Based on Eyring's model of viscous flow, a relation between viscosity and internal pressure for liqs. is established by a thermodn. method. The Eyring's viscosity formula can be derived assuming that the size of a hole equals the vol. occupied by a mol., rather than one-third the vol. of a mol. as considered by Eyring and his collaborators. The mechanism and activated energy for viscous flow of liqs. are discussed in accordance with this result.s

Key words: THERMODYNAMIC PROPERTIES, FORMULA, MECHANISM, LIQUID, ACTIVATION ENERGY, RHEOLOGICAL PROPERTY, VISCOSITY, INTERNAL PRESSURE, VISCOUS FLOW