CLIMATE. 



295 



2OE.L. ; the west coasts of Europe and Africa; the 3Oth 

 meridian W.L., in the Atlantic Ocean ; and the west coasts of 

 North and South America, projected on the plane of the looth 

 meridian W.L. The latter curve corresponds with remarkable 

 closeness to the mean curve here given. ' It is not intended 

 that these curves should include the rainfall upon meridians on 

 which the distribution in belts is interrupted by continental 

 influences, and by the irregular oblique belts of rain on the east 

 coasts." But it presents an admirable generalization upon 

 which, as a basis, the local disturbances may be studied. 



It will be noted that the maximum of rainfall in the tropi- 

 cal rain-belt lies several degrees to northward of the equator, 

 owing doubtless to the greater land area in the northern hemi- 

 sphere. There is thus, on the whole, a narrower belt of de- 

 ficient rainfall or aridity between the tropical and northern 

 temperate rain-belts, than in the southern hemisphere. The 

 southern temperate rain-belt touches only the extreme ends of 

 South America, Africa and New Zealand; elsewhere on the 

 ocean it has not been sufficiently observed as yet. The zones 

 of rainfall and aridity are, however, known to be subject to 

 seasonal oscillations of several degrees in latitude, owing to 

 the obliquity of the plane of the ecliptic, which shifts its posi- 

 tion upon that of the equator. 



Ocean Currents. Since water as a fluid is subject to the 

 same circulatory motions which cause winds, it is to be ex- 

 pected that ocean currents should exist corresponding to those 

 of the air, as characterized in general above. But as water 

 warms so much more slowly than air, its circulation would be 

 comparatively insensible were it not for the effects produced 

 by the air currents upon the surface of the sea, combined, as 

 in the case of the winds, with the effects of the rotation of the 

 earth. Without going into the details of the ocean currents in 

 the tropics, it may suffice to say that owing partly to the 

 moving and warming effects of winds, partly to the natural 

 circulatory motion of the water, two great warm currents flow 

 from the tropics northward, materially modifying what would 

 otherwise be the climates of the coasts they touch. 



The Gulf Stream. The current most generally known is 

 the Gulf Stream, flowing partly from the Gulf of Mexico and 

 the Caribbean Sea, partly from outside of the same along the 



