IJJB 



METEOROLOGY. 



[STOKMS, ETC. 



of the trade wind is various. In the Atlantic it prevails 

 . 8 to 28 or 30", but in tliu Pacific only to 25N.L. 

 In the southern hemisphere, the extent of ihe tiade wind 

 has been leas accurately determined. When first tlie 

 phenomena of trade wind* were noticed by Columbus 

 and his associate*, they caused the greatest consternation. 

 Accustomed to the fluctuating and irregular breezes of 

 Kurope, they regarded the continuance of a wind from 

 the east as emblematic of their perpetual banishment 

 from their native shores. The early Spanish navigators, 

 however, very soon learned to appreciate the value of 

 trade winds, by the aid of which treasure-laden 

 galleons could, setting out from Acapulco, manage to 

 arrive at Manilla almost without changing a sail. 



As respect* the upper current proceeding from the 

 equator to either pole, it varies, as might be anticipated, 

 in diilorent li>calities. Travellers, who have ascend.,! 

 the Peak of Teueritle, inform us that this upper current 

 is funnel in that locality, at an elevation of 9,000 feet ; 

 l'iit Humboldt, during his explorations on the Andes, 

 discovered the eastern trade wind to be blowing at an 

 elevation of 8,000 feet above the level of the sea. As the 

 upper or equatorial current loses its heat, its specific 

 gravity becomes greater, and it sinks lower and lower, 

 any well-marked directive tendency. 



On the ocean, and between 30' and 40, there is a 

 prevalence of westerly winds, especially in the southern 

 hemisphere. In the Atlantic this tendency is manifest ; 

 \\iienee it follows, that the voyage from Europe to 

 America occupies more time than a voyage in the reverse 

 direction. It is difficult to say what may be regarded as 

 the prevailing wind in these isles probably, however, a 

 south-western wind, as stated in the following table : 



Tablt representing ihe Relative Prevalence of Winds in 

 i \>u>tirie* for a Period of 1,000 days. 



The direction of winds is found, taking the average of 

 many years, to vary according to the season. In Europe, 

 ("mill winds are more prevalent than any others during 

 winter ; east winds belong more especially to the s] 

 west and north winds to the summer ; and towards 

 October the wind usually veers round to the south. 

 Usually, the wind is more strong in February and March 

 than at any other time ; and at all seasons the wind is 

 usually strongest at noon. 



STORMS. Whenever the air, from any cause, is thrown 

 into violent commotion, the result will be a storm . The 

 philosophy- of storms, notwithstanding the attention 

 which ha* been devoted to the subject, is by no means 

 well understood. In point of fact, the causes of storms 

 are numerous and complex. If we reflect on the agency 

 of temperature on the air, one prevalent cause of storms 

 will at least become manifest. If one portion of the 

 atmosphere be suddenly heated, violent commotion must 

 arise there must follow a storm. The laws of latent 

 heat demonstrate, that whenever water is suddenly con- 

 densed, the surrounding air must be raised in temperature ; 

 and thus we have one of the most frequent local causes of 

 storms. According to modern observations, storms are, 

 for the most part, circular whirlwinds progressing in a 

 north-eastern direction from the south to the north of 

 tlm trupic of Cancer. In proportion as a locality is 

 devoid of mountains and near the sea, so is it more 

 liable to be subject to storms. Perhaps the most violent 

 of all European storms are those which occur in the 

 south of France dating the prevalence of the north-east 

 wind, termed mistral ; but the most violent storms occur 

 in and near the tropics, and are termed tornadoei, 



I trotadoes, hurricane*, typhoons, &o. Hurricanes are 

 essentially tropical ; the Vest Indies sulfur from them 

 i more than any other region. Hurri i > are of \ 

 | occurrence in the \\Yst Indies ; but the inlands of Ti. 

 and Tobago, being protected by mountain <!> unions, 

 usually escape them altogether. The wind, during a 

 hurricane, frequently makes an entire circuit, blowing 

 from every point of the compass ; and it is by no means 

 en unusual occurrence for the wind to cease awhile 

 altogether, and then commence blowing again. IVrliaps 

 the most violent hurricane on record is the one which 

 occurred in 1780. It destroyed the fleet of Lord Uoduoy, 

 and a vast number of merchant ships. It killed r, 

 than 9,000 individuals in Martinique ; 6,000 in St. 

 Lucia ; and did immense damage at other places. 



The eastern, western, and southern coasts of Africa 

 are also subject to storms of almost equal violence with 

 the West Indian hurricanes : these storms, however, in 

 the localities under consideration, are called tornadoes. 

 At Sierra Leone and the adjacent parts, two or three 

 tornadoes usually usher in the dry season ; they are 

 sometimes accompanied with rain, and sometimes with- 

 out : when of the latter kind, they are called white tor- 

 nadoes. 



The term cyclone is now applied to those storms, which 

 ore produced by a rotatory motion of the air. In the 

 Northern Hemisphere, the rotation is contrary to the 

 motion of the hands of a watch ; whilst, in the Southern 

 Hemisphere, it proceeds in the same direction as they 

 move. The knowledge of the nature and motions of 

 cyclones is now so complete, that, in many cases, the 

 navigator, by watching the barometer and the direction 

 of the wind, may so guide his vessel's course as to escape 

 the violence of the storm. It is found, that near the 

 centre, and the circumference of a cyclone, a 

 usually exists, the force of the tempest being produced 

 between those positions. 



Typhoons may be described as hurricanes of the 

 Chinese and Japanese seas ; like hurricanes, they have a 

 rotatory motion, but they are more localised in their 

 action, having no distinct rectilineal progression. 



Hot Winds. Although heat may be regarded as pri- 

 marily the cause of all winds, it does not follow that all 

 winds must be hot ; indeed, we know that the result is 

 the direct opposite that many winds are very cold. 

 The temperature of a wind is for the most part totally 

 independent of the temperature which caused it, and is 

 determined by the nature of the surface over which it 

 blows. The principal hot winds are those denominated 

 the simoom, the harmattan, the chanisin, the sirocco, 

 and the solano. The term simoom, or tamitl, means 

 poisonous, and is derived from a belief of the Arabs, 

 that the devastating effects of this wind are attributable 

 to some poisonous emanation which it bears. There is 

 no foundation, however, for this notion. The terms 

 chamsiu and harmattan, are little else than Egyptian 

 and negro appellations respectively for the simoom. 

 The Egyptian term chamsin means fifty, and has re- 

 ference to the duration of the wind fifty days from 

 April 27th to June 18th. The simoom is the terror of 

 desert caravans. At its approach the horizon grows 

 dark ; the sun's rays scarcely penetrate with lurid gleam 

 the atmosphere charged with particles of burning sand. 

 The wind blows with fitful violence, scattering death and 

 desolation in its track, withering the trees and shrubs 

 which it encounters, suffocating animals, and burying 

 them under waves of sand. The camels no sooner per- 

 ceive the advent of the simoom, than rushing to the 

 nearest tree or bush, or Reeking the spur of some pro- 

 jecting rock, they place their heads in the direction op- 

 posite to which the wind blows, and endeavour to screen 

 themselves from its violence. The traveller throws him- 

 self on the ground on the lee-side of the camel, and 

 screens his head from the fiery blast within the folds of 

 his robe. Too frequently, all these precautions are un- 

 availing, both man and beast falling a prey to the ter- 

 rible simoom. In the western part of Asia, more espe- 

 cially in Arabia, the simoom only blows in the summer 

 months, and with maximum violence in July. It occurs 



