102 



THE OCEAN 



being ten times less absorbed than red rays. 

 Variations in colour may be due to materials 

 in suspension and solution ; thus in the neigh- 

 bourhood of coral reefs the water is usually 

 of a deep shade of blue, ascribed to calcium 

 carbonate in solution, while the green colour 

 of the water in the far south is due to the 

 abundance of diatoms and other minute plants. 

 Viscosity. — The viscosity or internal friction 

 of sea- water is important from its bearing upon 

 the floating powers of organisms and other 

 biological phenomena. Variations of viscos- 

 ity are almost entirely dependent on variations 

 of temperature, for within the common limits 

 of salinity (30 to 35 per thousand) variations 

 in viscosity due to differences in salinity may 

 be entirely neglected. Viscosity diminishes 

 with increase of temperature, as shown in the 

 following table : — 



