SOLAR VORTICES AND MAGNETISM IN SUN SPOTS ABBOT. 335 



That this probably occurs is shown by the fact that the D lines of sodium and 

 the b lines of magnesium are usually but slightly affected in the spot spectrum," 

 and are displaced through a very small distance when the Nicol is rotated. 

 Thus, at the level represented by these lines, which attain elevations in the 

 chromosphere probably not exceeding 5,000 miles, the field strength is reduced 

 to a small fraction of its maximum value. 



The following doublets have been measured in the spectrum of chromium : 



Table III. — Chromium doublets. 



In photographing these lines in the spark the strength of the field was 

 12.500 gausses. The strength of the field in spots, as indicated by the mean 

 separation of the chromium doublets, is therefore 2,600 gausses. * * * 



SIGN OF THE CHARGE THAT PRODUCES THE FIELD IN SUN SPOTS. 



If the evidence presented in this paper renders probable the existence of a 

 magnetic field in sun spots, it is of interest to inquire concerning the sign of 

 the charge which, accoriling to our hypothesis, produces the field. * * * 



In the case of the solar vortices we have to consider two sets of charged 

 particles, which may be entirely distinct from one another: (1) those whose 

 vibrations give rise to the lines in the spectra of spots, and (2) those that carry 

 the charge which, by the hypothesis, produces the magnetic field. The Zeeman 

 effect supplies the means of determining the direction of the lines of force of 

 the sun-spot fields, and photographs of the vortices, made with the spectrohelio- 

 graph, indicate the direction of revolution of the particles. Thus we are in a 

 position to determine the sign of the charge carried by the particles which pro- 

 duce the fields. As pointed out independently by Konig and Cornu, the violet 

 component of a magnetic doublet observed along the lines of force is formed 

 by circular vibrations, having the direction of the current flowing through the 

 coils of the magnet.'' From observations of circularly polarized light, made 

 in our INIount Wilson laboratory by Doctor St. John and confirmed by myself, 

 it appears that when the Nicol prism of the tower spectrograph stands at 60° 

 E. it transmits the violet component of a doublet produced in a magnetic field 

 directed toward the observer. From Biot and Savart's law the direction of 

 the current causing such a field is counter-clockwise, as seen by the observer. 

 In the same position the Nicol also transmits the violet component of a doublet 



•» Except for the strengthening of the wings, which may be produced by some 

 cause other than a magnetic field. 



^ See Cotton, Le phenomene de Zeeman, chaj). vii, Konig. Wied. Ann. Vol. 62, 

 p. 240, 1897. 



