168 



FIRST TEAR SCIENCE 



furious whirling motion is produced. Such storms are 

 called tornadoes. The warm moist air rises rapidly and 

 spreads out into a funnel-shaped cloud with the vertex 

 hanging toward the earth. In the center of the whirl the 



air pressure is much 

 diminished and the ve- 

 locity of the inrushing 

 whirling wind is tre- 

 mendous, being often 

 sufficient to demolish all 

 obstacles in its path. 



The length of the path 

 swept over by a tornado 

 is rarely over thirty or 

 forty miles and the width 

 generally less than a 

 quarter of a mile. The 

 rate of progress in the 

 Mississippi valley is from 

 20 to 50 miles an hour, 

 usually in a northeasterly 

 direction. These storms 

 are often wrongly called 

 cyclones. When storms 

 of this kind occur at sea, 



a water column is formed in the funnel-shaped part of the 

 storm and they then receive the name of waterspouts. 



83. Cyclones. In the belt of westerly winds are found, 

 as has already been noted, large storm areas called cyclones. 

 As the barometric pressure in the center of these areas is 

 lower than that of the surrounding region, they are marked 

 " Low " on the weather maps. Into these low-pressure 

 areas the air from all directions is moving, but on account 

 of the deflection due to the rotation of the earth, the wind 



A TORNADO. 



Notice the funnel-shaped cloud. 



