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Maxwell's theory explained the colours of sunlight.

In Maxwell's electromagnetic wave theory, different colours are understood to be different kinds of light waves. Each wave has a certain frequency—like the frequency of notes on a musical scale. Together, the different kinds of electromagnetic wave make up the electromagnetic spectrum.

Humans can only see a small range of the electromagnetic spectrum, the visible light waves from violet to red. Violet waves vibrate about twice as fast as red waves. On the scale of light, violet is a bit less than an octave higher than red. (Our eyes can see less than one octave of light, but our ears can hear nearly nine octaves of sound!)

Isaac Newton had shown that white light, such as sunlight, could be broken down into a spectrum of pure colours that could not be broken down any further, but could be recombined into white light.

Newton believed that different colours were different kinds of particle. This explanation did not convince everyone.

However at this stage, the wave theory could not explain different colours any better. In the 18th century, Leonhard Euler realised that different kinds of waves could produce different colours, but by this stage almost everyone believed the particle theory of light.

In the 19th century Euler's idea was proved correct. Each pure colour corresponded to a single 'note', while white light was a mixture of many different 'notes'.

The electromagnetic spectrum
magnifyThe electromagnetic spectrum

magnifyIsaac Newton

Newton's spectrum experiment
magnifyNewton's spectrum experiment
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