THE WORLD'S WONDERS. 35 



with the northern monsoon, the dry season with the south- 

 eastern. In South Africa and Australia winter is the rainy 

 season. In South America, in the same latitudes, summer 

 is the rainy season on the eastern side of the Cordilleras, and 

 winter on the western side. 



TORNADOES AND HURRICANES 



rage in the tropical world with a frequency, extent and violence 

 unknown in other climes. They sometimes move with a direct 

 velocity of forty-five miles per hour; but the violence and 

 destructiveness of a whirlwind depends less upon the velocity 

 with which the whole storm moves than upon the speed with 

 which the wind whirls around and in upon the centre. The 

 great Bahama hurricane of 1866 moved forward at the rate of 

 thirty miles per hour ; but the velocity of its whirling motion 

 was from 80 to 100, and for short intervals from 100 to 120 

 miles an hour. The diameter of the great storms of the trop- 

 ical Atlantic is often from 600 to 1,000 miles; those of 

 the Indian Ocean 1,000 to 1,500. These, however, move but 

 slowly. The smaller storms are usually more rapid than the 

 larger ones. 



The revolving motion accounts for the sudden and violent 

 changes observed during hurricanes. In consequence of this 

 rotation the wind blows in opposite directions on each side of 

 the axis of the storm ; the violence increases from the circum- 

 ference inward ; but at the centre the air is in repose. Hence, 

 when the body of a storm passes over a place, the wind begins 

 to blow moderately, and increases to a hurricane as the centre of 

 the whirlwind approaches ; then, in a moment, a dead calm suc- 

 ceeds, followed suddenly by a renewal of the storm in all its 

 violence, but now blowing in a direction opposite to which it had 

 before. From this rotary motion it follows that the direction of 

 the wind at any moment is no indication of the direction which 

 the body of the storm is pursuing. 



Water-spouts and cyclones belong to the same class of phe- 

 nomena as whirlwinds and hurricanes. In fact, water-spouts are 

 but whirlwinds at sea, while the term cyclone is used to distin- 



