STORMS. 97

 

 

As the inblowing winds come near the heated
area, they must blow with increased violence in
order to permit the same quantity of air to pass
over the constantly narrowing path.

Besides the rotary motion of the wind, the
storm moves or progresses over a parabolic path,
which in the tropics is generally toward the west,
and in the temperate zones toward the east. This
progressive motion of the storm is like'the similar

 

   
   
 
  

July to October.

Q5° “
30° “
35°
40° «

45° “ce

 

  

Fig. 88. Chart showing Path and Direction of Cyclone.

motion often noticed in a rapidly spinning top.
It is due to the combined influences of the inrush
of air, the earth’s rotation, and centrifugal force.

257. Peculiarities of Cyclones.—Cyclones rage
most furiously in the neighborhood of islands and
along the coasts of continents. They are most
powerful near their origin. As they advance the
spiral increases in size and the fury of the wind
gradually diminishes, because the amount of moist-
ure in the air is less. The rotary motion varies

 

  

 

 

from 80 to 100 miles an hour. The progressive
motion of the calm centre is more moderate—
from 20 to 50 miles an hour. This progressive
motion is least in the tropics and greatest in the
temperate regions.

The wind invariably rotates in the same direc-
tion in each hemisphere; in the northern, it ro-
tates from right to left, or in the direction oppo-
site to that of the hands of a watch ; in the south-
ern, from left to right, or in the same direction as
the hands of a watch. The cause of the regu-

NORTHERN HEMISPHERE,

°%,
te,

0
x +
2 Yor 0} yoo¥

SOUTHERN HEMISPHERE.

R,
Rag,
°

burn ous e

 

x
40 Suan 04 ae
“Pig, 89, Cause of the Rotation of the Wind,

larity of rotation is seen, from an inspection of
Fig. 89, tb, be due to the rotation of the earth.
The wind, blowing in from all sides toward the
heated area, is so deflected by the rotary motion
of the earth as to move in vast circles, from right
to left in the northern hemisphere, and from left
to right in the southern.

The force of the wind in these storms is tremendous.
So furiously does the wind lash the water that its tem-
perature is often sensibly raised by the friction.

The intelligent navigator always endeavors to avoid the
centre of the storm, since it is the most dangerous part.
This he can do by remembering the direction of the rota-
tion of the wind in the hemisphere he may be in; for if,
in the northern hemisphere, he stands so that the wind
blows directly in his face, the calm centre is on his right,
while in the southern hemisphere #¢ és on his left; and in-
stead of running with the storm, hoping to outsail it, he
will boldly steer toward its circumference.

258. Tornadoes and Whirlwinds are the same
as cyclones, except that they are more limited in
area. Their violence, however, often exceeds that