206 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



current in their favour ; most of thera experience no current at 

 all ; but, now and then, some do find a current setting to the 

 northward and westward, and operating against them at the rate 

 of 20 and occasionally of 50 miles a day. The intertropical 

 regions of the Atlantic, like those of the other oceans (§ 401), 

 abound with conflicting currents, which no researches yet have 

 enabled the mariner to unravel so that he may at all times know 

 where they are and tell how they run, in order that he may be 

 certain of their help when favourable, or sure of avoiding them 

 if adverse. 



409. TJie Greenland current. — There are other currents, such as 

 the Greenland Current, the cold current from Davis' Strait, the 

 ice-bearing current from the antarctic regions, all setting into the 

 Atlantic and the Gnlf Stream, one branch of which finds its way 

 into the Arctic Sea ; the other (§89) finds its way back to the 

 south partly as Eennell's current, all of which have been fully 

 treated of in Chap. II., or are delineated on Plates VI. and IX. 

 Judging by these, there would seem to be a larger flow of polar 

 waters into the Atlantic than of other waters from it; and I 

 cannot account for the preservation of the equilibrium of this 

 ocean by any other hypothesis than that which calls in the aid 

 of under currents. They, I have no doubt, like the water-ways, 

 the mineral veins, the passages in the bowels of the earth, bear 

 in their secret ways, an important part in the grand system of 

 the terrestrial economy. 



CHAPTER IX. 



§ 420-460. — THE SPECIFIC GRAVITY OF THE SEA, AND THE OPEN 

 WATER IN THE ARCTIC OCEAN. 



420. Interesfincj physical inquiries. — The crust of the planet 

 upon which we live, with the forces that have been and are at 

 work upon it, is the most interesting subject of physical inquiry 

 and study that can claim the attention of diligent students. 

 Precisely as the progi-ess of man has been upward and onward, 

 precisely has he looked more earnestly and with deeper longings 

 towards the mysteries that encircle this crust. It is but a shell, 

 and at most we can reach only a little way either above or below 

 its very surface, and jet upon the tablets of this thin shell are 



