46 ANSWERS to the OBJECTIONS 



" la chaleur de I'air, et bientot par-la elles y fubiflent une 

 " nouvelle evaporation, qui les fait difparoitre de nouveau. 

 " Ainfi ce phenomene rentre dans le cas general, d'une preci- 

 " pitation momentanee, fuivie d'une nouvelle evaporation, 

 " quand des vapeurs, ou pures, ou melees a I'air, viennent a 

 " depafler leur maximum, par I'adlion d'un air moins chaud 

 " qu'elles ; fi du moins leur produdlion n'eft pas aflez rapide, 

 " pour furmonter la caufe de nouvelle evaporation qui nait en 

 " meme terns de la nouvelle chaleur acquife par cet air." 



The fubjedl at prefent under confideration is the evaporation 

 of that vifible mift which is formed by the mixture of the 

 fleam and air ; and it is to be obferved, that the general law of 

 evaporation which M. de Luc attacks, has been invefligated 

 by means of the vifible condenfation of water which had been 

 evaporated. M. de Luc would make it appear, that, upon 

 this occafion of fleam mixed with air, the vifible condenfation 

 in the atmofphere was not formed according to the rule which 

 here is generalized ; becaufe, fays he, that water is again eva- 

 porated by means of the heat which the fleam had communi- 

 cated to the air. 



But this explanation which M. de Luc has offered to ac- 

 count for the evaporation again of the vifible mifl, appears to 

 be inconfiftent with his theory refpedling the condenfation of 

 the fleam. For, if the condenfation of the fleam be the effe^fl 

 of its being cooled by the air, while the air is neceffarily heated, 

 by it, How could the former flate of things be reflored without 

 an afCgnable reafon, or any known caufe ? that is to fay. How 

 could the air reflore to the water that heat which it had re- 

 ceived by communicating with the fleam ? or. How could the 

 condenfed fteam receive from the air any heat, or rob it of that 

 portion of heat which it had before imparted, and which is now 

 neceffarily required for its evaporation ? Here, furely, would be 

 an effedl without a caufe, or a caufe producing two oppofite 

 ^effe^ls. 



But 



