442 P. H. Carpenters Physical Investigations on the " Valorous." 



Hence, as I have urged on a former occasion, the prolonged 

 heating power of the northeast flow depends much more upon 

 the thickness of its moderately warm stratum than upon its 

 bringing with it a high surface-temperature. A layer of fifty 

 fathoms at 60°, flowing northeast over a bed of ocean-water at 

 40°, and exposed above to an atmosphere of 40°, would be 

 cooled down to that standard in two or three weeks. But a 

 layer of 900 fathoms thickness, ranging from 40° to 55°, would 

 retain an excess of temperature far longer. 



The advocates of the doctrine that the vis a tergo is the Gulf- 

 stream, which cannot be traced as a current by anv difi 

 feature further to the northeast than the parallel oi 40° and the 

 meridian of 30°, have to show in what way it can raise the tem- 

 perature of so thick a stratum of ocean-water as we have seen 

 to be affected in the western portion of the North Atlantic by 

 a warm flow of some kind. Whether, as Professor Wvville 

 Thomson maintains, the approximation of its boundaries be- 

 tween the British Islands on one side and Labrador and Green- 

 land on the other can possibly produce this result, is 



vhich it is for hydrographers to decide. For myself, I 

 cannot regard it as probable that a spent stream of iii % 

 thickness can give motion to a vast layer of 900 fathoms depth 



stream of 11 ft 

 ., of 900 fathoms ' " 

 On the other hand, the doctrine I advocate, that i 



upper stratum of the North Atlantic is slowly moving pole- 

 ward, to fill up the void left by the gravitation-underflow of 

 the coldest water toward the equator, and that this stratum 

 will also have an easterly tendency in virtue of the excess of 

 easterly momentum which it brings with it from a lower lati- 

 tude, seems adequately to account for the facts now brought 

 to light. The progressive closing in of the boundaries of this 

 poleward upper flow will obviously tend to deepen it. so as to 

 give it a more persistent heating power.* In the South At- 



; Southern Indian Oceans, on the other hand, the pro- 

 gressive opening-out of the ocean-boundaries, as we pass south- 



•. the equator, will tend in the same 'measure to reduce' 

 the thickness of the poleward upper flow, thus diminishing the 

 persistence of its heating power. And in this, as it seems to 

 me, we have the true explanation of the marked di 

 between the climate of Kerguelen's Land (latitude 50° S.), for 

 * ™ s P !* tion m& J 8eem inconsistent with the objection just taken t. 



