594 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5 1 



The fictitious gas cannot replace moist air in every respect. The 

 proof that the condensation has no influence on the available kinetic 

 energy, does not exclude the possibility that the proximity of 

 masses of relatively dry air and moist air should favor the origina- 

 tion of a storm. 



Since the available kinetic energy of the system is derived from 

 the buoyancy, therefore any diminution of density by reason of 

 the vapor content of a mass of air operates like an increase of tem- 

 perature. A particle of the fictitious gas remains in stable equilib- 

 rium in dry air, if it has the same temperature as the surrounding 

 air and if the vertical temperature gradient in that air is smaller 

 than X g/R. A particle of saturated moist air, having the same 

 exponential factor X [would not be in stable or neutral equilibrium 

 but unstable and] would rise because of its smaller density. 



In the example of the first analysis §38, if instead of the fictitious 

 gas we had used saturated moist air of the same temperature and 

 pressure, then for the altitudes o and h its densities would have 

 been respectively equal to that of dry air at 7 02 = 307.8° and p 02 = 

 76o mm mercury and that of dry air at T oh = 293.2 and p oh = $co mm 

 mercury. This 3 07. 8° corresponds to a difference of T m — T 01 = i.8° 

 from the value T 01 = 303. o° as there adopted and a difference of 

 3. 2 from the value T h2 = 2go° there computed for the altitude h or a 

 difference of 4.0 from the average temperature of the wholemass 

 of 2 [when it is composed of saturated air instead of the fictitous 

 gas]. Therefore for these two cases the available kinetic energy 

 is in the ratio 15/11 and the velocities V" are larger than in the 

 fictitious gas in the ratio 1.17/1. Or, if we require the velocity V 

 to be the same as before, then we need a smaller different e of tem- 

 perature between dry and moist air, viz., about 8° instead of n°. 

 All this relates to the unusual high temperatures of our examples; 

 for lower temperatures the influence of the moisture on the density 

 will be still smaller. 



§(41) The kinetic energy of a mass of air is derived from its 

 internal energy and from the work done by the force of gravity. 

 In the case of a continuous distribution of density the importance 

 of gravity in the production of great velocities can be concealed, 

 whence we derive the very common belief that the horizontal 

 gradient of pressure produces the storm. But it is now demon- 

 strated that, even when the distribution of pressure at the base is 

 as observed in storms still the horizontal movements of the masses 



