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THE POPULAR SCIENCE MONTHLY. 



more and more out of the vertical direction in proportion to the 

 duration of the passage of the sinker to the bottom, and render 

 the results less and less accurate. Moreover, as the weight of the 

 submerged portion of the rope in addition to the weight of the 

 sinker soon becomes so heavy that a man can not lift it, and there- 

 fore can not assure himself by the sense of touch when the lead has 

 reached the bottom ; and as the weight of the submerged parts is 

 sufficient at great depths to cause the unwinding of the reel, the 



line may continue to pass out long after the 

 sinker has reached bottom, and the length 

 unwound may thus bear no relation to the 

 depth to be measured. In addition to these 

 sources of error there is another arising from 

 the drift of the vessel during the period of 

 several hours which is required to effect a 

 deep-sea sounding with rope. 



These causes, tending to carry the line off 

 in the direction of the subsurface currents in 

 an ever-increasing complication of loops and 

 bends, and impeding more and more the ve- 

 locity of the fall of the plummet until it sinks 

 into the oozy soil without communicating to 

 the surface any evidence of its arrival at the 

 bottom, explain the reports of the vast depths 

 of the sea that astonished the public mind 

 less than half a century ago. Lieutenant 

 Berryman, of the United States brig Dolphin, 

 reported an unsuccessful attempt to fathom 

 mid-ocean with a line thirty-nine thousand 

 feet in length. Captain Denham, of her Bri- 

 tannic Majesty's ship Herald, reported bottom 

 in the South Atlantic at a depth of forty-six 

 thousand feet ; and Lieutenant J. P. Parker, 

 of the United States frigate Congress, in at- 

 tempting to sound the same region, let go his 

 plummet and saw fifty thousand feet of line 

 run out after it as though the bottom had 

 not been reached. The deepest spot in the 

 South Atlantic is not more than twenty thou- 

 sand feet beneath the rolling waves that sealed its mysteries fifty 

 years ago ; and the deepest spot yet discovered in the world not 

 more than twenty-eight thousand feet. 



By the use of wire for sounding great depths many of the dif- 

 ficulties and uncertainties which characterize the use of rope are 

 obviated, for the wire, being light in weight and of small cross- 

 section, is not greatly affected by submarine currents, but allows 



Fig. 3. The SouNDiNfi 

 Cylindkr as it is 



HOISTfcl) FROM THE 



Bottom after the 

 Sinker has slipped 



OFF. 



