Wikimedia
John Dalton was an English chemist, physicist, and meteorologist who is best known for his work in the development of modern atomic theory and his research into color blindness.
John Dalton was born in the county of Cumberland in England in 1766 and received his early education from his father who ran a private Quaker school. He started his own school aged 11 and at age 15, he joined his brother teaching in a school in Kendal [1]. He was barred from attending English universities because he was a dissenter (a Christian opposed to state religion and mandatory membership in the Church of England) but acquired scientific knowledge from John Gough, a blind philosopher with wide-ranging scientific interests. However, in 1793 he was appointed as teacher of mathematics at New College, Manchester (a dissenters’ college). On October 3, 1794, Dalton was elected as a member of the Manchester Literary and Philosophical Society and a month later, he presented his first paper entitled, “Extraordinary facts relating to the vision of colors with observations.” The society’s Memoirs and Proceedings have been published continuously since its first edition which, when it was launched in 1783, was the only regular scientific journal in the United Kingdom except for the Philosophical Transactions of the Royal Society. As a result of this paper, congenital color vision deficiency is still referred to as “Daltonism” because he was the first to describe the condition in detail and the paper also stimulated great debate amongst other investigators [1]. In 1800, he left New College and began private teaching and in 1808, he published the atomic theory for which he is most famous. He became President of the Manchester Literary and Philosophical Society in 1817, a post he retained until his death in 1844.
30.1 Dalton’s Color Blindness
Dalton noticed that only males were afflicted with his condition and we now know that color blindness, or color deficiency as it may more properly be referred to, is much more prevalent amongst males than females. He also recognized that the condition must be hereditary since he and his brother had the same condition.
The flower was pink but it appeared to me almost an exact sky-blue by day; in candlelight however it was astonishingly changed, not having then any blue in it but being what I call red – a color which forms a striking contrast to blue.
Thirty-six years prior to Dalton’s famous 1794 letter, Thomas Young had postulated that congenital color vision defects arose from the photoreceptors but Dalton refused to believe it [1]. As a result of his meticulous observations, Dalton believed that the fluids in his eyes must contain a blue colorant and he instructed that on his death his eyes be subject to a post-mortem analysis. No trace of the blue colorant was found. Interestingly, Dalton found twenty-five others (including, notably, his own brother) who suffered the same failure of color constancy though most saw no change. Dalton also wrote that the red end of the spectrum was “little more than a shade or defect of light.”
We now know that Young was essentially correct; that is, that congenital color vision defects result from genetic mutations that mean that one (or more) of the three visual pigments found in the cones of our retina have anomalous spectral absorption properties or are absent entirely. Young believed that Dalton was a protonope—that is, that he was missing the long-wavelength sensitive visual pigment. Although the post-mortem examination of Dalton’s eye did not reveal the blue colorant that Dalton had predicted, the remaining eye was preserved between two sheets of glass until it was analyzed by Mollen et al. who concluded that Dalton was indeed a dichromat but was a deuteranope rather than a protonope [2].
Dalton’s theory that color deficiency was caused by a long-wavelength absorbing colorant in the fluids of his eyes ultimately proved to be incorrect. He was also not the first to “discover” color blindness. However, he made a substantial contribution to the understanding of color blindness through his meticulous observations and he also inspired other scientists to study this fascinating phenomenon.
- 1.
Atomic theory
Although Dalton’s name is indelibly associated with color deficiency by far his most important work was in the area of atomic theory, which he formally first published in 1805. The main points of Dalton’s atomic theory were:- 1.
Elements are made of extremely small particles called atoms.
- 2.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
- 3.
Atoms cannot be subdivided, created, or destroyed.
- 4.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
- 5.
In chemical reactions, atoms are combined, separated, or rearranged.
There is uncertainty about how Dalton arrived at his atomic theory [3]. Also, there was no evidence available at the time to scientists to deduce how many atoms of each element combine to form compound molecules so that Dalton, for example, wrongly assumed that water was composed of a single oxygen atom combined with a single hydrogen atom. Nevertheless, the essential features of his theory have survived to this day and his theory can be said to be one of the bedrocks of modern chemistry.
Dalton made notable contributions to meteorology (where he made over 200,000 observations, published several important essays on the gas laws (his law of partial pressures became known as Dalton’s law), and wrote about rain, the color of the sky, and refraction.
- 1.