From the inception of the theory of elasticity with Navier A821) and Cauchy A828), the dynamical problems of elasticity and the subject of wave propagations in elastic solids have been under intense study by a large number of workers. In fact the literature is so extensive that any desire to write accounts on the subject immediately induces discouragement on the part of a prospective author. For it is impossible to do justice to all aspects of this wide field in any one- or two-volume treatise. Perhaps, partially, it is this concern that kept this important field barren of books for nearly two centuries.