THE WEATHER BUREAU 397 



but this is gradually supplanted b}^ a single lirecze, and later 

 the wind nicreases to a gale, the clouds become matted, the 

 sea rough, rain falls, and the winds are gusty and dangerous as 

 the vortex core comes on. Here is the indescribable tempest, 

 dealing destruction, impressing the imagination with its wild 

 exhibition of the forces of nature, the flashes of lightning, the 

 torrents of rain, the cooler air, all the elements in an uproar, 

 which indicate the close approach of the center. In the midst 

 of this turmoil there is a sudden pause, the winds almost cease, 

 the sky clears; but the waves rage in great turbulence. This 

 is the eye of the storm, the core of the vortex, and it is per- 

 haps, twenty miles in diameter, or one thirtieth of the whole 

 hurricane. The respite is brief, and is soon followed by the 

 abrupt renewal of the violent wind and rain, but now coming 

 from the opposite direction, and the storm passes off with 

 the several features following each other in the reverse order." 

 C3xlones or general storms may be 1,000 miles in diam- 

 eter. Hurricanes operate on a path averaging 600 to 800 

 miles wide. Tornadoes are much smaller. They may be 

 only a mile wide at the top and but a few feet at the 

 bottom, but they are much more dangerous than either a 

 cyclone or a hurricane. They form in all parts of the tem- 

 perate zone — at sea they are water spouts, and on the 

 desert they are sand storms. Sometimes a whole family of 

 tornadoes will be born at once from the same cloud. As 

 man}^ as fifteen tubes have been observed at one time. In 

 winter months they occur only in our gulf states, but in sum- 

 mer they occur in the north, in Nebraska, South Dakota, 

 Iowa and Minnesota. The average is twenty five a year. 

 They are simple examples of vortex motion. A mass of air 

 rotating at a low level runs into a vortex, and a tube is pro- 

 jected downward. The velocity of the lower end of the tube 

 may reach 200 miles an hour, and it is the partial vacuum 

 caused by the whirl and the sudden inrush of the outside air 

 that causes the disastrous explosive effects. Tornadoes 

 wrecked $31,000,000 worth of property in this country dur- 

 ing the years from 1889 to 1896. Twenty three million 

 dollars of this amount was destroyed by three whirls alone. 

 The Louisville tornado, March 27, 1890, destroyed property 



