631 



II.— TEMPERATUKE OF THE SEA, &c. 



1. Tables of Temperatures of the Sea at Various Depths 

 below the Surface, taken between 1749 and 1868. Collated 

 by Professor Prestwich, F.R.S. 



The first experiments were made by bringing up water by 

 means of a bucket with valves ; this was employed by Scoresby, 

 who showed that in the seas around Spitzbergen, while at the 

 surface the temperature varied from 29° to 42°, at depths of from 

 2,000 to 4,000 feet the temperature was generally about 34° or 36°. 

 The apparatus was improved by Lenz, and remarkable results 

 were obtained by him in Kotzebue's expedition in 1823. Sir John 

 Ross sometimes used Six's thermometers, and at others took the 

 temperatures of the silt from the bottom. Six's thermometers 

 were also used by Parry and on most subsequent expeditions. 



The observations made in the Mediterranean with these instru- 

 ments, which were very probably protected by an outer coating, 

 have a remarkably close agreement with those recently made by 

 Dr. Carpenter. 



The experiments of Scoresby, Martins, and Ross show that in 

 Polar regions the temperature at depths is higher than the 

 average surface temperature, and this applies to Arctic and 

 Antarctic regions. From the experiments of Ross, Sabine, and 

 Parry, this rule is not found to hold good in Baffin's Bay, where 

 the temperature falls from 30° and 32° at the surface to 29° and 

 28° '5 at the greatest depths attained. 



The facts show that at depths in the tropical seas the tempera- 

 ture is about 34° or 35° F., and Lenz has shown that this could 

 only be maintained by a constant slow under current from the 

 poles to the equator, and has also shown, by making observations, 

 that a belt of cooler water exists at the equator, and that the 

 temperature at equal depths is lower at the equator than a few 

 degrees to the north or south of it. He concluded that this arose 

 from the circumstance that the deep-seated Polar waters there 

 met and rose to the surface. 



As bearing out this, he showed that the waters in the same 

 zone were of lower specific gravity, which was also noticed by 

 Humboldt : — 



*' Lenz shows that in the Arctic Ocean the bathymetrical 

 isotherm of 35° is deepest on the west of Spitzbergen, while nearer 

 Greenland, and again nearer Norway, the deep waters are colder. 

 The several isothermal surfaces of 40°, 50°, 60°, 70°, and 80° are 

 then traced southward, attaining their maximum depth between 

 50° and 40° latitude, and rising thence towards the equator. 



" Taking another zone on the western side of the Atlantic, from 

 Baffin's Bay to the Equator, he shows that the highest isotherms 



