22 THE EXPLORATION OF THE SEA [PART I 



Deep-sea dredging or trawling presents difficulties of a very 

 real kind. First of all an immense length of trawl rope is 

 necessary to lower the net down to the depths at which it is 

 proposed to fish. To obtain a strong, yet light rope is in itself a 

 problem. Formerly hempen rope was used, thus the Challenger 

 used three-inch rope of this nature. Nowadays steel wire rope is 

 exclusively used, the compactness, strength and ease of stowing of 

 this being undoubted. Nevertheless the Challenger dredged in 

 3875, and trawled in 2650 fathoms. Then in deep-sea trawling or 

 dredging a large and heavy ship is of necessity used, and the 

 momentum of this presents other difficulties. For a small ship 

 will give and take to the variable tension of the trawl rope, but in 

 a large vessel a sudden movement of the latter, such as is caused 

 by a sea striking her, may easily put such a tension on the trawl 

 warp that the latter may part, with the loss of part of it as well as 

 the fishing instrument. This is avoided by the use of the apparatus 

 known as the "Accumulator" or Dynamometer. In the Challenger 

 this was constructed of tw^o strong discs connected together by 

 forty cords of rubber each one inch in diameter. To each disc a 

 number of lanyards were attached ; one series of these were con- 

 nected with a block which was secured to the foreyard near the 

 end of this. The other series of lanyards were connected Avith a 

 block which carried the dredging rope. When the ship rose to a 

 sea the rubber cords in the accumulator were extended and some 

 of the increased tension was taken off the trawl rope. Latterly 

 strong coiled steel springs have been used in place of the rubber 

 cords, and in some cases rubber pads acted as the material used to 

 take the extra strain. But the management of the trawl rope and 

 fishing gear in deep-sea work involves problems which are quite 

 outside the scope of this work, and for some account of the 

 methods involved I may refer the reader to the description of the 

 fishing gear used in the Siboga Expedition ^ or to the admirable 

 work on deep-sea trawling in the description of the United States 

 research vessel Albatross'^. In deep-sea trawling the form of 



1 See Reports of this Expedition. Livr. iv. gives an account of the equipment 

 of the ship, 1902. 



2 See Tanner, Bull. U.S. Fish. Commission, Vol. xvi. (for 1896), 1897. This 

 paper is full of interest. 



