Wind and Gravitation Theories of Oceanic Circulation. 243 



to produce a surface-flow from the equator to the poles ; but to 

 induce such an effect, some slope there must be, or gravitation 

 could exercise no power in drawing the surface-water pole- 

 wards. 



The researches of the c Challenger ' expedition bring to light 

 the striking and important fact that the general surface of the 

 North Atlantic, to be in equilibrium, must stand at a higher 

 level than at the equator. In other words, the surface of the 

 Atlantic is lowest at the equator, and rises with a gentle slope 

 to well nigh the latitude of England. If this be the case, then 

 it is mechanically impossible that, as far as the North Atlantic 

 is concerned, there can be any such general movement as Dr. 

 Carpenter believes. Gravitation can no more cause the surface- 

 water of the Atlantic to flow towards the Arctic regions than it 

 can compel the waters of the Gulf of Mexico up the Mississippi 

 into the Missouri. The impossibility is equally great in both 

 cases. 



In order to prove what has been stated, let us take a section 

 of the mid-Atlantic, north and south, across the equator ; and, 

 to give the gravitation theory every advantage, let us select that 

 particular section adopted by Dr. Carpenter as the one, of all 

 others, most favourable to his theory, viz. section marked No. 

 VIII. in his memoir lately read before the Royal Geographical 

 Society *. The section referred to is shown in the accompanying 

 diagram (p. 244). Its peculiarity, as will be observed, is the thin- 

 ness of the warm strata at the equator as compared with those of 

 the heated water in the North Atlantic. The fact that the polar 

 cold water comes so near the surface at the equator is regarded 

 by Dr. Carpenter as evidence in favour of the gravitation theory. 

 On first looking at his section, it forcibly struck me that, if it 

 was accurately drawn, the ocean, to be in equilibrium, would re- 

 quire to stand at a higher level in the North Atlantic than at 

 the equator. In order, therefore, to determine whether this is 

 the case or not, I asked the Hydrographer of the Admiralty to 

 favour me with the temperature-soundings indicated in the sec- 

 tion, a favour which was most obligingly granted. The follow- 

 ing are the temperature-soundings at the three stations A, B, 

 and C. The temperatures of C are the mean of six soundings 

 taken along near the equator : — 



* Proc. Roy. Geog. Soc. vol. xviii. p. 362. 



R2 



