48 



DEPTHS OF THE OCEAN 



Large closing diameter at the mouth and 9 metres long, one of silk and the 



"^*^' other of net ; one of these is depicted open on the right and 



shut on the left in Fig. 30. They proved to be our most 



successful pelagic appliances. We used them sometimes as 



vertical nets and sometimes for towing. The closing mechanism 



(Fig. 31) was constructed 

 on Nansen's principle. A 

 slip-weight sets free the 

 cords that support the 

 ring, which falls down 

 and leaves the whole 

 hanging by a noose. This 

 noose draws the net to- 

 gether so that nothing 

 more can enter it. Two 

 sizes of mesh are used in 

 the construction of these 

 nets ; in the fore part a 

 mesh of about i centi- 

 metre and in the after 

 part one of almost J centi- 

 metre from knot to knot. 

 In deep waters, how- 

 ever, and especially out 

 in the open ocean, even 

 these large appliances, if 

 merely used as vertical 

 closing nets, fail to furnish 

 a representative picture 

 of the animal life. The 

 animals can only be cap- 

 tured by long horizontal 

 hauls, and therefore to 

 ascertain what exists at the 

 different depths we must 

 tow a large number of 

 appliances simultaneously. 



Fig. 31. — Closing Mechanism. 



Method of 

 using tow- 

 nets. 



Fh 



> shows the plan we generally adopted during the 

 Atlantic cruise of the " Michael Sars." Two lines were used : 

 a long line from the big winch for the deep-water appliances, 

 and a shorter one from the after winch for lesser depths. 

 Silk tow-nets either i metre or f metre in diameter, and 

 Petersen's young-fish trawls were alternately attached, and to 



