§430, 437. THE SPECIFIC GRAVITY OF THE SEA, ETC. 215 



not proportionably lighter. This is the trade-wind region. These 

 winds evaporate as they go ; but can it be possible that they are 

 so regulated and adjusted, counterpoised and balanced, that the 

 salt which they, by evaporation, leave behind, is just sufficient to 

 counterbalance the dilatation due the increasing warmth of the 

 sea ? It is even so. 



436. It is the trade-winds, then, which prevent the thermal and 

 Influence of the trade- spcclfic gravity curvcs from Conforming with each 

 d?/'graviV^o^f ^s'ea othcr lu intertropical seas. The water they suck up 

 '''^*^^- is fresh water, and the salt it contained, being left 

 behind, is just sufficient to counterbalance, by its weight, the ef- 

 fect of thermal dilatation upon the specific gravity of sea w^ater 

 between the parallels of 84° north and south. As we go from 

 34° to the equator, the water grows warm and expands. It would 

 become lighter, but the trade- winds, by taking up vapor without 

 salt, makes the. water Salter, and therefore heavier. The conclu- 

 sion is, the proportion of salt in sea water, its expansibility be- 

 tween 62° and 82° (for its thermal dilatability varies with its tem- 

 perature), and the thirst of the trade- winds for vapor are, where 

 they blow, so balanced as to produce perfect compensation ; and 

 a more beautiful compensation can not, it appears to me, be found 

 in the mechanism of the universe than that which w^e have here 

 stumbled upon. It is a triple adjustment: the power of the sun 

 to expand, the power of the winds to evaporate, and the quantity 

 of salts in the sea — these are so proportioned and adjusted that 

 when both the wind and the sun have each played with its forces 

 upon the intertropical waters of the ocean, the residuum of heat 

 and of salt should be just such as to balance each other in their 

 effects, and to preserve the aqueous equilibrium of the torrid zone. 



437. Nor are these the only adjustments effected by this ex- 

 compensaiinginflu. q^^isitc Combination of compensations. If all the 

 ^°'=^- intertropical heat of the sun were to pass into the 

 seas upon which it falls, simply raising the temperature of their 

 waters, it would create a thermo-dynamical force in the ocean 

 capable of transporting water scalding hot from the torrid zone, 

 and spreading it, while still in the tepid state, around the poles. 

 The annual evaporation from the trade-wind region of the ocean 

 has been computed, according to the most reliable observations 

 (§ 800), to be as much as 16 feet, which is at the rate of half nn 



