INTERPRETATION OF RESULTS 



495 



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the results may be charted directly in the form of numbers per section, with an accom- 

 panying distance scale below, as has been done in the preliminary study of the uneven- 

 ness of oceanic plankton (Hardy, 1936). If the machines are being used for a periodic 

 survey of an area, such as is being done in the North Sea, it is desirable to employ more 

 refined methods of charting. The quantities of plankton recorded, both on different 

 lines taken simultaneously and upon the same line at different intervals of time, should 

 be strictly comparable. They may be made comparable by converting the number of 

 organisms taken per section to the number taken per mile tow and the results (numbers 

 per mile per section) graphed accordingly. 

 Fig. 21 shows a graph of a typical record z - 

 obtained by the Type II recorder in the E 

 North Sea. The analysis was made by my t' 

 colleagues, Dr G. T. D. Henderson and 

 Mr J. H. Fraser. 



We have above indicated that a statement 

 that each section of the gauze represents 

 say 1, 1-5 to 2 miles of sea traversed can 

 never be strictly correct. Each section of the 

 graduated gauze covers exactly the area of 

 the cross-section of the water tunnel at its t. 

 point of traverse. Let us suppose that the 

 gauze banding is being wound on at such a 

 rate that any point upon it crosses the water 

 tunnel in the same time as the machine has 



travelled 1 mile through the sea. In Figs. + u" 



22-25 let the horizontal lines tu and t'u' 

 represent the roof and floor of the water 

 tunnel or their continuations, and let A, B, 

 C, D and E be points in the sea half a mile x ~ 



apart along the path of the water tunnel 

 which is being towed forward. Let XY 

 be a section of the moving gauze banding t 

 which takes a path across the water tunnel 

 represented by its dotted continuation. In ■£' 

 Fig. 22 let X begin to cross the tunnel just 

 as the point A in the sea crosses the path 

 of the gauze. Now let X be wound across 

 the water tunnel in the same time that the 



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if- 



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Fig. 24. 



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Fig- 25- 



machine is towed through a mile of sea, so that in Fig. 23 X will have reached the 

 position X' when C is passing through the gauze ; Y will now be at Y' . In Fig. 24 the 

 section XYh&s, wound completely through the tunnel to X" Y", and E will be passing 

 through the gauze of the following section. 



