Wheatstone's wave machine, c 1842.

Sir Charles Wheatstone, the famous English scientist, devised this model to illustrate the wave theory of light. Made by John Newman, a London instrument maker, in the 1840s, the model uses white beads mounted on sliding rods to represent a light wave. By pasing a wooden template, with a wavy edge, along the base of the rods a wave motion can be generated. On this example, two sets of rods are mounted at right angles to each other, allowing the behaviour of polarised light to be visibly demonstrated. Models of this type were popular demonstrations during the 19th century being widely used to explain the wave nature of light.