THE ATMOSPHERE. 77 



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 imnds. — Before we proceed to describe 

 this system, let us point out the principal belts or bands of wind 

 that actual observ^ation 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 

 ci'ossing 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 iccsting 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 jjarallel of 10° N., and 

 enters the equatorial calm belt, w^hich, 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 



♦ Nautical Monograph, No. 1, 1859. 



