438 DISSERTATION on the 



to become eledric, than in any other flate of the atmofphere 'i 

 or, in other words, Why they become, in a more eminent de- 

 gree, ideo-ele(5tric ? 



^dly, Air poflefTes, like the other fluids we call menjrua, the 

 power of diflblving different bodies, efpecially water, which 

 laft procefs we term evaporation ; and, like the other menflrua, 

 this power is modified by the degree of heat it pofTeffes, fo 

 that, cateris paribus, warm air can difTolve, and hold in folu- 

 tion, a much greater quantity of water than cold air. 



4tbij, Suppose that air, heated to a given degree, holds in 

 folution as much water as it is able to difTolve, that is to fay, 

 that it is faturated with it, and it then cools down fo confi- 

 derably, that it cannot hold in folution the fame quantity it 

 did at firft ; there fliould, in that cafe, take place a large pre- 

 cipitation, or a large portion of the diffolved water fhould fe- 

 parate itfelf from the cooled air ; fo that it muft remain 

 charged with a much fmaller quantity than before it lofl its 

 heat. 



Sthly, It follows, then, that the atmofphere is never drier 

 than during great frofl, and never more humid than during 

 great heat ; and this affertion will appear a paradox only to thofe 

 who confound a dry with a drying air, and a wet with a wet- 

 ting air ; or who do not refledl that a dry air may not be of a 

 drying nature, and that a humid atmofphere may not be of a 

 wetting quality. I hope, likewife, nobody will maintain, that 

 the apparent purity, and perfe6l tranfparency of the air, in a 

 fine fummer day, is a proof of its not being charged with he- 

 terogeneous matter, as that tranfparency is only the efFe<5l of a 

 perfedl folution of the water it contains. — It is evident, by the 

 common chemical operations, performed every day, that every 

 perfedt folution is clear and tranfparent, and that when it be- 

 comes turbid, a precipitation is at hand. Let us confirm this 

 fadl. Sir, by a phenomenon we have an opportunity of feeing 

 very often in fummer, viz. that we (ball find the air full of 



broken 



