§ 695-697. MONSOONS. 871 



bound Indiaman, who, wlien on his way to Calcutta, crosses the 

 equator in August, for example, will find the southeast trades, as 

 he approaches the line, to haul more and more to the south. As 

 he advances still farther north they get to the west of south. Fi- 

 nally, he discovers that he has got the regular southwest mon- 

 soons, and that he has passed from the southeast trades into them 

 without any intervening calm. This in summer is the rule ; it 

 has its exceptions, but they are rare. Examining the logs of a 

 number of vessels taken at random for the passage in August, we 

 find, by 421 observations therein recorded, they had the wind 

 thus: 



Southeast from 10" to 5° south calms. 



South " 5° south to equator 3 " 



Southwest " equator to 5° north 3 " 



Southwest " 5° to 10° north " 



695. In like manner, and with like force, Jansen maintains that 

 Lieutenant Jansen. thc uorthwcst mousoou of Australia is the north- 

 east trade-wind turned aside. 



696. The influence exerted upon the winds by the deserts of 

 MonsoonainthePa- Africa and the overheated plains of Asia is felt at 

 "^'^^ sea for a thousand miles or more. Thus, though 

 the desert of Gobi and the sun-burned plains of Asia are, for the 

 most part, north of latitude 30°, their influence, in causing mon- 

 soons (§ 692) is felt south of the equator (Plate VIII.). So, too, 

 with the great desert of Sahara and the African monsoons of the 

 Atlantic; also with the Salt Lake country and the Mexican 

 monsoons on one side, and those of Central America in the Pa- 

 cific on the other. The influence (§ 298) of the deserts of Arabia 

 upon the winds is felt in Austria and other parts of Europe, as 

 the observations of Kriel, Lamont, and others show. So, also, do 

 the islands, such as the Society and Sandwich, that stand far 

 away from any extent of land, have a very singular but marked 

 effect upon the wind. They interfere with the trades very often, 

 and turn them back ; for westerly and equatorial winds are com- 

 mon at both these groups in their winter time. Some hydrogra- 

 phers have even taken those westerly winds of the Society Isl- 

 ands to be an extension of the monsoons of the Indian Ocean. 



697. It is a curious thing is this influence of islands in the 

 trade-wind region upon the winds in the Pacific. Every naviga- 



