‘On Colour Vision’ by James Clerk Maxwell

Collections - Posted 28-10-2019

Amongst the Gladstone pamphlet collection held at the National Library are hundreds of papers from the collection of The Reverend Bartholomew Price, a mathematician who held the Sedleian Professor of Natural Philosophy chair at Oxford University. They are mainly pamphlets sent to Price by other scientists in Great Britain. They were presented to the Library by his son, W.A. Price, in 1939.

It is obvious from the handwritten notes on many of these leaflets that Price was held in high esteem in the scientific community at the end of the nineteenth century. Amongst the authors of these pamphlets are famous names such as James Clerk Maxwell, Charles Lutwidge Dodgson (Lewis Carroll), Sir George Stokes and William Thomson (Lord Kelvin). Many of these pamphlets are rare and in some cases the only copies known to be in existence (the pamphlets, together with the presentation inscriptions on them provide evidence of how the scientists of the period exchanged their ideas).

James Clerk Maxwell’s pamphlet On Colour Vision is intriguing. This is a text of a demonstration lecture given by the author in 1871 at the Royal Institution of Great Britain. He observes that the science of colour is both a mental science in which our own nature determines the laws of colour observation and a physical science where clearly defined laws of nature can be applied.

Maxwell begins by showing how the laws of Newton are applied to colour observation. By passing light through a prism, Newton showed that white light is not the most pure form of light, as was previously thought, but was composed of all the colours of the spectrum. Objects that we call coloured when illuminated by white light make a selection of these rays, and our eyes receive from them only a part of the light which falls on them, e.g. a red object absorbs all parts of the spectrum apart from the red part which it scatters. However if they receive only the pure rays of a single colour of the spectrum they can only appear that colour, e.g. any object will look red when red light is shone on it- unless it absorbs red, in which case it will look black.

He describes how mixing red and green paint produces a very drab yellow. However when red and green light are mixed the result is a very bright yellow. This is because the red paint, when scattered, is robbed of its brightness by getting mixed with particles of green paint and vice versa. However the yellow light produced by green and red light is a pure colour and not divided into two portions like the mixture.

Maxwell goes on to compare our perception of colour to our perception of musical chords. It appears to our consciousness that each colour is uniform whereas we can easily make out the separate components of a musical chord.

The leaflet delves into describing other aspects of colour science such as colour blindness, and the yellow spot on the retina.  For example did you realise that the extreme part of the retina is insensitive to red? According to Maxwell if you hold a red flower and a blue flower in your hand as far back as you can see your hand you will lose sight of the red flower while you can still see the blue flower. Also if light is diminished, red objects will look darker in proportion to blue objects. I wonder if you, the reader, can confirm whether these observations are true? The third notable observation, which should definitely not be tried at home, is that a kind of colour blindness can be experienced by taking doses of Santonin. Maxwell himself ends the pamphlet by apologising to the readers for not taking the drug to confirm whether this is true!

Hywel Lloyd

Assistant Librarian

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