Winds in Gambia region. Simooms. the prevalent winds are east and west; in South Bengal, north and south. In the consideration of the prevailing winds of Western Africa, we have to divide the whole western course into three great sections, viz., the first, that portion which lies within the northeastern trade winds, i.e., from lat. 9° north to lat, 14° 44′ north; the second, within the zone of calms, from lat. 3° north to lat. 9° north; and the third, from lat. 3° north to lat. 0-36' 10" south. In the first section, including the Casamanza, the Gambia, and Senegal, the winds divide the year into two portions, exactly as the monsoon of the Indian Ocean. The first commences in October, and terminates in the end of April. During this portion of the year the wind blows from the east and northeast for the most part; occasionally only the sea breeze from the south-west blows in the afternoon. At the commencement of this monsoon, or the breaking up of the south-west monsoon, storms and tornadoes are frequent, and the wind fixes to the east and north-east, when it blows constantly for days from east and south-east by east, which it does in November, December, and January. The wind is dry, cold, and accompanied with thick haze, forming the harmattan, of which we shall hereafter speak. From February to April it blows a hot wind almost constantly from north-east, occasionally interrupted by the sea breeze, which is cool and refreshing. The second portion of the year commences in April, and terminates in October. At this time the prevailing winds are from south-west, west, and north-west; occasionally from north-east. These winds blow through the whole of the rainy season, and are moist, healthy, and pleasant, and are well charged with evaporation from the ocean over which they blow. Their commencement is marked with storms and tornadoes also, but the rains are late and not plentiful. In April and May the simoom blows over this portion of Western Africa. It is exceedingly hot, and destroys vegetation, and blows from every point of the compass. Of its character I shall speak hereafter when writing on the hot season. year, Variable To show how variable the wind is at this time of the I have appended in full the observations on the weather which I made at Macarthy's Island, River Gambia, in May 1866: 1. Strong north wind, varied round the compass in course of day. 3. N., N.E., noon; afternoon and evening, S. W.; night, N.E. 6. N. morning; afternoon, E.S.E.; night, strong S. W. by S. 8. S.W. morning; afternoon, S.; thunder towards S.; tornado, evening, N. and N.E. 9. Very sultry all day; lightning, evening, S. to E. 10. N.E. during the day; strong S. and S.W. at night; lightning, evening, S., N., and W. 11. N.E. morning; evening and night, S.W. 12. Sultry all day. 13. S.W. in the morning; evening, N.E.; heavy rain at night. 14. Light N.E. in morning; evening, strong S.W. 15. S.W. all day. 16. S.W. all day; calm in evening; strong S.W. at night. 17. W. to S.W. during the day; strong N.W. at night. 18. S. to S.W. all day. 19. N. morning; S.W. and S. afternoon and night. 20. N.W. in morning; S.E. afternoon; S.W. night. 21. S.E. all day, very strong; blowing a gentle gale in evening. 22. Strong S.E. all day. 23. S. W. morning; strong N.W. in the afternoon and evening. 24. N.W. morning; N. evening; cloudy all day. 25. Sultry and cloudy all day, S.W. prevalent. 26. Cloudy all day; S.W. by S. blowing gently; a few drops of rain in afternoon. 27. S.W. morning; noon, E.; afternoon, S. W. by S.; evening, N.E. winds. K Sierra Leone region. In the second section, including Sierra Leone, Liberia, Grand Bassam, the Gold Coast, and the Slave Coast (Lagos and other places), we come to the region of variable winds; their predominant direction is in opposition to the general course of the trade winds, and, consequently, in a westerly or south-westerly direction. They are subject to frequent changes both in velocity and direction. The movements of these winds are generally in different strata superimposed one upon the other. The land and sea breezes alternate regularly with each other near the shore of this portion of the continent, the sea breeze setting in between ten and half-past twelve in the forenoon and noon, and continuing till between five and seven; between seven and nine the land breeze commences, and continues till between eight and ten. The blowing of the south-west sea breeze from the quarter where the sun has not yet travelled is a merciful providence of the Creator to keep down the intense heat which must be the result of the sun's action on this zone of calm, as it cools and moistens the air, and makes it fit for habitation both for vegetable and animal life. "The general temperature between midnight and noon is cooler than the temperature from noon to midnight. Towards sunrise it is a cooler time than any other part of the twenty-four hours; and, taken at equal distances from the meridian over which the sun is passing, the quarters over which the sun has passed are more heated than those towards which it has been longest absent." Winds, then, from parts where the sun has passed, as the north-east wind of the first section, are considerably hotter than those from where it is travelling to, as the south-west, the predominant in this zone; and this explains why the Gambia and Senegal are hotter than Sierra Leone, Liberia, and the Gold Coast, although these places are in the hottest zones. I have in the second section, under the headings of remarks, detailed the directions of the various winds found on the coast. As the Gold Coast is the centre of this zone, suffice that I here give its prevailing winds in the different months, as observed by myself,-January, N.E., E.N.E., NW., and W.; February, S.W.-early part, N.E. and E.; March, S. and S.W.; April, W., S., and S.W.; May, S.E., N., N.E., and S.W.; June, S. W. and W.; July, N.W. and W.; August, N.W., W., and S.W.; September, S. W. and N.W.; October, S. and S.W.; November, N.W., W., and S.W.; December, N.W., N.E., E., and S.W. The most prevalent wind, therefore, is from a westerly direction (S.W.); and Freetown being protected in that direction from it by its lofty chain of mountain, stagnation of noxious effluvia, to a certain extent, is the result, and its beneficial influence is lost. The north-east and easterly winds in these regions, blowing just before sunrise, are generally very cool and pleasant. In the third section, including the Gaboons, a part of Lopez region. Fernando Po, Princes' and St Thomas' Islands, the north-west and south-west winds are generally prevalent; but they are not so constant as in the first section, but variable as in the second. The force and velocity of winds are determined by Force of the anemometer. The following is the result obtained by Mr winds. Smeaton, and confirmed by Mr Hutton : velocity of The force of wind is as the square of the velocity by the density. The velocity can be ascertained by taking the square root of 200 times the pressure; the pressure in pounds, or parts of a pound, per square foot, by multiplying the velocity for one hour by 60, and then square the hour velocity, and multiply by 005. The velocity of tropical tornadoes, according to Humboldt, is in its extreme at the rate of 200 or 300 miles an hour. According to Colonel Beaufoy, frequently, in violent storms of wind, the current does not reach any considerable altitude. Often there is perfect calm at the height of 1600 feet. The converse is also true. There are many cases where winds may be noticed at considerable distances above the surface of land or sea, moving with great celerity, whilst the lower strata of the atmosphere is perfectly still and tranquil, as in the account of Hurricane in the Clouds, to be hereafter noticed. Sir H. James, in his "Instruction for Meteorological Observers," gives the following naval terms for expressing the amount of wind. The velocity noted can scarcely be said to be correct : In October 1860 the following daily observations of the direction of the wind were recorded in the Military Hospital of Freetown:— |