THE SPECIFIC GRAVITY OF THE SEA, ETC. 217 



from the equator, at a mean temioerature of 81<^, is miicli greater 

 than, according to the same laws, it ought to be. The ob.sei-ved 

 difierence of its specific gravity at 64° and 81° is .0015 ; whereas 

 it ought to be .0025. Now as we approach the equator, the water 

 is wanner, and it shoukl therefore, were it of equal saltness, be 

 proportionably lighter; but instead of the specific gravity of 

 equatorial water being .0025 lighter — as by thermal laws it 

 ought to be — than sea water at the temperature of 01° in latitude 

 34°, it is only .0015. What makes the equatorial water of the 

 sea so much heavier than according to thermal laws it ought to 

 be ? Let us inquire : 



435. An anomaly. — The anomaly is in the trade-wind region, 

 and is best developed (Plate X., Fig. 2) in the North Atlantic, 

 between the parallel of 40° and the equator. Though it is suffi- 

 ciently apparent both in the North and South Pacific {Fig. 1) — it 

 is masked by the Gulf Stream in the North Atlantic — commencing 

 at the polar borders of these winds, the anomaly is developed as 

 you approach the equator. The water grows warmer, but not 

 proportionably lighter : this is in 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 to the increasing warmth of the 

 sea ? 



436. Influence of the trade-winds upon the speciflc gravity of sea 

 ■water. — It is the trade-winds, then, which prevent the thermal 

 and specific gravity curves from conforming with each other in 

 intertropical seas. The water they suck up is fresh water, and 

 the salt it contained, being left behind, is just sufficient to counter- 

 balance, by its weight, the eff'ect of thermal dilatation upon the 

 -specific gi'avity of sea water between the parallels of 34° north 

 ^nd south. As we go from 34° to the equator, the water grows 

 Avarm and expands. It would become lighter, but the trade- 

 winds, by taking up A'apour without salt, make the water Salter, 

 and therefore heavier. The conclusion is, the proportion of salt 

 in sea water, its expansibility between 62° and 82° (for its 

 thermal dilatability varies with its temperature), and the thirst of 

 the trade-winds for vapour are, where the}' blow, so balanced as 

 to produce perfect compensation ; and a more beautiful compen- 

 sation cannot, it appears to me, be found in the mechanism of the 

 universe than that which wo have here stumbled iipon. It is a 

 triple adjustment : the power of the sun to exj^and, the power of 



