Replica. This apparatus was inspired by the work of Sir Isaac Newton (1642-1727) in showing that white light is made from a range of colours called the spectrum. This example, made in the late 19th century, consists of a circular disc of card that is painted with narrow wedges of colours in the hues of the rainbow. The sequence of colours, in the order of the spectrum, is repeated fourfold around the disc. If spun at high speed, the colours on the disc will appear to merge into a off-white tinge due to the persistence of human vision.
© Science Museum / Science & Society Picture Library