(610.) 
Dalton— 
his early 
circum- 
stances ; 
Cuar, VI.. § 3] 
by the latter (a fact sparingly alluded to by Lavoi- 
sier), to give to the true theory a stable foundation. 
That metals calcine, and that flames burn by the aid 
of the vivifying principle of the atmosphere abstracted 
from it, and which adds its weight to the compounds 
produced, was the primary step made by Lavoisier ; 
to which, by cautious, yet rapid inductions, he added 
the knowledge of oxygen as the usual (he believed 
the sole) acidifying principle, and demonstrated the 
true nature of carbonic acid, To these various phe- 
nomena thus happily reconciled, he added the theory 
of respiration, confirming it by the effects observed 
in air which has undergone that process. These, and 
many other consequences of the ‘ oxygen theory,” 
were developed in a numerous series of admirable 
memoirs. The reception of it was anything but in- 
HEAT.—LAVOISIER—DALTON. 
933 
stantaneous; and the hesitation and delay which oc- 
curred, enable us, as Dr Whewell has well remarked, 
to estimate the force of mind which was required to 
promulgate the theory,—as the subsequent course of 
discovery, and its infinite applications in practice, best 
attest its importance. 
Lavoisier was still occupied in extending the  (609.) 
conclusions of his chemical doctrines, when he was ; 
overtaken by the unprovoked sentence to a violent 4 eo 
death. Like Archimedes, he begged a short respite 
for the completion of experiments in which he was 
immediately engaged, but he was silenced by the brutal 
reply that “the Republic had no need of philoso- 
phers.” He left a name equal to any in the science 
of his time, and adorned by the memory of public 
and private virtues, 
§ 3. Datton.— Theory of Gases and Vapours—Law of Expansion by Heat.—Atomic Theory of 
, Chemistry.—Guy-Lussac. 
Joun Darron, the chief author of the theory of che- 
mical equivalents or the Atomic Theory (as he preferred 
to call it), and of many important researches on the 
constitution of elastic fluids, was born at Eaglesfield, 
near Cockermouth in Cumberland, on the 5th of 
September 1766.1 His parentage was humble, and 
his family belonged to the sect of Quakers, whose 
tenets he, to the close of his life, professed. Had 
we wished to invent a striking antithesis in the per- 
sonal histories of the cultivators of science, or to 
illustrate merely the various soils on which rich 
crops of discovery may be reared, we could scarcely 
have imagined more striking contrasts than in the 
social positions and advantages of Black, Cavendish, 
and Dalton—three of the nameswhich we have selected 
in illustration of the history of physics of their age. 
contrasted Cavendish we have seen connected with one of the 
with those 
of Caven- 
dish and 
Black. 
noblest families in England, and wealthy almost be- 
yond the dreams of the covetous ; spending his life 
in or near London, and enjoying every facility of di- 
rect communication with the first scientific celebrities 
at home and abroad ;—Black, almost the beau ideal 
of an Academic, not wealthy indeed, but surrounded 
by all the opportunities of study, of information, and 
of social intercourse which he desired; passionless 
almost to a fault ; admired by his pupils and friends ; 
enjoying, in short, all the advantages which educa- 
tion and a literary position can afford for the prose- 
cution of a favourite study;—Dalton, on the other 
hand, poor and hardly winning a well-earned sub- 
sistence by private tuition, from the time he was 
himself a child until near the close of his long ca- 
reer,—with few friends, a scanty education, and a 
scantier library,—attaining, through his unaided and 
long almost unheeded efforts, and by means of an 
apparatus constructed entirely by himself, a position 
in the world of science unquestionably not second to 
that of either of his more highly-favoured contem- 
poraries. 
At the age of thirteen he had commenced the ardu- 
ous office of an instructor; and from 1781 to 1792 
pursued the same occupation in a humble sphere 
at Kendal, where he fortunately became acquainted 
with Mr Gough, a blind gentleman of some fortune, 
who devoted his time to the prosecution of science 
in nearly all its branches, and particularly of mathe- 
matical subjects, of which he has left an enduring 
record in many ingenious papers, published chiefly 
in the Manchester Transactions and in Nicholson’s 
Journal. He patronized young Dalton, giving him 
free access to his library and apparatus, and receiv- 
ing from himin return the benefit of his assistance in 
prosecuting his experiments. Dalton always recog- 
nised (as he had unquestionably good reason to do) 
the merits of his patron, and the importance of the 
advantages which he had derived from his advice 
and example. Indeed, without some such fortunate 
concurrence of circumstances (and something simi- 
lar may be noted in the history of nearly all self- 
educated men), it could hardly haye been hoped that 
Dalton would have been so well grounded in the ma- 
thematical principles of at least some branches of 
Natural Philosophy as he probably was. For, though 
his discoveries bear mainly on the science of chemis- 
try in the wide sense in which it was then under- 
stood, yet geometrical precision is after all their fun- 
damental characteristic ; and whether in treating of 
the constitution of a gas, or of the scale of a thermo- 
meter, or of the composition of a salt, it is evident that 
numbers and ratios were the ideas predominating in 
1 Life of Dalton, by Dr Henry, in the publications of the Cavendish basis The present section was originally written 
before the appearance of this biography. 
am unfor- 
nate 
(611.) 
