The St. Johns herald., 1889-12-19
THE TRApE-WLNps.
Their Cause and Nature Explained In
 Simple Language.

simple Language.
 In order that we may distinctly un- derstand the cause and nature of the trade-winds, it is necessary to bear in mind that the earth in the center Of its circumference, at an equal dis tance from the poles, is divided by 8 line called the equator into two heni- spheres-the northern and the south ern. Across the equator, cutting it obliquely, there passes another great circle called the ecliptic, which de- scribes the path the sun traverses. It extends 231 degrees north and 23l degrees south of the equator, which is the utmost limit the sun traverses; for, when arrived at either of these boundaries, he again seems to return towards the equator. It must be very evident that the region of the earth included within a circle drawn 235 degrees north and 234 south of the equator-which will comprehend tho greatest portion of Africa, consider able part of Asia and America, and many large, fertile and populous isl ands in the East and West Indies will receive constantly the solar rays in direction so little oblique as to cause the most intolerable heat. It is, therefore, called the torrid zone; and the limits at which the sun stops, and appears to retrace his course, have received the name of tropics, or circles of return. This being pre- missed, and it being also remembered that the earth revolves daily, "her silent course advancing" round the sun from west to east, the cause of the trade-winds will be readily under stood.
 The rays of the sun, in it's apparent motion from east to west, rarify the air beneath, and the air so rarifed rises into the higher regions of the at mosphere. While this takes place, the colder air from the adjoining tenn perate zones rushes in to supply its place. But it is from the polar regions north and south that these colder cur rents originally come; and did the earth remain at rest, such would be their obvious direction. Instead of this, however, north of the equator the direction of the trade winds is from the northeast; south of the equator, from the southeast; the cause of which is thus explained:
 The velocity with which the earth revolves is inconsiderable at the poles, but increases as we advance, and is at its maximum at the equator; the winds, 1 in sweeping from the poles, do not ac- quire 8 corresponding velocity with the motion of the earth as they ad- vance towards the equator; therefore, moving more slowly than the earth, they are left behind; so that, to the observer who imagines himself at rest, the air appears to move in direction contrary to the rotation of tho earth. viz, from eastto west.
 The external limits of the trade winds are thirty degrees north and thirty degrees south of the equator; but each limit diminishes as the sun advances to the opposite tropic. The larger the eXpanse of ocean over which they sweep, the more steadily do they blow; accordingly. they are more steady in the Pacific than in the Allan tic, and in the South than in the North Atlantic Ocean. Within the region of the constant trade-winds rain seldom occurs, but it falls abundantly in the adjoining attitudes. The reason is, that rain is produced by the sudden mixture of air of different tempera- lures charged with moisture; but the constant circulation and intermixture of the air from the upper strata of the atmosphere maintains so equal a temperature in these latitutes as not to occasion the condensation of vapOr which is necessary for the production of rain.
 Within the limits of the trade-winds, contrary to what might have been supposed from the latitude, the atmo- sphere is peculiarly cool and refresh ing. The climate of the Sandwich Islands is far more cool than might be supposed, judging from their latitude. To the trade-winds must this alone be attributed; and thus has Nature ren- dered a region, which would otherwise have been parched. arid and uninhab- itable, exuberant in beauty and mag nifcence.-N. Y. Ledger.