Page:Physical Geography of the Sea and its Meteorology.djvu/103

 Rh the Observatory more than a million of observations on the force and direction of the winds at sea. The discussion of such a mass of material has thrown much light upon the circulation of the atmosphere; for, as in the ocean (§ 201), so in the air, there is a regular system of circulation.

204. Different belts of winds.—Before we proceed to describe this system, let us point out the principal belts or bands of wind that actual observation has shown to exist at sea, and which, with more or less distinctness of outline, extend to the land also, and thus encircle the earth. If we imagine a ship to take her departure from Greenland for the South Shetland Islands, she will, between the parallels of 60° north and south, cross these several bands or belts of winds and calms nearly at right angles, and in the following order:—(1.) At setting out she will find herself in the region of south-west winds, or counter-trades of the north—called counter because they blow in the direction whence come the trade-winds of their hemisphere. (2.) After crossing 50°, and until reaching the parallel of 35° N., she finds herself in the belt of westerly winds, a region in which winds from the south-west and winds from the north-west contend for the mastery, and with nearly equal persistency. (3.) Between 35° and 30° she finds herself in a region of variable winds and calms; the winds blowing all around the compass, and averaging about three months from each quarter during the year. Our fancied ship is now in the "horse-latitudes." Hitherto winds with westing in them have been most prevalent; but, crossing the calm belt of Cancer, she reaches latitudes where winds with easting become most prevalent. (4.) Crossing into these, she enters the region of north-east trades, which now become the prevailing winds, until she reaches the parallel of 10° N., and enters the equatorial calm belt, which, like all the other wind-bands, holds fluctuating limits. (5.) Crossing the parallel of 5° N., she enters where the south-east trades are the prevailing winds, and so continue until the parallel of 30° S. is reached. (6.) Here is the calm belt of Capricorn, where, as in that of Cancer (3), she again finds herself in a region of shifting winds, light airs, and calms, and where the winds with westing in them become the prevailing winds. (7.) Between the parallels of 35° and 40° S., the north-west and south-west winds contend with