in. (757 mm.) at sea-level extends in January from about latitude 7° N. to latitude 25° S., following pretty closely the coast-line in its southern portion, while in the interior lies a nearly oval area of mean pressure below 29.7 in. (754.4 mm.). On the Gold Coast and in the Bight the winds consequently blow from southwest instead of from south-east and north-east; but they blow with great unsteadiness. This unsteadiness is partly due to the irregularity of pressure-distribution on this coast, as is shown on the chart for January. A small area of pressure below 29.8 (757 mm.) occupies Guinea, perhaps due to the resistance of the Cony range (although these hills are only between 2000 and 3000 feet in height) to the lower strata of the north-east winds blowing off the Sahara. But the irregular winds of the Gulf of Guinea are principally due to the great precipitation, especially in thunderstorms, which characterises this district. Here we have, in what would otherwise be the equatorial calm-belt, the deflected south-east Trade, which, having passed over a great oceanic surface, carries an unusual amount of vapour, commingling with air-currents from the north-east. We have therefore here, projecting from the African coast as its base into the Atlantic, a triangular area possessing the characteristics of the equatorial calms in an exaggerated degree. The climate is especially unfavourable to Europeans, and the navigator experiences oppressive calms frequently interrupted by violent squalls in different directions. 132. On the eastern coast of South America, at the same period of the year, we find a very similar area of undesirable weather where the equatorial belt widens out and sultry calms alternate with heavy rainfall. Over the central and southern portions of South America there is an elongated oval of pressure below 29.8 in. (757 mm.), whose major axis lies nearly from the north-east to south-west, but this area is neither so extensive as that characterising South Africa, nor are its central barometric pressures so low. The winds which tend to blow clockwise around it are almost broken by the gigantic chain of the Andes, the largest chain of mountains in the world, which has nothing corresponding to it on the western coast of South Africa. On the north-eastern side of this area the Trades blow nearly from east, and in the valley of the Amazon, in particular, they penetrate as far as 60° W. longitude. Even at this season of the year the equatorial belt narrows towards the western portions both of the Atlantic and Pacific. The south-east Trades preserve to a great extent their direction, except very near to the eastern coast of South America and to the north-eastern coast of Australia. But the north-east Trades on the eastern sides of both oceans acquire a more northerly direction and an increase of force owing to the great areas of high barometric pressure occupying the greater part of North America and of Eastern Asia. The northerly winds in the Gulf of Mexico, the effect of the earth's deflection on which is checked by the land, often blow with great fury, attaining the force of the northerly storm which, as we shall hereafter see, also occupies the western side of the West Indian hurricane; the weather, however, accompanying the former winds belongs chiefly to the high-pressure systems. 133. It will now be convenient to turn our attention to the seasonal change which takes place in a system of winds belonging to the equatorial belt towards the commencement of the summer of the northern hemisphere over the Atlantic and Pacific. It has been already stated that on the Atlantic in the northern winter the north-east Trades scarcely anywhere cross the line owing to the great predominance of land in that hemisphere. A reference to Charts I. and II. will show that in mid-Atlantic no very great seasonal change in this system of winds occurs, but near the continents the changes are considerable. South of the Congo the area of low pressure which characterised the summer season of South Africa has been replaced by an area of high pressure, while north of the line, farther to the north than even latitude 30°, a large area of relatively low pressure, which is in reality a westward extension of the still more remarkable area over the whole of Southern Asia, extends to the western coast - line, and some distance into the Atlantic off Cape Verd. On the northern and western sides of this area the winds under the influence of the earth's rotation move counter-clockwise, and are therefore experienced as north-easters in the northern portion of the Sahara, and as south-westers farther north than Sierra Leone, which station now experiences the detestable character of its wet season. Towards the eastern shores of America, on the other hand, the winds suffer deflection to the northward owing to the low-pressure area which now occupies the southern portion of the United States. This latter area is an elongated oval, whose greatest diameter lies north and south, and whose lowest barometric pressures occupy Utah and Arizona, a little to the south-east of the region occupied by the highest pressure in the northern winter. In the Western Pacific what we have hitherto regarded as the equatorial calm-belt loses its characteristic position by widening out indefinitely to the northward for reasons which we shall presently revert to. 134. We have now to examine the equatorial system of winds between the Pacific and east coast of Africa, that is to say, over the China Seas, the Indian Ocean, the Arabian Sea, etc. In the summer of the southern hemisphere the northern belt of high pressure, which upon a globe of homogeneous surface should lie south of latitude 30°, and which actually does so over the Atlantic and Pacific, is joined to two great poleward extensions of high pressure, the one extending to the high northern latitudes of America, the other, of far vaster extent and intensity, over the Asiatic continent; see Chart I. This latter, with its corresponding low-pressure area in summer, may be regarded as par excellence the great "centre of atmospheric action" in our globe; next to which in importance follow the areas of low pressure occupying in the northern winter the |