APPARATUS USED WITH PLANKTON NETS 



191 



organisms which may have remained behind. These buckets were made by Messrs 

 E. R. Watts and Sons. 



Buckets for Horizontal Nets. For N 70 horizontal 

 nets simple light cylindrical buckets, made from sheet 

 brass, were used; they were 2| in. in diameter and 5 in. 

 tall, with a wired strengthening rim round the top. The 

 bucket is slipped inside the canvas cod-end until the 

 rim comes just below the silk netting; here it is tied 

 securely with twine. 



The buckets used for the N 100, N 200 and N450 

 nets, though differing in size, are all of the same pattern 

 — that shown in Fig. 15. They are made of zinc with a 

 wired edge at the top. Those for the N 100 nets have 

 three rings on the side for the attachment of the longi- 

 tudinal ropes ; in those for the N 200 and N 450 nets the 

 ropes are tied below the bucket. In all three the canvas 

 cod-end is secured by a brass band with a fly nut. 



The dimensions of the three buckets are as follows : 



Fig. 15. Buckets for 

 N 100 horizontal 



N 450 and 

 nets. 



Diameter... 

 Height ... 

 Width of band 



N 100 

 6 in. 



12 in. 

 I in. 



N 200 N 450 



8 in. 12 in. 



16 in. 18 in. 



I m. 



m. 



These buckets and securing bands were found very convenient; but in time the 

 former became distorted by the pressure exerted by the fly nut ; to give greater strength 

 a narrow band of galvanized iron was fixed on the inside, just below the rim. 



The bucket for the TYF is the standard one made by the Marine Biological Associa- 

 tion at Plymouth for this type of net. It is of galvanized iron 7I in. in diameter and 

 ii| in. in height, and is fitted with four hinged lugs for attachment to the net, each 



4I in. from the top. 



In handling the plankton nets specified above attempts have been made in one or 

 two directions to introduce improved methods. The smaller nets, N70 and N 100, towed 

 vertically or horizontally and used for routine observations, have with few exceptions 

 been closed before being hauled, and the same procedure has been adopted, though 

 with less success, with the larger nets. Depth gauges of various kinds have, moreover, 

 been employed to determine the level at which horizontal nets were being towed. Before 

 giving an account of the methods of handling the various plankton nets it will be con- 

 venient to describe this subsidiary apparatus. 



The closing mechanisms used may be divided into three classes : those for vertical 

 nets, those for i m. and 70 cm. horizontal nets and those for large horizontal nets. 



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