The consequences of a simple, phenomenological, theory of lattice thermal conductivity with respect to the effect of point imperfections are summarized. The experimental results of Berman et al. on the effect of varying the concentration of Li 6 on the conductivity of lithium fluoride are analyzed in detail.1 Rev. 95, 954 (1954). At low temperatures, considering normal three-phonon scattering processes, the relaxation times must obey r -1^a >«r 5_~« . 8 The ordinary theory of Umklapp processes would give BT 3 e~6 ,aT , where 0 is the Debye temperature and a is a constant characteristic of the vibrational spectrum. P. G. Klemens, in

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The motion of two fully relativistic classical spinless point particles interacting electromagnetically is studied in the special case of almost circular orbits. The equations of motion are dqfevence-dqferential equations with half-retarded plus half-advanced ~ignard-Wiechert potentials. As expected on both physical and mathematical grounds we find multiple stable solutions and conclude that ordinary (Newtonian) initial conditions are not sufficient to determine the trajectories. In addition to the stable solutions we find an infinity of divergent solutions. Alternatives for dealing with the extraneous solutions are discussed. The exact equations of motion can in certain limits be approximated by differential equations. Our solutions serve to delimit the range of applicability of the approximations.