B. TERRESTRIAL PHYSICS AND METEOROLOGY. 59 



From these three theoretical considerations Dr. Carpenter 

 long ago deduced the following generalization : That in all 

 the great ocean-basins the general bottom temperature will 

 approach that of the polar area, in proportion to the freedom 

 of their communication with it. And in this action he an- 

 ticipates that the bottom temperature of the South Atlantic 

 will be lower than that of the North Atlantic, in consequence 

 of its greater freedom of communication with the polar area ; 

 and that while the bottom temperature of the North Atlan- 

 tic will probably not be as low as 35, except near the line of 

 the main arctic or antarctic under-flow, that of the South At- 

 lantic will probably be as low as 32; and, furthermore, that 

 the influence of the stronger antarctic glacial flow will very 

 probably extend to the north of the equator. 



Again, he maintained that the depression of the bottom 

 temperature will be found to depend, not upon a mere glacial 

 stream of a few hundred feet in depth, but upon the creeping 

 flow of the whole under-stratum of from 1000 to 2000 fath- 

 oms in thickness ; and that, as the arctic and antarctic under-* 

 flows must meet at or near the equator, while the surface 

 stratum is continually drawn toward each pole, there will be 

 a constant ascent of glacial water under the Line, showing 

 itself by the nearer approach of cold water to the surface in 

 the inter-tropical than in the extra-tropical zones. 



All these predictions he finds signally verified by the tem- 

 perature soundings of the Challenger, so that he feels that he 

 is justified in maintaining that his original hypothesis in re- 

 gard to ocean temperatures is established beyond cavil. 



The upward movement of the cold water under the equa- 

 tor, according to Dr. Carpenter, is indicated by three distinct 

 facts : first, that the polar water is met with much nearer the 

 surface than in any other part of the area explored by the 

 Challenger, the isotherm of 40 there lying within 300 fath- 

 oms from the surface, and the whole mass of water thence to 

 the bottom at 2475 fathoms, where it sinks to 34.4, being 

 unmistakably polar ; second, that the surface temperature is 

 thus kept down to a much lower level than it reaches in shal- 

 lower waters or in inland seas, where there is no cold bottom 

 water to come up and reduce it; third, that the specific grav- 

 ity of the surface water of the equatorial band has the low 

 standard which the bottom water has brought thither from 



