By coordinating our information on viscosity, diffusion, melting, and other rate and thermodynamic properties, we arrive at a detailed picture of liquid structure. Thus we find that a liquid is best thought of as a solid to which a large number of empty equilibrium positions are added. In fact the expansion on melting, as well as the expansion with a rise in temperature, arises almost entirely from this introduction of new equilibrium positions, and only to a minor extent from lattice expansion. We shall obtain information as to the number, size and energy of formation of these empty lattice points.