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The magnetic and dielectric properties of γ-ferric oxide, magnetite, Mn-Zn ferrite and Ni-Zn ferrite have been measured at wavelengths from 60 cm. to 1.23 cm. The pronounced magnetic dispersion and absorption which occur are attributed to the decay of the rotational magnetization, due to Larmor spin resonance in the internal anisotropy field H_N. The theoretical relation H_N = 2K/M, where K is the anisotropy coefficient, and M the saturation intensity, agrees satisfactorily with the observations, and|K| has been derived for each material. An inverse relationship between H_N and the initial susceptibility is shown to account quantitatively for the magnetic resonance observed in high-permeability materials at much lower frequencies

The electrolytic tank method was developed to record rapidly the potential variations which occur in the field of the immersion objective in the absence of space charge. The axial distribution over the region explored was found to conform with a law of the form V = Ae^kz. Here A is a voltage scale factor while k is a geometrical scale factor. The experimental results appear to show that for constant black-out voltage the gradient at the cathode remains constant over part of the range explored, independent of geometry. The ratio of accelerator to modulator voltage for zero gradient at the cathode varies inversely as the square of the hole diameter. A determination of the emitting area of the cathode was also made from the field plots.

Quantitative studies of extra-foveal colour vision are inherently difficult owing to the poor discrimination and rapid adaptation found in the parafoveal and peripheral areas of the retina Measurements of the luminosity, colour mixture and hue discrimination curves have been made by a single observer using a field subtending 1° 20' and located at 2° and 4° from the fovea. The results suggest that for high retinal illumination parafoveal colour vision does not differ in essential characteristics from foveal colour vision, but at low illuminations colour perception becomes reduced to a type of dichromatic vision similar to the tritanopic form of defective colour vision and to that reported for small-field foveal vision.

The grain yield per absorbed quantum has been evaluated experimentally for four different photographic emulsions over a wavelength range of 1·-0.01 A., i e. from very soft X rays to gamma rays emitted from radium The tests were carried out with both heterogeneous and monochromatic X rays A grain yield of 1.0 per absorbed quantum appears to hold within a range of wavelengths of 1.2-0 37 A. (10 kV -33 kV). From 0.37 A. to short wavelengths (gamma rays) an increase of grain yield linear with quantum energy is obtained At a wavelength of 0.0123 A (1,000 kV.) about 80 grains are rendered developable per quantum absorbed The rate of increase of grain yield with quantum energy is different for different emulsions. For a slow and fine-grain chloro-bromide emulsion the grain yield was found to be less than unity for wavelengths below 0.12 A (i.e 100 kV) The results are consistent with the hypothesis that grains are made developable not only by the direct action of X rays but also by secondary electrons produced by the X rays. These are effective only when they are energetic enough to reach grains in the neighbourhood of that absorbing the original X-ray quantum.

The fading of a radio wave once reflected from an irregular ionosphere is discussed in terms of the variable diffraction pattern produced at the ground. It is pointed out that fading may arise either by a drift of the diffraction pattern past a receiver, or by irregular variations in the pattern, or by both mechanisms together It is shown how, from observations at three receiving points, it is possible to deduce the rate at which the pattern is changing and the velocity with which it drifts over the ground This velocity is of interest as it may be related to the wind velocity at ionospheric heights in the atmosphere, but the relation of the diffraction pattern to the irregular ionosphere which produces it is not discussed in detail

During the last twenty years, enhancements of the mean level of atmospherics, on 11 km. wavelength, have been associated with some other phenomena such as simultaneous fade-outs of the field intensity of stations on decametric wavelengths, perturbations of terrestrial magnetism or Wolf numbers relative to solar activity.

More recently a search has been made for occasions on which the association between the different phenomena is not so close. It has been found that the usual fade-out on short waves does not occur in the same manner on all stations recorded; sometimes, indeed, an enhancement of short duration takes place at the beginning of the expected fade-out. This enhancement is probably due to the reception of a radioelectric radiation from the sun.

The author gives some examples of such phenomena which can be used for a better forecasting of radioelectric disturbance due to abnormal solar activity.

From the study of ionospheric data recorded at Poitiers (46° N.) it appears that two sorts of scattered echoes take place in the neighbourhood of F2 critical frequencies.

The first one seems to be produced by the multiplication of magneto-ionic components. This scattering ends with ground sunrise; it exists during both quiet and perturbed ionospheric conditions; it is far more frequent and stronger when the nights are longer. Its existence seems to be connected with nocturnal thermal and convective disorder.

The second sort of scattering is mainly recorded during the second part of the night, after F2 penetration, at a virtual height of about 800 to 1,200 km. The sharp lower boundary of these reflections, which disappears a few moments after sunrise, leads to the postulation of an ionospheric G region, whose existence has been often discussed. This sort of scattering is connected with magnetically disturbed conditions and, chiefly, with meteoritic periods.

The detailed mechanisms involved in the formation of the E, F₁, F₂ and D layers by solar ultra-violet radiation are discussed Use is made of the results of some recent calculations on the continuous absorption cross section of atomic oxygen and nitrogen, and of the evidence on the ionic composition of the layers that is provided by the analysis of the emission spectrum of the upper atmosphere during twilight. The uncertainties existing at present are emphasized