On the occurrence of lunar periods in solar activity and the climate of the earth
The litterature about sunspots is enormously comprehensive and so are also the hypotheses enounciated concerning the origin and the periodicity of the suns activity. Without going into details I think we can discern two different lines of thought which rule our present conceptions regarding this problem. We can ascribe the different manifestations of solar activity either to external causes, i. e. to planetary influence, or to processes of volcanic nature or otherwise in the interior of the sun which give birth to periodic outbursts of spots, faculty etc.
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