§ 1. The present paper gives the results of the spherical harmonic analysis of the quiet solar diurnal variations (Sq) of the Earth's magnetic field for the summer months, May to August, 1933. Schuster [see 1 of “References” at end of paper] was the first to apply in 1889 Gauss's expansion in terms of spherical harmonics to the analysis of diurnal variations. The spherical harmonic analysis of the Earth's permanent and transient magnetic fields is of the utmost importance, first, because it permits generalizing the empirical data in the form of an analytical expression and, second, because it offers information regarding the structure of this field (its potential and its origin). The spherical harmonic analysis of the diurnal variations has therefore been repeatedly undertaken by many investigators [2 to 7]; but from time to time, with accumulation of new observational data (of greater reliability, or referring to other epochs), it becomes desirable to have recourse to new analyses.

The residual field from Cosmos 49 is presented in chart form. This map displays vast areas (1000–4000 km across) of negative and positive ΔT (the T are differences between measured and model fields) that are of the order of a few tens of gammas. The external field does not exert any essential influence on the ΔT distribution. The frequency spectrum of ΔT is similar to that of the model field used for the greater part of the chart, but within the ‘contrast zones’ the ΔT spectrum contains higher harmonics. There is no apparent correlation between the ΔT distribution and near‐surface anomalies or the thickness of the magnetoactive layer of the earth's crust. The correlation with heat flow distribution is somewhat more distinct within certain regions. It appears that the greater part of ΔT is due to a poor representation of the main geomagnetic field. However, the authors do not exclude the possibility of intermediate anomalies of inductive origin within the mantle, which could contribute to the higher‐frequency part of the ΔT spectrum.

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