Of M. BE LUC 55 



is practicable, I think we may be allowed to fay that natural 

 appearances confirm our theory. 



Long before writing the Theory of Rain which is now in 

 queftion, 1 had afcertained the diffolution of nitre in water, to 

 proceed, not uniformly with the heat, but in a rate that was 

 increafing. I had alfo accurately meafured feveral of the ordi- 

 nates of the curve which this progrefs formed, by carefully 

 evaporating folutions faturated in different degrees of heat ; 

 and I had once fome thoughts of corroborating the proportion, 

 with regard to the rule of vapour by the meafured curve, with 

 regard to the folution of nitre. But as fuch analogical reafon- 

 ing in phyfics is only proper to lead to conjecture ; and as, in 

 the cafe of vapour, we find the moft direct proof that the rule 

 is to increafe at a growing rate with the heat, I gave nothing in 

 my paper but what was necefTary to afcertain the principle fo 

 far inveftigated. M. de Luc has indeed difputed it; but any 

 perfon who has read his later publications, will hardly expect, 

 that, with his meteorological ideas, our author mould, on this 

 occafion, be altogether free of partiality. 



Having thus anfwered every objection which M. de Luc 

 has made, it may be proper farther to obferve, that it was 

 not for want of other examples to eftablilh- the principle of 

 heat and evaporation, that I confined myfelf to thofe which 

 M. de Luc has now difputed. I confidered them as all un- 

 exceptionable, and as perfectly in point. I therefore thought 

 them fufEcient to eftablim the truth of the propofition which 

 had been affumed. I might have referred to the mift formed 

 in a fummer evening upon meadows heated by the fun during 

 the day, and evaporating humidity when the air grows cool; 

 as alfo, to the vifible fmoak, in the winter feafon, from the 

 furface of water, a degree or two only above the freezing 

 point, when the atmofphere upon that furface is about 15 ° 

 colder. In like manner, I might have cited the experiments 



wherein 



