Table of contents

In certain observations of a downcoming radio wave, made for the purpose of measuring horizontal drifts of ionospheric irregularities, time shifts between fading curves obtained at three spaced receiving points are used to calculate the velocity and direction of drift of the amplitude pattern over the ground. Two simplifying assumptions about the pattern are frequently made, namely (i) the detail remains constant as it moves, and (ii) it is statistically isometric, i.e. the separation of two points for which the amplitudes have a given fixed correlation is independent of direction.

The errors that arise if assumption (i) is wrong have been considered in a published paper. But a more general analysis, not relying on either assumption may be applied to the three fading curves, and the result expressed (either analytically or graphically) as the error of a calculation which makes the two assumptions. One important result is that if assumption (ii) is not valid the error in direction of drift may be quite serious. Thus, in an application to amplitude patterns produced by vertical reflection at 2.4 Mc/s (principally from the E layer), errors in individual results averaged 15°. Because the structure of the pattern varied from sample to sample, the error was not, in this case, systematic. But, in some applications, a preferred direction of the pattern structure could, if ignored, lead to wrong conclusions about preferred directions of drift.

Observations of radio stellar scintillation on a frequency of 38 Mc/s were made with three spaced receivers. Suitable records were analysed to determine the average shape of the irregularities in the amplitude pattern on the ground. It was found on all occasions that the irregularities were elongated by a factor of at least 5:1, indicating that the ionospheric irregularities responsible for the amplitude pattern were also very elongated. The directions of stretching were consistent with the hypothesis that the irregularities in the ionosphere were extended along the earth's magnetic lines of force. Further evidence is presented which confirms the hypothesis. It is pointed out that under these conditions it is not possible to determine true velocities of drift from the time shifts between fading curves obtained at spaced receivers, and that the results of previous workers may be seriously in error.

The movement, and the diffusion, of irregularities of the kind here considered are briefly discussed.

Recent experiments (e.g. Llewellyn Jones and Morgan 1953) have shown that the emission of electrons from smooth cathodes having a thin tarnish film requires the initial deposition of positive ions and that the process then depends on the magnitude of the applied field (~10⁴ v cm^-1). The mechanism of this emission has hitherto been thought to be one of high-field cold emission through the surface barrier. The nature of this barrier is considered in more detail and it is shown that cold emission is improbable. An alternative theory of field dependent thermal emission is proposed which takes into account the existence of patch fields due to variation in the work function over the surface and uses a more realistic value for the degree of field enhancement near the surface. It is shown that, with this mechanism, the predicted emitting areas can be of more probable dimensions.

Recent experiments on electron emission in spark gaps with fields of the order of 10⁵ v cm^-1 have been interpreted in terms of a Fowler-Nordheim emission process. It is shown that a better explanation is thermionic Schottky emission allowing for surface irregularities, although it is not yet possible to distinguish between the two types of law. Expressions are derived giving relationships between the parameters in the two interpretations. The work function (~1.5-2 eV) and emitting area (1-10^-8 cm²), for agreement with the Schottky effect, should be capable of a much simpler physical explanation than the extremely low values obtained from a Fowler-Nordheim interpretation. A large error can be introduced in the latter case by neglecting thermionic emission. If it is assumed that the emitting surface is heated locally to 500°C, the work functions in the Schottky interpretation are of the order of 4 eV.

A second-order differential equation in the variables p and T is obtained which is valid for all phase equilibria of the first and second orders. On the basis of this equation, Ehrenfest's treatment of second-order phase changes is presented as a degenerate case of first-order transitions involving discontinuous changes of volume which are very small but non-zero. The ensuing discussion, in which special reference is made to the case of liquid helium, indicates how a fuller understanding of the nature of a second-order transition can be achieved by regarding it as the limiting case of a first-order transition.

Liebmann's method of tracing paraxial rays is critically reviewed, corrections being made to the higher terms of his formulae. A new and very accurate method of ray tracing is described, which is a development of that used by Burfoot; the predictor is one used by Goddard and the corrector is the double integration formula on which the method of Stormer is based. Like Goddard's, this method is applicable to marginal as well as to paraxial rays. The results of numerical tests of various methods are compared. The methods of Gautier and Laudet are discussed. The use of the constancy of the Wronskian determinant as a criterion of accuracy of paraxial ray tracing is considered, examples being given of instances in which it is and is not reliable.

The Bitter figure technique is used to study domain structures on polycrystalline alnico specimens with coercivities ranging from 0 to 100 oersteds, in which recognizable domains are recorded. In low coercivity specimens the domains are bounded by comparatively straight walls but they show more irregular outlines in high coercivity specimens.

The sounds, recorded on a microphone in air and on a hydrophone beneath the liquid, when a solid body strikes the surface are recorded and correlated with cine-photographs of the cavity formed on entry. Measurements of base pressure on a projectile forming a cavity are also made. It appears that the major contribution to the sound comes from pulsations of the cavity.

With the use of a double-cone diamond indenter, directional hardness studies are made on virgin surfaces of cast single crystals of Sn and Bi. The crystallographic orientations are determined by x-rays. Surface flow effects associated with the indenter are studied by multiple-beam interferometry. Hardness variations are measured over a 180° orientation range on each surface studied and they depend on the particular crystal face indented. Thus on a tin (311) face the ratio of maximum to minimum hardness goes through the range 1.6: 1 whilst on a (554) face of bismuth the range is as great as 4.5: 1.

It is demonstrated by interferometry that slip mechanism plays a primary part in producing directional variations in hardness.

It is shown that in rare instances a mode of growth by plane sheets operates on the octahedral faces of diamond which leads to the formation of six-sided growth features containing alternate angles of approximately 90° and 150°. It is shown that the edges of these are effectively parallel to the directions <431>. These may possibly arise through intersection of {221} with the (111) face.