PNEUMATICS. 315 



426. Hence, if two portions of air, of different 

 temperatures, and both saturated with humidity, be 

 mixed together, a precipitation of humidity must 

 necessarily take place. 



If the abscissae AB, AB' (fig. 28.) be the tempera- 

 tures of two equal portions of air, and the or- 

 dinates BC, B'C' represent the quantities of humi- 

 dity contained in them, the curve CFC', which re- 

 presents the dissolving power, corresponding to dif- 

 ferent temperatures, will be convex toward AB, 

 and will, so far as experiment has shewn, be a lo- 

 garithmic curve. Now if CC' be joined, and if 

 BB' be bisected in D, the perpendicular DE will 

 represent the humidity contained in a given weight 

 of the mixture of the two portions of air, AD the 

 temperature of the mixture, and DF the quantity 

 of humidity which the air of the temperature AD 

 is able to contain. The quantity precipitated from 

 each portion of the air is therefore EF ; so that the 

 whole quantity precipitated is 2 EF. 



In general, if T and t are the temperatures of two 

 equal portions of air, H and h the humidity con- 

 tained in them when saturated, the quantity of hu- 

 midity precipitated from the mixture will be, 



H + h % V H h. 



427. If, therefore, large portions of the atmo- 

 sphere, of different temperatures, and saturated, or 



nearly 



