9 



about this centt^i- moving in a direction contrary to that of Uio hands 

 of a watch. If you will place a circle of card-board on the map of the 

 United States in such a position that the western one-third of the 

 disc rests on the State of South Carolina and the eastern two-thirds 

 rest over the ocean, and then move the disc northeast parallel to the 

 coast, at the same time rotating the disc so that its northern edge 

 moves to the west, you will form a very good idea of the movement of 

 such a storm center and the mnds that circle about it. Such storms 

 may be several hundred miles across. They are called cyclonic or low- 

 area storms. Many of them move across the United States every year 

 coming from west of the ]V[ississippi Eiver and generally moving a lit- 

 tle north of east at the rate of 600 to 900 miles per day. East of the 

 storm center the air is ^varm and moist, frequently rains fall, the 

 winds are from the south aud east and the barometer falls. After the 

 storm center has passed, the weather clears, the air becomes dryer, 

 the temperature falls, winds come from the north and west and the 

 barometer rises. When such storms are accompanied by high winds 

 they are called cyclones or hurricanes. We should distinguish sharply 

 between cyclones and tornadoes. A cyclone is a great storm 200 miles 

 or more wide and its path is often 2,000 miles long. A tornado is a 

 local storm of great violence, 100 to 600 yards wide and from one to 

 50 miles long. It generally has a funnel-shaped cloud that rotates 

 and moves forward in the same way as a low-area storm. The area of 

 greatest violence moves forward from 20 to 50 miles per hour in 

 nearly all cases from southwest to northeast. Tornadoes are asso- 

 ciated with low-area storms. They are likely to occur 200 to 300 

 miles southeast of the low-area, at points where the air is both very 

 warm and very moist. In the lower Missouri and the upper Missis- 

 sippi valleys tornadoes occur more frequently than at any other point 

 in the world. You can determine the direction of a low pressure 

 area very readily. If you stand with the back squarely to the wind, 

 the low area is always to your left. The experiment is easily tried and 

 you can verify it by the observations of the weather bureau which 

 are published in the large daily papers. 



There is another kind of storm which is just the reverse of the low- 

 area of cyclonic storm. In its center is an area of high pressure about 

 which the winds rotate in the same direction as the hands of a watch. 

 It is not a storm in the common meaning of the term since it is asso- 

 ciated with clear, cool, dry weather. It is often called an anti-cyclone. 

 Just as the low-area storm is often associated with the tornado, so the 

 p,nti-cyclone is often associated with the cold wave. This term was 

 coined by the Signal Service and means that the temperature will fall 



