170 



GENERAL SCIENCE 



in all directions (Figure 144). Trees are uprooted and 

 whirled about like feathers. Some of the effects, such as 

 driving straws through pine boards and removing the 

 feathers from chickens, are almost incredible. Such storms 

 move forward at the average rate of about thirty miles 



U. S. Weather Bureau. 

 FIG. 144. A House Wrecked by a Tornado at Binghamton, N. Y. 



an hour, but the rotary speed of the air in the whirls may 

 reach a velocity of 500 miles an hour. 



The centrifugal force of the rapidly whirling mass is 

 sufficient to produce an area of very low pressure. As a 

 tornado passes over a lake or the ocean, a column known 

 as a water spout sometimes forms in the vortex (Figure 

 145) . Some scientists hold the opinion that the water spout 

 is formed by water which is drawn up from the ocean into 

 the vortex of the whirl, while others think that the water 

 comes from the clouds. 



