IS 



ON SPONTANEOUS EVAPOHATION. 



and as it cannot be published entire, I have thought I 

 should gratify the levers of natural philosophy, if I ex- 

 tracted from it what relates to the relation between evapo- 

 ration and heat, giving it in as concise a form as possible. 

 !<: evaporation Before I entered into the particular investigation of the 



proportioiidl to clianges, which the state of the air occasions in evaporation, 



tliosuitace ex- » ' 



posed :>iini)ly ? I thought it would be right to examine the general law, 



which it follows in all cases, and endeavour to decide the 

 grand question, whether, as most philosophers think, eva- 

 poration be proportional to the extent of surface of the wa- 

 ter in contact with the air; or whether it depend also on 

 some function of the other dimensions of the body of water 

 exposed to evaporation, as Muschenbroeck * and Cotef 

 assert. 



*fiult!r .-.■imilar With this view I have made a number of experiments; 



• irrumstaiices ^^jj^ after having varied them in all ways, I have constantly 

 found, that, under similar circumstances, evaporation is pre- 

 cisely proportional to the extent of the surface of the water 

 in contact with the air. I found too, that, when these two 

 gentlemen imagined they had observed the existence of 

 another law, it was because, from the arrangement of the 

 vessels employed in their experiments, the water contained 

 in them was heated and cooled unequally, whence arose 

 accidental variations of the evaporation, concealing the true 

 luw; and which would not have taken place, if these vessels 

 had been placed in air of a constantly uniform temperature, 

 or if they had been surrounded with a large body of earth, 

 or some other substance, as Mr. Sedilleau long ago ob- 

 served +. 



^feasllrcof When we find, that evaporation, under similar circura- 



T.nporation. stances, is proportional to the surfaces, we require nothing 

 more, to express its measure, than the number of lines the 

 surface of the water is lowered by this evaporation in a giveir 

 time. For this time I have taken four and twenty hours, 

 or one day. 



• Essays on the Experiment., of the Academy del Cimento, Tome I 

 •f the Academical CoUeciion, part. etr. p, 142. 



f Journ. de Physique, vol. XVIII, p. 30G. 



X Anc, Mem. UerAcad. des Sciences, torn. X, p, 33. 



The 



