256 CARNEGIE INSTITUTION OF WASHINGTON, 



attention has been given to comparative photographs of prominences 

 in Ha and K light, comparative photographs of hydrogen fioccuU with 

 the center and the red and violet edges of Ha, and series of photographs 

 of the Ha flocculi surrounding bipolar spot-groups, in connection with 

 laboratory investigations of vortex phenomena. 



FIELDS OF FORCE IN THE SOLAR ATMOSPHERE. 



The typical hydrogen flocculi connected with sun-spots may be clas- 

 sified under three heads: (1) unipolar floccuU, consisting of curved or 

 radial lines surrounding single spots; (2) bipolar floccuU, surrounding a 

 bipolar spot group, and resembUng imperfectly the lines of force about 

 a bar magnet; and (3) multipolar floccuh, more or less similar to bipolar 

 flocculi, but influenced in form by the presence of numerous small 

 spots, of either polarity, in a complex spot group. The fields of force 

 thus made manifest in the solar atmosphere have been explained by 

 some investigators as hydrodynamic phenomena, while others have 

 attributed them to the influence of the magnetic fields in sun-spots 

 on falUng hydrogen ions, which would be caused to move along paths 

 closely resembling the fines of force. While it is probable that both 

 hydrodynamic and electromagnetic forces influence the structure of the 

 floccuU, it is important to learn, if possible, which of these is dominant. 



As explained in another section of this report (p. 280), laboratory 

 experiments on vortices have indicated that bipolar Ha floccufi, if of 

 hydrodynamic origin, should exhibit a characteristic configuration, the 

 chief features of which are an arched structure on one side of the axis 

 of the group and a more nearly radial structure on the opposite side. 

 From the known direction of rotation of the spot vortices, it follows 

 that the arch should fie above the axis (toward the poles) in the case of 

 high-latitude groups and below the axis (toward the equator) in the 

 case of low-latitude groups. 



In Mr. EUerman's hands the 13-foot spectroheliograph has yielded 

 many photographs of Ha flocculi of the finest quality, surpassing any 

 we have obtained previously. The presence of many small spots in 

 active bipolar groups usually compficates the structure, and makes 

 comparison with our artificial bipolar vortices somewhat difficult. In 

 many cases, however, the structure closely resembles that of our bipolar 

 smoke vortices, suggesting a hydrodynamic origin; but in other 

 instances the appearance of the lines of force of a magnetic field is 

 more clearly suggested. It is thus evident that much more work 

 will be necessary before definite conclusions can be drawn. 



We are indebted to Professor Frost for the use of some excellent 

 negatives of Ha flocculi made by Professor Fox with the Rumford 

 spectroheliograph of the Yerkes Observatory. 



