210 THE PHYSICAL GEOGRAPHY OF THE SEA. 



the mysterious heavings of its green waters, lent their charm to 

 the scene. They suggested fancied myths, and kindled in the ar-' 

 dent imagination of the daring mariners many longings. The 

 temperature of its waters was only 36° ! Such warm water could 

 get there from the south only as a current far down in the depths 

 below. The bottom of the ice of this eighty miles of barrier was 

 no doubt many — perhaps hundreds of — feet below the surface 

 level. Under this ice there was also doubtless water above the 

 freezing point. 



430. Nor need the presence of warm water within the arctic 

 Undercurrents change Circle cxcitc surprisc, whcn wc recollcct that the 

 temperature slowly, ^^^d watcrs of the frigid zouc are transferred to 

 the torrid without changing their temperature perhaps more than 

 7° or 8° by the way. This transfer of cold waters for a part of 

 the way may take place on the surface, and until the polar flow 

 (§ 89) dips down and becomes submarine. At any rate, officers 

 on the Coast Survey have found water at the bottom of the Gulf 

 Stream, in latitude 25° 30' IST., as low in temperature as 35°. 

 Now, if water flowing out of the polar basin at the temperature 

 of 28° may, by passing along the secret paths of the sea, reach the 

 Gulf of Mexico in summer at a temperature of only 3° above the 

 freezing point of fresh water, why may not water, leaving the tor- 

 rid zone at a temperature of 82°, and traveling by the same hid- 

 den ways, reach the frigid zone without losing more than the cold 

 currents gained in temperature, viz., 7° ? In 1840, Sir James C. 

 Boss, being in the antarctic regions with the surface water at 

 32°, found the temperature in depth to be 38°. 8 at 400 fathoms, 

 and 39°.8 at 600. At a greater depth there is a greater press- 

 ure ; and there ought to be (§ 404) a stated temperature, that 

 after passing a certain depth in the deep sea grows higher and 

 higher as the depth increases. The thermal laws of "deep-sea" 

 temperatures for fresh and for salt water are very different. In 

 September, when the surface water of Loch Lomond and Loch 

 Katrine — Scottish lakes — which are between 500 and 600 feet 

 deep, is 58°, that at the bottom is uniformly 41°, which is very 

 near the point of maximum densit}^ for fresh water. Saussure 

 has shown the same for the Italian lakes ; only, at the depth of 

 1000 feet in the Lake of Geneva, it was a little warmer, probably 

 on account of pressure (§ 404), than it was at less depth in Lakes 



