46 ANSWERS to the OBJECTIONS 



" la chaleur de l'air, et bientot par-la elles y fubiffent unc 

 " 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 l'air, viennent a 

 " depaffer leur maximum, par Paction d'un air moins chaud 

 " qu'elles ; fi du moins leur production n'eft pas affez rapide, 

 " pour furmonter la caufe de nouvelle evaporation qui nait en 

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



The fubject at prefent under consideration is the evaporation 

 of that vifible mifl 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 inconfiflent with his theory reflecting the condenfation of 

 the fleam. For, if the condenfation of the lleam be the effect 

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

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

 an affignable 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 fleam 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 effect without a caufe, or a caufe producing two oppofite 

 .effects. 



But 



