308 THE PHYSICAL GEOGRAPHY OF THE SEA. 



CHAPTER XVI. 



THE DEIFT OF THE SEA. 



Data used for Plate IX., ^ 893. — The Antarctic Flow, 896.— A large Flow from the 

 Indian Ocean, 902. — Patches of colored Water, 905. — The Lagullas Current, 909. 

 — An imraense Current, 911. — Tide Rips, 914. — Pulse of the Sea, 920. — Diurnal 

 Change of Sea Temperature, 922.— The Fisheries, 925.— The Sperm Whale, 926. 



887. There is a movement of the waters of the ocean which, 

 though it be a translation, yet does not amount to what is known 

 to the mariner as current, for our nautical instruments and the art 

 of navigation have not been brought to that state of perfection 

 which will enable navigators generally to detect as currents the 

 flow to which I allude as drift. 



888. If we imagine an object to be set adrift in the ocean at the 

 equator, and if we suppose that it be of such a nature that it would 

 obey only the influence of sea water, and not of the winds, this 

 object, I imagine, would, in the course of time, find its way to the 

 icy barriers about the poles, and again back among the tepid wa- 

 ters of the tropics. Such an object would illustrate the drift of 

 the sea, and by its course would indicate the route which the sur- 

 face-waters of the sea follow in their general channels of circula- 

 tion to and fro between the equator and the poles. 



889. The object of Plate IX., therefore, is to illustrate, as far 

 as the present state of my researches enables me to do, the cir- 

 culation of the ocean, as influenced by heat and cold^ and to in- 

 dicate the routes by which the overheated waters of the torrid 

 zone escape to cooler regions on one hand, and, on the other, the 

 great channel-ways through which the same waters, after having 

 been deprived of this heat in the extra-tropical or polar regions, 

 return again toward the equator ; it being assumed that the drift 

 or flow is from the poles when the temperature of the surface 

 water is helow, and from the equatorial regions when it is above 

 that due the latitude. Therefore, in a mere diagram, as this plate 



