SOLAR MAGNETIC PHENOMENA.^ 



By GEORGE E. HALE. 



(Read April 24, 1914.) 



The discovery by Stark of the electrical analogue of the Zeeman 

 effect establishes a new point of view for the solar physicist. It is 

 now known that an electric field, like a magnetic field, may cause the 

 spectral lines of a light-source placed within it to break up into 

 several components. Furthermore, these components, when observed 

 at right angles to the lines of force, are plane polarized in both cases. 

 Thus there are important points of resemblance between the Zee- 

 man and Stark effects, and it becomes necessary to review the evi- 

 dence on which the proof of the existence of solar magnetism is 

 based. Is it possible that electric fields, rather than magnetic fields, 

 are responsible for the observed spectroscopic phenomena? 



Fortunately, as a brief consideration of the observations will 

 show, this evidence is not open to the charge of ambiguity. The 

 phenomena described in my papers on the magnetic fields of sun- 

 spots and .the general magnetic field of the sun are unmistakably 

 those of the Zeeman effect. They are clearly ascribable, in their 

 broad features, to magnetic rather than to electric fields, and if the 

 latter exercise a secondary influence, it is not easily recognizable. 



Here an important opportunity for further research is presented. 

 The separation of electrons in sun-spots should give rise to electric 

 fields, which may be sufficiently intense to produce an appreciable 

 Stark eff'ect. Other regions of the solar atmosphere where the con- 

 ditions are most favorable for the production of electric fields are 

 also open to investigation. But our knowledge of the spectroscopic 



1 Abstract. The complete details of the paper, which will be published 

 in a series of articles in the Astrophysical Journal, include the results of 

 investigations on the radial and tangential spot field; the rate of change of 

 field-strength with level, both for spots and the general field; the relationship 

 between field-strength and spot area ; the complex fields of spot groups ; the 

 phenomena of bipolar spots, etc. 



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