Hyperbolic Paraboloid, surface string model, 1872.

Hyperbolic paraboloid, a skew quadrilateral with its opposite sides equal and strings equaly spaced.This is one of a large set of ruled surface models made by Fabre de Lagrange, following designs introduced in the early 19th Century. They illustrate surfaces which can be traced out in space by the movement of a straight line. This model consists of a series of threads strung acros a skew quadrilateral with its opposite sides equal in length.