Sect. V.] Meteorologi}. 245 



the solution of water in air, aiul taught that this 

 effect is produced by tlie chemical combination, 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 evaporation, according 

 to the celebrated doctrine of lattiit heat taught 

 by professor Black. He made a number of curi- 

 ous observations and experiments on this subject ; 

 by which he ascertained tiiat water, after its 

 ascent into the atmosphere, does not exist in a sen- 

 sibly hinnicl form; whence he concluded that it 

 passes into a form entirely dilTerent from itself, and 

 probably becomes air. This doctrine is evidently 

 founded on the mutual convertibility of water into 

 air, and the reverse, discovered by Cavendish and 

 some later chemists. The same theory, of the 

 combination of water with heat, was also embraced 

 by M. Lavoisier, and appears to be now the most 

 popular mode of interpreting the phenomenon in 

 question. 



Beside forming and giving to the world this 

 ingenious theory of evaporation, INI. de Luc has 

 also rendered essential service to the science of 

 meteorology by his patient* and persevering ob- 

 servations on the comparative degrees of moisture 

 in the atmosphere in ddferent situations. On this 

 subject he has brought to light a nund)er of facts 

 equally new and interesting. His countryman, M. 

 de Saussure, has also laboured very successfully 

 in the same field of inquiry*; and though not al- 

 ways with an entire coincidence of opinion and 

 result, yet with sufficient agreement on most im- 



* Essai sur rilj/Sf'^ffictrie, 4io. 1/83. 



