The empirical correction to Stokes’ law proposed by Robinson and Stokes has been extended for small ions to provide a concordant set of radii forthe hydrated ions. Ions with a crystal ionic radius of about 2 Á. exhibit a minimum hydrated radius of 3.3 A. corresponding to the maximum in the equivalent conductance. The internal consistency of the set of radii is demonstrated by correlation with the temperature coefficient of equivalent conductance, the viscosity¿-coefficient and the partial molar ionic entropy. Except for thesmall monatomic ions with the minimum hydrated radius, the hydrated ionic radius at 25 is demonstrated to be a linear function of the viscosity B-coefficient. The significance of this relation is discussed in terms of the structural modification rendered by the ions to water.