170 FIRST YEAR SCIENCE 



of which it deposits when made to ascend. These whirls 

 move in a general eastward direction with varying veloc- 

 ities, but averaging about 20 or 30 miles per hour. To 

 these is due the larger part of the rain which falls in 

 middle latitudes. Areas of high pressure in which the 

 air moves spirally downward and outward from the center 



REMAINS OF FARM BUILDINGS DESTROYED BY A TORNADO. 



as has already been stated ( 74) are called anti-cyclones. 

 These are areas of dry, cold weather. 



84. Paths of Cyclonic Storms across the United States. 

 The map on page 173 shows the paths of a large number of 

 cyclonic storms across the United States. It will be seen 

 from this that although these paths vary considerably, yet 

 the general direction is a little north of east. The move- 

 ment of the cyclone is in the direction of the prevailing 

 winds of the middle latitudes. 



In summer time the average rate of motion of "the cy- 

 clone across the continent is about 500 miles per day, 

 while in winter it is 800. The velocity of the wind in the 



