Diagram, engine for grinding hyperbolic glasses by Christopher Wren Drawing of Christopher Wren's 'engine' for grinding hyperbolic glasses. This follows on from Wren's publication in Philosophical Transactions of the Royal Society, vol. 4, no. 48 (1669), which shows that a section through the axis of a cylinder was a hyperbolic surface, which could then be applied to create a machine to grind hyperbolic lenses. This drawing, however, is not much more than a geometric diagram with shading, and does not take into account the wheels, cogs and other arrangements necessary to translate this into an actual machine. Includes 2 cylinder with a hyperbolic surface and a disk. Parts are lettered. Subject: Engineering / Geometry [1669]