364 



Biology in America 



was designing a sounding machine to be employed with wire 

 line, but wire was first actually used for this purpose by 

 two American captains, Belknap and Sigsbee, of the explor- 

 ing vessels, "Tusearora" and " Blake" respectively. They 

 employed piano wire about one-tenth of an inch in circum- 

 ference, with an obvious saving of space. For trawling 

 Sigsbee used a wire rope made up of forty-two piano wires 

 twisted about a tarred rope at the center. 



For sounding at great depths a heavy weight is necessary 

 to hold the line plumb against the currents of the sea and 



SIGSBEE SOUNDING MACHINE IN USE ON THE * ' ALBATROSS ' ' 

 Courtesy of the U. S. Bureau of Fisheries. 



the drift or swing of the ship even when at anchor, and this 

 descends at a rapid rate. With a weight of thirty to forty 

 pounds, the line runs out at the rate of about seven feet a 

 second, while with weights up to four or five hundred pounds, 

 which are employed in deep sounding, the speed is much 

 greater. The depth is determined from the number of revo- 

 lutions of the wheel which carries the line, and the end of 

 the sounding is noted by the sudden slackening of the speed 

 of the line in its descent. This point is naturally very difficult 

 to observe in a rapidly moving line. To overcome this diffi- 

 culty sounding machines of various types have been devised, 

 all of them founded on the principle of Lord Kelvin 's original 



