DEEP SEA SOUNDING. 



711 



it is entered on the chart thus : 3,200, meaning no bottom 



was reached at that depth. 



This method of sounding answers very well for comparative! j 

 shallow water, but it is useless for depths much over 1,000 fath- 

 oms, or six thousand feet. The weight is not sufficient to 

 <.arry the line rapidly and vertically to the bottom; and if a 

 heavier weight is used, the ordinary sounding line is not strong 

 enough to draw up its own weight, and that of the lead from 

 a great depth, and so breaks. No impulse is felt when the 

 lead touches the bottom, and so the line continues running out, 

 and any attempt to stop it breaks it. In some cases the slack 

 of the line is carried along by currents, and in others it is 

 found that the line has been running out by its own weight 

 and coiling in a tangled mass on top of the lead. 



These sources of error vitiate the results of very deep soundings. 

 Thus Lieutenant Walsh, of the U.S. schooner Taney, reported 

 34,000 feet without touching bottom; and the U.S. brig Dol 

 phin used a line 39,000 feet long without reaching bottom. 

 An English ship reported 46,000 feet in the South Atlantic 

 and the U.S. ship Congress 50,000 feet without touching bottom 

 These are, however, known to be errors, so that no soundings 

 are entered on charts over 4,000 feet, and few over 3,000. 

 The U.S. Navy introduced the first great improvement in 

 deep soundings. This consisted in using a heavy weight and 

 a small line. The weight, a 32 or 68-pound shot, was rapidly 

 run down, and when it touched bottom, which was shown 

 by the sudden change in the rapidity with which the line was 

 run out, the line was cut and the depth estimated from the 

 length of cord remaining on the reel. This, however, cost the 

 loss of the shot and the line for each sounding. 



One of the first attempts at deep sea dredging was zna^e in 

 1818, by Sir John Ross, in command of the English navy ves- 

 sel Isabella, on a voyage for the exploration of Baffin's Bay 

 with a machine of his own invention, which he called a "deer 



