Natural History. 1 9 1 



some others, had spoken of the solubility of water' 

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

 who treated the subject with precision, or who ap- 

 plied it systematically to the explanation of mete- 

 orological phenomena. This opinion was after- 

 wards, in substance, adopted by Dr. Hutton, and 

 exhibited in his ingenious Theory of Ram,^ and 

 continued for a nvmiber 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 

 generally considered as superseding the doctrine of 

 Hamilton and Hutton. Observing that eva- 

 poration takes place in vacuo, as well as in the 

 open air, M. De Luc rejected the opinion that 

 vapour is the solution of water in air, and taught 

 that this effect is produced by the chemical cofn- 

 bination, or union of the particles of heat with 

 those of water. Hence he accounted for the great 

 loss of sensible heat, in every process of evapora- 

 tion, according to the celebrated doctrine of latent 

 heat taught by Professor Black. He made a 

 number of curious observations and experiments 

 on this subject, by which he ascertained that 

 water, after this ascent in the atmosphere, does 

 not exist in a sensibly humid form; whence he 

 concluded that it passes into a form entirely dif- 

 ferent from itself, and probably becomes air. This 

 doctrine is evidently founded on the mutual con- 

 vertibility of water into air, and the reverse, dis- 

 covered by Cavendish and some later chemists. 

 The same theory, of the solution of water in heat, 

 was also embraced by M. Lavoisier, and appears 

 to be now the most fashionable mode of inter- 

 preting the phenomenon in question. 



b Transactions of the Royal Society of Edinburgh^ vol. I. 



c See Recherches sur les Modif cations de V Atmosphere^ par J. A. De Lu**. 

 8vo. a vols. Geneva. 1772. And also Idees sur la Mcteorologie^ a more 

 full and satisfactory work, by the same author. 17S6. 



