500 DISCOVERY REPORTS 



not so good : out of fifty-three runs nine did not record the full distance through me 

 chanical failure, giving an efficiency of only 83 per cent ; but in the year before it was 

 again higher, giving 91-8 per cent efficiency. 



The successful running of the machine is dependent upon careful preparation in 

 loading (p. 470) and thorough cleaning and inspection after each record. 



POSSIBLE FUTURE DEVELOPMENTS 

 IN THE MACHINE DESIGN 



From time to time small improvements are made in the design, and later publications 

 will record alterations which are found desirable. It may not be out of place to refer 

 briefly to some of the possible more important developments in design that can be 

 foreseen. 



First place must be given to Mr J. O. Borley's valuable suggestion, already briefly 

 referred to (p. 499), for getting over the difficulty of successfully recording vertically 

 migrating organisms by moving the diving planes so as to make the machine take an 

 undulating path through the water. An extension of the worm shaft VE (Figs. 4, 10) 

 through the body of the machine would provide the necessary drive to operate a 

 movement of the planes. The planes could be moved very slowly by a cam action, so 

 that the machine would make a complete oscillation in depth between say 50 and 5 m. 

 (the range to be adjusted according to the depth of the area investigated) for every mile 

 of tow, so that each section examined would cover twice the whole range of depth and 

 be the equivalent of a double oblique haul. Such an oscillation of 50-m. depth (or less) 

 in a distance of a mile would mean only a very gradual climb and fall of the machine, so 

 that no undue strain should be anticipated. At first sight a regular alteration in the tilt 

 of the diving plane might seem to be the simplest method of achieving this result ; but 

 this would mean a continual movement of the centre of pressure in relation to the centre 

 of gravity of the machine, and this might well be fatal to the maintenance of stability 

 at high speeds. A better method would seem to be a regular alteration in the area of the 

 diving plane without altering its angle of incidence ; this could be done by arranging 

 extensions on each side to slide in and out by a rack and pinion action driven from an 

 extension of vertical shaft VE just referred to. Such an arrangement would give a 

 periodic increase and decrease in the downward thrust without in any way disturbing 

 the stability of the machine. Experiments are shortly to be made in this direction. 



It is hoped in later machines to improve greatly the condition of the plankton col- 

 lected by eliminating the tendency to crushing in the process of winding on the storage 

 spool. This could be done by enlarging the formalin tank to make room for another 

 spindle, on the ends of which would be mounted narrow reels holding rolls of strip 

 rubber, which would wind on to the storage spool between the edges of the layers of gauze 

 and so take off the pressure of winding from the centre section containing the plankton. 

 Fig. 27 shows how this may be achieved, the rubber strips being shown in black. As 

 already explained, the plankton is not subjected to any pressure in passing between the 

 driving rollers (p. 469). 



