30 BRITISH IND US TRIES. 



because they are virtually outside the cavity of the 

 net, and their openings are at the farther end of it. 

 The water, however, which has expanded the body 

 of the net, then makes its way through the flapper 

 or valve, and enters the purse, which, being made 

 with a much smaller mesh than the rest of the net, 

 offers so much resistance, that it cannot readily 

 escape in that direction ; return currents are conse- 

 quently formed along the sides, and these currents 

 open the mouths of the pockets, which face the purse 

 or small end of the net ; and the fish, in their efforts 

 to escape, finding these openings, follow the course of 

 the pockets, until they are unable to proceed any 

 further. The whole of the net is therefore fully ex- 

 panded, but it is so by the pressure of the water in 

 one direction through the middle, and in the opposite 

 one at the sides. 



In an ordinary deep-sea trawl, the meshes are of 

 four sizes, diminishing from 4 inches square near the 

 mouth to 1 J inch at the cod or small end ; and the 

 twine used for the under part of the net is usually a 

 size larger than that for the back. 



A large trawl such as has now been described is 

 therefore an immense bag-net, frequently 50 feet wide 

 at the mouth, and upwards of 100 feet in length. It 

 is towed over the ground by the " trawl- warp," usually 

 a 6-inch rope, 150 fathoms long, and made up of two 

 lengths of 75 fathoms each, spliced together. The 

 end of this warp is shackled to two other pieces, each 

 15 fathoms long, and called the " spans or bridles," 

 which lead one to each end of the beam, and are 



