CYCLONES AND TORNADOES. 749 



wind in advance of it will be easterly, blowing off an area of high 

 barometer into the low ; and the barometer will continue to fall. 

 Toward the north of the storm, the wind will be north ; and to the 

 south of it the wind will blow from the south, frequently causing 

 what are known on the Western plains as " sand-storms " ; while, if 

 the storm occurs during the winter season, the wind and snow in the 

 northern portion is called a "blizzard." In the rear of the storm the 

 wind will be westerly, shifting to northwest, frequently blowing a 

 gale ; the barometer will rise and the temperature will fall, sometimes 

 rapidly, and clearing weather will follow. 



Thus it will be observed that the true axis is the " storm-center," 

 and that the storm revolves on this axis as it moves forward in an 

 easterly, northeasterly, or southeasterly direction. This is the true 

 cyclone. It may be only a few hundred miles in diameter, or its in- 

 fluence may be felt from British America to the Gulf of Mexico. It 

 may be accompanied by what are known as local showers or storms ; 

 or the rains may be general, and of several days' duration. The great- 

 est precipitation is frequently in advance of the storm-center, and may 

 be either rain or snow, depending upon the season of the year and 

 the temperature. During the spring and summer months the area of 

 low pressure is usually accompanied by precipitation in the form of 

 local showers, or thunder-storms, of more or less severity, in which 

 case the strongest air-currents move with the local storm-cloud, and 

 are known as simply high winds, sometimes approaching the severity 

 of a hurricane, but seldom extending over any considerable area of 

 territory. 



The true cyclone usually travels from the Rocky Mountains to the 

 Atlantic coast, in nearly a straight line. Sometimes the distance is 

 traversed in four days and nights, exceeding the speed of a railway 

 express-train ; but frequently the progress is slow, and the time re- 

 quired much longer, depending largely upon the atmospheric condi- 

 tions met with in the vicinity of the Great Lakes. 



Frequently, while the wind may be blowing from the southeast or 

 northeast, or between these points, the storm is approaching from an 

 opposite direction, and pushes out its cloudy streamers, or " feelers," 

 hundreds of miles in advance. There is, then, no such thing as a 

 " northeast storm," as far as the interior of this continent is concerned. 



TORNADOES. 



The origin and movement of continental cyclones being under- 

 stood, we naturally turn, next, to the investigation of tornadoes. 

 These seem to occur most frequently in the Western States, and are 

 usually confined to the territory between latitude 35 and 45 north, 

 and longitude 10 and 25 west. They are purely local in effect, al- 

 though their cause may be remote ; always depend upon and fre- 

 quently accompany the meteorological conditions developed during the 



