TRANSACTIONS OF THE SECTIONS. 49 



stitiites a vrra causa adequate to maintain the Vertical Circulation advocated by the 

 Author. The /«f/s ot" the case, as determined by recent Deep-sea Temperature 

 observations, made for the most part with Tliermometers protected against pressure, 

 are as follows : — 



1. In hig-h Northern Latitudes the temperature of the surface of the Sea, near the 

 border of the Ice-barrier, is but little above ^2'^ F. ; and at small depths below the 

 surface, according to the recent observations of Payer and \\'eyprecht, it falls below 

 32°. Making allowance for the known influence of pressure upon tlie thermometers 

 with which temperature-observations at great depths have been made in these 

 regions, there is every reason to believe that — save in cases in which the tempera- 

 ture of the upper stratum may be modified by local causes — there is a progressive 

 descent from -32° to 29° or even lower; so that the average temperature of the entire 

 column of Polar Water may be considered to be not above 30°. 



2. In lower Latitudes the temperature of the surface of the Sea is gTeatly influ- 

 enced by Solar radiation ; but the superheathu/ thus produced does not generally 

 extend in a marked degree much below 100 fathoms. Beneath this is a stratum of 

 which the temperature may be said to range from about 52° to 4o° in aU but the 

 highest Latitudes ; but the depth of this stratum varies considerably, being about 

 400 fathoms near the Faroe Banks, about 700 fathoms off the coast of Portugal, 

 and 1000 or 1200 fathoms nearer the Equator. 



3. Beneath this stratum is a " stratum of intermixture," in which the Thermo- 

 meter falls rapidly, — sometimes as much as 10° in 200 fathoms ; and below this the 

 temperature again becomes more uniform, sinking very gradually from 39° or 38° to 

 35° or even to 32°, at depths of more than 2000 fathoms, even under the Equator. 



4. Thus the Intertropical column may be regarded as consisting of: — (1 ) a super- 

 heated stratum, of which the temperature ranges fi-om 84° at the surface to 52° at 

 200 fathoms ; (2) an upper warm stratum of (say) 1000 fathoms depth, of which 

 the temperatm-e ranges from 52° to 45° ; (3j a stratum of intermixture of about 200 

 fathoms depth, in which the thermometer falls from 45° to 39° ; and (4) of a cold 

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

 beneath 1400 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 <S»«-water progressively diminishes in bulk and increases in specific 

 gravity down to its freezing-point, it is maintained by 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 pressin-e 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 loAvering the surface, will produce an indraught of water into the 

 Polar area, which, in its tmn, will acquire by cooling the same excess of Specific 

 Gravity, thus producing a continual dowmvarcl movement ; whilst, on the other 

 hand, the cold outflow, being subject to the heating influence of the crust of the 

 Earth beneath and of the warmer water above, 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 deep outflow of Polar Water will produce a superficial 

 indraught into the Polar area, and nixist ultimately derive its supply from the sur- 

 face of the Intertropical sea, there will be a continual movement of the upper 

 stratum from the Intertropical towards the Polar area : and 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 off 

 the West Coast of Africa the temperature of the Sea at 200 fathoms is about 5° 

 lower over a bottom deep enougli to be covered by the Polar outflow, 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 was put aside through the general acceptance of the doc- 

 trine of a uniform Deep-sea temperature of 39^^ F., which was supposed to have 

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



