82 



NATURE 



[May 28, 1903 



was in the chair. The address was presented by Mr. 

 Norman Smith, a former student under Prof, van 't 

 Hoff. The professor, who was enthusiastically re- 

 ceived, said the question was often asked, nowadays, 

 whether the atomic theory had not outlived its utility. 

 His reply was that, in dealing with natural pheno- 

 mena, with states of unstable equilibrium, the atomic 

 theory was indispensable for essential explanations. 

 He had come to regard the conception of the carbon 

 atom as the centre of a tetrahedron as childish, but it 

 contained the germ of a profound truth, the solution 

 of which must be left to the future. He suggested 

 that valency was due to an equilibrium. Tne four 

 mutually repellent " electric atoms " of Helmholtz were 

 kept in equilibrium by their attraction for the carbon 

 atom at the centre. 



Later in the morning Earl Spencer, Chancellor of 

 the Victoria University, conferred the honorary degree 

 of Doctor of Science on Prof. Clarke and Prof, van 't 

 Hoff, who were presented by Prof. Dixon. After the 

 conclusion of the ceremony Prof, van 't Hoff laid the 



Memorial Tablet over door of house in which John Dalton was born. From 

 a photograph supplied by Mr. A. Humphreys. The inscription on the 

 tablet re.ads : — "John Dalton, D.C.L., LL.D., the Discoverer of The 

 Atomic Theory, was born here Sept. 6, 1766. Died at Manchester 

 July 27, 1844." 



first stone of the proposed extension of the Owens 

 College Chemical Laboratories, and was presented, as 

 a memento of the occasion, with a silver trowel by the 

 College Chemical Society. The celebrations were con- 

 cluded by a soiree held at the Owens College on 

 Thursday night, when Dr. Harden gave an interesting 

 account of John Dalton, and many Dalton relics were 

 exhibited by the Manchester Literary and Philosophical 

 Society, Prof. H. B. Dixon, Mr. Theodore Neild, Mr. 

 G. W. Graham and Mr. G. S. WooUey. E. C. E. 



THE ATOMIC THEORY AND THE 

 DEVELOPMENT OF MODERN CHEMISTRY. 



MANCHESTER celebrated last week, just a 

 little prematurely, the centenary of John Dalton 's 

 atomic theory. It was on September 6, 1803, that he 

 drew up in his notebook his first table of weights of 

 the " ultimate atoms " of hydrogen (which he took as 

 his unit), oxygen, " azot," carbon, sulphur, and of 



NO. 1752, VOL, 68] 



water, ammonia, nitrous gas, nitrous oxide, and oth* 

 binary compounds of these elements. With regard 1 

 the genesis of the theory in his own mind much douh 

 has prevailed until recently. Dalton himself tol' 

 Thomas Thomson in 1804 that he had been led to tlu 

 theory from his work on marsh gas and olefiant gas. 

 He told W. C. Henry in 1824 that his speculations 

 were suggested by the work of Richter. And yet, 

 oddly enough, as Sir Henry Roscoe and Dr. Harden 

 have shown in their " New View of Dalton 's Atomic 

 Theory " the evidence is dead against the accuracy of 

 these plausible statements. Dalton 's own notebook 

 shows that his atomic theory preceded his work on 

 marsh gas, and his notes for a lecture delivered in 

 1810 give a history of his ideas which agrees with all 

 the facts. ^ 



It was from Newton that Dalton derived his belief 

 in the atomic hypothesis. And we can trace the " solid 

 massy, hard, impenetrable, moveable particles " of 

 Newton, through his friend Boyle, through Gassendi, 

 and through Bacon (who considered Democritus to be 

 the greatest of Greek philosophers) back to Epicurus 

 and to the originators of the atomic theory, Demo- 

 critus and Leucippus. Dalton 's theory of atoms is 

 historically the Greek theory of atoms. But with a 

 difference. 



Boyle, who was a far more thoroughgoing atomist 

 than is generally supposed, really rejects the hypothesis 

 of different elements which he himself originated, con- 

 sidering that differences of atomic structure and 

 arrangement of a single form of matter would account 

 for all chemical transformations.^ 



But Boyle's own definition of an element, as a sub- 

 stance which could not be decomposed, proved far more 

 fruitful than his atomic beliefs, and the work of his 

 successors — of Marggraf, of Black and Cavendish, of 

 Scheele and Bergman, of Priestley and Lavoisier— had 

 gradually established in the minds of chemists the idea, 

 rejected by Boyle, that there existed a series of elements 

 not convertible into one another. It was to that series 

 of elements, unknown to the ancients, that Dalton ap- 

 plied the atomic hypothesis. He came to the conclu- 

 sion that the atoms were not of all kinds of shapes and 

 forms, as had been previously supposed, but that the 

 atoms of the same element were all identical in 

 weight, while the atoms of different elements were 

 different in weight. It was an idea that might con- 

 ceivably have occurred to some chemist fifty years 

 earlier. But, in spite of Black's work, the phlogiston 

 theory had led chemists before Lavoisier to lay small 

 stress on the notion of weight. Dalton could hardly 

 have come much earlier than he did. The first an- 

 nouncement of his theory was made in a paper read in 

 October, 1803, at a meeting of the Manchester Literary 

 and Philosophical Society, in the house of which he had 

 his laboratory; the paper was not published until 1805. 

 Dalton 's views were not fully placed before the world 

 until the publication of the first volume of his " New 

 Systems of Chemical Philosophy," in the years 1808- 

 1810.^ 



Meanwhile Dalton had been carrying out re- 

 searches which confirmed his view, and, together with 

 certain assumptions, led to the most important of 

 generalisations. Dalton himself never disengaged the 



1 Save for an obvious clerical error of 1805 for 1803. 



2 "I see not, why we must needs believe, that there are any primogeneal 

 and simple bodies, of which, as of pre-existent elements, nature is obliged 

 to compound all others. Nor do I see why we may not conceive, tbat she 

 may produce the bodies accounted mixt out of one another by variously 

 altering and contriving their minute parts, without resolving the matter 

 into any such simple or homozeneous substances, as are pretended " (" The 

 Sceptical Chymist," part vi., folio edition, vol. i., p. 369). See also p. 366, 

 a reference 10 an experiment by which Boyle thought he had " de-^troyed 

 refined gold and brought it into a metalline body of another colour and 

 nature " : and p. 367, an earlier announcement of the view just qu ted. 



3 The first part of this volume aiipeared in 1808, the second in 1810. The 

 first part of the second volume only appeared in 1827. The work was not 

 completed. 



