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Issue 7 - The light fantastic

History & Heritage

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Scotland Magazine Issue 7
March 2003


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The light fantastic


Sir David Brewster would perhaps be surprised that he is remembered principally for his invention of the kaleidoscope. This prodigious scientist and inventor in fact left a far greater legacy.

Born in 1781 in Jedburgh, near the English border, he was a child prodigy and had built a telescope by the age of 10, aided by mentor James Veitch, 10 years his senior. Initially, however, Brewster studied theology and became a minister, but found himself unable to speak in public and rapidly turned his attentions full-time to what he was best at: science.

The physics of light was his main interest, and by the time he was in his 20s, his research of optics was really taking off. He had already constructed several more telescopes and often built his own instruments or improved existing ones to aid experimentation. Brewster also wrote about optics, and edited other works, and his first paper accepted by the Royal Society, Some Properties of Light, was published in 1813.

A major scientific distinction for Brewster came through his studies of the polarisation of light by reflection and biaxial crystals, and ‘Brewster’s Law’ still offers a clear way to calculate the angle at which light must strike a material for maximum polarisation (the concentrating of light waves onto one plane).

It was in 1816 that Brewster perfected the invention of the kaleidoscope, and patented it the following year. The device was a great success, and people from all walks of life found it fascinating and charming. Unfortunately, due to problems with the patent, manufacturers were able to mass-produce kaleidoscopes without Brewster receiving the financial reward rightly due him.

His explanation of the process of designing and building the instrument appeared in Treatise on the Kaleidoscope, published in 1819.

The kaleidoscope works using a minimum of two mirrors which run the length of the interior of a tubular casing. The number and type of reflections created depends on the number of mirrors and their angles.

Two- and three-mirror arrangements are most common. Two mirrors are set up in a ‘V’ shape, with the third side blacked out. This creates a mandala/’cathedral window’ image. Three mirrors are arranged in the same formation, but using the third mirror to make the third side of the triangle, and create continuous honeycomb of images. A case at the bottom of the mirror chamber allows viewing of an object or objects, and is sometimes removable so that the object(s) can be changed at will.

Brewster successfully modified and improved the stereoscope, an instrument which shows images of two pictures from slightly different points of view, creating 3-D effect. He was also involved in early study of photography.

Groundwork in optics, including the construction of a large, polyzonal lens using stepped circular segments, mirrored the work of French physicist Augustin Fresnel, who went on to invent the Fresnel lens, used in lighthouses. The incredibly powerful, focused beam this large lens produces is created by the use of concentric, stepped circles, with the central lens also acting as a magnifying glass, concentrating the beam of light and projecting it long distances.

Sir David Brewster’s contribution to science was recognised in various ways: he was elected to the prestigious Royal Society and won their Copley, Rumford and Royal medals for his work in optics, and was knighted in 1831. More recently, a symposium marking the bicentenary of
Brewster’s birth was held at Edinburgh’s Royal Museum of Scotland in November 1981, examining the achievements of this gifted scientist.