244 Natural History. [Chap, III, 



investigation of the subject, and proposed a 

 new theory. He held that evaporation is the 

 gracUial solution of zoater in air, and that the 

 former is suspended in the Jatter in the same 

 manner as salts, or other soluble substances, are 

 suspended in aqueous fluids*. The same doc- 

 trine, in substance, had been suggested before by 

 several philosophers; particularly by M. le Roy, 

 in 1751; by Dr. Franklin, in 1756; and by 

 Muschenbroeck, in 1769 f- ^^^^ though these, and 

 some others, had spoken of the solubility of water 

 in air, before Dr. Hamilton, yet he was the llrst 

 who treated the subject v.ith precision, or "who 

 applied it systematically to the explanation of 

 meteorological phenomena. This opinion was 

 afterwards adopted by Dr. Hut ton, and exhibit- 

 ed in his ingenious Theory of Rain J, and con- 

 tinued for a number of years to be the popular 

 doctrine. 



In 1786, M. de Luc, of Geneva, published a 

 new theory on this subject §, which has been since 

 general!}^ considered as superseding the doctrine of 

 Hamilton and liutton. Observing that evapora- 

 tion takes place in vacuo, as well as in the open 

 air, M. de Luc rejected the opinion that vapour is 



* Essaj/ on the Ascent of Vapours^ Sec This essay was first 

 read l)efore the Royal Society in 170\5, and was afterwards pub- 

 lished, w ith others, under the title of r/iilosophical Assays, by 

 Hugh Hamiltrm. D.D. IvU.S. 



f Bishop Watson's Chemical Esstn/s, \o],\, p. 31/. 



X Transactions of the Royal Society of Edinburgh, vol. i. 



§ See Rechtrches sur les Modifications de I* Atmosphere, par J, A. 

 de Luc, 8vo, 2 vols, Gene\a, 1/72 ; and also Jdees sur la AJctco" 

 roLy^ie, a more full and bali.-fiicLory ^^ ork, by the same author^ 



irso. 



