328 THE PHYSICAL GEOGRAPHY OF THE SEA. 



935. In B, notice the great " Sun Swing" of the winds in Sep- 

 tember, indicating that the change from summer to winter, in that 

 region, is sudden and violent ; from winter to summer, gentle and 

 gradual. 



In some districts of the ocean, more than a thousand observa- 

 tions have been discussed for a single month, whereas, with regard 

 to others, not a single record is to be found in any of the numer- 

 ous log-books at the National Observatory. 



936. Typhoons. — The China Seas are celebrated for their furi- 

 ous gales of wind, known among seamen as typhoons and white 

 squalls. These seas are included on the plate (VIII.) as within 

 the region of the monsoons of the Indian Ocean. But the mon- 

 soons of the China Sea are not five-month monsoons (§ 788) ; 

 they do not prevail from the west of south for more than two or 

 three months. 



937. Plate Y. exhibits the monsoons very clearly in a part ot 

 this sea. In the square between 15° and 20° north, 110° and 

 115° east, there appears to be a system of three monsoons; that 

 is, one from northeast in October, November, December, and Jan- 

 uary ; one from east in March and April, changing in May ; and 

 another from the southward in June, July, and August, changing 

 in September. The great disturber of the atmospheric equilibrium 

 appears to be situated among the arid plains of Asia ; their influ- 

 ence extends to the China Seas, and about the changes of tha 

 monsoons these awful gales, called typhoons and white squalls, are 

 experienced. 



938. In like manner, the Mauritius hurricanes, or the cyclones 

 of the Indian Ocean, occur during the unsettled state of the at- 

 mospheric equihbriura which takes place at that debatable period 

 during the contest between the trade-wind force and the monsoon 

 force (§ 796), and which debatable period occurs at the changing 

 of the monsoon, and before either force has completely gained or 

 lost the ascendency. At this period of the year, the winds, 

 breaking loose from their controlling forces, seem to rage with a 

 fiiry that would break up the very fountains of the deep. 



939. So, too, with the West India hurricanes of the Atlantic. 

 These winds are most apt to occur during the months of August 



