12 



THREE CRUISES OF THE " BLAKE. 



OO 



the hemp-lijie soundings by the great diminution of speed in the 

 running out of the rope after the sinker has struck, 

 "^ but by the instantaneous action of the sinker on the 



wire when striking bottom ; the wire stops, and in 

 less than a second the momentum of the reel is 

 checked by the friction - rope attached to it. The 

 dropping of the shot is detected on deck with as 

 great certainty as if it had been followed by the eye 

 to the very bottom ; indeed, the percentage of error 

 m soundings made with piano-wire is probably not 

 more than one fourth of one per cent. The error in 

 soundings made by the old methods can only be de- 

 termined after the rope-soundings have been corrected 

 by wire-soundings. To those who are not famihar 

 with the practical working of deep-sea soundings as 

 formerly carried on, a few figures enabling them to 

 compare the old with the new methods may be inter- 

 esting. In the " Challenger " the 

 deep-sea soundings were made with 

 a rope of eight tenths of an inch 

 in ciicumference, nearly as large as 

 the steel-wire rope which we used 

 in dredging, and having a breaking weight of 1,200 

 pounds. The time occupied in lowering the sound- 

 in o- machine and its weights, often more than 300 

 pounds, was three to four times as great as on the 

 " Blake." We employed a steel wire (No. 20, Amer- 

 ican gauge), with breaking weight of 240 pounds, 

 weighted for the deepest soundings only, with a sixty- 

 pound shot. The time required to reel in with Cap- 

 tain Sigsbee's wire machine was generally below one 

 minute and a half per one hundred fathoms, some- 

 times not more than fifty seconds, while the time re- 

 quired to strike bottom averaged from fifty to seventy- 

 five seconds per one hundred fathoms in the deepest 

 soundings up to two thousand fathoms. In depths 

 less than one thousand fathoms or so, an ordinary 

 thirty-four pound lead with a Stellwagen cup for ob- 

 taining bottom specimens was used. The lead was reeled in 



Fig. 9. — Comparative 

 Size of Hemp and 

 Wire used for Sound- 

 ing. (Sigsbee.) 



Fig. 10. 

 Sounding 

 Lead with 

 Stellwagen 

 Cup. (Sigs- 

 bee.) 



