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From Citizendium, the Citizens' Compendium
Daltonism refers to dichromacy characterized by a lowered sensitivity to green light resulting in an inability to distinguish green and purplish-red. It is an inherited defect in perception of red and green, or in other words, red-green colorblindness.
The term is derived from the name of John Dalton (1766-1844), a British chemist whose pioneer work on the properties of gases led to his formulation of the atomic theory. Through his lifetime John Dalton became a well known and respected chemist and physicist.
Dalton also described his and his brother's affliction of colorblindness with defective perception of red and green in the first scientific paper he published, "Extraordinary facts relating to the vision of colours, with observation" (Mem Literary Philos Soc Manchester 5: 28-45, 1798). It is the first recognized account of red-green colorblindness.
“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.”
He postulated that shortage in color perception was caused by discoloration of the liquid medium of the eyeball called aqueous humour. According to his research he believed that the aqueous humour was bluish and therefore filtered out all the colors.
One of his last wills was to get an autopsy of his eyes after death. Unfortunately there wasn’t any bluish liquid found. It was his final experiment and proved that the condition called Daltonism is not caused by the eye itself, but some deficient sensory power.