THE SPECIFIC GRAVITY OF THE SEA, ETC. 205 



dent imagination of the daring mariner's many longings. The 

 temperatm-e 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 siu-face level. Under 

 this ice there was also doubtless water above the freezing-point. 



430. Xor need the presence of warm water within the arctic 

 undei- currents clrclo cxcito sm^risc, whcu WO rccollcct that the 

 tio^iy. ^^^^^^ "'^^ cold waters of the frigid zone 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 sm-face, and until the polar flov/ 

 (§ 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' N., 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 temperatm^e of only 3° above the 

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

 rid zone at a temperatm^e of 82°, and travelling by the same hidden 

 ivays, reach the frigid zone without losing more than the cold cur- 

 rents gained in temperature, "vaz., 7° ? In 1840, Sir James C. 

 Eoss, 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 pressure ; 

 and there ought to be (§ 404) a certain 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" tempera- 

 tures for fresh and for saltwater are very different. In September, 

 when the surface water of Loch Lomond and Loch Katrine — Scot- 

 tish lakes — which are between 500 and 600 feet deep, is 58°, that 

 at the bottom is uniformly 41°, which is veiy near the point of 

 maximum density for fresh water. Saussure has sho'^n the same 

 for the Italian lakes ; only, at the depth of 1000 feet in the Lake 

 of Geneva, it was a Httle warmer, probably on account of pressure 

 (§ 404), than it was at less depth in Lakes Lucerne and Thun. 

 In these it was 41°, or 1° colder than the bottom of Geneva, their 

 surface water being about 60°. In Lago Sabatino, near Eome, with 

 the surface water at 77°, Barlocci reports 44° at the depth of 490 

 feet. The winter in Eome is not severe enough to cool such a mass 

 of water below 44°. But with the exception of the Lake of Geneva, 



