METHODS I? 



METHODS IN THE FIELD 



The plankton samples were collected by three types of standard net : the 50 cm. 

 diameter net which was hauled vertically and is referred to throughout as the " N 50 V ", 

 the 70 cm. diameter net referred to as the "N 70 V" or the "N70H" according 

 to whether it was hauled vertically or horizontally, and the 100 cm. net which was used 

 horizontally and is referred to as the "N 100 H". The results obtained with the 

 Continuous Plankton Recorder are described in a separate paper to be published later ; 

 occasionally, however, the results obtained by this instrument will be referred to when 

 they have a bearing upon the present work. The instrument at this period was used as 

 an experimental rather than a routine method. A full description of the nets, illustrated 

 with text-figures, and of the method of using them has already been published by Kemp 

 and Hardy (1929) in vol. 1 of the Discovery Reports. For convenience, a brief summary 

 of the principal features will be given here. 



The N 50 V, designed for the capture of diatoms particularly and the smaller plankton 

 forms generally, is made of the finest silk bolting cloth : that with 200 meshes to the 

 linear inch. The front section of the net consists of a canvas cylinder 26 in. long and 

 50 cm. in diameter ; this is attached to a galvanized iron ring of the same diameter and 

 the ring is provided with three towing bridles. Behind the canvas cylinder is the net 

 proper, it is 5 ft. 5 in. long and tapers from a 50 cm. diameter in front to a 6 cm. 

 diameter behind, where it joins a small canvas cylinder, 7-5 cm. long, for attachment 

 to the special brass collecting bucket. Wire stay ropes, 9 ft. long, similar to the bridles, 

 extend downwards from the ring, assist in supporting the bucket and meet below to 

 support a 7 lb. lead. 1 



The N 70 V, designed for the capture of the medium and smaller sized organisms of 

 the macroplankton, from the small or young Euphausians and the largest Copepods 

 downwards, is made with two grades of silk netting: 40 meshes to the inch in 

 front and 74 behind. The galvanized iron ring has a diameter of 70 cm. At first, wire 

 bridles were used, but when it was found that these sometimes fouled the closing 

 mechanism they were replaced by rigid brass rods. From the ring extends a cylinder 

 of coarse netting, 21 in. long, joined behind to a canvas band, 10 in. wide, furnished with 

 brass rings to take the closing rope. The catching part of the net tapers from this band 

 to a small canvas cylinder, 9 in. in circumference, for attachment to the brass bucket. 

 This — the net proper — has a total length of 7 ft. 7 in. and is made in two sections: one 

 3 ft. 2 in. long of 40 meshes to the inch, and one behind 4 ft. 5 in. long of 74 meshes to 

 the inch. Stay wires extend from the ring, assist in supporting the bucket and meet 

 below to support a 40 lb. lead. 



The net is closed by releasing the towing bridles from the closing mechanism and 

 allowing the net to be caught and throttled by the closing rope passing through the rings 

 round the canvas band described above. 



1 Wire stay ropes have since appeared liable to chafe the silk of the net and in recent work they have been 

 replaced by ropes of manilla. 



