140 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(624.) 

 Its recep 



England, 



(625.) 



sac's law 

 volumes. 



a discovery of such magnitude. Dalton's earlier re- 

 searches were far more physical than chemical ; and 

 it is evident that the effort of representing to his 

 mind, geometrically and atomically, the condition of 

 mixed gases and vapours, led him to form clear 

 ideas on the definiteness of chemical combinations. 

 The delay in publishing his views, no doubt de- 

 pended on his desire to present them to the public 

 in the form of a somewhat wide induction, although 

 it is certain that his own opinion was fully formed 

 from a knowledge of only one or two cases of multi- 

 ple proportions, and especially the combinations of 

 hydrogen and carbon. It cannot be fairly urged as 

 "onclusive against the theory of atoms, that cases 

 .ccur difficult to reconcile with the author's formal 

 statement of it. There is no great theory not even 

 that of gravitation itself which has not met with 

 similar apparent contradictions. 



The reception of the views of Dalton was some- 



- w j iat g^ua^ ve t might be called rapid, considering 

 the obscurity of the author, and his provincial resi- 

 dence. The energy of Dr Thomson of Glasgow con- 

 tributed more than any other circumstance to com- 

 pel the attention of chemists. He personally brought 

 it under the notice of Wollaston and Davy ; and the 

 former, who, by his habits of precise thought and ac- 

 curate experiment, as well as from his extensive che- 

 mical knowledge, would of all others have been the 

 most likely to see its importance and probability, 

 was doubly predisposed in its favour by having been 

 himself for some time in possession of facts illus- 

 trating the numerical laws of combination similar to 

 those which Dalton possessed. Wollaston published 

 these in the Philosophical Transactions for 1808, in 

 which he expressly states, that Dalton had antici- 

 pated him in the results of his enquiry into multiple 

 combinations of elements. Davy, as might have been 

 expected, was less prepared to accept a doctrine 

 having the form of a mathematical law ; he did so, 

 however, after a short resistance. In his Chemical 

 Philosophy he ascribes most if not all the merit of 

 it to Higgins, and is supposed to have looked coldly 

 upon Dalton's growing fame ; but it is gratifying to 

 add, that in almost his last appearance in public as 

 president of the Royal Society, when presenting Dal- 

 ton with the first royal medal, he should have ex- 

 pressed himself in terms of cordial praise. 



j n F rance the new doctrine soon spread, notwith- 

 standing its violent contradiction to the theories of 



of Berth ollet. Gay-Lussac was amongst its earliest 

 an <l most enlightened advocates; and he had the 

 good fortune to add, in 1809, a new law to the 

 principles of chemical combination, which is, that 

 the gases, in uniting chemically, combine in equal or 

 multiple volumes, and when any condensation occurs 

 after they have united, it amounts to an exact frac- 

 tion (| or 1) of their joint bulk. This was the only 

 addition made for a very long period to Dalton's 

 laws, even if we consider the theory of Isomorphism 



and of Substitutions to take the same rank ; and as 

 it evidently includes the idea that the atomic weights 

 of the gases have a simple numerical relation to their 

 densities, it confirms Dalton's views of the great sim- 

 plicity and uniformity of constitution of those bodies. 

 In Sweden the doctrine of definite proportions found 

 one of its earliest advocates in Berzelius, and his 

 analyses contributed perhaps more than those of 

 any other chemist to its perfect establishment. 



It is not to be concluded, however, that the atomic (626.) 

 or theoretical part of Dalton's laws obtained the same " Chemic 

 currency with the conditions of chemical combina- 1 g nts " 

 tion which they serve to define. Wollaston and 

 Prout were perhaps the most favourably disposed 

 to the doctrine of atoms, though the former invented 

 the term " chemical equivalents" to escape from the 

 theoretic inference, and the latter believed that Dal- 

 ton's law was only a portion of a more complicated 

 one regulating chemical combinations. Wollaston 

 even sought evidence in favour of ultimate atoms, 

 from considerations of a purely mechanical kind, 

 such as the existence of a limit to the atmosphere 

 (Phil. Trans. 1822). We may however admit, with 

 those who have taken an opposite view, that the 

 finite extent of the atmosphere is consistent with a 

 continuous mathematical law suitably assumed, and 

 without reference to atoms at all ; if, indeed, we can 

 imagine a medium varying enormously in density, 

 yet possessing perfect continuity of body. But we 

 will not enlarge farther on these almost metaphysi- 

 cal considerations. 



During the period from his settlement in Man- (627.) 

 Chester in 1793, to the publication of his Chemical ^J^-d 

 Philosophy in 1808, Dalton was occupied in tuition, history 

 first in the Mosley Street Institution, where he lee- continued 

 tured on mathematics and natural philosophy for six 

 years, and afterwards, privately, in a very humble 

 and unpretending manner. His speculations and ex- 

 periments gradually became more and more strictly 

 chemical ; and, aware that his atomic theory was to 

 be the great foundation of his fame, he spared no 

 pains in illustrating it by numerous analyses. Con- 

 temporary chemists have testified to the ingenuity 

 and fidelity of these. Yet, isolated as he was, and 

 unacquainted perhaps with those niceties of manipu- 

 lation which are suggested by the experience of pro- 

 fessional chemists, and rapidly communicated in great 

 cities, his numerical conclusions were often inexact. 

 Probably he felt some discouragement from this, at 

 well as from the indifferent reception of the later parts 

 of his Chemical Philosophy, in which he had to admit 

 the inaccuracy of his theoretical scales of heat and 

 expansion. At all events, his publications became 

 more scanty and less original, though he was still near 

 the meridian of life. The reality of his discoveries 

 had been somewhat coldly acknowledged, and he felt 

 little temptation to adventure himself in a more bust- 

 ling arena, for which his habits and circumstances 

 seemed to unfit him. Nevertheless, he had been, as 



