SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 391 



velocity of 2 meters per second, the precipitation on a base of one square 

 meter in one bour would amount to 33.6 kilograms, corresponding to a 

 deptb of rainfall of 33.G millimeters. This, therefore, would give a rain- 

 fall of greater intensity than has ever yet been observed at Vienna. It 

 is, therefore, certainly not necessary to take refuge in the assumption of 

 a conversion of heat into electricity in order to explain the heaviest rains 

 of thunder-storms by the ascending currents of moist air. 



Wettstein then considers the mixing of warm and colder air. He as- 

 sumes that a cubic meter of air saturated at 25° is mixed with a cubic 

 meter of air also saturated at 0'^; there result 2 cubic meters having, 

 if we at first neglect the latent heat of condensation, a mean tempera- 

 ture of 120.5. These two cubic meters contain 22.83 -f 4.87 = 27.70 

 grams of aqueous vapor ^; but at 12o,5 0. only 21.92 grams can be 

 contained as vapor in 2 cubic meters, therefore 5.78 grams will be con- 

 densed. This condensation liberates a quantity of heat which is suffi- 

 cient to warm the air by 5o.6, so that its temperature rises to 18*^.1. 



At this temperature, however, 2 cubic meters of air can contain 

 30.08 grams of vapor, or more than is contained in the two masses of 

 air together. It follows, thence, that precipitation can also not be pro- 

 duced by mixture. 



Here again we have to do with the same vicious reasoning as in the 

 preceding case.^ In consequence of the warming of the air due to 

 the condensation of vapor, 5.78 grams of the latter will not be con- 

 densed, but less. By trial we easily find that the mixing will bring 

 about a temperature of somewhat less than 140.9 C. ; 2.44 grams of vapor 

 will condense, whose latent heat suffices to raise the temperature of the 

 air by not quite 2^.4 C. above that which would have been given by a 

 mixture of dry air. The case here assumed of the combination of masses 

 of air saturated at 25° and at 0° certainly occurs very seldom in naturej 

 even differences of 10^ in the temperatures of currents of air are not 

 frequent. We assume, however, now the very favorable case of a mix- 

 ture of a saturated stratum of air 1,000 meters deep with a saturated current 

 15° colder throughout its entire extent. In its lower portions, the warm 

 air has a temperature of 25°, its upper portion 20° ; consequently the 

 cold current has, respectively, 10c> and 5^. Since each cubic meter of 

 warm and of cold air mutually interpenetrate each other, there will be 

 condensed from every j^air of cubic meters in the lowest strata about 

 1.0, but in the highest strata 0.8; on the average, therefore 0.9 gram 

 of vapor. This gives for the entire depth of the stratum of air 0.45 

 kilogram of water per square meter, therefore a depth of rainfall of 0.45 

 millimeter. The mixed stratum has now attained a mean temperature 

 of about 10°, but since the cold current continually supplies new masses 

 of air averaging 7^.5 C, the precipitation continues with diminish- 

 ing intensity until the temperature has sunk to 10° at the bottom, but 

 at the top to 5°. The maximum quantityof water that can altogether fall 

 for a cooling of 7^.5 would be about 11.9 kilograms per square meter, 



