1911] Kofoicl: Self-closing Plankton Net. 323 



ance of the impervious head of the net in hauling in. Burck- 

 hardt's experimental proof that the net remains empty when 

 loAvered open may be valid in quiet waters, but would be less 

 probable in a net subject to the surge of a ship. In any event, 

 with the net open in descent, a certain element of uncertainty 

 is always present which is entirely eliminated in the net closed 

 in descent. 



The Voigt (1902) horizontal closing-net is sent down closed, 

 and opened and closed again by concentric messengers. The 

 first releases the oblique door which falls to a horizontal position 

 by its own weight. The second releases the square frame or rim 

 of the net, which also falls into a horizontal position upon the 

 door and thus closes the mouth of the net again. The weight 

 of the frame alone is depended upon to keep the net closed. 

 The net is simple and apparently effective. For marine work 

 the no less than five vertical bars of the frame, as well as the 

 considerable horizontal parts, offer an impediment to entering 

 plankton of the larger sorts. A self-locking device on both the 

 door and rim would be necessary for use at sea to keep these 

 parts in place. The model is one deserving further elaboration. 



In the explorations of the ''Puritan" off Capri, Lo Bianco 

 (1903) used a closing-net of very large size, planned and built 

 in the Krupp works at Essen. The net is now at the Naples 

 Station. It is constructed in the main after the pattern of the 

 Chun-Petersen net, for vertical work, with hinged semicircular 

 jaws, opened by and closed by messengers. Its operation was 

 satisfactory. 



The Garstang closing-net operated at the Plymouth Station 

 since 1903 is planned for horizontal towing, with diagonally 

 suspended quadrilateral rim as in the Giesbrecht net. It is 

 opened and closed by messengers. It is very compact, all of 

 the parts being included in the large, cylindrical, vertical axis, 

 and the hinged frame sliding, upon it. It is rather light for 

 work at sea with a vertical cable, and the trips are not always 

 successfully discharged by the messengers. I have not found 

 a description of this net. 



The "Scotia" closing-net devised by Bruce (1904) is essen- 

 tially like the "Nansen" net, being available only for vertical 



