258 Mr. J. Croll on the Physical Cause of Ocean-currents. 



Ocean. Then the Arctic Ocean also would possess more heat 

 than the Atlantic in tropical regions * for the Atlantic in these 

 regions possesses only 570 parts, whereas the Arctic Ocean pos- 

 sesses 766 parts. It is true that more rays are cut off in arctic 

 regions than in tropical ; but still, after making due allowance 

 for this, the Arctic Ocean, if Dr. Carpenter's theory be correct, 

 ought to be as warm as, if not warmer than, the Atlantic in tropi- 

 cal regions. 



We may therefore conclude that there can be no such large 

 quantity of warm water, in addition to that of the Gulf-stream, 

 as Dr. Carpenter supposes, flowing into the North Atlantic from 

 the equatorial regions; for there is not heat in those regions suf- 

 ficient to supply such a current. We may also conclude that, 

 at least in respect of the Atlantic, it is not correct that there is 

 more warm water flowing from the equatorial regions into the 

 southern hemisphere than into the northern ; for a very large 

 proportion of the heat conveyed by the Gulf-stream is derived 

 from the southern hemisphere. In fact the great equatorial 

 current, the feeder of the Gulf-stream, comes from the southern 

 hemisphere. 



The entire area of 7 .,700,000 square miles of sea in equatorial 

 regions lying to the north of the equator would not be sufficient 

 to supply the current passing through the Narrows of Bahama. 

 Were the heat of the Gulf-stream all derived from the northern 

 hemisphere, the following would then represent the relative 

 quantities of heat per unit surface possessed by the Atlantic in 

 the three zones, assuming that one half of the heat of the Gulf- 

 stream passes into the arctic regions, and the other half remains 

 to warm the temperate regions : — 



From the Equator to the Tropic of Cancer . . 773 

 From the Tropic of Cancer to the Arctic Circle 848 

 From the Arctic Circle to the North Pole . . 610 



These figures show that, were it not that a very large propor- 

 tion of the heat possessed by the Gulf- stream is derived from 

 the southern hemisphere, the Atlantic, from the equator to the 

 tropic of Cancer, would be as cold as from the tropic of Cancer 

 to the North Pole. 



The comparatively high temperature which prevails in the 

 northern parts of the Atlantic and in the Arctic seas is there- 

 fore to a considerable extent due to heat derived from the south- 

 ern hemisphere. And no doubt this transference of heat from 

 the southern hemisphere to the northern by means of ocean- 

 currents, as was mentioned on a former occasion *, is the cause 



* Phil. Mag. vol. xxxix. p. 103. 



