P. H. Carpenters Physical Investigations on the "Valorous." 4-to 



example, or that of Heard Island (latitude 53° S.), and that of 

 Ireland, (lying between the parallels of ol£° and 54|° N. lati- 

 tude), the summer temperature of the former being but little 

 above the winter temperature of the latter. 



The " Challenger " temperature-sections have most conclu- 

 sively shown that the entire warm upper stratum in the South 

 Atlantic is very much thinner than that of the North Atlantic ; 

 and while I fully admit that a part of this difference is due to 

 the fact that a far larger portion of the equatorial current is 

 deflected into the latter than into the former, I cannot see that 

 the Gulf-stream by any means accounts for the descent of the 

 isotherm of 40° in latitude 56° N. to a depth of 900 fathoms. 



The " Valorous " temperature-soundings seem to me to be of 

 peculiar interest and value, in fi story expla- 



nation of the comparatively high bottom-temperature of the 

 North Atlantic. I have always attributed this to the compara- 

 tive narrowness of the channels of communication between the 

 Arctic and the North Atlantic basins, which restrict the flow 

 of the coldest polar water from the former into the latter : and 

 long before the " Challenger " Expedition sailed, I had ven- 

 tured the prediction that the South Atlantic, on account of the 

 perfect freedom of its communis I etic, would 



have a colder bottom, and that the influence of the Antarctic 

 underflow would probably extend to the north of the equator. 

 By Sir Wyville Thomson, on the other hand, it was argued 

 from the commencement that the whole cooling of the deep 

 stratum of the North Atlantic is due to the A 

 and this conviction he repeats in his last utterance on the sub- 

 ject, on the ground of the continuity of the isotherms from the 

 South into the North Atlantic * The question arises, however, 

 why the deep stratum of the North Pacific, which is undoubt- 

 edly fed from the Antarctic, should be so decidedly colder, as 

 the "Challenger" and " Tuscarora " soundings show it to be, 

 than the deep stratum of the North Atlantic ; and this ques- 

 tion appears to me to find an entirely satisfactory answer in 

 shed by the Second Section, that the Arctic 

 Basin is for the most part separated from that of the North At- 

 lantic by an intervening ridge, which (like many siini: 

 discovered by the " Challenger ") allows water of about 36 , 

 but not colder water, to pass from the. former into the latter. 



; 



Bay and the " Lightning Channel " would help to reduce the 

 deep temperature of the North Atlantic generally to the 

 35°-36° shown in the "Challenger" Sections; but it is only 

 when, on approaching the equator, a bottom-temperature below 

 % that I can recognize the influence of the 

 Antarctic underflow. 



* Proceedings of the Royal Society, voL xxiv, P- 632. 



