208 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



column was introduced into the sea-joiunal was, that liydrographers 

 might find in it data for computing the djiiamical force which the 

 sea derives for its currents from the difference in the specific gravity 

 of its Yv^aters in difierent chmes. The Conference held, and rightly 

 held, that a given difference as to specific gravity between the 

 v>'atcr in one part of the sea and the water in another would give 

 rise to certain cm'rents, and that the set and strength of these 

 currents would be the same, whether such difference of specific 

 gravity arose from difference of temperatm^e or difference of salt- 

 ness, or both. 



434. According to Kodgers' observations, the average specific 

 srieriiic gravity of gravity of sca water, as it is taken from the sea on 

 average s.'u water, ^j^g parallels of 34° north and south, at a mean tem- 

 perature of 64°, is just what, according to sahne and thermal laws, 

 it ought to be; but its specific gravity when taken from the 

 equator, at a mean temperature of 81°, is much greater than, 

 according to the same laws, it ought to be. The observed 

 difference 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 warmer, and it should therefore, were it of equal saltness, be 

 proportionably lighter ; but iastead of the specific gravity of equatorial 

 water beiag .0025 lighter — as by thermal laws it ought to be — than 

 sea water at the temperatm-e of 61° in latitude 34°, it is only .0015. 

 What makes the equatorial water of the sea so much heavier than 

 accordiag to thermal laws it ought to be ? Let us inquire : 



435. The anomaly is ui the trade-wind region, and is best de- 

 An anomaly. vclopcd (Plate X., Fig. 2) ia the North Atlantic, 



betvveen 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 GuK Stream in the North Atlantic — commenciag 

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

 Influence of the spccific gravity cmTcs from conforming wdth each 

 thfiecifi?^a?uy otlicr iu intertropical seas. The w^ater they suck up 

 of SUV water. jg fpesh watcr, and the salt it contained, being left 



