  A theory is presented to account for the increase in surface tension of water
in the presence of electrolyte. Unlike the original ``grand-canonical''
calculation of Onsager and Samaras, which relied on the Gibbs adsorption
isotherm and lead to a result which could only be expressed as an infinite
series, our approach is ``canonical'' and produces an analytic formula for the
excess surface tension. For small concentrations of electrolyte, our result
reduces to the Onsager-Samaras limiting law.
