viii Atmospheric Phenomena 129 



regions the land and sea-breezes are often not strong enough 

 to reverse the direction of the prevailing winds, and merely 

 alter the strength. On the south-east coasts of the Fiji 

 Islands, for example, the prevailing south-east trade wind 

 is intensified during the day and much reduced at night, 

 while on the north-west coasts the wind is reduced through 

 the day and strengthened at night. Land and sea-breezes are 

 always light on a low flat island or coast ; but when a range 

 of mountains rises near the sea very strong winds are pro- 

 duced, the mountain slope acting like a flue, aiding the 

 ascent of the hot air by day and the descent of cold air by 

 night. On account of the lofty backbone of the Blue 

 Mountains the sea-breeze in Jamaica is the strongest known. 

 185. Monsoons. Over the centre of continents far 

 removed from the ocean the range of air -temperature is 

 greatest, the great dryness ( 164) favouring radiation and 

 producing very high temperatures in summer and very low 

 temperatures in winter. Over the sea the range of tempera- 

 ture is le'ast. The continents by heating the air in summer 

 set up ascending currents which last for months, so that the 

 pressure of the air is greatly lowered, and surface winds blow 

 in toward the continent from the surrounding seas. In 

 winter the air being cooled by the continents produces de- 

 scending currents ; the pressure becomes much higher than 

 that over the less chilled seas, and consequently surface winds 

 blow outward from the continents during the winter months. 

 These winds changing with the seasons are called Monsoons. 

 They are produced exactly like land and sea-breezes, only 

 with a period of a year instead of a day. Just as in the 

 former case, monsoon winds may be too feeble to reverse 

 the direction of the prevailing winds, and may succeed only 

 in modifying their force (see Plate VII.) The monsoon effect 

 of most continents is comparatively insignificant, and is con- 

 fined to a small part of the coast. In the southern continents 

 these winds are slightly developed, because in the widest part 

 of South America and Central Africa the annual range of 

 temperature is very small, and in the narrower part farther 

 south the influence of the vast expanses of the neighbouring 

 oceans predominates all the year round. In Australia the 



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