Abstract
THOSE who are familiar with Prof. Hale's brilliant discovery of magnetic fields in sun-spots, and are aware of the difficulties connected with that investigation, will greatly admire his courage in seeking to establish the much weaker general magnetic field of the sun itself. The following condensed account of the method adopted and results obtained is given, to some extent, in Prof. Hale's own words. As a general problem of physics, Schuster's suggestion that every rapidly rotating body may produce a magnetic field is of fundamental importance. A direct test by laboratory experiments cannot be made because of the limitations of size and rotational velocity, but advantage may be taken of the heavenly bodies where these limitations do not obtain. The most promising object for such an investigation is the sun. It is here that the direct method of determining the magnetic field by observation of the Zeeman effect is most readily employed, since the sun is bright enough to permit the use of the very high dispersion required. Further, it is possible to observe at a great number of points on the surface, and since observations may be made in both hemispheres the most perfect test of the Zeeman effect can be applied by looking for a reversal of the sign of the displacement with the polarity. The present minimum of solar activity has furnished a particularly favourable opportunity for the investigation, in consequence of the general absence of local strong fields due to spots and other disturbances.
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The General Magnetic Field of the Sun 1 . Nature 91, 505–509 (1913). https://doi.org/10.1038/091505e0
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DOI: https://doi.org/10.1038/091505e0