loo DISCOVERY REPORTS 



in length, with a metre sheave suspended at the end of it, projects from the top of the 

 post, and when swung outboard is fixed securely at an angle of 45° from the rail by 

 means of a light tubular steel stay which extends from a position on the deck or the rail 

 to the outboard end of the derrick. An alternative deck position for this stay is provided, 

 so that the davit can be turned inboard and secured in that position. The wire passes 

 first to a sheave at the top of the post, thence down to another sheave attached to the 

 head of an enclosed spring accumulator mounted alongside the post, up again over a 

 third sheave also at the top of the post, thence to the metre sheave at the end of the arm 

 and so down to the water. The metre sheave is connected by a flexible drive to a large dial 

 counter, reading to 10,000 metres and fixed to the rail in a position facing the operator 

 working the machine. The advantages of the new davits lie in the height of the horizontal 

 arm above the water, which allows water bottles and nets to be hauled up to, or above, 

 the level of the rail, in the ease with which the dial can be read and in the very efficient 

 accumulator mechanism. The latter consists of a tubular casing to the top of which the 

 sheave is attached. Inside it are compression springs and a rod. The rod is attached at 

 its upper end to the top of the springs and at its lower end to the deck, so that tension on 

 the wire causes the sheave and casing to move upwards against the springs. Slight 

 tension, such as occurs when a net is being lowered, engages a light spring, but heavy 

 tension, as when the net or instrument is being hauled up, brings a second and stronger 

 spring into operation. The casing in which the springs work is watertight and is kept 

 filled with oil. 



In cold weather in the Antarctic the sheaves on the davits sometimes freeze in 

 their bearings. To thaw them paraffin flares were formerly used (Plate X, fig. i), but 

 steam jets on flexible connexions have now been installed for this purpose. 



APPARATUS 



The water bottles, plankton nets, release gears, dredges and trawls are mostly 

 similar to those described in vol. i, pp. 181 et seq. ; but both in apparatus and methods 

 some innovations have been made. 



The working of large closing nets has been notably improved by the use of a closing 

 band operating on the inside instead of on the outside of the net. When a large net is 

 closed in the ordinary way with an outside closing band and hauled towards the surface 

 the resistance to the water is distributed asymmetrically, and the resulting surging of 

 the net has been found to cause serious damage to the enclosed organisms. With 2-m. 

 stramin nets the difficulty has been overcome in the following way (see Fig. 5). A 

 closing band of 6-mm. wire is passed through rings on the inside of the net and fixed to 

 the release gear. A stray line of similar wire doubled is attached at one end to the re- 

 lease gear and at the other end to the shackle at which the bridles meet. This stray line 

 is of such a length that when the bridles are released the ring of the net falls back until 

 the closing band has completely throttled the net. The stray line and bridles then, 

 however, take up the weight of the ring and upper part of the net which maintain their 



