John Dalton - A Visual Error

The man who gave his name to colour blindness - 'Daltonism' - was neither an optician, nor a physician but a chemist. He donated his own eyes to colour vision science and the results of this altruistic act were very interesting, even if they disproved their donor's own theories.

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Chemical colour samples

Chemical colour samples, as in this (20th century) set of 22 test-tubes with cork stoppers containing various coloured chemicals including Iodine of Mercury and Carmine may have influenced Dalton's interest in colour perception, but the main influence appears to have been his own eyesight and problems encountered in identifying and distinguishing between the colours he saw in everyday life, let alone the laboratory.
 

Portrait of John Dalton 1842

John Dalton - President of the
Litry & Phill Socy, Manchr

etching by J. S. Stephenson
1842

John Dalton (1766-1844) described his own colour vision deficiency - seemingly the first ever account of living with the condition - in a paper entitled Extraordinary Facts Relating to the Vision of Colours with Observations given to the Manchester Literary and Philosophical Society on 31 October 1794 (later published in 1798). In this paper Dalton described how his interest in colours began in 1790, when he started studying  botany and had problems naming the colours of plants. He then recalled reading an article thirteen years earlier about a chap Mr Harris up in Cumbria (where he himself came from), who 'could not distinguish colours' and had contacted the Harris family as part of his study.

Dalton saw only the blue, violet and yellow parts of the spectrum correctly.

That part of the image which others call red, appears to me little more than a shade or defect of light; after that, the orange, yellow and green seem one colour, which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow

In a letter written by Dalton to Elihu Robinson in February 1794 he claims to have discovered his colour blindness 'last Summer' and that he had been collecting silk ribands in various colours from a friend who was a dyer in order to compare his perceptions with those of his acquaintances.

One of his friends had a grassy green coat which Dalton saw as red. He was shown a pink flower in daylight and described it as 'sky blue' in daylight but when taken into candlelight he said no it was 'red'. He discovered that only his brother shared the same perception and concluded that the two of them must have an hereditary problem. He suggested this was an inherited 'coloured medium' or blue colouration in the humour of the eye.

In order to test his theory he graciously donated his own eyes to medical science after his death. The doctor Joseph Ransome removed the eyes the day after he died and quickly disproved the colouration theory. Dalton had been in error!

Book describing Dalton's molecular biography

More excitingly, Ransome left one of the eyes intact, thus enabling Mollon, Dulai and Hunt, after a gap of two centuries (1994), to take a retinal sample and conduct a DNA analysis. They have claimed that this project was the first instance where an hereditary defect has been identified in an historic figure, allowing the compilation of a 'molecular biography'. They even conducted analysis on the types of flowers and even the eighteenth century sealing wax that Dalton had described in his writings. Mollon, Dulai and Hunt concluded that Dalton had in fact been a deuteranope with a single long wave (LW) opsin gene coding for an LW visual pigment.

'Daltonism'

Although he was not the first to investigate colour blindness the name of Dalton  has been used to describe the condition in many countries ever since, even in  languages such as Spanish and Russian. Dalton himself appears not to have  minded. The word was popularised in print from an early date, being traceable to Prevost of Geneva who referred to daltonien in 1827.

Professor William Whewell, Master of Trinity College, Cambridge campaigned against the use of Dalton's name to described colour blindness. He preferred a name that some sources suggest he first heard from Sir John Herschel - that people with unusual colour vision should be described as 'Idiopts'. The Edinburgh Review of 1842 was clear that Idiopts was 'a term not wanted - and one which, when submitted to the eye of a compositor, will infallibly part with one of its most essential letters'!

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