EXPLANATION OF THE PLATES 



Plate I. — A few of the instrumenta used in oceanic research. 

 [The figures are drawn to different scales.] 



Plate II. — Map showing the depth of the ocean. Depths 

 less than 1000 fathoms are uncoloured, while depths 

 between 1000 and 4000 fathoms are indicated by shades 

 of blue, and red colouring is used to show those deeps 

 in which depths of over 4000 or 5000 fathoms have been 

 recorded. 



Plate III. — Map showing the distribution of salinity in the 

 surface waters of the ocean. Salinities under 34 per 

 thousand are shown by shades of blue, between 34 and 

 38 per thousand by shades of purple, and over 38 per 

 thousand in the Mediterranean and Red Sea by red 

 colouring. 



Plate IV. — Map showing the annual range of temperature 

 in the surface waters of the ocean. A shade of blue indi- 

 cates a small range (less than 10° F.) both in polar regions, 

 where the temperature is low, and in tropical regions, 

 where the temperature is high. Shades of pink indicate 

 a range between 10° and 30° F., and shades of purple 

 a range between 30° and 50° F., while red colouring is 

 used to show the two areas of greatest range in the 

 north-west Atlantic and north-west Pacific, where the 

 annual range of temperature in each two-degree square 

 exceeds 50° F. 



Plate V. — Map showing the principal surface currents of the 

 ocean, the relatively warm currents being indicated by 

 red arrows, and the relatively cold currents by blue 

 arrows. 



Plate VI. — Map showing the distribution of density in the 

 surface waters of the ocean. Low densities (less than 

 r024) are indicated by shades of blue, and are limited 

 almost exclusively to the tropical regions, where con- 

 sequently the water tends to remain at the surface. 

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