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SummaryThe east-west position coordinates of the sources of 22 type II radio bursts, measured in the range 40-70 Mc/s using a swept-frequency interferometer, are analysed and discussed, in conjunction with dynamic spectra obtained in the frequency range 15-210 Mc/s. Many bursts are multiple and consist of a number of separate bursts excited by disturbances ejected in different directions from the vicinity of an optical flare, which may be equally complex.A statistical analysis of position data for type II and type III bursts, which reveals a remarkable similarity in the general behaviour of the two types of bursts, confirms the hypothesis of generation of the radio emissions by plasma oscillations. Other topics discussed are the relative intensities of fundamental and second harmonic bands of the same burst, the relative positions of the sources of fundamental and second harmonic bands of identical frequency, and the relative positions of the sources of the two ridges of a split band.Many type II bursts exhibit temporal changes of position at a single frequency. These are indicative of tangential movements in the solar atmosphere, with speeds of the order of 1000-2000 km/s. The spectra of these bursts with movement on the disk are characterized by little or no drift of frequency with time, and by broad bandwidth.A mean radial distribution of electron density in the disturbed corona is derived. This distribution does not differ greatly from that found optically for the average coronal streamer.

SummaryThe effective diffusion coefficient for a meteor trail is calculated from the theory of ambipolar diffusion and the physical constants of the upper atmosphere. The absolute value of the diffusion coefficient so calculated, and also its gradient with height, are confirmed by measurement of the rates of decay of a large number of meteor echoes of known heights. The individual values show considerable scatter, most of which is attributed to a regular diurnal variation in the value of the diffusion coefficient. Amplitude fluctuations in persistent echoes are also briefly discussed.

SummaryThe directions of the reflection points of sporadic meteor trails for March and September 1953, and the hourly echo rates of sporadic meteors obtained from the Adelaide radio survey of meteor activity over 1952-1956 are analysed. Diurnal and annual variations in the sporadic echo rate are predicted from contemporary theory on the reflection of radio waves from meteor trails for several model distributions. A sporadic distribution is derived which consists of a concentration of direct short· period orbits to the plane of the ecliptic superimposed upon a more uniform distribution uf near.parabolic orbits. This distribution is consistent with the results of radar, visual, and telescopic surveys in the northern hemisphere. The density of sporadic meteors round the Earth's orbit is also derived.

SummaryProperties of 24 sources of type IV emission at metre wavelengths (including the long-lived continuum storms) have been observed by interferometry in the frequency range 40-70 Mc/s and by dynamic spectroscopy in the frequency range 15-210 Mc/s. The characteristics investigated are the positions, movements, and angular sizes of the sources, and the spectrum and polarization of the emission.Two varieties of the metre-wave type IV burst with distinctive characteristics, notably in height and movement of the source and in polarization of the emission, have been recognized. These two varieties have been designated "moving" and "stationary" type IV bursts; they are probably separate phenomena related only through a common initiating disturbance. The stationary type IV emission appears to emanate from near the plasma level, but there is no appreciable dispersion of position with frequency over a narrow range of frequencies. No physical distinction is found between the shorter stationary events and the beginnings of the long-lived continuum storms, but notable changes in source properties develop towards the ends of continuum storms.