CHAPTER XVIII 



DEEP-SEA SOUNDINGS* 

 Wire Sounding — Dredging — Nature of Ocean Bottom — Submarine Sentry. 



In the first edition of this work the method of deep-sea sounding 

 with a hempen Hne was alone described. Hemp has now been 

 entirely superseded by wire, and therefore the machines em- 

 ployed in wire-sounding and the methods of using wire will 

 alone be treated of. 



Besides the advantage of weight, greater compactness of the Advan- 

 apparatus, the celerity with which the weight descends, and the -^frV 

 greater speed at which it can be reeled in, wire, from its small 

 size and the smoothness of its surface, enables in many cases 

 soundings of greater accuracy to be obtained. In sounding in 

 a surface current with hemp, the line was carried along with 

 the current, and it was impossible to keep the ship over the 

 lead. The result was that when the lead reached the bottom 

 the ship was a long way astern, and an empirical correction had 

 to be made to arrive at the vertical depth. With the fine wire 

 now used the friction is so slight that the ship can be kept over 

 the lead without the wire getting under the bottom, and the 

 length of wire out is the depth. 



Soundings with wire can be carried out at night with equal 

 facility as in daytime, and in almost any circumstances of 

 wind and weather short of a fresh gale, against which the ship 

 could not steam or face the sea. 



The machine used in surveying vessels for wire deep-sea Lucas 

 sounding is that devised by Mr. Lucas, of the Telegraphic M^^^^^®- 

 Construction and Maintenance Company, and has undergone 

 several modifications. 



* This chapter is entirely from information supplied by Captain A. M. 

 Field, E.N., supplemented by notes from Captain \V. U. Moore, E.N. 



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