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A discussion of the two‐gas theory of the transmission of geomagnetic disturbances through the atmosphere (to several earth radii) is extended, with the following results: (i) The central problem concerning the main phase of a geomagnetic storm is the mechanism of penetration of solar ions into the geomagnetic field. An explanation is given depending on a combination of a uniform electric space‐charge field and a system of irregular fields. (ii) A model of the main phase of a geomagnetic storm is given, the principal feature of which is a ‘magnetic tail’ extending from the earth on the dark side. (iii) The model may help to explain some other effects: the Gegenschein, electrons with auroral energies, the location of the Van Allen zones, and diurnal cosmic‐ray variations, (iv) All observed geomagnetic disturbances have their sources initially in current systems in the lower ionosphere. Some are subsequently maintained by current systems in the earth itself and in the region of interaction between the solar and terrestrial plasmas. Others, mainly polar and equatorial, are maintained by ionospheric currents driven by space‐charge electric fields, (v) Any ring current outside the geomagnetic field could cause an increase in the horizontal component. A westward‐flowing ring current embedded in the field could cause either an increase or a decrease in the horizontal component. The basic effect is not the current but a sustained inward or outward mechanical force on the material in which the current flows.

Measurements are described of galactic radiation at frequencies of 1210 and 3000 Mc/s. The results provide extensions of previous radio emission spectra by more than 2� octaves. The intensity of radiation from near the galactic centre was measured and an estimate made of the direction of the maximum of such radiation. A new " discrete source " of peculiar spectrum was discovered very close to the centre of the Galaxy. Evidence suggests that the power output of this and some other sources in the radio spectrum may exceed the total power output of the Sun. Radiation was also observed from the direction of the Crab Nebula, from the known " radio source " in Centaurus, and from the Moon. Two nebulae (M 31 and NGC 7293) were investigated with negative results. The spectra of two sources are given between the limits 18.3 and 1200 Mc/s.