RAINS AND HURRICANES. 



477 



the north-western 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. 



At sea, it rains almost daily within the calm belt, rarely within that of the trade 

 winds. On the land within the tropics the rainfall is in many regions enormous. 

 The average annual fall in the most favored parts of the temperate zone is about 40 

 inches; in the tropics it exceeds 100. In some portions it is vastly greater. On the 

 western Ghauts the mean annual quantity is 300 inches. On the Himalayas, Mr. 

 Yule measured 264 inches in the single month of August, of which 150 inches fell in 

 five successive days. Hooker and Thomson measured here 500 inches in seven 

 months ; and during a terrific shower 30 inches fell in four hours, and Castlenau 

 measured the same quantity during a single storm on the Amazon. 



Tornados and hurricanes rage in the Tropical World with a frequency, extent and 

 violence unknown in other climates. They sometimes move with a direct velocity of 

 45 miles an hour ; but the violence and destructiveness of a whirlwind depend less 

 upon the velocity with which the whole storm moves than upon the speed with which 

 the wind whirls around and in upon the center. The great Bahama hurricane of 1866 

 moved forward at the rate of 30 miles an 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 tropical 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 circumference 

 inward ; but at the center the air is in repose. Hence, when the body of the storm 

 passes over a place, the wind begins to blow moderately, and increases to a hurricane 

 as the center of the whirlwind approaches ; then in a moment a dead calm succeeds, 

 suddenly followed by a renewal of the storm in all its violence, but now blowing in a 

 direction opposite to that 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. The progressive motion may continue for days in one 

 direction, while the wind accomplishes many gyrations from every point of the compass. 

 During a part of the course of a storm the wind blows in just the opposite direction 

 from that which the hurricane is taking, just as when a carriage-wheel, and every 

 point of its circumference, is really moving forward, during a part of each revolution 

 any point in the circumference is at the same time moving back with a still greater 

 velocity. 



We have already referred to the insular character of a considerable portion of the 

 Tropical World. Nine-tenths of the islands which dot the ocean lie within the tropics. 

 These islands are divided into two great classes. The one class is of volcanic origin, 

 upheaved from the depths of the ocean ; or, rather, they are peaks of lofty mountains 

 whose sides and base lie deep in the water. There are two opposite theories to 

 account for the existence and present appearance of these islands. According to one 

 theory, a continent once occupied a large part of the Pacific Ocean within the tropics, 



