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THE POPULAR SCIENCE MONTHLY. 



Fig. 2. 



the weight runs down. Another method of measuring the depth con- 

 sisted in running down a weight attached to a line, which was cut at 



the surface as soon as the weight was 

 supposed to have reached bottom, from 

 a sudden change in the rate of running 

 out, and the depth was then calculated 

 by the length of cord left on the reel. 



The ordinary system of sounding 

 fails at great depths, and cannot be de- 

 pended upon for more than 6,000 feet. 

 The weight is not sufficient to carry the 

 line rapidly and vertically to the bot- 

 tom, and, if a heavier weight be used, 

 the line is in danger of breaking. No 

 impulse is felt when the lead strikes the 

 bottom, and the line goes on running 

 out, and, if stopped, is liable to break. 

 Sometimes the line is carried along by 

 submarine currents, forming loops or 

 bights, and it often continues to run 

 out and coil itself in a tangled mass di- 

 rectly over the lead. These sources of 

 error vitiate very deep soundings, so 

 that the reports that have been made 

 of measurements in the Atlantic of 

 39,000, 46,000, and 50,000 feet, without 

 reaching bottom, are now regarded as 

 exaggerations. In the last charts of 

 the North Atlantic, on the authority of 

 Rear-Admiral Richards, no soundings 

 are entered beyond 24,000 feet, and very 

 few beyond 18,000 feet. 



The ordinary deep-sea lead, which is 

 a prismatic block about two feet in 

 length, and from 80 to 120 pounds in 

 weight, has a simple provision for bring- 

 ing up material from the bottom, which 

 is called " arming " that is, the lower 

 end, which is slightly cupped, is covered 

 with a thick coating of soft tallow. If it 

 5 reaches the bottom, mud, shells, gravel, 

 21125 ooze, or sand, sticks to the tallow, and, 

 when drawn up, affords a sample of the 

 nature of the ground. As the interest 

 in the bottom of the sea increased, there was a more eager curiosity 

 to scrutinize the particles thus procured for chemical and microscopical 



The Bull-dog Sounding-Machine 



