SOUNDING 201 



quently and with greater accuracy, while good samples 

 of the deposit were obtained. 



During the " Challenger " Expedition (1872 to 

 1876) sounding with wire had not passed the experi- 

 mental stage ; all that was known for certain was that 

 the same wire could not be used for many soundings 

 without breaking. The " Challenger " made use of 

 a specially made hempen sounding line. It had to 

 carry on each occasion a load of valuable instruments, 

 and in this it was brilliantly successful. Wire rope 

 is suitable for sounding pure and simple ; indeed, the 

 systematic investigation of the form of the bottom of 

 the ocean can only be rapidly carried out with wire. 

 For deep sea researches, where many valuable ther- 

 mometers and other instruments must be sent to the 

 bottom in deep water, hemp rope is much more trust- 

 worthy than wire. However, during the recent 

 " Michael Sars " Expedition in the North Atlantic a 

 6-strand wire 3 or 4 millimetres in circumference was 

 used, with excellent results, to carry several thermo- 

 meters and water-bottles down to depths of over 

 1,000 metres. 



In the ordinary routine on board the " Challenger " 

 the soundings were made with the Baillie machine 

 (see Fig. 157), the sinker weighing 336 pounds, the 

 tube 25 pounds, and the attached water-bottle 20 

 pounds. The effective sinking - weight was 333 

 pounds in water ; every 100 fathoms of line used in 

 sounding added 6 pounds to this effective sinking- 

 weight. In very shallow water there was acceleration 

 in the rate of descent, but in deep water there was 

 continual and progressive retardation. With wire 

 there is continuous acceleration if allowed to run free 

 like the hemp line. 



In recent years soundings have been made by 



