344 THE PHYSICAL CONDITION OF THE OCEAN. 



many years, and our knowledge of tliem is approacliing a point beyond 

 wliicli it is doubtful whether we shall ever much advance, except in 

 small details. For though, while iudisi)utably the waters continually 

 move in each great area in generally the same direction, the velocities 

 vary, the limits of the different streams and drifts vary, mainly from 

 the ever-varying force and direction of the winds. 



After long hesitation and much argument, I think it may be now 

 safely held that the iirime motor of the surface currents is the wind. 

 Not, by any means, the wind that may blow, and even persistently blow, 

 over the portion of water that is moving, more or less rapidly, in any 

 direction, but the great winds which blow generally from the same 

 general quarter over vast areas. These, combined Avith deflection from 

 the land, settle the main surfiice circulation. 



I do not know if any of my hearers may have seen a very remark- 

 able model, devised by Mr. Clayden, in Avhich water disi)osed over an 

 area shaped like the Atlantic, and sprinkled over with lycopodium dust 

 to make movement apparent, was subjected to air impelled from various 

 nozzels, representing the mean directions of the permanent winds. It 

 dispelled the last doubt I held on the subject, as not only were the 

 main currents reproduced, but the smaller effects and peculiarities of 

 the Atlantic drifts were produced with surprising accuracy. 



There is a small current, long shown on our charts, but which I had 

 always regarded with suspicion. I refer to the stream which, after 

 traveling from the Arctic Ocean southward along the east coast of 

 Greenland, turns sharply round Cape Farewell to the northward into 

 Davis Straits, where it again doubles sharply on itself to the south- 

 ward. This is exhibited in the model in all its details, and is evidently 

 caused by the i^ressure of the water forced by the mimic Gulf Stream 

 into the Arctic region, where it has no escape except by this route, and 

 is pressed against the land, round which it turns as soon as it can. 

 This is, no doubt, the explanation of the real current. The very 

 remarkable winter e(i[uatorial current, which runs in a narrow belt east- 

 ward, just north of the main stream traveling Avest, was also reproduced 

 with extraordinary tidelity. The winds, however, that are ordinarily 

 considered permanent vary greatly, while in the monsoon areas the 

 reversal of the currents caused by the opposite winds exercise a great 

 influence on the movements of the water far beyond their own limits, 

 and anything like a prediction of the i^recise direction and rate of an 

 oceanic stream can never be expected. The main facts, however, of 

 the great currents can be most certainly and simply explained in this 

 manner. The trade winds are the prime motors. They cause a surface 

 drift of no great velocity over large areas in the same general direction 

 as that in which they blow. These drifts after meeting and combining 

 their forces eventually impinge on the land. They are diverted and 

 concentrated and increase in speed. They either pour through pas- 

 sages between islands, as into the Caribbean Sea, are pressed up by 



