The conductivity ratio of diluted and concentrated standard seawater has been measured very accurately in a salinity range from 0 to

and at temperature from -1 to

C. All the data have been fitted into polynomials which are compared with previous data. The specific conductance of seawater is deduced and a polynomial for the full range of salinity and temperature is proposed. Data presented in this paper have been used, with those of Dauphinee presented in this issue, to elaborate the new "Practical Salinity Scale 1978."