PHYSICAL PROPERTIES OF SEA WATER 17 



Surface tension (dynes/cm^) = 75.64 - 0.144 + 0.0399 CI 7oo. 

 The surface tension is decreased by impurities, and in the sea is mostly 

 smaller than stated. 



Refractive Index. The refractive index, n, increases with increas- 

 ing salinity and decreasing temperatures. It also varies with the wave 

 length of light, and hence a standard must be selected, usually the D line 

 of sodium. In fig. 3A the relation between refractive index, tempera- 

 ture, and chlorinity is shown. 



Electric Conductivity. The electric conductivity of sea water 

 depends on temperature and salinity (chlorinity). The specific conduct- 

 ance of sea water is shown in fig. SB as a function of these two variables. 



Eddy Viscosity, Conductivity, and DifFusivity 



General Character of Eddy Coefficients. It has been repeat- 

 edly stated that the coefficients of viscosity, heat conduction, and diffu- 

 sion that have been dealt mth so far are applicable only if the water is at 

 rest or in laminar flow. By laminar flow is understood a state in which 

 sheets (laminae) of liquids move in such an orderly manner that random 

 fluctuations of velocity do not occur. However, the molecules of the 

 liquid, including those of dissolved substances, move at random, and, 

 owing to this random motion, an exchange of molecules takes place 

 between adjacent layers. 



In nature laminar flow is rarely or never encountered, but, instead, 

 turbulent flow, or turbulence, prevails. By turbulent flow is understood a 

 state in which random motion of smaller or larger masses of the fluid are 

 superimposed upon some simple pattern of flow. The character of the 

 turbulence depends upon a number of factors, such as the average 

 velocity of the flow, the average velocity gradients, and the boundaries of 

 the system. In the presence of turbulence the exchange between adjacent 

 moving layers is not limited to the interchange of molecules, but masses of 

 different dimensions also pass from one layer to another, carrying with 

 them their characteristic properties. As a consequence the instantaneous 

 distributions of velocity, temperature, salinity, and other variables in the 

 sea are most complicated, and, so far, no means have been developed for 

 studying these distributions. Measurements by sensitive meters have 

 demonstrated that in a given locality the velocity of a current in the sea 

 fluctuates from second to second, as does the wind velocity, but in most 

 cases observations of ocean currents give information only as to mean 

 velocities for time intervals that may vary in length from a few minutes to 

 twenty-four hours or more. Similarly, special measurements have 

 demonstrated that the details of the temperature distribution are very 

 complicated, but in general observations are made at such great distances 

 apart that only the major features of the distribution are obtained. 

 Inasmuch as it is impossible to observe the instantaneous distributions in 



