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SCIENCE. 



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



east, and, tlierefoi'e, the direction of their 

 courses is not, during that portion of their 

 journey, influenced by the rotation of the 

 earth, and as the flow in the opjjosite direc- 

 tion of the ]S"orth Equatorial and the South 

 Equatorial Current is perennial, if not 

 strictly constant, and lastlj', as there is so 

 great a discharge of water from the Equa- 

 torial Currents into the North Atlantic, a 

 constant replenishment of the waters at the 

 sources of the Equatorial Currents is im- 

 plied with a certainty which involves the 

 certainty that the level of the ocean oif the 

 southern coast of Africa is lower than that 

 off the coast of Central America. That the 

 difference between these levels, whatever it 

 may be, is relatively but a small factor in 

 the movement of the G-ulf Stream, is self- 

 evident, but as an entering factor it is proper 

 that it should be mentioned. We can justly 

 conceive, however, of a modified Gulf 

 Stream, even if the level of the Caribbean 

 Sea and the Gulf of Mexico were precisely 

 the same with that on the African coast, 

 at the sources of the Equatorial Currents, 

 because it is dynamically part of a move- 

 ment larger and inclusive of the waters of 

 the whole globe; but we cannot conceive of 

 diflerence of oceanic level not being an in- 

 dispensable factor in the movement of the 

 Gulf Stream as it actually exists, and in 

 that larger movement. Whatever agencies, 

 single or collective, are in play must be as- 

 sociated with differences of ocean levels. 

 Assume changes in the present diflFerences 

 of level, and we must recognize that the 

 phenomena of ocean movement would enter 

 upon new phases. Assume that there is no 

 difference of level anywhere, and we should 

 see that the present phenomena would be- 

 come inexplicable. 



It obviously does not follow from apprecia- 

 tion of the valuable results in pelagic history, 

 in the physical hj'drography of the sea, and in 

 other departments of knowledge obtained by 

 the Challenger expedition, that one must 



agree in opinion with the distinguished chief 

 of its scientific staff in all of his conclusions. 

 Comparing the opinion of Dr. Carpenter 

 with the opinion about to be cited from Sir 

 Charles Wyville Thomson, it will become 

 evident that the former, although accepting 

 the fundamental fact acquired by the Chal- 

 lenger, does not, any more than the j)resent 

 writer, agree with a certain one of the con- 

 clusions of Sir Charles Wyville Thomson 

 wdth reference to the cause of the general 

 vertical oceanic movement. Both Sir 

 Charles Wyville Thomson and Dr. Carpen- 

 ter ascribe the general vertical oceanic 

 movement to the welling up of the cold 

 waters of the Southern Ocean into the At- 

 lantic and the North Pacific. But, where- 

 as both believe that condition to depend 

 upon a movement sustained merely by the 

 difference in density between the polar and 

 the equatorial waters. Sir Charles Wyville 

 Thomson additionally believes the excess 

 of water received at the equator from- the 

 Southern Ocean, as compared with the 

 amount received from north of the equator, 

 to be owing to the excess of precipitation 

 over evaporation in the southern hemi- 

 sj)liere, which, of course, involves the ex- 

 cess of evaporation over precipitation in the 

 northern hemisphere. Now, although it is 

 recognized that there is in the southern 

 hemisphere an excess of precipitation over 

 evaporation, the degree, in that particular, 

 of diflerence between the two hemisi^heres 

 is not, as Sir CharlesWyville Thompson him- 

 self admits, even appi-oximately known, and 

 whatever it vh&y legitimately be assumed 

 to be, it is hardly to be recognized as capa- 

 ble of producing the relativelj' great gen- 

 eral flow from the Southern Ocean to the 

 extent indicated by him. Moreover, the 

 theorjf is not comjjatible with the fact that 

 as the equator is approached from either pole 

 the speciflc gravity of the surface water of 

 the ocean becomes higher and higlier, and 

 then lower and lower, until the \^ater reaches 



