SOLAR VORTICES AND MAGNETISM IN SUN SPOTS ABBOT. 327 



Without entering at present into further details, a single suggestion relating 

 to the possible existence of magnetic fields on the sun may perhaps be offered. 

 We know from the investigations of Rowland that the rapid revolution of 

 electrically charged bodies will produce a magnetic field, in which the lines of 

 force are at right angles to the plane of revolution. Corpuscles emitted by the 

 photosphei'e may perhaps be drawn into the vortices," or a preponderance of 

 positive or negative ions may result from some other cause. When observed 

 along the lines of force, many of the lines in the spot spectrum should be double, 

 if they are produced in a strong magnetic field. Double lines, which look like 

 reversals, have recently been photographed in spot spectra with the 30-foot 

 spectrograph of the tower telescope,* confirming the visual observations of 

 Young and Mitchell. It should be determined whether the components of these 

 double lines are circularly polarized in opposite directions, or, if not, whether 

 other less obvious indications of a magnetic field are present. I shall attempt 

 the necessary observations as soon as a suitable spot appears on the sun. 



A MAGNETIC FIELD IN SUN SPOTS. 



Carrying out his projected observations on the polarization of sun 

 spot spectrum lines, ]Mr. Hale has obtained a most striking proof of 

 the existence of magnetic fields in sun spots. An abstract of his 

 ])aper^ on this subject follows: 



The discovery of vortices surrounding sun spots, which resulted from the use 

 of the hydrogen line Ha for solar photography with si)ectr()heliograph ^ dis- 

 closed possibilities of research not previously foreseen. Photographs taken 

 daily on Mount Wilson with this line suggest that all sun spots are vortices, 

 and provide material for a discussion of spot theories which will soon be under- 

 token. Revealing, as they do, the existence of definite currents and whirls in 

 the solar atmosphere, they afford the requisite means of testing the operation 

 in the sun of certain physical laws previously applied only to terrestrial phe- 

 nomena. The present paper describes an attempt to enter one of the new fields 

 of research opened by this recent work with the spectroheliograph. 



ELECTRIC CONVECTION. 



In 1876 Rowland discovered that an electrically charged ebonite disk, when 

 set into rapid rotation, produced a magnetic field, capable of deflecting a mag- 

 netic needle suspended just above the disk.<^ It thus appeared, in accordance 

 with Maxwell's anticipation, that a rapidly moving charged body gives rise to 

 just such effects as are caused by an electric current flowing through a wire. 

 Rowland's whirling disk therefore corresponds to a short wire heUx, within 

 which a magnetic field is produced when a current is passed through it. 



Recent studies of the discharge of electricity in gases prove that gases and 

 vapors, when ionized by one of several means, contain electrically charged 



''J. J. Thomson, Conduction of Electricity through Gases, p. 164. 



* Hale, Contributions from the Mount Wilson Solar Observatory, No. 23 ; 

 Astrophysical Journal, Vol. XXVII, p. 204, 1908. 



''Astrophysical Journal, Vol. XXVIII (November), 1908. 



<*Hale, " Solar Vortices," Contributions from the Mount Wilson Solar Observa- 

 tory, No. 26; Astrophysical Journal, Vol. XXVIII, p. 100, 1908. 



•^Rowland, " On the magnetic effect of electric convection," American Journal 

 of Science (3), Vol. 15, p. 80, 1878. 

 88292— SM 1908 22 



