THE GULF STREAM. 37 



water there than the winds take up again ; and these are the re- 

 gions in which the Gulf Stream enters the Atlantic. 



33. Along the shores of India, where experiments have been 

 carofully made, the evaporation from the sea amounts to three 

 fourths of an inch daily. Suppose it in the trade- wind region of 

 the Atlantic to amount to only half an inch, that would give an 

 annual evaporation of fifteen feet. In the process of evaporation 

 from the sea, fresh water only is taken up, the salts are left behind. 



Now a layer of sea water fifteen feet deep, and as broad as the 

 trade-wind belts of the Atlantic, and reaching across the ocean, 

 contains an immense amount of salts. 



34. The great equatorial current (Plate VI.) which sweeps from 

 the shores of Africa across the Atlantic into the Caribbean Sea is 

 a sui-face cun-ent ; and may it not bear into that sea a large por- 

 tion of those waters that have satisfied the thirsty trade-winds 

 with saltless vapor ? If so — and it probably does — have we not 

 detected here the foot-prints of an agent that does tend to make 

 the waters of the Caribbean Sea Salter, and therefore heavier than 

 the average of sea water at a given temperature ? 



It is immaterial, so far as the correctness of the principle upon 

 which this reasoning depends is concerned, whether the annual 

 evaporation from the trade- wind regions of the Atlantic be fifteen, 

 ten, or five feet. The layer of water, whatever be its thickness, 

 that is evaporated from this part of the ocean, is not all poured 

 back by the clouds in the same place whence it came. But they 

 take it and pour it down in showers upon the extra-tropical regions 

 of the earth — on the land as well as in the sea — and on the land 

 more water is let down than is taken up into the clouds again. 

 The rest sinks down through the soil to feed the springs, and re- 

 turn through the rivers to the sea. Suppose the excess of precip- 

 itation in these extra-tropical regions of the sea to amount to but 

 twelve inches, or even to but two — it is twelve inches or two inch- 

 es, as the case may be, of fresh water added to the sea in those 

 parts, and which therefore tends to lessen the specific gravity of 

 sea water there to that extent, and to produce a double effect, for 

 the simple reason that what is taken from one scale, by being put 

 into the other, doubles the difference. 



