oes ote Cie ae ee a Ee yee ene 
W. Ferrel—Cyclones, Tornadoes and Waterspouts. 43 
basin, give rise to gyrations around the central point toward 
which the air from all sides flows. When these gyrations com- 
mence above, as they usually do, since the air there is most 
frequently in the state of unstable equilibrium, they gradu- 
ally extend downward for the gyrations cause a great diminu- 
tion of tension and of density, and the air consequently in the 
center rushes up with great velocity and that below of the still 
unagitated strata is drawn in to supply its place, which like- 
wise runs into gyrations around the center, so that the gyra- 
tions in a very short time extend down to the earth’s surface. 
The whole column of gyrating air is like a tall flue containing 
very rarefied air, the centrifugal force of the gyrations acting 
us a barrier to prevent the inflow of air from all sides into the 
interior, and if the gyrations at the earth’s surface were as rapid 
s those above, it would be similar to such a flue with all the 
diminished on account of the friction at the surface, and this 
motion of the air, near the surface, is more nearly radial, or at 
least very much inclined inward from the direction of the tan- 
ie It is the same somewhat in the case of large cyclones. 
is much greater than it is at a moderate elevation above, and 
overcome the greater must be this radial component, and where 
there is little friction this radial component is very small and 
the gyrations nearly circular. ; 
Where the air near the earth’s surface is nearly saturated 
with moisture it has to ascend to only a very moderate altitude, 
at the outer border of the tornado, to have its tension and 
temperature so reduced that the vapor is condensed into cloud, 
and nearer the center, where the tension is diminished by the 
centrifugal force of the gyrations, the stratum in which conden- 
sation and cloud-formation commences is brought down to the 
case a considerable area of the earth’s surface in the central 
part of the tornado is covered with dense cloud and enveloped 
in darkness. The indrawing, gyratory and ascensional currents 
