i82 DISCOVERY REPORTS 



"cod-end" of the net tapers to join a canvas cylinder E, made to slip over and be 

 clamped to the collecting bucket. 



With the exception of the TYF the nets were made to our designs by the Marine 

 Biological Association at Plymouth. They were all treated with copper-soap preserva- 

 tive as described by Dr W. R. G. Atkins^, who kindly supplied much helpful advice 

 as to the manner in which it should be applied. In spite of the fact that the nets were 

 often kept under most unfavourable conditions, it was only on the rarest occasions that 

 a net was found to have rotted : the use of copper soap as a preservative is strongly to 

 be recommended. 



Specifications of Plankton Nets 



The design and function of each net will now be described in turn. Full details are 

 included in order that references may be given and repetition avoided in future papers 

 on plankton results. 



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

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

 inch. Its use formed part of the routine at each full station, a vertical haul being made 

 with it from 100 m. to the surface at a speed not exceeding i m. per second. Like the 

 N 70, next to be described, it is similar in size and mesh to that being used by Professor 

 Hjort^ in his plankton investigations in the northern whaling areas, so that comparisons 

 between the conditions in the two hemispheres may more easily be made. 



The ring, which has an opening of 50 cm. diameter, is made of galvanized iron, f in. 



thick with round cross section, and has at three equidistant points a pair of small 



eyes of | in. opening, one on each side of it, as shown in Fig. 7. These eyes form 



the points of attachment in front for the 



three bridles and behind for the lines 



attached to the bucket and weight. The 



bridles are of 3 mm. diameter phosphor- --^:^;--____^ ^ 



bronze rope, 3 ft. in length and with a 



, .... , 1 mi Fig. 7. Small tow-net ring. 



brass eye spliced mto each end. 1 hese 



are secured to the eyes on the ring by small shackles and drawn together at a towing 



shackle in front. 



In this net the sections A and D (Fig. 6) are continuous and of the same canvas 

 material, making a cylinder 26 in. long. At its front edge it is sewn on to the ring R 

 and behind to the conical net; on its outside are sewn six small brass rings at equal 

 intervals, each 3 in. from its hind end, so that the net may be closed by a throttling 

 rope if desired. The actual net, BC, 5 ft. 5 in. long, is of one material and tapers from 

 a diameter of 50 cm. to one of 6 cm., where it joins the small canvas cylinder, 7-5 cm. 

 long, for the attachment of the bucket. The netting employed is the silk bolting cloth 

 made by Messrs John Staniar and Co. of Manchester, and known as their "No. 25 



^ Atkins, JoMrw. Marine Biol. Assoc, n.s., xiv, p. 63, 1926. 



^ Nets of similar type are described and figured by him in Murray and Hjort's Depths of the Ocean, 

 p. 46, London, 1912. 



