We have made measurements of the far-infrared absorption at 7°K in NaCl. The natural ${\mathrm{Cl}}^{35}$ and ${\mathrm{Cl}}^{37}$ isotopes acting as simple mass defects result in absorption in the acoustic band and yield information about phonon frequencies at critical points. The theory of this effect is derived and applied to NaCl. Similar measurements on LiF are also reported. We believe this to be the first observation of isotope-induced band-mode absorption in alkali halides.

The temperature dependence of the low-temperature specific heat of alloys of the class Pd: Ni is calculated using a localized exchange model in the dilute limit. An approximate extension of the theory leads to a singular mass enhancement at the ferro-magnetic critical concentration and a strong $T^3\ln T$ dependence in this region.

An absolute intensity measurement of cosmic-ray neutrons in the atmosphere, in the energy range from thermal to 20 MeV, leads to a value of 0.36±0.06 neutron ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ for the albedo neutron leakage flux at 42° geomagnetic latitude near solar minimum. The significance of this value for evaluating the contribution of the cosmic-ray albedo-neutron-decay source for the high-energy protons in the inner radiation belt is discussed.

The flux of cosmic-ray electrons in the energy interval of 17-63 MeV was measured in three high-altitude balloon flights during the summer 1967 near Fort Churchill, Manitoba. The average flux was found to be 0.3±0.2 electrons/${\mathrm{m}}^2$ sec sr MeV. Implications of this result on models of the origin of galactic cosmic-ray electrons and their solar modulation are discussed.

We have measured the cross section for photoproduction of $\varphi$ mesons at 0° by 1800-MeV photons. Approximately 165 $\varphi \text{'}\mathrm{s}$ were observed, yielding a cross section $\frac{d\sigma }{\mathrm{dt}}=(0.75\mathrm{}\pm 0.17)$ μb/Ge${\mathrm{V}}^2$/nucleon for $\mathrm{}\left|t\right|=0.175\mathrm{}$ Ge${\mathrm{V}}^2$. This value is consistent with a "vector-dominance" prediction using ${\rho }^0$ photoproduction data, SU(3) coupling constants, and a quark-model prediction for the $\rho$- and $\varphi$-nucleon cross sections.

The interaction of two weakly coupled resonant systems is considered. It is shown that if one system is treated quantum mechanically and the other classically, the results that depend on the zero-point oscillations of the quantum-mechanical system cannot be expected to be physically meaningful.

$\mathrm{KN}$ finite-energy sum rules, with phase-shift analyses as input, are evaluated to determine the $t$ dependence of the relevant Regge-exchange amplitudes. The spin nonflip contributions are similar to those deduced from high-energy Regge fits; however, the spinflip contributions of the high-energy fits are inconsistent with the sum-rule results. The implications for polarization and $K^{+}n$ charge exchange are discussed.

Electron-proton coincidences from the reaction $e^{-}+p\to e^{-}+p+{\pi }^0$ have been measured for pion-nucleon center-of-mass energies in the region of the $N^{*}\mathrm{}\left(1236\right)\mathrm{}$ resonance at four-momentum transfers near 1, 3, 6, and 10 ${\mathrm{F}}^{-2\mathrm{}}$ [0.05 to 0.4 ${(\mathrm{B}\mathrm{e}\mathrm{V}/\mathit{c})}^2$]. Data have been obtained for pion polar angles between 100° and 180° c.m. over a wide range of azimuthal angles. The results are compared with the dispersion theories of Adler and Zagury.

We have analyzed recent data on neutral pion electroproduction in the region of the $N^{*}\mathrm{}\left(1236\right)\mathrm{}$ resonance phenomenologically to determine the magnitude of the dominant magnetic dipole amplitude and its interference with the ${E_1}^{+}$ electric quadrupole amplitude. Evidence is found for the existence of significant scalar multipoles. The four-momentum-transfer dependence of the magnetic dipole amplitude is interpreted in terms of the $\gamma N{N}^{*}$ transition form factor between 0.05 and 0.4 ${(\mathrm{B}\mathrm{e}\mathrm{V}/\mathit{c})}^2$.

An extension to multiperipheralism is made of the Dolen-Horn-Schmid duality argument relating Regge poles to low-energy resonances. The Deck model is thereby interpreted as predicting the existence of the $A_1$, rather than as undermining experimental evidence for this resonance. It is shown in general that Dolen-Horn-Schmid duality permits a vast simplification in the calculation of multiple-production processes.

The complex electrical conductivity is calculated by the strong-coupling theory for superconducting lead and tin. The theory is shown to be internally consistent and in agreement with Palmer and Tinkham's experiments. We demonstrate that the real part is simply related to the real part of the gap function for large frequencies.

We derive a dispersion relation valid for arbitrary wavelength of the spin-independent oscillations of a electron fluid. Analytic expressions for the long-wavelength limit can be obtained quite easily. In addition, results for all wavelengths can be obtained numerically for the situation in which the Fermi-liquid interaction is approximated by a finite series of spherical harmonics.

ENDOR measurements of the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ nuclei in the first four shells in Ca${\mathrm{F}}_2$ containing ${\mathrm{Yb}}^{3+}$ ions in the cubic site are reported. The results are compared with those of isoelectronic ${\mathrm{Tm}}^{2+}$ ions.