938 MATHEMATICAL AND PHYSICAL SCIENCE. 
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 
[Diss. VI. 
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 certain that his own opinion was fully formed It is not to be concluded, however, thatthe atomic (626.) 
from a knowledge of only one or two cases of multi- or theoretical part of Dalton’s laws obtained the same “ Chemical 
. . . . . +e . . equiva- 
ple proportions, and especially the combinations of currency with the conditions of chemical ecombina-j,n4.» 
(624.) 
Its recep- 
tion in 
England, 
(625.) 
and France, 
Gay-Lus- 
hydrogen and carbon. It cannot be fairly urged as 
conclusive against the theory of atoms, that cases 
occur 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- 
what gradual, yet 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- 
eurate 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. 
In France the new doctrine soon spread, notwith- 
standing its violent contradiction to the theories of 
sac’s law of Berthollet. Gay-Lussac was amongst its earliest 
volumes. 
and 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 $) 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 
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- 
chester in 1793, to the publication of his Chemical 
Philosophy in 1808, Dalton was occupied in tuition, history 
first in the Mosley Street Institution, where he lec- 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 
ay Ya 
