54 ANSWERS to the OBJECTIONS 



be produced. Now, the mixture, whether of fleam or moid 

 air, with the open atmofphere, in uniting with fo much air, muft 

 foon be brought to the mofl extreme cafe of this kind, that is, 

 to the greateft inequaUty of the mixed bodies, and to the fmal- 

 lefl: quantity of condenfed vapour. Neverthelefs, according to 

 the rigour of the rule, no portion of warm faturated air can 

 be mixed with cold air in the fame faturated flate, without 

 there being produced a certain quantity of condenfation, which 

 will then remain permanent, fo long as the proper conditions 

 are preferved. In like manner, as two faturated folutions of a 

 faline fubftance, e. g. of nitre, in different temperatures with 

 regard to heat, when mixed and preferved in the fame tempera- 

 ;ture, precipitate a quantity of fait, which is never reaffumed 

 'by the water, unlefs the heat of that fluid be increafed above 

 the medium temperature which the mixture had produced. 

 This laft is a definite and a pradlicable experiment ; the other, 

 with the atmofphere, is an indefinite experiment which cannot 

 be made. And I am furprifed that M. de Luc ftiould not 

 have feen the fubjecSl in the proper light. 



In this cafe of warm and humid air mixing with the colder 

 atmofphere, as for example, the vapours coming out from the 

 vent of a malt-kiln, it is evident to obfervation, that the mill 

 which is delivered into the air difappears only in proportion as 

 it is difperfed in the atmofphere, that is to fay, as it meets with 

 unfaturated air by which it may be diffolved. Now, this diffo- 

 lution is proved by fome other obfervations, which it is ex- 

 tremely eafy to make. Thefe 2X&,firJl, that, ceteris paribus, it re- 

 quires very little difperfion of the mift or vifible vapours in the 

 atmofphere, in order that they may be diffolved when the air 

 is dry ; and that, on the contrary, when it is moift, the vapour 

 continues vifible long after it is fo difperfed. 2(ily, That it re- 

 uires a lefs difference in the temperatures of the two mixed 

 airs to produce a vifible mift, when the atmofphere is moifl 

 than when it is more dry. So far, therefore, as this experiment 



is 



