SCIENTIFIC BALLOON ASCENSIONS VON BEZOLD 307 



value for unstable equilibrium. After the beginning of condensa- 

 tion this limiting value is smaller than in the dry stage." 



(d) "There is no limit of this kind for the cooling, so that the 

 increase of temperature with altitude in the lowest stratum at the 

 time of the so-oalled inversion of temperature can attain values 

 that may amount to many times the greatest possible diminution 

 of temperature for the same differences of altitude. On the twenty- 

 fourth of February, 1891, there was observed a positive gradient 

 of io°, whereas for the negative gradient — i.o° constitutes the limit 

 that can scarcely be exceeded." 



(e) "This difference in the processes of warming and cooling 

 brings about a lowering of the average temperature of the lower 

 strata or a steeper ascent in its lowest portion of the curve of con- 

 dition for temperature." 



(/) "Similar considerations must obtain with reference to the 

 absorption and emission by the atmosphere itself which may be 

 very considerable in the lowest strata as shown by the growth of 

 ground-fog from below upward. Here, then, these processes must 

 also contribute to diminish the rate of diminution of temperature 

 with altitude." 



(g) "Finally it must not be forgotten that at the season of 

 excessive transfer of heat (to the atmosphere) above the surface of 

 water or wet soil, the evaporation also contributes to depress the 

 temperature of the lowest stratum." 



(h) "The masses of air ascending from the ground carry upward 

 with them the heat acquired below (allowing for that which is used 

 in expansion) and that too not only the heat shown thermometrically 

 as they leave the ground, but also that which had been used to 

 evaporate the accompanying water. The heat used for this latter 

 purpose becomes appreciable in the strata in which condensation 

 takes place, where it diminishes the temperature gradient and that 

 too in proportion as the loss of the precipitation is greater; but as 

 sensible heat this first becomes evident in the descending current 

 of air and thus gives rise to that form of transfer of heat that I 

 have called 'complex convection.' " 7 



(i) "Finally, at the greatest altitudes where absorption and emis- 

 sion disappear and almost no aqueous vapor is present, the adia- 

 batic ascent and descent of dry air is the only cause of the change 

 of temperature with altitude." 



7 See von Bezold's 2d memoir translated in Mechanics of the Earth's 

 Atmosphere, 1891, p. 255. — C. A. 



