1871.] 



Theory of the Ocean. 



555 



diverted by the local winds; for trie power of winds to divert even the "mighty 

 Gulf-stream " of 3 J knots is shown in the ' Notes on the Gulf-stream/ by 

 A. D. Bache, Superintendent of the United States Coast Survey, who 

 shows it to be driven sometimes out of its usual course fully thirty miles 

 by N.W. and westerly gales. 



In concluding these remarks upon the errors regarding the under- 

 current theory, I feel that it is due to our distinguished transatlantic 

 hydrographers and geographers, that as theirs were the pioneer efforts in 

 such investigations on a large scale, it was natural that they should have 

 been defective, from the little attention given to such researches previously. 

 But it is necessary that these errors should now be well understood, and 

 shown to have arisen from a fallacious estimate of the experiments, that 

 the philosophical naturalist and physicist be no longer misguided by them, 

 and thus attribute so grand and large an influence to undercurrent, as 

 erroneously shown by the experiments of Lieut. Walsh and Lee, and as 

 the assumed necessary result of the small difference of density between one 

 part of the ocean and another ; for surface-current circulation and return 

 can and, indeed, must tend largely to restore it, aided by the rain and river 

 supply of fresh water met with in its circulation and return. This is even 

 shown to be so under the equator, from the large African rivers and also 

 from the Amazon and others joining the equatorial current, from the 

 elaborate investigations (the twenty years' researches) of the late Dr. 

 Forchhammer, as summarized in his most interesting and valuable dis- 

 cussion of these analyses in his paper in the Philosophical Transac- 

 tions for 1865, wherein the analyses and temperatures of the sea- 

 water are given from all parts of the globe, and a most remarkable and 

 able deduction of the surface-currents from them. But the learned Doctor, 

 misguided, no doubt, by the supposed existence of the great undercurrent 

 movement in the Atlantic as propounded by Capt. Maury, and also by the 

 misunderstanding of the facts and the incompleteness of the observations 

 for correctly ascertaining the conditions existing between the Baltic and 

 German Ocean, and so, as a philosophical physicist, thus misled, was in- 

 duced to ascribe a greater influence to undercurrent circulation than to 

 superficial, as a means of restoring the equilibrium from reduced or increased 

 densities. I have before admitted that where two currents meet, such as the 

 Polar and Gulf-stream, both strong in force and of great difference in density 

 or temperature, and in directions nearly at right angles such as these two, 

 an undercurrent or intermediate current of appreciable amount may exist. 



That denser water will intermix with lighter water in its deeper portion, 

 when they meet and when depths are equal and difference of the densities 

 great, as between pure fresh and sea-water, I am aware from my experi- 

 ence at the mouths of large rivers. 



This is a fact experienced every year at the Damietta and Rosetta mouths 

 of the Nile for five or six weeks, during the lowest condition of the Nile, 

 when there is only a surface-outflow there ; and it extends five or six miles 



