Transformations of a conoid, string surface model, 1872.
© Science Museum / Science & Society Picture Library
Model exhibiting the transformation, first of a conoid into a cylinder, second of the tangent paraboloid of the conoid, into the tangent plane of the cylinder. 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.