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step. His first chemical memoir was an ‘Experimental Enquiry into the Proportion of the several Gases or Elastic Fluids constituting the Atmosphere’ (Manch. Memoirs, i. 244, 2nd ser.). It was read on 12 Nov. 1802, and disclosed the insight obtained through study of the combinations of oxygen with nitrous gas, into the law of multiple proportions. With a view to explaining the various absorption of gases by water, he undertook to determine the comparative weights of their atoms. He remarked in a paper on the subject read 21 Oct. 1803 (ib. p. 271): ‘An inquiry into the relative weights of the ultimate particles of bodies is a subject, so far as I know, entirely new. I have lately been prosecuting the inquiry with remarkable success. The principle cannot be entered upon in this paper, but I shall just subjoin the results, as far as they appear to be ascertained by my experiments’ (ib. p. 286). A list of twenty-one atomic weights followed, that of hydrogen being taken for unity. To oxygen was assigned the number 5.5, to water 6.5, nitrogen 4.2, carbon 4.3. Inexact as these results were, their attainment marked an epoch in chemistry. There is reason to believe that they were inserted not long previous to the publication, in November 1805, of the paper containing them.
On 26 Aug. 1804 Dalton explained in conversation his theory of combining weights to Dr. Thomson, who in 1807 added a sketch of it to the third edition of his ‘System of Chemistry’ (iii. 424). The attention of the Royal Society was drawn to it by both Thomson and Wollaston in 1808; and Dalton, who had already lectured upon the subject at Edinburgh and Glasgow, published his views in ‘A New System of Chemical Philosophy’ (Manchester, part i. 1808, part ii. 1810). In this work he developed those primary laws of heat and chemical combination to which he had been gradually led since 1801, and laid the foundation of chemical notation by representing graphically the supposed collocation of atoms in compound bodies. Extended and revised tables of atomic weights were appended (pt. i. p. 219; pt. ii. 546). Dalton's curious inaptitude to receive the ideas of others was exemplified in an appendix disputing with Davy the elementary nature of chlorine, sodium, and potassium, and with Gay-Lussac the validity of his law of combining volumes, in reality, could he have seen it, a beautiful confirmation of his own law of combining weights.
The atomic theory was now fairly before the world. It met with very general applause, but only gradual acceptance. Berthollet and Davy were the most conspicuous objectors; but Davy retracted so far, after a few years, as to declare it the greatest scientific advance of recent times. The innovation of attributing fixed weights to the ultimate particles of matter, by which their combining proportions were strictly determined, gave a hitherto unknown definiteness to chemical analysis, and brought it within the scope of numerical calculation. There had, as usual, been partial anticipations. The claims of Dr. Bryan Higgins, professor of chemistry in Dublin, were brought forward by Davy in the Bakerian lecture of 15 Nov. 1810 (Phil. Trans. ci. 15), and still more emphatically by himself in 1814 (Experiments and Observations on the Atomic Theory). Higgins had undoubtedly, as early as 1789, laid a loose and temporary grasp on the doctrine of atomic combination, but its generalisation and proof were entirely due to Dalton, who read Higgins's ‘Comparative View’ only when he found himself under the suspicion of plagiarism from it. He declined all controversy in the matter, and it was publicly acknowledged by Davy in 1827 that Dalton ‘first laid down, clearly and numerically, the doctrine of multiples, and endeavoured to express, by simple numbers, the weights of the bodies believed to be elementary’ (Six Discourses, p. 128).
The outward circumstances of Dalton's life remained, meanwhile, unchanged. After the removal of New College to York in 1799 he supported himself by giving private lessons in mathematics at half-a-crown an hour, besides performing analyses and doing other work as a professional chemist at ridiculously low charges. His wants were few, and his habits economical to the verge of parsimony. Yet he could be generous on occasions. He gave largely, even at times lavishly, to objects deemed by him worthy; and in his later years he made liberal allowances to two distant female relatives. A fixed routine left no space in his laborious and abstemious life for recreation other than a game of bowls every Thursday afternoon at the ‘Dog and Partridge,’ and a yearly visit of intense enjoyment to Cumberland. He ascended Helvellyn in all between thirty and forty times. Asked the reason why he had not married, he replied, ‘I never had time.’ It is certain, however, that he cherished all his life the memory of one hopeless attachment.
One day in the autumn of 1804 Mrs. Johns, wife of the Rev. W. Johns, who kept a school in Faulkner Street, Manchester, seeing him pass, asked why he never called to see them. ‘I do not know,’ was the answer; ‘but I will come and live with you, if you will let me.’ He was as good as his word, took pos-