454 



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



with a Fauna essentially Boreal, could not, it was argued, be accounted for 

 in any other way than by the supposition of an under-current of Polar 

 water coming down from the North or North-east ; whilst, conversely, 

 the existence in the Warm area of a minimum temperature of 46°, ex- 

 tending to 500 or 600 fathoms' depth in the Latitude of 60° (of which the 

 normal deep-water temperature would be at least 8° less), together with 

 the warmer temperate character of its Fauna, seemed equally indicative of 

 a flow of Equatorial water from the South or South-west. How far this 

 flow is part of the "Gulf-stream" proper, — that is, of the current of 

 heated water which issues through the "Narrows" from the Gulf of 

 Mexico, — or is attributable to some more general cause, was reserved as a 

 matter still open to discussion ; but it was urged that the existence of two 

 such different Submarine Climates in such close proximity may be taken 

 as an example of that continual interchange between the Ocean-waters of 

 Equatorial and Polar regions, which is as much a Physical necessity as 

 that interchange of Air which has so large a share in the production of 

 winds. For the water that is cooled by the Polar atmosphere must sink 

 and displace the water that is warmer than itself, pushing it away towards 

 the Equator, so that in the deepest parts of the Ocean there will be a pro- 

 gressive movement in the Equatorial direction ; whilst, conversely, the water 

 heated by the Tropical sun, being the lighter, will spread itself north and 

 south over the surface of the ocean, and will thus move towards the Polar 

 regions, losing its heat as it approaches them, until it is there so much 

 reduced in temperature as to sink to the bottom, and thence return towards 

 its source. 



93. The doctrine of the Warm and Cold Areas, and of the probable 

 source of their difference, has been fully and carefully tested by the Tempe- 

 rature-soundings taken during the Third Cruise of the 'Porcupine;' and 

 the result has been a complete confirmation of it in every particular ; 

 whilst an entirely new and important set of data has been afforded by the 

 Temperature-soundings taken during the First and Second Cruises, in 

 support of the doctrine that a general interchange of Equatorial and Polar 

 waters is continually taking place in the great Oceanic basins. 



94. The total number of Temperature-soundings taken during the 'Light- 

 ning' Expedition, in water of more than 100 fathoms' depth, was only 15 ; 

 of which 8 were in the Warm area, and 6 in the Cold. These were all 

 Bottom- soundings only. The total number of Stations at which Tem- 

 perature-soundings were taken during the Third Cruise of the 'Porcupine,* 

 in water of more than 100 fathoms, was 36; of these, 17 were in the 

 Cold area, and 14 in the Warm, whilst 5 showed an intermediate range, 

 in accordance with their border position. But besides these Bottom- 

 soundings, Serial Soundings were taken at different depths in three 

 Stations; of which No. 87 was in the Warm area, and Nos. 52 and 64 

 in the Cold. In the first of these, which was at a point about 125 miles 

 to the N.W. of Stornoway, the temperatures were taken at 50, 100, 150, 



