310 I'lIYSICAL GEOGRAPHY OP THE SEA, AND ITS METEOROLOGY. 



approbation of the Congress of the United States ; for that body, 

 in a spirit worthy of the representatives of a free and enlightened 

 people, had authorized the Secretary of the Navy to employ three 

 public vessels to assist in perfecting the discoveries, and in con- 

 ducting the investigations connected therewith. 



668. Tlie ]jJ an finally adopted. — The plan of deep-sea soundings 

 finally adopted, and now in practice, is this : Every vessel of the 

 navy, when she puts to sea, is, if she desires it, furnished with 

 a sufficient quantit}^ of sounding-twine, carefully marked at every 

 length of one hundred fathoms — six hundred feet — and wound 

 on reels of ten thousand fathoms each. It is made the duty of 

 the commander to avail himself of every favourable opportunity 

 to try the depth of the ocean, whenever he may find himself out 

 upon " blue water," For this purpose he is to use a cannon-ball 

 of 32 or G 8 pounds as a plummet. Having one end of the twine 

 attached to it, the cannon-ball is to be thrown overboard from a 

 boat or a steamer, and suffered to take the twine from the reel 

 as fast as it will. The reel is made to turn easil3^ A silk thread, 

 or the common wrapping-twine of the shops, would, it was 

 thought, be strong eriough for this purpose, for it was supposed 

 there Avould be no strain upon the line except the very slight one 

 required to drag it down, and the twine having nearly the specific 

 gravity of sea water, this strain would, it was imagined, be very 

 slight. Moreover, when the shot reached the bottom, the line, it 

 was thought (§ 561), would cease to run out; then breaking it 

 off, and seeing how much remained upon the reel, the depth of 

 the sea could be ascertained at any place and time simply at the 

 expense of one cannon-ball and a few pounds of common 

 twine. 



669. Discovery of currents in the depths of the sea. — But practical 

 difficulties that were not expected at all were lurking in the 

 way, and afterwards showed themselves at every attempt to 

 sound; and it was before these practical difficulties had been 

 fairly overcome that the great soundings (§ 667) were reported. 

 In the first place, it was discovered that the line, once started 

 and dragged down into the depths of the ocean, never would 

 cease to run out (§ 662), and, consequently^ that there was no 

 means of knowing when, if ever, the shot had reached the 

 bottom. And, in the next place, it was ascertained that the 

 ordinary twine (§ 666) would not do ; that the sounding-line, 

 in going down, was really subjected to quite a heavy strain. 



