Measurements of some temperature and pressure dependent relationships of the electrical conductivity of seawater at various salinities were made using four-electrode conductivity cells. At atmospheric pressure the measurements were of the effect of temperature over the range from the freezing point to about 35\deg C on 1) r_{T} (the ratio of the electrical conductivity of 35\permil seawater at temperature T to that at 15\deg C) and 2) R_{T} (the ratio of the electrical conductivity of a given seawater at temperature T to that of 35\permil seawater at the same temperature) at various salinities. The results under 1) have been combined with those of Dauphinee [1] and expressed as a fourth degree equation in temperature by Perkin and Lewis [2]. The results under 2) confirm the temperature dependence of the findings of Dauphinee [1] and of Poisson [4] for R_{T} as a function of salinity (weight dilution) at various temperatures. Measurements of the effect of pressure on the electrical conductivity of seawater were made for salinities of 2, 14, 22, and 35\permil over pressure and temperature ranges of 0 to 1000 bars above atmospheric pressure and the freezing point to 30\deg C, respectively. These results complement those of our earlier work [5] using a two-electrode conductivity cell on 31, 35, and 39\permil salinity seawaters over approximately the same pressure and temperature ranges. "Best" least squares polynomial fits in pressure and temperature to the new and to the old observed values of percentage increase in conductivity at 35\permil agree within the equivalent of 0.006\permil salinity at 1000 bars. The accuracy of the new results, which at 35\permil is probably not worse than the equivalent of 0.003\permil salinity at 1000 bars, is superior to that of the earlier ones. Perkin and Lewis [2] have fitted rational functions in P, T, R, and \sqrt{R} where R is the ratio of the electrical conductivity at P, T, and salinity S to that at 0 bars, 15\deg C and 35\permil , to the combined old and new edited data. They obtained a standard deviation of 1.3-ppm salinity for their oceanographic fit and a standard deviation of 1.3-ppm salinity for their general fit.

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