RELATION OF VAPOUR AND AIR. 561 



the bubbles* (the coat of which he determined to 

 be l-50,000th of an inch thick,) and Hamberger, 

 who maintained the truth to be the adhesion of 

 particles of water to those of air and fire. The 

 latter doctrine had become much more distinct in 

 the author's mind when seven years afterwards 

 (1750) he published his Elementa Phy sices. He 

 then gave the explanation of evaporation in a 

 phrase which has since been adopted, the solution 

 of water in air ; which he conceived to be of the 

 same kind as other chemical solutions. 



This theory of solution was further advocated and 

 developed by Le Roi 4 ; and in his hands assumed a 

 form which has been extensively adopted up to our 

 times, and has, in many instances, tinged the language 

 commonly used. He conceived that air, like other sol- 

 vents, might be saturated; and that when the water 

 was beyond the amount required for saturation, it 

 appeared in a visible form. The saturating quantity 

 was held to depend mainly on warmth and wind. 



This theory was by no means devoid of merit ; 

 for it brought together many of the phenomena, 

 and explained a number of the experiments which 

 Le Roi made. It explained the facts of the trans- 

 parency of vapour, (for perfect solutions are trans- 

 parent,) the precipitation of water by cooling, the 

 disappearance of the visible moisture by warming 

 it again, the increased evaporation by rain and 

 wind ; and other observed phenomena. So far, 

 4 Ac. R. Sc. Paris, 1750. 



VOL. II. O 



