Perpetual motion: A garden fountain worked by water from upper cistern which is filled with water from an Archimedian screw. The screw is driven by a perpetual motion device using a wheel and lead balls. The balls are supposed to force the wheel round as they fall from the inside of the wheel to its outer circumference. Engraving from Theatrum Machinarum Novum by George Andreas Bockler (Nuremberg, 1673).