146 WEIBEL AND THUUAS: 14ECORDING SALINITY 



of their boundary conditions which could hardly be obtained by 

 repeated single measurements of temperature. 



The temperature, however, is not nearly so reliable a clue to 

 the location of currents and the origin of water masses as is the 

 salinity. A body of sea water may change considerably in tem- 

 perature in moving from one place to another, but unless the 

 evaporation or rainfall is excessive its concentration will change 

 comparatively little. By salinity is meant the number of grams 

 of salt or solids in one kilogram of sea water. The composition 

 of these salts is very nearly constant everywhere in the open 

 ocean, but the salinity, or concentration of the total salts, varies 

 from place to place. 



From a consideration of the properties of sea water that vary 

 with the salinity, the electrical conductivity seemed to be the 

 most susceptible to continuous measurement, if the difficulty 

 due to the variation of conductivity with temperature can b(^ 

 overcome. This difficulty is avoided by the use of a method 

 which is compensated for temperature. 



This paper describes the method of measurement and the ex- 

 perimental work done towards the production of an apparatus 

 to give a continuous record of sea-water salinity to the accuracy 

 required in the most precise oceanographic research. The work 

 has not been finished, but from the results obtained we believe 

 that the method is practical and sufficiently important to war- 

 rant publication at the present time, even though the apparatus 

 is not yet built. 



DESCRIPTION OF THE METHOD 



The method consists in measuring the ratio of the resistance of 

 sea water in two equal or nearly equal electrolytic cells A and B 

 (fig. 1); one cell A is sealed and contains sea water of a known 

 average salinity, the other cell B is open and has flowing through 

 it the sea water to be measured. This ratio is obtained by a 

 Wheatstone bridge using alternating current to eliminate polari- 

 zation effects in the cells. A calibration of the apparatus can 

 be made at any time by using sea water of known salinity in the 



