METHODS 



out of service for this purpose. However it is still a simple and excellent 

 small sampler and is now used, in a slightly modified form, by a number 

 of research laboratories, hi particular, the staff of the Edinburgh Occano- 

 graphic Laboratory (under the Scottish Marine Biological Association) still 

 use it for their regular surveys of the plankton of the herring grounds: 

 I say 'still' because the Edinburgh laboratory is the present thriving con- 

 tinuation of what was originally Professor Hardy's Hull laboratory. 



An essentially similar instrument to the 'Hardy' Plankton hidicator has 

 been made and used in Japan and is called instead the 'Handy Plankton 

 hidicator' ! Japanese workers, especially Professor Motoda, have designed 

 many interesting and useful additions to the range of our plankton samplers. 

 A larger version of the 'Hardy' hidicator is the Icelandic sampler (Plate V), 

 designed to give a rather bigger catch but with the maximum simplicity. 



The second type of gear designed by Professor Hardy was first used on 

 F.R.S. Discovery. An improved model is now used b)' the Edinburgh Labor- 

 atories and is towed from commercial ships at their normal cruising speeds. 

 It is called the ' Continuous Plankton Recorder ' (Fig. 6 and Plate V). This 

 instrument samples continuously, mile after mile, the plankton on the steamship 

 route. Basically it is the high-speed net again — a metal tube, streamlined, con- 

 stricted at the front, with stabilizing fins and a 'paravane' diving plane rigidly 

 fixed to it. As the instrument is towed the water-flow over it drives a small 

 'propeller' which acts through a gear-box and slowly winds on a long length of 

 plankton silk which is drawn across the path of the inflowing water. The 

 aperture is small, only | inch square, to keep the sample to reasonable pro- 

 portions. A column of water | inch square and lOO miles long would contain 

 2^ million cubic inches of water or 15,500 gallons = 70,000 litres. The area 

 of silk exposed to the passage of water is 4 inches ■ 2 inches to give a 

 relatively large filtration area and to help prevent clogging. As it collects 

 the plankton the silk, graduated in numbered divisions, is gradually wound 

 on exposing a fresh surface. The silk is then met by another roll of un- 

 graduated silk and both silks wind on together, with plankton safely 

 sandwiched between the two, into a tank loaded with formalin preservative. 

 The speed of the silk can be varied from about 2 inches to i mile to 2 inches 

 to 10 miles according to the length of tow and degree of precision required 

 in the knowledge of the plankton distribution. The paravane is designed to 

 take the Recorder to depths of about 10 metres (33 feet) within quite a range 

 of towing speeds, (S to 16 knots. It is first loaded by the scientists and then 

 it can be handled by the crew and collected on the return of the ship to its 

 base port or sent to Edinburgh from a distant port. It thus has to stand heavv 

 weather and heavy treatment in transit and is therefore very robust, weighing 

 about 1561b. The regular surveys initiated at Hull and developed in 



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