690 



DEPTHS OF THE OCEAN 



depends hrst of all on the salinity and temperature, but the 

 influence of salinity and temperature is essentially different in 

 regard to specific gravity and to viscosity. This fact is easily 

 seen from the following table, compiled from Knudsen's 

 tables for specific gravity and from Ostwald's measurements for 

 viscosity : — 



We see from this table that within the common limits of 

 salinity, 30 to 35 per thousand, the salinity influences viscosity 

 very little ; in other words, viscosity is almost entirely dependent 

 on temperature. If the viscosity of pure water at o C, is placed 

 at 100, ordinary sea-water at 0° C. has a viscosity of 102-103 ; 

 at lo"" C. it has decreased by one-fourth,' and at 25" C. by one- 

 half. Sea-water at 25^ C. is only half as viscous as the same 

 water at 0° C, that is, the same body sinks twice as rapidly 

 at 25'' as at o'^ C. Variations in salinity alone, it will be 

 observed, influence the specific gravity as well as variations 

 of temperature. In the ocean specific gravity and viscosity 

 therefore do not run parallel, but they run in the same direction. 

 Thus a body, which can maintain its specific gravity in- 

 dependent of changes in temperature and salinity, will have its 

 velocity of sinking increased with falling specific gravity and 

 viscosity of the sea-water, and its floating faculty will be 

 augmented when viscosity as well as specific gravity increase. 

 Osmotic Temperature, and especially salinity, influence the floating 



pressure, faculty of Hving bodies, through changes in osmotic pressure. 

 If the salinity of a cell is higher than that of the surrounding 

 water, the cell will, if not surrounded by an impermeable 

 membrane, give off salt and absorb water. The volume of 

 the cell will then increase, but although the cell actually 

 increases in weight, its specific gravity will decrease. In 



