Volutor, instrument for drawing spirals, one piece missing, with wooden box, (B980, A204590), patented by Henry Johnson, and made by F. Hoffman, London, 1857

Although patented in 1857, this instrument is similar to those presented to King George III a century earlier. Turning the handle simultaneously produces both rotational and linear motion, the latter by means of the string that wraps around the conical pulley. The resulting curve is a ‘volute’ or Archimedean spiral, used for the capitals of ionic columns in classical architectural drawing. Johnson suggested several designs for voluters around this time.