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Colour Vision

As a child James Clerk Maxwell had always been fascinated by light. This interest was encouraged when his uncle, John Cay, took him to visit James Nicol of Edinburgh. Nicol demonstrated to them the colour exhibited by polarised light through unannealed glass and was so impressed by Maxwell's eagerness to learn that he gave him a pair of polarising prisms. It is therefore unsurprising to find that Maxwell went on to make quite an impact in this field.

However, it is with Newton that the story of colour theory originates. He laid the foundations, stating that mixing the seven colours of the spectrum in different proportions could produce any compound colour. Not long before Maxwell's birth, Thomas Young expanded on this work using spinning coloured disks to develop the theory that the eye recognises three primary colours - red, green and violet. This theory was then altered by Brewster, who noticed that the third colour was not violet but blue. A further development came when German scientist, Hermann von Helmholtz, pointed out the difference between experiments conducted by mixing pigments as opposed to rays of the spectrum.

In 1849 Maxwell began his work on the subject. This work was presented to the Royal Society of Edinburgh in 1855 in his paper entitled, Experiments on Colour, as perceived by the Eye, with remarks on Colour-blindness. He demonstrated, using a coloured top (figure 5.2.1), that any natural colour could be produced from the three primary colours - red, green and blue. Most of this work was not new and merely reiterated what was already known. However it was excellently produced and was a good prelude to his later work.

Maxwell's major paper in optics, On the Theory of Colour Vision, was presented to the Royal Society of London in 1860 and was awarded the Rumford Medal. It showed that colour blindness was due to individuals being unable to recognise red light and conclusively proved his theory of three primary colours. Most of the experiments for this work were conducted in Maxwell's London home with the help of his wife, Katherine Mary Dewar daughter of the Principle of Marchisal College, Aberdeen. These were wonderfully constructed and made use of a colour box designed by Maxwell himself.

Maxwell's final achievement in optics was producing the first ever colour photograph. He displayed the picture of a Scottish tartan ribbon at a lecture on his colour investigations at the Royal Institute in May 1861. He took a black and white photograph through three filters - green, red and blue - and then projected and superimposed the results through the same filters. Later it was noticed that this should not have worked, as the collodion process he had used was not red sensitive. However Maxwell was lucky as the process, which was sensitive to the ultraviolet passed by the filter, compensated for the error.
[Early photographic process using glass plates coated with iodised collodion sensitised with silver nitrate solution and exposed in the camera while still wet. This technique is still used by many large photograph companies to develop important film.]

Maxwell's work on colour vision, although very clever, was probably some of his least astonishing work. It was not ground breaking like his work on gases or the electromagnetic field, nor did it contain the same originality of thought. However it was easier for his contemporaries to understand and it received more recognition than some of his other works. It is merely in comparison to his greater works that this excellent combination of mathematics and experimental physics is made to look ordinary.


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Kevin Johnson May 2002