CHAP. VI., 3.] 



HEAT. LAVOISIER DALTON. 



135 



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- 



(609.) 



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 

 conclusions of his chemical doctrines, when he was 

 overtaken by the unprovoked sentence to a violent death. 

 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. DALTON. Theory of Oases and Vapours. Law of Expansion by Heat. Atomic Theory of 



Chemistry. GuY-LusSAC. 



(610.) 

 alton 

 is early 

 rcum- 



JOHN DALTON, 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 names which we have selected 

 in illustration of the history of physics of their age. 

 mtrasted Cavendish we have seen connected with one of the 

 ith those no ki es t families in England, and wealthy almost be- 

 ish and y n( l 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 



lack. 



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 him in 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 have 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 



(611.) 



1 Life of Dalton, by Dr Henry, in the publications of the Cavendish Society, 

 before the appearance of this biography. 



The present section was originally written 



