190 



Messrs. Carpenter and Jeffreys on 



[Dec. 8, 



Southern stations, there is a more gradual reduction of about the same 

 amount (9°) between 500 and 1000 fathoms. Now thisresul tis in remark- 

 able conformity with what might be anticipated on the hypothesis advanced 

 in the last Report. For if the whole upper stratum of Oceanic water be 

 slowly moving northwards from the region with which we are now concerned 

 towards that explored in the Third Cruise of 1869, whilst the lower stratum 

 is slowly moving southwards beneath this, it might be expected that the 

 further North the warm stratum advances, the more would it show the 

 influence of the colder stratum beneath, in the lowering of the Temperature 

 of the portion that immediately overlies it. And conversely, in proportion as 

 the cold stratum advances Southwards, we might anticipate that the tem- 

 perature of its upper layer would be gradually raised, so that even when 

 the "stratum of intermixture" has been entirely passed through, we should 

 find the Temperature at corresponding depths somewhat higher than at 

 stations further north, — which is just what seems actually to be the case*. 



82. The data at present in our possession seem to point to the inference that 

 the relation between the upper warm and the lower cold strata of the Ocean, 

 on different parts of the surface of the Globe, is such as may be diagram- 

 matically expressed thus : — 



P. E. P. 



P. E. P. 



At the Poles (p p, p p) the cold stratum occupies the whole depth, from 

 the surface to the bottom ; but as we pass towards the Equator we find it 

 lying further and further down, its surface forming an inclined plane 

 on which the warm stratum rests. The warm stratum, on the other hand, 

 has its maximum depth at the Equator, and gradually thins-off towards the 

 p l es . — This is just what would be expected on the hypothesis of a General 

 Vertical Circulation (§124 et seq.); since in the Polar-Equatorial flow of the 

 cold stratum its surface would be continually gaining heat by contact 

 with the warm stratum above, so that its superficial portion would be (so to 

 speak) progressively transferred to the warm stratum ; whilst, on the other 



* Prof. Wyville Thomson, in his Lecture on " Deep-Sea Climates " (' Nature,' 

 July 28, 1870), has expressed the opinion that the cold stratum in the North Atlantic 

 is derived rather from the Antarctic than from the Arctic basin. Putting aside the 

 difficulty of accounting for a constant «rcfiow of Antarctic water into the Northern 

 Hemisphere, without a corresponding onflow, a strong argument against it may be 

 drawn from the facts stated above. For if the cold stratum have a Southern source, we 

 should expect its own temperature to be lower, and its effects upon the superincumbent 

 stratum to be more marked, the further south it is examined, — the contrary of which 

 proves to be the case. 



