142 THE PHYSICAL GEOGRAPHY OF THE SEA. 



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 it."* Both officers and men were amazed 

 at the sight. 



272. The experiments in deep-sea soundings have also thrown 

 much light upon the subject of under currents. There is reason 

 to believe that they exist in all, or almost all parts of the deep 

 sea, for never in any instance yet has the deep-sea line ceased to 

 run out, even after the plummet had reached the bottom. 



If the line be held fast in the boat, it invariably parts, showing, 

 when two or three miles of it are out, that the under-currents are 

 sweeping against the bight of it with what seamen call a swig- 

 ging force, that no sounding twine has yet proved strong enough 

 tp withstand. 



Lieutenant J. P. Parker, of the United States frigate Congress, 

 attempted, in 1852, a deep-sea sounding off the coast of South 

 America. He was engaged with the experiment eight or nine 

 hours, during which time a line nearly ten miles long was paid 

 out. Night coming on, he had to part the line (which he did 

 simply by attempting to haul it in) and return on board. Exam- 

 ination proved that the ocean there, instead of being over ten 

 miles in depth, was not over three, and that the line was swept 

 out by the force of one or more under currents. But in what di- 

 rection these currents were running is not known. 



273. It may, therefore, without doing any 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 (§ 34) 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 wherever there is such a difference, 

 whether it be owing to difference of temperature or to difference 

 of saltness, &c., it is a difference that disturbs equilibrium, and 

 currents are the consequence. The heavier water goes toward 

 the lighter, and the lighter whence the heavier comes; for two 

 fluids differing in specific gravity (§36), and standing at the same 



* Lieutenant Walsh. 



