546 Dr. W. B. Carpenter — 



200 fathoms ; (2) an upper warm stratum of (say) 1,000 fathoms' depth, of which 

 the temperature ranges from 52" to 45° ; (3) a stratum of intermixture of about 200 

 fathoms' depth, in which the thermometer falls from 46° to 39° ; and (4) of a cold 

 stratum occupying the whole of the deeper portion of the great Oceanic basins beneath 

 1,400 fathoms, its temperature falling with increase of depth, so that in its deepest 

 portion the thermometer has been seen as low as 32°. The average of the entire 

 column may thus be about 45°. 



Now, as Sea water progressively diminishes in bulk and increases in Specific Gravity 

 down to its freezing point, it is maintained hy the Author that supposing the Polar 

 and Intertropical columns to be equal in height, the excess of weight in the former 

 will produce a lateral pressure at its lower portion, which will occasion an outflow of 

 Polar water along the floor of the ocean, towards the Equator ; this deep outflow, by 

 lowering the surface, will produce an indraught of water into the Polar area, which, 

 in its turn, will acquire by cooling the same excess of Specific Gravity, thus producing 

 a continual doimiward movement ; while on the other hand the deep outflow, being 

 subject to the heating influence of the crust of the earth beneath, and of the warmer 

 water ahove, will be gradually thinned as it passes towards the Equator, so as to lie 

 at a greater and greater depth beneath the surface. As the continual indraught into 

 the Polar area must ultimately be supplied from the surface of the Intertropical sea, 

 there will be a continual movement of the upper stratum fi-om the Intertropical 

 towards the Polar area ; while as the last-arrived Polar water will always be colder 

 than that which preceded it, the former will take its place beneath the latter, so that 

 there will be a continual upward movement of the water in the Intertropical area. — 

 Of this upward movement of colder water from below, a very curious indication has 

 lately been obtained in the fact that oflf the west coast of Africa the temperature of 

 the sea at 200 fathoms is about 6° lower over a bottom deep enough to be covered by 

 the Polar overflow, than it is over a bottom of only 700 or 800 fathoms' depth. 



The doctrine of a vertical circulation advocated by the Author was long since 

 suggested by Pouillet as the best explanation of the facts then known in regard to 

 Ocean-temperature ; but it was put aside through the general acceptance of the 

 doctrine of a uniform deep-sea temperature of 39 1°, which was supposed to have been 

 established by Sir James Ross's observations, and which was adopted and promulgated 

 by Sir John Herschel. The corrections supplied by more recent and trustworthy 

 observations have aff'orded a new set of data; on- the basis of which it has been 

 argued by the Author, that such a Circulation must necessarily take place under the 

 conditions above specified, and that it gives an adequate scientific rationale for the 

 facts determined by observation. And his views on this subject have been accepted 

 by Sir John Herschel and Sir William Thomson. 



Now, it is obvious that if this doctrine of a Vertical Oceanic Circulation, sustained 

 by antagonism of Temperature, be admitted, the thermal condition of any Inland Sea 

 that is cut ofl" from any but a superficial communication with the great Oceanic basins, 

 and at the same time corresponds with them in depth, must be very difi'erent. Of 

 such a sea, the Mediterranean is a typical example. It consists of two very deep 

 basins : the Western, which extends from the Strait of Gibraltar to the Adventure 

 and Skerki Banks that connect Sicily with the coast of Tunis, having a depth which 

 ranges, over a large part of its area, to 1,000 — 1,600 fathoms; whilst the Eastern, 

 which extends from Malta and the eastern coast of Sicily to the Levant, is yet 

 deeper, its bottom having in some parts a depth of nearly 2,000 fathoms. The Strait 

 of Gibraltar, which constitutes the sole channel of communication between the 

 Mediterranean basin and the outside Atlantic, and which has a depth of about 500 

 fathoms between Gibraltar and Ceuta, gradually shallows, as it widens, towards its 

 western embouchure between Capes Trafalgar and Spartel ; where there is a " ridge," 

 or "submarine watershed," of which the average depth is about 120 fathoms, certain 

 passages across it approaching 200 fathoms in depth. Through this Strait there is a 

 double current, modified in force and direction by Tidal action, as the researches which 

 the Author carried on last August in conjunction with Captain Nares have shown : 

 the predominant movement of the upper stratum being inwards, while that of the 

 fower stratum is outwards ; and the quantity of water which thus enters the Mediter- 

 ranean from the Atlantic being considerably greater than that which ^om'.s out of the 

 Mediterranean into the Atlantic. The surplus of the upper current goes, as was 

 maintained nearly 200 years ago by Dr. Halley, to make up for the loss sustained by 

 the water of the Mediterranean, in consequence of the excess of evaporation from its 

 Buiface over the whole quantity restored to it by rain and rivers ; whilst the outward 



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