May 1993/February 1997
Peaucellier's Linkage (1864), adapted from Mathematics Meets Technology, by Brian Bolt; © 1991 Cambridge University Press.
Drag the red point around the circle. Fixed rods create the blue rhombus. Peaucellier's linkage is of special interest in that its follower (the black point) travels exactly along a line. (Prior linkages, such as a sewing machine's driver, typically only approximate lines.) In practice, Peaucellier's linkage contains too many jointed parts to be mechanically reliable.