M 





WIND. 





winds, KuiU. in his ' Manual of Meteorology,' remark.. " In Uie space 

 between the two trade-winds the ir U beated to the highest degree. 

 There the ascending current* uf air are the inot rapid ; and by this 

 quick ascent the velocity of the wind blowing along the surface of the 

 ea it greatly diminished. Beaides it would aeem that the upper and 

 lower current of the air come into contact with one another at a com- 

 paratively small elevation above the surface of the globe. Theae two 

 circumstance* appear to be the reason why no regular winds are met 

 with v> iihiu the region of the caluw." 



We ni'W proceed to review the actual and local phenomena of these 

 winds. Two currents of air are fuiind within their limit*, of v. lu. h 

 the lower runs to the south-west, north of the equator, and to the 

 uorth-west, south of it, and the upper in the opposite direction. In 

 this manner a kind of atmospherical circulation is formed, which is 

 admirably adapted for the preservation of animal life. The existence 

 of this counter-current uf air in the upper regions had only been 

 inferred from the theory, and nothing could be adduced to prove it, 

 except that within the trade-winds the clouds, which rarely make their 

 appearance in this region, generally take a direction which corresponds 

 to that of the supposed current of air. But in 1812 an event took 

 place which was rather more decisive in favour of the theory. In the 

 eruption of the volcano of St. Vincent, considerable quantities of ashes 

 and other volcanic matter descended on and spread over the island of 

 Barladoea. This event certainly excited a high degree of surprise, as 

 in this part of the Caribbean Sea the trade-wind always blows with a 

 considerable force, so that vessels sailing from St. Vincent to Barbadoes 

 arj obliged to make a circuitous course of some hundred miles to reach 

 the place of their destination. It con hardly be questioned that the 

 volcanic matter was raised, by the eruption of the volcano, to such on 

 elevation that it reached the counter-current, which, blowing from the 

 west, carried it to Barbadoes. Humboldt adduces also, in support of 

 the theory, the strong south-western wind which he experienced at the 

 top of the Peak of Tenerilfe, whilst all the other parts of the isldhds 

 were under the sway of the trade-wind ; and this observation is also 

 confirmed by Glass, who, in hia ' History of the Canary Islands,' states 

 that during the trade-winds the most elevated parts of those islands 

 experience a continual westerly wind, which blows with considerable 

 force. Confirmatory facts on this point, as observed by Professor C. 

 1'iazzi Smyth, will bo found at the end of the article Ci.oi'n. Lastly, 

 we may adduce, in corroboration of the theory, the instantaneous 

 change of wind which is frequently experienced when the limiU of the 

 trade-winds are passed. 



It has been already observed that the boundary of the trade-winds 

 towards the nearest polo does not always occur in the same part of the 

 ocean, but changes with the seasons. The difference is considerable. 

 At the greatest southern declination of the sun, in December and Janu- 

 ary, the northern boundary of the north-east trade-wind of the Atlantic 

 occurs to the south of 25 N. lat, whilst in the opposite season, from 

 June to September, it occurs about '.',>." N. 1,-it. Thus we find a tract 

 of sea, seven degrees of latitude in width, which is alternately exposed 

 to the sway of the trade-winds and of variable winds, and n< arly in the 

 middle uf this tract the Canaries are situated. These islands, there- 

 fore, are within the trade-winds for six months, and for the remainder 

 of the year without them. Von Buch, in hia description of these 

 islands, has given an account of the regular manner in which the 

 trade- wind advances towards the north, with the progress of the sun 

 in the northern hemisphere, and in which it recedes when the sun 

 IHIMCS the equator on his return to the southern hemisphere, observing 

 that the south-western wind, which is always found in the upper 

 regions of the atmosphere above the trade-winds, does not make its 

 appearance on the south, as may be inferred from the direction in 

 which it blows, but is first experienced at Madeira, whence it gradually 

 advances to TencriUe and the other Canaries. Whilst this south- 

 western wind advances from north to south, it also descends by degrees 

 from the upper to the lower regions, and to the surface of the globe. 

 On TencriUe this takes place in October, when the south-west wind is 

 experienced on all mountains COOO feet high, but generally on. 

 panes, and sometimes several weeks, before the couth-western wind 

 inks to the level of the Ma. 



The trade-winds are only met with on the sea; but in some coun- 

 tries of the globe between the tropics, or near them, regular and 

 constant easterly winds occur, which m;iy owe then- origin to the some 

 cause. These winds only occur in extensive level plain.-, where there 

 is nothing to break their force or to change their direction ; for if the 

 wind conies in contact with high land or mountains, its regular pro- 

 gress U obstructed, licit I.V..T a considerable tract of low level land the 

 wind paw** without being much changed in its direction and velocity, 

 particularly if the land be barren and destitute of moisture. In the 

 Sahel, or western part of the Sahara, an easterly wind blows all the 

 year round with great force, but in the eastern district of the Great Desert 

 it is lea* constant and lens violent, so that in all respect* it may be 

 compared with a trade wind. An easterly wind is also alway 

 on the plain drained by the Amazonas; and by it* assistance the 

 voyage against the strong current of the river may be accomplished 

 nearly in the same time as the voyage downward* by means of the 

 current Humboldt found that this easterly wind, which, near the 

 mouth of the Amazonas is moderate, has acquired such a force at the 

 base of the Andes, that it is almost impossible to keep one's footing 



against it. A similar easterly wind, though of less strength, u found 

 in the great plain which is traversed by the lower course 



i :.-, 



The countries just mentioned, in which these easterly winds blow 

 constantly, are contiguous to those parts of the Atlantic Ocean 

 trade-winds in general ore regular all the year round. I'.nt the trade- 

 winds of the ocean and the laud-winds of the plains do not come into 

 contact with one another. They are separated by a tract of tl.. 

 in which other winds prevail. This tract lies within the ocean, and 

 extends along the coasts of the continents; its width varies greatly. 

 Where it lies east of the trade-wind it is usually a hundred mile- 

 but it is of inconsiderable breadth when the hind lies to the west of 

 the trade-winds. The continuity of the easterly winds < 

 interrupted liy the difference of the temperature of the air incir 

 on the sea and on the land. This difference changes with the seasons, 

 the air over the land being hotter than that of the sea when the sun is 

 near, and colder when it is far oil', llcncc it follows that during the 

 first period the v. ind blows from the sea to the land, and in the second 

 from the land to the sea. Thus a kind of monsoon is produced 

 the coasts of the continents, even within the region of the trade-winds. 

 ,A large island in such a situation is therefore sun., v <! 1 \ 

 blowing from all quarter.*. When the land of Australia is hen 

 the presence of the sun in the southern hemisphere, the wind gi -m -i illy 

 blows from the westward upon the north-western coast, and from the 

 south-wc.-t, upon the western coast; from the south-west, south, and 

 south-east on the southern eoa-t : and from the south-east and east 

 upon the east coast. In the opposite season, however, the winds are 

 less regular, because the greatest part of the island is then without the 

 reach of the trade-winds. 



The trade-winds occur on both sides of the equator in the Atlantic 

 and Pacific oceans, but they vary considerably in extent and f< 

 both oceans. Some account of this difference is given under the heads 

 of ATLAXIKJ OCKAX and l'\ ,x, in GKOG. Div. \\ 



here add, respecting the last-mentioned sea, that the trade, v,. 

 the southern parts appear to be subject to great changes in dii 

 and force, and that they properly occur only along the coasts of 

 America, where a constant south-easterly wind is met with at t: 

 tance of 500 to 600 miles from the coast : but in the middle of th 

 Southern Pacific the trade-wind seems by no means regular and con* 

 utaut. Admiral Fitzroy, in speaking of the Paamuto Islands, or the. 

 Dangerous Archipelago of the Low Islands, says that among them a 

 steady south-easterly trade-wind prevails from March to October, but 

 that in the rainy season, from October to March, westerly v ind*, 

 squalls, and rains are frequent; and in the abstract of 1 

 logical journal we find that in running from the Galapagos to i > 

 he experienced only south-eastern winds near the equator; and that in 

 the remainder of his voyage the wind blew almost constantly from the 

 north-east, north-north-east, or north-east by east. Kotzebuc. 

 first voyage, observed it as a remarkable circumstut 

 Easter Island and 14 51' S. lat. he met only with winds l.lowim- 

 north, north-east, and east-north-east. This anomaly in the trade- 

 winds of the Southern Pacific is probably produced by the innum. 

 islands and coral rocks which cover that ocean between the equator 

 and the southern tropic, and extend from 130 W. long, to the coast of 

 Australia. Horsburgh says, probably from his own observation, that 

 " where shoal coral-banks shoot up out of the deep water in m my 

 places between the tropics, a decrease of the prevailing wind is fre- 

 quently experienced ; for when a steady wind is blowing over t! 

 face of the deep water, no sooner does a ship get upon th' 

 shoal coral-bank than a sudden decrease of the wind is . .;: n pe: 

 This is, in his opinion, occasioned by the atmosphere hanks 



being less rarefied by the increased evaporation than thai over the 

 deep water, and consequently not requiring so great a supply of 

 restore the equilibrium as the circumjacent parts, which arc morn 

 rarefied and heated." When .such effects, according to the stat 

 of this intelligent hydrographer, are produced by single coral-bunks in 

 the midst of the ocean, we may easily comprehend that t ) 

 and immense extent in the Southern Pacific not only diminish their 

 foroe, but change the direction of the trade- winds, and that 

 and islands affect them nearly to the same extent as a Large continent. 

 It appears that in the Southern Pacific the trade-winds are rcplu< 

 the north-eastern, northern, and western winds only during the | 

 when the sun is in the southern hemisphere. A south-eastern trade- 

 wind prevails also in the Indian Ocean from within a feu 

 the eastern side of Madagascar nearly to the coasts > 



a the parallels of 10 and 23" S. Lit. ; but in this ocean from 

 10 S. lat. to the coasts of Hindustan the winds are periodical ; the 

 influence of the land issuing in a complete reversal of the north-east 

 trade during a considerable portion of the year, and the production of 

 MOXHOONS, that is of winds which blow half the year in one, and tin; 

 other half in the contrary direction, as explained at length in the 



'I to them. 



Kven very limited local movements of the atmosphere are modified 

 by the same cause. It is a remark as old as Bacon, and afterwards 

 confirmed by Mariotte in France, Sturm in Germany, and Toaldo in 

 Italy, and since by " many other writers both in Europe and North 

 America, that the wind has a decidedly preponderating tend, 

 veer round the compass according to the sun's motion, that is, to pass 



