John Dalton's preserved eyeball finally settled his colour-blindness theory in 1995
John Dalton guessed that his odd colour vision came from tinted fluid inside his eyeballs. He was wrong, but he was right that it ran in families, since his brother shared it. In 1995, researchers examined one of Dalton's preserved eyes and found he had deuteranopia, a missing green-sensitive pigment.
Dalton described the condition in 1794, weeks after joining Manchester's Literary and Philosophical Society. To him, red looked like little more than a shadow, while orange, yellow and green blurred into a single fading yellow. His account was the first scientific description of colour blindness, which several languages still call Daltonism.
He was born in 1766 to a Quaker weaver in Cumberland and was earning his own living by ten, working for a wealthy Quaker, Elihu Robinson, who got him interested in mathematics and the weather. That interest never faded. From 1787 he kept a weather diary for 57 years, logging more than 200,000 observations. Before planes and balloons, the only way to take readings high up was to climb, so he spent holidays hiking Lake District fells with a barometer, and until the Ordnance Survey mapped the area in the 1860s he was one of the few authorities on its mountain heights.
Gases led him to atoms. In lectures in October 1801 he examined mixed gases, vapour pressure and the expansion of gases with heat, and in 1803 he set out the law of partial pressures that carries his name. Pondering why water dissolves some gases more readily than others, he suspected it depended on the weight and number of their particles. His notebooks suggest the atomic idea came to him first as a physical notion about the atmosphere, though one recent study argues he developed it to reconcile Cavendish's and Lavoisier's analyses of nitric acid.
His 1808 A New System of Chemical Philosophy proposed that each element is made of identical atoms with a characteristic weight, combining in whole-number ratios. To assign formulas he assumed that two elements forming only one compound joined one atom to one, so water was taken to be one hydrogen paired with one oxygen, an assumption nobody could independently confirm. His real breakthrough was a method for calculating relative atomic weights, a priority no rival ever took from him.
Source: John Dalton
