The Lie-Königs theorem has been sharpened to consider the question of the canonical representation of symmetry groups of even-order differential equations. An application to instantaneous action-at-a-distance relativistic mechanics yields the existence and uniqueness of a Hamiltonian formulation within the framework of the canonical representations of the Lorentz group.

We propose an experiment in which a frequency shift in atomic spectra would be sought as evidence of the theoretically predicted mass shift of an electron in an intense photon field. It is shown that the effect would be readily measurable if it exists.

Superconvergence sum rules are constructed for partial-wave scattering amplitudes. $\pi \pi$ scattering is discussed.

The coexistence curve of ${\mathrm{He}}^4$ has been measured over the range $0.1 \mathrm{mdeg}<T_c-T<\mathrm{}250\mathrm{} \mathrm{mdeg}$. The data for $T_c-T<\mathrm{}100\mathrm{}$ mdeg fit an expression of the form $|\rho -{\rho }_c|\propto {(P_c-P)}^{{\beta }_P}$, where $\rho$ is the density of either the liquid or the vapor, and $P$ is the pressure; ${\rho }_c=0.0701\mathrm{}\pm 0.0006$ g/${\mathrm{cm}}^3$, $P_c=1705.0\mathrm{}\pm 0.8$ Torr [$T_c=5.1890\mathrm{}\pm 0.0006°$K], and ${\beta }_P=0.355\mathrm{}\pm 0.004$.

Experiments are described on the propagation of quantized vortex rings in He II across an array of quantized vortex lines. Both scattering and capture of the charge carriers are observed.

It has been found that the diffusion coefficient of Se in CdSe is inversely proportional to the Cd partial pressure for most of the CdSe solidus region. This simple relation implies interstitial Se as the diffusing defect. Other diffusion studies indicate that a similar situation prevails in all of the II-VI compounds.

The magnetic moments of the first $2^{+}$ states in the even Te nuclei have been systematically investigated. The $g_R$ values obtained increase from 0.44 for ${\mathrm{Te}}^{120}$ to 0.93 for ${\mathrm{Te}}^{128}$. Not only are these values in strong disagreement with theory but the higher values are also substantially greater than $\frac{Z}{A}$.

Under the assumption that the sign and magnitude of ${K_1}^0-{K_2}^0$ mass difference is due to the contribution of the two-pion intermediate state in the self-energy dispersion integral, it is found that the $I=0\mathrm{}$ $S$-wave pion-pion interaction is strong near the $K$ mass. The possibility of a di-pion resonance above 500 MeV is suggested.