The main result of this paper is that two centers of dilatation in an infinite, isotropic domain do posses an interaction energy according to the linearized version of Toupin's strain-gradient theory of elasticity—in contrast to the classical theory of elasticity, where the interaction energy was shown to be zero. The center of dilatation has been adopted by many investigators as a representation of point defects in crystalline solids, so the above result may have significance in evaluating the long-range interactions which may occur between point defects.

• Received 8 May 1969

DOI:https://doi.org/10.1103/PhysRev.186.666