140 Royal Sociefp. 



and removed in 1793 to Manchester, where he contiiWied, to >jrosui« 

 during the whole of his after-life. i.,!ti n onfoo h/um til) 



I, It was doubtless his long residence among the lakes and mountiins 

 ofCuraberland, and his consequent early fanailiarity with the ever- 

 varying conditions of the atmosphere observable in that district, 

 that gave the first impulse to his genius, affd materially influenced 

 his subsequent scientific career. Ilis earliest important publication 

 was a Treatise on Meteorology, which furnished a clear compendium 

 of all the facts then ascertained, and made known various original 

 views, especially on the altitude of the Aurora Borealis. From ob- 

 serving and recording the sensible atmospheric changes, the phaeno- 

 menaof dew, of clouds and of temperature, he was naturally impelled 

 to inquire into the constitution of the atmosphere, and more gene- 

 rally of mixed elastic fluids, and into the theory of evaporation and 

 the laws of heat. On these questions he made public, through the 

 Transactions of the Manchester Society, a series of experimental 

 memoirs, of which it is impossible to over-estimate the importance. 

 His first conception of the mutual relations of mixed gases was, that 

 each gas stood in the relation of a vacuum to the particles of all other 

 gases ; but in his New System of Chemical Philosophy he subse- 

 quently relaxed the strictness of this original proposition, by con- 

 ceding that the particles presented some mechanical impediment to 

 commingling. He ascertained the form of the vapours of water and 

 some other liquids at different temperatures, and dispelled by these 

 experiments and others of equal importance the obscurity in which 

 the theory of vaporization had been left by De Luc and Saussure. 

 He first showed that a given space, whether void or filled with any 

 gas, in contact with water, contains precisely the same amount of 

 aqueous vapour, and thus established the non-existence of chemical 

 affinity between the gas and the steam of water. It is impossible not 

 to be impressed with the beautiful simplicity of the instruments by 

 which these important results were wrought out. Four barometric 

 tubes, filled with mercury, over which were admitted small columns 

 of water, alcohol, ether and sulphuret of carbon, were the means 

 employed for the admeasurement of the comparative forms of the 

 vapours at different atmospheric or artificial temperatures. Among 

 these successive memoirs is one of great merit on the heat evolved 

 during the entrance of air into a vacuum. He showed the inade- 

 quacy of the thermometer to serve as a measure of this evanescent 

 elevation of tempei'ature, and by an ingenious contrivance obtained 

 a much closer approximation to the true heat. 



The first part of his New System of Chemical Philosophy will pro- 

 bably constitute the most durable monument of his scientific genius ; 

 in this small volume are condensed the results of many years' patient 

 thinking and of much laborious research ; those larger portions, 

 which are devoted to the measure of temperature and the theory of 

 specific heat, may still be studied with advantage, though they were 

 deemed by Dr. Dalton himself to have been in great part superseded 

 by the labours of MM. Petit and Dulong. The short concluding 



