JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. Ill DECEMBER 19, 1913 No. 21 



TERRESTRIAL MAGNETISM.— Pre^mmar?/ results of a first 

 analysis of the sun's general magnetic field.^ L. A. Bauer, 

 Department of Terrestrial Magnetism, Carnegie Institution 

 of Washington. 



The question whether the sun, like the earth, is surrounded by 

 a magnetic field, received renewed interest from Hale's certain de- 

 tection in 1908 of magnetic fields iii sun-spots, by means of the 

 effect of magnetism on light discovered by Zeeman in 1896. Pre- 

 vious investigators had shown that for a direct magnetic effect 

 attributable to the sun to be readily measurable on the earth, the 

 sun's magnetic moment would have to reach a very large fig- 

 ure. Accordingly our surmises hitherto have had to be confined 

 exclusively to certain phenomena exhibited by the coronal stream- 

 ers and motion of solar prominences, and by polar lights and 

 magnetic perturbations. 



It is a source of extreme satisfaction, therefore, that the means 

 were given Hale to institute a direct attack and undertake the 

 systematic detection of a possible general solar magnetic field, 

 employing the same method which had proved successful in the 

 case of sun-spots. As the probable field-intensity now was on 

 the order of about one-tenth to one-hundredth of that encoun- 

 tered in the spots, the instrumental difficulties seemed almost 

 insuperable. The observed displacements of the spectrum lines,, 

 to be ascribed to the sun's general magnetic field, are, in fact, 

 found to be so small that but for the superior instrumental appli- 



1 Presented before the Philosophical Society of Washington, November 22, 1913. 

 To be published more fully in J. Terr. Mag. and Atmos. Elec, 19. 1914. 



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