of hyperbolic paraboloids , which allow for wide areas without supports. 46. The latest mercury mirrors start out as shells cast in approximately paraboloid shapes from strong, rigid epoxies and Kevlar. 47. Paraboloids are also observed in the surface of a liquid confined to a container and rotated around the central axis.48. As it moves, it will pass through the other two paraboloids , like a ghost passing through a wall. 49. In a constant gravity field, the free surface of the liquid, if present, is a concave paraboloid . 50. Some special cases of hyperboloids ( of either one or two sheets ) and elliptic paraboloids are surfaces of revolution.
