Staircase vault: model for exhibiting some properties of this ruled surface, by showing how it is obtained from the deformation of a cylinder (douelle de la vis St. Gilles carree)

This is one of a large set of ruled surface models made by Fabre de Lagrange, in Paris, France, 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 particular model shows a staircase vault which is obtained by the deformation of a cylinder.