PLANKTON NET SPECIFICATIONS 185 



lashed to the ring has the cylindrical section A, 3^ ft. long, made of ^ in. mesh (knot 

 to knot) netting. The band D is of tarpaulin canvas, 6 in. wide, with six galvanized 

 iron rings, 2 in. in diameter, sewn on the outside at equal intervals to take the 

 closing rope. The conical catching part of the net, BC, is io| ft. long, has a circum- 

 ference in front of 1 1 ft. (100 cm. diameter), and tapers to a circumference of i ft. 8 in., 

 where it joins a cylindrical section of canvas i ft. long for attachment to the bucket. 

 Of the two sections B is 3I ft. long and made of 4 mm. mesh (knot to knot) netting, 

 and C is 7 ft. long, made formerly of silk bolting cloth (Staniar's "Quadruple Extra 

 Heavy Quality", No. 16), having 15 meshes to the inch, but replaced later, after July 

 1927, by stramin. The silk netting with only 16 fine threads to the inch was not strong 

 enough and, even after being supported on the outside by a lacing of stout cord, had 

 continually to be patched or renewed. The stramin is very strong and its threads, 

 although only 1 1 or 12 to the linear inch, are very coarse, so that the filtration is no more, 

 in fact rather less, than that of the silk netting formerly employed. 



Down the length of the net run three i in. circumference ropes of log line. These 

 are sewn through long thin strips of canvas to the netting sections B and C, sewn to 

 the canvas band D, and in front threaded through the netting A and tied to the ring; 

 behind they have a free end of about 18 in. for tying to the rings of the bucket. 



The closing rope is 15 ft. long, and at one end has a large eye through which the 

 other end passes, forming a noose. 



The N 200 net, similar to the N 100 only larger and of wider mesh, is designed to 

 capture the rarer and faster-swimming pelagic forms which might escape the N 100, 

 or to collect, if necessary, such forms as Euphausians in greater quantity than does the 

 N 100. This latter necessity rarely arose since the N 100 usually provided more than 

 sufficient material. 



The ring is of galvanized steel, having a stream-line cross section as 

 shown in Fig. 10, and an opening 2 m. in diameter. It was made up 

 from two "half-rounds" and one "flat" riveted together: to those un- 

 acquainted with hydrodynamics it is surprising what a great difference 

 there is in the resistance of a towed net with round-section frame and 

 that of one with a stream-line frame. Along the hind margin of the 

 frame are a number of J in. holes at 4 in. intervals for lashing on the 

 net. At one point an eye zh in. in diameter is attached to the frame, 

 as shown in Fig. 12, as a fair-lead for the closing rope; by this means, 

 when the bridles are released, the frame is held by one edge, and is '^f j°^g stream- 

 thus less liable to surge from side to side while being hauled to the line frame for 

 ,- the N 200 net. 



suriace. 



The bridles consist of three 2 in. circumference ropes each 12 ft. long. The cylindrical 

 section, y^, is of i in. mesh (knot to knot) netting and is 7 ft. long. The band D is of 

 tarpaulin canvas 6 in. wide, with eleven 2| in. galvanized iron rings sewn on at equal 

 intervals. The catching part of the net BC has a total length of igh ft., and tapers from 



