312 THE PHYSICAL GEOGRAPHY OF THE SEA. 



from it ; the men witli their oars keeping the boat from drifting, 

 and maintaining it in such a position that the line should be " up 

 and down" the while. That the line would continue to run out 

 after the cannon ball had reached bottom, was explained by the 

 conjecture that there is in the ocean, as in the air, a system of cur- 

 rents and counter currents one above the other, and that it was 

 one or more of these submarine currents, operating upon the bight 

 of the line, which caused it to continue to run out after the shot 

 had reached the bottom. In corroboration of this conjecture, it 

 was urged, with a truth-like force of argument, that it was these 

 under currents, operating with a swigging force upon the bights 

 of the line — ^for there might be several currents running in differ- 

 ent directions, and operating upon it at the same time — which 

 caused it to part whenever the reel was stopped and the line held 

 fast in the boat. 



570. A powerful train of circumstantial evidence was this (and 

 Evidence in favor of it was dcrivcd from a source wholly unexpected), 



a regular system of . , . ^ , p 



oceanic circulation, gomg to provc thc existeucc 01 that systcm 01 oce- 

 anic circulation which the climates, and the offices, and the adap- 

 tations of the sea require, and which its inhabitants (§ 465) in tlieir 

 mute way tell us of This system of circulation commenced on 

 the third day of creation, with the "gathering together of the wa- 

 ters," which were " called seas ;" it will probably continue as long 

 as sea water shall possess the properties of saltness and fluidity. 



571. In making these deep-sea soundings, the practice is to 

 Method of making a time the huudrcd fathom marks (§ 568) as they suc- 

 deep-sea soundmg. cggsively go out ; aud by always using a line of the 

 same size and " make," and a sinker of the same shape and weight, 

 we at last established the law of descent. Thus the mean of our 

 experiments gave us, for the sinker and twine used, 



2 m. 21 s. as the average time of descent from 400 to 500 fathoms. 



3 m. 26 s. " " " 1000 to 1100 " 



4 m. 29 s. " " " 1800 to 1900 " 



572. Now, by aid of the law here indicated, we.could tell very 

 The law of the plum- nearly whcu the ball ceased to carry the line out, 

 met' s descent. j^^ J whcu, of coursc, it began to go out in obedi- 

 ence to the current and drift alone ; for currents would sweep the 

 line out at a uniform rate, while the cannon ball would drag it 

 out at a decreasing rate. The development of this law was cer- 

 tainly an acliievorncnt, for it enabled us to show that tlic depth 



