472 



Messrs. Carpenter, Jeffreys, and Thomson [Nov. 18, 



Polar stream which seems to occupy all the deeper parts of the basin to 

 within about 1000 fathoms of the surface, and thus carries back Polar 

 water to the Equatorial area. 



1 18. These inferences are fully borne out by the Temperature-soundings 

 recently taken by Commander Chimmo, R.N., and Lieut. Johnson, R.N., at 

 various points of the North-Atlantic Basin ; for although the temperatures 

 of these Soundings were recorded by unprotected Thermometers, yet the 

 error to which the best of those instruments are subject from the effects of 

 pressure at different depths can now be estimated, and the requisite correc- 

 tion applied to each observation, so as pretty certainly to give the true tempe- 

 rature in each case within a degree. These Soundings give a temperature 

 of about 39° at 1000 fathoms, which is almost exactly accordant with the 

 average of our own ; but the " stratum of intermixture," indicated by the 

 rapid reduction of temperature with increase of depth, seems to lie rather 

 nearer the surface, the rapid reduction commencing at about 400 fathoms 

 instead of at about 500. Below 1000 fathoms, at depths progressively 

 increasing to 2270 fathoms, the temperatures are in extraordinarily close 

 accordance with our own, the minimum, however, apparently falling a 

 little lower. Thus at 22/0 fathoms, the temperature recorded by an un- 

 protected Casella thermometer was 44° ; but the estimated correction for 

 the instrument at that depth being 9°, the real temperature would be 

 35°. 



119. It has thus been shown that the hypothesis advanced in our pre- 

 ceding Report, when worked out in connexion with the peculiar Geo- 

 graphical relations of the Arctic to the North-Atlantic basin, goes far to 

 account for the two orders of phenomena which have now been examined, 

 namely : — 



(I.) The movement of a vast body of warm water, extending to a depth 

 of several hundred fathoms, in a north-east direction, which moderates the 

 cold of the Boreal area by bringing into it the warmth of that vast expanse 

 of the North-Atlantic Ocean which is heated beneath the Tropical sun. 



(II.) The existence of a flow of ice-cold water, at depths greater than 

 300 fathoms, in a south-west direction along the floor of the channel be- 

 tween the North of Scotland and the Faroe Islands, which contributes, 

 with other frigid streams from the Arctic basin, to diffuse over the North- 

 Atlantic sea-bed, at depths greater than 1000 fathoms, a Temperature below 

 39°, ranging downwards with increase of depth to about 35°. 



And it further appears : — 



(III.) That the " Gulf-stream" may be regarded as a kind of intensifi- 

 cation of the ordinary flow of Surface-water from the Equatorial to the 

 Polar area, this intensification being due to the peculiar local conditions 

 which produce an extraordinary "superheating" of water in the Gulf of 

 Mexico, and the diffusion of this superheated water thence over a vast 

 proportion of the North-Atlantic area, raising its Surface-temperature by 

 several degrees. 



