An attempt to identify the solar M-regions

An attempt was made to identify persistent bright calcium flocculi with the solar M-regions postulated by J. Bartels to be the source of charged particles causing the 27-day recurrences in terrestrial-magnetic activity. Sketches of the bright flocculi on calcium spectroheliograms, arranged in rows of 27 days each, were compared with corresponding charts showing recurrences in magnetic activity. Identification was limited to two objectives, namely, (1) for years near minimum when bright flocculi and magnetic disturbances are scarce and therefore rendered more conspicuous and (2) for three of the most prominent sequences in magnetic activity from 1917, through 1931.