70 



WIND. 



and stronger, and the north-east weaker, and more 

 easterly. The effect is reversed when he gets to- 

 wards the tropic of Capricorn. The trade-winds 

 would blow regularly round the whole globe with- 

 in the distance of about thirty or forty degrees from 

 the equator each way, if the space within those li- 

 mits were all covered with water ; but the uneven 

 surface and unequal temperature of the land divert 

 und derange them. It is on this account that the 

 trade-winds are constantly experienced only over 

 the open ocean. The larger the expanse of ocean 

 over which they range, the more steadily they blow; 

 thus, in the Pacific, they are commonly more steady 

 than in the Atlantic ocean, and in the South than 

 in the North Atlantic. In sailing from the Cana- 

 ries to Cumana, on the north coast of South Ame- 

 rica, it is hardly necessary to touch the sails of the 

 vessel. The voyage across the Pacific, from Aca- 

 pulco, on the west coast of Mexico, to the Philip- 

 pine islands, is performed with equal facility ; and, 

 if there were a channel through the isthmus of 

 Panama, a westward passage from the Atlantic to 

 China would be more speedy and safe than the 

 usual navigation thither round the cape of Good 

 Hope. The only interruption to the evenness 

 of this voyage would be in the Caribbean sea and 

 the gulf of Mexico, where the trade-wind blows 

 impetuously, and is sometimes interrupted by 

 westerly winds. It would not be possible, how- 

 ever, to return by the same route, because, in 

 sailing east, way must be made to the north- 

 ward, in order to get beyond the region of the 

 trade into that of the variable winds. Both in 

 the Atlantic and in the Pacific ocean, the current 

 of the trade-winds becomes broader, and more di- 

 rectly east in its course, as it advances from one 

 side to the other of those extensive basins. On 

 the west coast of Africa, owing to the rarefaction 

 which the air undergoes over that continent, the 

 wind is mostly turned towards the shore : from 

 cape Bojador to cape Verde, it is generally north- 

 west, and thence to the island of St Thomas, under 

 the equator, it bends gradually, first to the west, 

 and then to the south-west. Along the coasts of 

 Chili and Peru, a south wind prevails. These are 

 two instances of the interruption which the trade- 

 winds experience in the neighbourhood of large 

 masses of land. In the Indian ocean, the south- 

 east trade-wind prevails between 28 and 10 of 

 south latitude, from within a few degrees of the 

 east side of Madagascar, nearly to the coast of New 

 Holland ; but, from the tenth degree of south la- 

 titude to the northern shores of that ocean, the 

 uniformity of the tropical movements of the atmos- 

 phere is destroyed by the monsoons, which belong 

 to the class of periodical winds. These blow half 

 the year from one quarter, and the other half from ' 

 the opposite direction. When they shift, variable 

 winds and violent storms prevail for a time, which 

 render it dangerous to put to sea. They, of course, 

 suffer partial changes in particular places, owing to 

 the form and position of the lands, and to other 

 circumstances; but it will be sufficient to give 

 their general limits and directions. Northward 

 from the third degree of south latitude, a south- 

 west wind blows from April to October ; from 

 October to April, a north-east. These monsoons 

 extend over the China sea ; but here they incline 

 more to the direction of north and south. Between 

 the third and tenth degrees of south latitude, a 

 north-west wind blows from October to April, and 

 a south-east during the other six months of the 



year : the former is seldom steady in the open sea ; 

 but in December and January, it sometimes ex- 

 tends northward a degree or two beyond the equa- 

 tor. These two monsoons have the greatest 

 strength and regularity in tin- .lava sea, and thence 

 eastward towards New Guinea. The facts above 

 exhibited may be thus summed up: From April 

 to October a south-west wind prevails north of 

 the equator ; southward of this, a south-east wind ; 

 from October to April, a north-east wind north 

 of the equator, and a north-west between the equa- 

 tor and 10 of south latitude; south of this, the 

 usual trade-wind, which is in motion through the 

 whole year. In attempting to account for these 

 movements of the atmosphere over the Indian 

 ocean, the first thing which strikes us is, that the 

 north-east and south-east monsoons, which are 

 found the one on the north, and the other on tb<- 

 south side of the equator, are nothing more than 

 the trade-winds blowing for six months, and then 

 succeeded, for the remainder of the year, by winds 

 directly opposite. It is also to be noticed that the 

 south-west monsoon in the northern, and the north- 

 west monsoon in the southern hemisphere, each 

 prevails while the sun is perpendicular to their 

 respective regions. They are, therefore, connected 

 with the immediate presence of that luminary. If 

 the Indian ocean were not bounded, as it is, by 

 land on the north, the trade-winds would blow 

 over it (at least in the central parts) as they do 

 in the Atlantic and Pacific oceans. But it is well 

 known that water, owing to its transparency, is 

 very little warmed by the sun's rays, whereas 

 the land is powerfully heated by them ; conse- 

 quently, when the sun is between the equator and 

 the tropic of Cancer, India, Siam, and the adja- 

 cent countries, become much hotter than the ocean; 

 the air over them is rarefied, and ascends : colder 

 air then rushes in from the Indian ocean, and a 

 south-west wind is produced. When the sun, how- 

 ever, has crossed to the south of the equator, these 

 countries become gradually cool, and the north- 

 east trade-wind resumes its course. At the same 

 time, the north-west monsoon commences in the 

 southern hemisphere, in consequence of the air 

 over New Holland being rarefied by the presence of 

 the sun. The monsoons in the Red sea blow in 

 the direction of the shores; and a similar effect is 

 observed in the Mozambique channel, between 

 Africa and Madagascar, where these winds follow 

 the line of the channel. On the coast of Brazil, 

 between cape St Augustine and the island of St 

 Catharine, and in the bay of Panama, on the west 

 of the isthmus of that name, periodical winds occur 

 somewhat similar to the monsoons of Asia. The 

 land and sea-breezes, which are common on coasts 

 and islands situated between the tropics, are ano- 

 ther kind of periodical winds. During the day, 

 the air over the land is strongly heated by the sun, 

 and a cool breeze sets in from the sea ; but, in the 

 night, the atmosphere over the land is cooled, while 

 the sea, and, consequently, the air over it, retains 

 a temperature nearly even at all times; accordingly, 

 after sunset, a land-breeze blows off the shore. 

 The sea-breeze generally sets in about ten in the 

 forenoon, and lasts till six in the evening. At se- 

 ven, the land-breeze begins, and continues till eight 

 in the morning, when it dies away. These alter- 

 nate breezes are, perhaps, felt more powerfully on 

 the coast of Malabar than elsewhere. Their effect 

 there extends to a distance of twenty leagues from 

 the land. During summer, the sea-breeze is very 



