Table of contents

The permanent magnet alloy Alcomax has been investigated after different heat treatments using two techniques. Curves of saturation intensity against temperature have been obtained using a Sucksmith balance, and curves of coercivity against temperature by extraction from a solenoid. It is concluded that maxima in the coercivity curves are associated with subsidiary Curie points. Reversible changes in room temperature coercivity produced between 600°C and 700°C are also associated with the appearance and disappearance of subsidiary Curie points.

If the permanent magnet alloy Alcomax III is quenched from a high temperature instead of the usual treatment it has the properties of a rather unusual soft magnetic material. The permeability is almost constant up to flux densities over 5000 gauss and the ratio of remanence to saturation intensity is less than 0.1 Details of these properties are given and their theoretical implications considered

The thermal expansion of alkali halides has been investigated at very low temperatures and at high temperatures. Attention has been concentrated on the isotropic cases, for which a formal expression for the Gruneisen constant has been obtained. It is shown that the Gruneisen constant is expected to increase somewhat as the temperature is increased. It is further shown that the contributions from the individual vibrations to the Gruneisen constant at low temperatures vary over a very wide range. The Gruneisen rule, however, is shown to require only that a certain average value of these contributions should not vary with frequency.

It is found at Ibadan that during the daylight hours fE_s is lower on magnetically disturbed days than on quiet days. It is also found that on two or three occasions in each month a series of abnormally low values of fE_s occurs. An investigation of the behaviour of the horizontal and vertical components of the earth's field during these times reveals that there is a simultaneous decrease in the magnitude of the equatorial electrojet current which is in turn responsible for the large diurnal ranges in H and Z near the equator. The behaviour of the F2 layer parameters f₀F2, y_mF2 and h_mF2 during periods of low fE_s, shows that the F2 layer always becomes denser, lower and thinner during these periods.

This indicates an immediate connection between the electrojet, the production of equatorial E_s and vertical drifts in the F2 layer.

Extensive air showers corresponding to primary cosmic rays ranging from 10¹⁴ to 3 × 10¹⁵ eV were recorded at Auckland for the year 1955. The results do not confirm the large sidereal diurnal effect reported previously.

The knowledge, to date, of optical absorption in ZnS is surveyed and discussed. The method used for determining the optical absorption and refractive index of a solid over a range of wavelengths is discussed and equations deduced for the transmittance and reflectance of a thin absorbing film on a thick substrate. The practical determination of the refractive index and extinction coefficient from the measured values of transmittance and reflectance is discussed in some detail. A description is given of the experimental procedure and precautions used in determining the optical constants of evaporated layers of ZnS. The results are discussed in relation to previous work. The effects of change of temperature at which the measurements are made, and of exposure of the films to air are noted and discussed.

The variation with temperature of the reflecting power of nickel has been measured by a null method at five wavelengths in the near infra-red region of the spectrum. The results are in satisfactory agreement with those calculated from previous work on emissivity. There was no conclusive evidence for a significant change in reflectivity at the Curie point.

This paper presents an attempt to correlate theoretically the various phenomena relating to jet formation and penetration into metallic targets by lined cavity charges on the basis of a simple modification of the non-steady state hydrodynamic theory. The modification consists in adding to the theory a couple of new assumptions suggested by experimental results and it appears that this modified theory accounts adequately for the stretching of the jet as it travels in space, the break-up of the jet into particles, the waver of the jet and the strength of the jet and target materials. In order to check the theory, numerical evaluations have been carried out in case of standard M9Al steel cones for which experimental results of Eichelberger are available. The good quantitative agreement between the published experimental values of Eichelberger and the theoretical results show that the theory provides an accurate description of the variation of depth, velocity and time of penetration with stand-off and nature of target material.