92 



SCIENCE. 



[N. S. Vol. II. No. 30. 



thus see at a glance, not onlj- that they are 

 polar waters which we find immediately be- 

 low the surface under the equator, but that 

 the moderate temperature and densitj^ of 

 the surface are due to their proximit3- and 

 intermingling \vith others. Starting, as they 

 do, with greater densitj^ than that which, 

 without their translation, would be pos- 

 sessed by waters at the equator, they be- 

 come, through conduction and convection 

 of heat, of less density than the equatorial 

 surface water, because their pristine den- 

 sity was due to cold, which they flnallj' lose. 

 To suppose that the whole bodj^ of Avater in 

 the Caribbean Sea and the Gulf of Mexico 

 should rise in temperature throiagh all its 

 strata, intermediately to its passage out of 

 the Straits of Florida, would be preposter- 

 ous ; but when we remember that the course 

 taken by these various strata before cul- 

 minating in a current departing for the high 

 seas represents weeks of time and coincident 

 confinement in a landlocked embayment of 

 the ocean, we ought to perceive that theu' 

 increase in volume, if not general, must be 

 considerable. 



Dr. Carpenter, whose influence was 

 largely instrumental in bringing about the 

 voyage of the Challenger, and who freely uses 

 the data collected by it, says, in his article. 

 The Atlantic, in the last edition of the Ency- 

 clopfedia Britannica : " It is not a little re- 

 markable that the siibsurface stratum of 

 water, having a temperature above 40 F., 

 is thinner under the equator than it is in 

 anj' other portion of the Atlantic from the 

 FarSe Islands to the Cape of Good Hoj^e. 

 Notwithstanding the rise of the surface- 

 temperature to 76°-80° F., the thermometer 

 descends in the first 300 fathoms more 

 rapidly than anywhere else; as the polar 

 water is met with at a much less depth than 

 in the North Atlantic, and 100 fathoms 

 nearer to the surface, than even in the 

 cooler South Atlantic ; whilst the tempera- 

 ture of the bottom is but little above 32° 



F." Again, he remarks, in the same arti- 

 cle: " The isotherm of 40° F., which, in lati- 

 tude 22° North, lies at a depth of 700 

 fathoms, gradually rises as the equator is- 

 approached, and it is between the equator 

 and 7° South Latitude, where the tempera- 

 ture rises to nearly 80° F., that cold water 

 is soonest reached — the isotherm of 40° F. 

 rising to within 300 fathoms of the surface,, 

 while that of 55° F., which in latitude 22° 

 North lies at nearly 400 fathoms' depth,, 

 and in latitude 22° North at about 250 

 fathoms, actually comes up under the 

 equator within 100 fathoms of the surface." 



Both Dr. Cai-penter and Professor Lenz, 

 of St. Petersburg, however, the latter of 

 whom, from observation made as early as 

 182-5-1826, in the voyage of the Kotzebue, 

 had propounded a theorj' of such oceanic 

 circulation as that implied by the preceding 

 facts. Dr. Carpenter, in ignoi-ance of hav- 

 iug been anticipated, adopted the same 

 views, ascribing the general oceanic move- 

 ment to a general vertical oceanic circula- 

 tion sustained merely by the difference of 

 temperature between the polar and the 

 equatorial regions; which theory unwar- 

 rantablj' omits the agencj' of the rotation 

 of the earth on its axis as one of the pri- 

 marj' factors in the phenomena concerned. 



It is generallj' conceded that the Gulf 

 Stream is no longer recognizable as a cur- 

 rent bej^ond 30° West Longitude, but it is 

 not therefore to be supposed that all the 

 waters belonging to it just previously are 

 frittered away and have mysteriously dis- 

 appeared. As it gradually thins and spreads 

 out in its passage towards the northeast- 

 ward across the Atlantic, and at the same 

 time graduallj' diminishes in temperature, 

 it becomes more and more a portion of the 

 grand sweep of surface water from the 

 equator towards the northeast, becoming 

 an integral portion of that movement; and 

 because it is no longer recognizable as a 

 current beyond 30° West Longitude, it does 



