THE DEPTHS OF THE OCEAN. 299 



569. But practical difficulties that were not expected at all 

 Discovery of currents AYcre lurkiiiQ; in tlic wav, and afterwards showed 



in the depths of the ,^ -, , i i i i t i -j 



sea. themselYes at every attempt to sound ; and it was 



before these practical difficulties had been fairly overcome that 

 the great soundings (§ 567) were reported. In the first place, it 

 was discovered that the line, once started and dragged do^n into 

 the depths of the ocean, never would cease to run out (§ 562) 

 and, consequently, that there was no means of knovring when, if 

 ever, the shot had reached the bottom. And, in the next place, 

 it was ascertained that the ordinary twine (§ 566) would not do ; 

 that the sounding-line, in going down, was really subjected to 

 quite a heavy strain, and that, consequently, the U\me to be used 

 miLst be strong ; it was therefore subjected to a test which re- 

 quhed it to bear a weight of at least sixty pounds freely suspended 

 in the air. So we had to go to work anew, and make several 

 himdred thousand fathoms of sounding-twme especially for the 

 pm'pose. It was small, and stood the test required, a pound of it 

 measuring about six hundred feet in length. The officers in- 

 trusted with the duty soon found that the soundings could not be 

 made from sailing vessels mth any certainty as to the depth. It 

 was necessary that a boat should be lowered, and the trial be made 

 from it ; the men with 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 

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

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

 of the hne, 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 hne — for there might be several cm^rents nninmg in different 

 dkections, 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 tliis (and 

 Evidence in favour of it ^yas dcrivcd froiii a sourco whoUv unexpected), 



a regular system of . . , , . , /. , i , " j / • 



oceanic circulation, gomg to provo tlio cxistencc 01 that systcui 01 occanic 

 chculation which the climates, and the offices, and the adaptations 

 of the sea reqmre, and which its inhabitants (§ 465) in theii* mute 



