102 =. S Whitfield on Tornadoes in the Southern States. 
the earth without heating, except slightly, the atmosphere 
through which they pass. The surface warms the air near it, 
while, at the same time, radiation more easily takes place from 
the superior strata, thus reducing the temperature of the upper 
regions. Since air expands and grows lighter with increase of 
temperature, and contracts and becomes heavier from diminished 
heat, it follows that, under this influence, “the atmosphere is | 
in a state of unstable equilibrium, and the lower strata tend con- 
tinually to rise and take the place of the upper.” The ascending — 
air, coming under diminished pressure, expands, and therefore — 
cools, t a variable height, depending on the dew point, or the 
quantity of vapor, the cooling causes condensation or cloud. 
Condensation of vapor sets free latent heat. This liberated 
Owmg og 
to the “ unstable equilibrium,” caused by surface heat and rad | 
‘The lower strata tend continually to rst — 
and take the place of the upper.” Here he has stated the effect 
for the cause. The fact is, that the upper strata tend continually 
to descend and take the place of the lower. : 
Espy, endeavoring to establish a favorite theory, makes the 
quite untenable assertion “that the air of the upper regions 
specifically hotter than the air at the surface ;” which means 
f it means anything, that a pound of air in the upper regions 
contains absolutely more heat at a given pc oleae than 4 
‘Sap at the surface. All this belongs to a philosophy which 
as been long since exploded; and in fact, every sound philoso” 
