PLANKTON NET SPECIFICATIONS 



183 



First Standard Quality Double Twist Silk", having approximately 200 threads to the 

 linear inch. It was found that these nets, being made of such fine material, frequently 

 split ; in future they will be made with an outer cover of wide mesh netting to take the 

 strain of the pressure when hauling. 



The brass collecting bucket, which is separately described with those 

 for the other nets on page 189, is secured to the small canvas cylinder at 

 the tail of the net by means of a brass band and tightening screw. The 

 wire stays supporting the bucket are of the same material as the bridles, 

 but 9 ft. long; they are attached by small shackles to the eyes on the 

 ring, seized to the eyes on the bucket holder and when, as usually, the 

 net is used vertically, meet below at a shackle supporting a 7 lb. lead. 

 The net as rigged for vertical use is shown in Fig. 8. 



The N 70 net is designed for the capture of the medium and smaller 

 sized organisms of the macroplankton, from small or young Euphausians 

 and largest Copepods downwards, and is made with two grades of silk 

 netting: 40 meshes to the inch in front and 74 behind. As explained 

 elsewhere the use of this net formed part of the routine at all full stations, 

 being used vertically and horizontally or obliquely. When used vertically 

 it was hauled at a speed of i m. per second, and closed by messenger, 

 closing mechanism and throttling rope when it had fished through the 

 required layer. An account of the routine work with these nets will be 

 found on pages 199-201. 



It will first be described as rigged for vertical use. 



The ring is similar to that used in the N 50, but has an opening 70 cm. 

 in diameter. At first phosphor-bronze bridles were used, but when it was 

 found that these sometimes fouled the closing mechanism on the way 

 down, so preventing or precipitating its action, they were replaced by 

 three brass rods. These are j in. thick, 32 in. long and have an eye at 

 each end carrying a brass ring; they are each shackled to the frame at 

 one end and at the other meet in a shackle for attachment to the closing 

 mechanism, thus forming a rigid tripod. 



The section A (Fig. 6) is 21 in. long and made of strong J in. mesh 

 (knot to knot) netting. In front, where it has a rope margin, it is lashed 

 to the frame, and behind it joins the canvas band D, which is 10 in. wide 

 and has, like the N 50, six brass rings to take the closing rope. The Fig.8. The N 50 

 catching part of the net BC tapers from this to the small canvas cylinder, "^'- ."SS^'^ f""" 

 9 in. in circumference, for attachment to the bucket. It has a total 

 length of 7 ft. 7 in., but is in two sections; the first, B, 3 ft. 2 in. long, is made from 

 Messrs Staniar's "Quadruple Extra Heavy Quality Double Twist Swiss Silk" bolting 

 cloth. No. 40, having 40 threads to the linear inch, and the second section, C, 4 ft. 5 in. 

 long, from the same quality bolting cloth, No. 74, having approximately 74 threads 

 to the linear inch. 



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