John Dalton was born more than two hundred years ago near Cockermouth in Cumberland. His origins were humble, and his education informal. All his life he remained the quiet, modest Quaker, and just as his work displays the force and originality of mind that enabled him to educate himself, so also it shows the weaknesses of one who was self-taught, without early subjection to criticism and discipline.
All his life, too, John Dalton was a teacher, from the age of twelve onwards. In 1781 he moved to Kendal, where he taught school first with his cousin George Bewley and later with his own brother Jonathan. After twelve years of this he was brought to Manchester in order to instruct in mathematics and science at the New College in Mosley Street; from 1799 onwards, however, he lived by giving public and private instruction in mathematics and chemistry without any institutional appointment. He remained in Manchester for the rest of his life, making only occasional excursions to London, and to other cities where the British Association meetings were held, and once in 1822 to Paris. It is not for me to speak of John Dalton’s long life in Manchester, of his long connection with the Literary and Philosophical Society, and of the scientific distinction he brought to this city. But I cannot refrain from remarking on the strange coincidence that Dalton, who founded the atomic theory of nineteenth-century chemistry and Ernest Rutherford who destroyed it, were both associated with Manchester. How vivid a picture of the development of science during this century – and of this city too – is conveyed to us by reflecting on the very different circumstances and researches of Dalton on the one hand and Rutherford on the other.
Since the time of Rutherford this has ceased to be true. We can today no more believe in the reality of Dalton’s atoms than we can in that of Newton’s atoms, or those of Democritus. And even through the nineteenth century there was a persistent doubt whether atomism was more than a useful figment. But there is no doubt that John Dalton made an enormous contribution to science – for in the long run it was to be virtually as great in physics as in chemistry – when he, for the first time, made positive, verifiable statements about the ultimate structure of things. This had never been done before. No one before Dalton, was able to make any precise, definite pronouncements about atoms, or indeed to show in any very clear and compelling way that there was a direct advantage to be gained by thinking of matter as having an atomic structure. Dalton did this by taking the atom out of the speculations of physicists and making it the foundation of a verifiable theory of chemical combination. Dalton did not invent the atom, but he made it scientifically useful. And it strikes me, by the way, as being one of those steps in intellectual history that are really idiosyncratic. One can often say ‘This was bound to be found out by someone very soon’; not so of Dalton’s atomic theory. Few if any chemists of this time and perhaps long after would have followed the particular path in thought that John Dalton took.