> 
= 
H.. A. Hazen— Tornadoes. 183 
gentle convection currents set: in motion, these will heat the 
next stratum, and so on 
his is the explanation given by Prof. Hann of Vienna, who 
futhermore considers the formation of cumulus cloud in summer 
to be due to the action of vapor immediately at a height where 
the dewpoint is reached, but that no great interchange of air 
. from the lower to the upper atmosphere will take place from 
the action of heat alone. : 
gain, the evaporation and condensation of moisture are 
advanced as important factors; it is stated for example: “ Of 
great importance is the action of vapor, as a great storehouse of 
solar energy, required in the process of its evaporation, gener- 
ally known as ‘latent heat,’” and “condensation is attended 
with the production of just as much heat energy as was lost in 
the process of evaporation.” Admitting for a moment that a 
warm vapor-laden current of air has found its way to some height 
above the earth, where is the evidence that a condensation will 
produce any more forcible effect than would have been noted 
ing would produce any sudden display of 
orce. The fact that efforts at a computation of the probable 
liberation of energy arising from such action have given most 
Iverse results, with even an absolute denial of any sudden 
release of energv, shows that such an hypothesis must be accep- 
ted with caution and should be supported by indubitable prac- 
tical tests, 
on it a storm-center. Through the center of this draw a line 
from southwest to northeast and we shall find on the north- | 
