r, which presses against the retreating side of the great
whirlwind.

In front of the storm the warm and generally moist relatively warm
air, pressing in toward the point of uprise and overlaid by the upper
cold air, is brought into a condition where it tends to form small
subordinate shafts up through which it whirls on the same principle,
but with far greater intensity than the main ascending column. The
reason for the violence of this movement is that the difference in
temperature of the air next the surface and that at the height of a
few thousand feet is great. As might be expected, these local
spinnings are most apt to occur in the season when the air next the
earth is relatively warm, and they are aptest to take place in the
half of the advancing front lying between the east and south, for the
reason that there the highest temperatures and the greatest humidity
are likely to coexist. In that part of the field, during the time when
the storm is advancing from the Rocky Mountains to the Atlantic, a
dozen or more of these spinning uprushes may be produced, though few
of them are likely to be of large size or of great intensity.

The secondary storms of cyclones, such as are above noted, receive the
name of tornadoes. They are frequent and terrible visitations of the
country from northern Texas, Florida, and Alabama to about the line of
the Great Lakes; they are rarely developed in the region west of
central Kansas, and only occasionally do they exhibit much energy in
the region east of the plain-lands of the Ohio Valley. Although known
in other lands, they nowhere, so far as our observations go, exhibit
the paroxysmal intensity which they show in the central portion of the
North American continent. There the air which they affect acquires a
speed of movement and a fury of action unknown in any other
atmospheric disturbances, even in those of the hurricanes.

The observer who has a chance to note from an advantageous position
the development of a tornado observes that in a tolerably still air,
or at least an air unaffected by violent winds--generally in what is
termed a "sultry" state of the atmosphere--the storm clouds in the
distance begin to form a kind of funnel-shaped dependence, which
gradually extends until it appears to touch the earth. As the clouds
are low, this downward-growing column probably in no case is observed
for the height of more than three or four thousand feet. As the funnel
descends, the clo