Farey's ellipsograph, 1817.
© Science Museum / Science & Society Picture Library
This engraved ellipsograph, kept in a mahogany case, was made by John Farey of London. An ellipsograph is used to draw ellipses, which consist of a combination of two circular motions. The drawing pencil is fixed in position in a central ring, which then revolves. At the same time, the ring is carried round in a circle, and the pencil traces the combination of these two paths.