204 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
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 conducting the investigations 
connected therevi^ith. 
429, The plan of deep-sea soundings finally adopted, and now 
in practice, is this : Every vessel of the Navy that will, when she 
puts to sea, is, if she desires it, furnished with a sufficient quantity 
of sounding-twine, carefully marked at every length of one hun- 
dred fathoms — six hundred feet- — and wound on reels of ten thou- 
sand fathoms each. It is made the duty of the commander to 
avail himself of every favorable 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 thirty-two pounds as 
a plummet. Having one end of the twine attached to it, the can- 
non ball is to be thrown overboard from a boat, and suffered to 
take the twine from the reel as fast as it will. - . 
The reel is made to turn easily. A silk thread, or the common 
wrapping-twine of the shops would, it was thought, be strong 
enough for this purpose ; for it was supposed there would 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 wa- 
ter, this strain would, it was imagined, be very slight. Moreover, 
when the shot reached the bottom, the line, it was thought 421), 
would cease to run out ; then breaking it off, and seeing how 
much remained upon the reel, the depth of the sea could be ascer- 
tained at any place and time, simply at the expense of one cannon 
ball and a few pounds of common twine. 
430. But practical difficulties that were not suspected at all 
were lurking in the way, and afterward showed themselves at ev- 
ery attempt to sound ; and it was before these practical difficul- 
ties had been fairly overcome that the great soundings (§ 428) 
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 422), and, consequently, that there was 
no means of knowing when, if ever, the shot had reached the bot- 
tom. And, in the next placQ, it was ascertained that the ordinary 
twine 427) would not do ; that the sounding-line, in going down, 
was really subjected to quite a heavy strain, and that, consequent- 
ly, the twine to be used must be strong ; it must be subjected to 
