1871.] 



Theory of the Ocean, 



551 



Postscript, June 23rd, 1871. 



As the undercurrent theory, in its larger view, as first put forth by Capt. 

 Maury, will remain a source of error still for the misguidance of the phy- 

 sical geographer and philosopher, whilst the fallacy or mistaken facts 

 also remain uncontradicted, upon which it was mainly and originally founded 

 by the eminent author of the 'Physical Geography of the Sea,' it is 

 therefore now necessary for me to show, after what I have previously 

 written on the question, that the assertion of an undercurrent of from 1 to 

 If knot per hour in the Atlantic as counter to a surface-current of much 

 smaller amount on the outside of the Gulf-stream, is based upon a mis- 

 taken estimate of the results of the experiments that were supposed to 

 indicate such an undercurrent. 



Capt. Maury says, in p. 141, 1 Physical Geography of the Sea/ when 

 discussing his undercurrent views in the chapter headed " Undercur- 

 rents :" — 



" Lieut. J. C. Walsh, of the United States schooner ' Taney,' and Lieut. 

 S. P. Lee, in the United States brig ' Dolphin,' both, while they were car- 

 rying on a system of observations in connexion with the wind and 

 current charts, had their attention directed to the subject of submarine 

 currents. They made some interesting experiments on the subject. A 

 block of wood was loaded to sinking, and by means of a fishing-line or a 

 bit of twine let down to the depth of 100 or 500 fathoms ; a small float, 

 just sufficient to keep the block from sinking further, was then tied to the 

 line, and the whole let go from the boat. 



" To use their own expression, it was wonderful, indeed, to see this bar- 

 rega move off against wind and sea and surface-current at the rate of over 

 one knot an hour as was generally the case, and on one occasion as much as 

 If knot. The men in the boat could not repress exclamations of surprise ; 

 for it really appeared as if some monster of the deep had hold of the weight 

 below, and was walking off with the line. Both officers and men were 

 amazed at the sight." 



In paragraph 273 he says, " It may, therefore, without doing violence to 

 the rules of philosophical investigation, be conjectured that the equilibrium 

 of all the seas is preserved, to a greater or less extent, by this system of 

 currents and counter currents at and below the surface. If we except the 

 tides and the partial currents of the sea, such as those that may be created 

 by the wind, we may lay it down as a rule that all the currents of the ocean 

 owe their origin to difference of specific gravity between sea-water at one 

 place and sea-water at another ; for whenever there is such a difference, 

 whether it be owing to difference of temperature alone or difference of 

 saltness, &c, it is a difference that disturbs equilibrium, and currents are 

 the consequence. The heavier water gives towards the lighter, and the 

 lighter whence the heavier comes ; for two fluids differing in specific gravity, 

 and standing at the same level, cannot balance each other." 



