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Detail of Powell's machine for demonstrating wave motion

The nature of light has puzzled people for centuries. Some physicists thought that light travelled like a wave, while others thought that it travelled as a stream of particles shooting through space. Wave machines like this one became a popular way of visualising and explaining waves, and were also used as teaching models.

Demonstrating waves

This wave machine, from the collections of the Whipple Museum (Image 1), demonstrates how waves move. As you turn round the crank handle, the white balls at the top move up and down, giving the effect that the wave is moving along.

These are known as 'transverse' waves, and are the same type of waves made in rippling water. The other main type of wave is a 'longitudinal wave', such as sound waves.

Light: waves or particles?

The nature and behaviour of light has been a puzzling question for hundreds of years. Some experiments indicated that it behaved like a stream of particles, whilst others seemed to show that it acted like waves. The debate between supporters of the rival theories raged during the 19th century. Supporters of the wave theory of light built wave machines so that they could demonstrate the waves and their motion.

Today's physicists know that, strange as it may seem, light has properties of both particles and waves. This is explained by the theory of quantum mechanics.

Read more: the wave theory of light

Design and manufacture

Powell's machine for demonstrating wave motion
Powell's machine for demonstrating wave motion, made by Elliott Bros.; late-19th century (Wh.2007).

This wave machine was made by the company Elliott Brothers in the late-19th century, after a design by Baden Powell (1796-1860). Powell was Savilian Professor of Geometry at Oxford from 1827 and was also the father of Robert Baden-Powell, founder of the boy scout movement. In his 1841 book Powell wrote:

"For the sake of those readers ... who may be commencing their acquaintance with the undulatory theory, it may not be out of place here to mention a method of imitating the different kinds of vibrations producing a wave by mechanical means. ... A glance at an illustration of this kind enables the mind to grasp the idea at once, even when unaccustomed to the mathematical analysis of it. (1)

Much of Powell's early work was on the wave theory of light, but in later years he moved away from physics as the mathematics became more and more complex.(2)

Powell's wave machine was based on one constructed by George Biddell Airy (1801-1892) some years before. Unfortunately, no details of Airy's machine appear to have survived.

References

  1. B. Powell, On the General and Elementary View of the Undulatory Theory as Applied to the Dispersion of Light (London, 1841), lv.
  2. P. Corsi, 'Powell, Baden (1796-1860)', Oxford Dictionary of National Biography (Oxford: Oxford University Press, 2004), available online at: Oxford DNB (available to subscribers only).

Chris Haley

Chris Haley, 'Wave machines', Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2015.

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