102 DISCOVERY REPORTS 



a striker of sufficient length to pass beyond the splice and swivel at the end of the warp. 

 By means of snatchblocks the strain on the warp was partly taken up by a large accu- 

 mulator spring which gave a very clear indication of the moment when closure was 

 effected. With this apparatus vertical hauls have been taken successfully to a depth of 

 3000 m. ; but the release gear often proved unreliable, especially in a sea-way. In the 

 richly populated waters of the Antarctic this method is likely to prove of value, but in 

 the warmer parts of the Atlantic the plankton is so scanty that adequate quantities cannot 

 be taken in vertical hauls. The operation is in any case laborious and protracted. 



A continuous plankton recorder is sometimes in use in the ' Discovery II '. It was de- 

 signed by Professor A. C. Hardy and is an improved form of the model referred to in 

 vol. I, p. 189. A description of it will appear in Discovery Reports, vol. xi (in press). 



A new type of depth gauge (Plate XIII) is now used with deep horizontal or oblique 

 townets. The mechanism is similar in principle to that of the Budenberg gauge, with a 

 Bourdon tube working through a link motion which magnifies the movement and actu- 

 ates a pen which traces the changes in depth on a circular card rotated by clockwork. 

 This mechanism is mounted on a heavy steel base and is enclosed in a cylindrical steel 

 cover which fits into a circular groove in the base. The groove is lined with a hard 

 rubber washer. Experience with the Budenberg gauge showed that the leakage of water 

 into the mechanism, which occurred at all depths over 400 m., was due to the method of 

 securing the cover on the base. It was found impossible to get an equal strain on the 

 twelve screw studs which hold the two halves together, and experiments showed that 

 when the gauge was closed down omitting every other stud, there was, if anything, less 

 leakage. In the new gauge the base and cover are mounted in a frame consisting of two 

 vertical steel bolts joined by square steel bars. Through the upper bar is a large screw of 

 fine thread which bears on the centre of the cover. Thus in place of the twelve studs used 

 in the Budenberg gauge only a single screw is employed, and when this is tightened the 

 cover descends evenly on the rubber washer and forms a watertight joint which in 

 frequent tests has shown no sign of leakage even at a depth of 5000 m. 



The apparatus and methods used in hydrological work are similar to those employed 

 in the 'Discovery', though it may be mentioned that reversing and Nansen-Pettersen 

 thermometers made by Messrs Negretti and Zambra, reversing water bottles by Messrs 

 R. and W. Munro, Ltd., and Nansen-Pettersen water bottles by Messrs Elliot and 

 Garrood of Beccles, have given entirely satisfactory results. 



SOUNDING MACHINES! 



Although the Lucas and Kelvin machines are retained in the ' Discovery II ', sounding 

 is now carried out almost exclusively with the echo-sounding machines. These are of 

 the British Admiralty pattern and are supplied by Messrs Henry Hughes and Son, Ltd. 

 They include firstly the oceanic pattern of Deep-Water Sounder with improved hammer 

 of the balanced head type, an 'Acadia' Pattern Recorder, which can be used with the 



1 We are indebted to Mr H. F. P. Herdman for the information given in this section. 



