Since 1952 a total of 635 magnetograms of the sun have been obtained in a systematic investigation of weak magnetic fields in the photosphere. The frequent records give the location, polarity, and intensity of weak fields down to a fraction of 1 gauss, although with resolution limited to about 0·04 of the solar diameter.
Confirmation of previously reported results in 1954 comes from continuation of the series and from observations with a second, improved magnetograph on Mount Wilson. Three types of field pattern are found: (1) the poloidal field in high heliographic latitudes, consistently positive in the north, negative in the south, with intensity of the order of 1 gauss; (2) BM (bipolar magnetic) regions, often weak and extended, but which when strong are associated with plages, spots, flares, coronal emission, chromospheric fine structure, and filaments; and (3) UM (unipolar magnetic) regions, rather extended and weak, occurring in low latitudes, and associated in time with 27-day recurrent geomagnetic storms and cosmic-ray fluctuations. Attention is directed to the probable disposition of the magnetic flux in the high atmosphere and in interplanetary space, consistent with the observed magnetic areas and with the restriction div H = 0.
Alfvén has argued that the interpretation of the small Zeeman displacements is meaningless and irrelevant because the rather strong turbulent fields presumed to prevail in granules might be coupled systematically, in respect to magnetic polarity, with the intensity of the absorption lines used for measurement. But this would produce a bias, with a shift of zero point of magnetic intensity, for all observed fields on the disk, and no such bias is observed. The measurements, while limited in resolution, are on an absolute scale, and show, for the ‘quiet sun’, vast areas with only small random fields no greater than a few tenths of 1 gauss.