l82 REPORTS ON INVESTIGATIONS AND PROJECTS. 



two distinct vortices, with nearly radial axes. The necessary criteria of 

 selection can probably be found by a comparative study of the principal 

 members of a bipolar group, special attention being directed to the inclina- 

 tion of the axes of the vortices to the line of sight (if it can be determined 

 by the Zeeman effect), the direction of flow (inward or outward) of the 

 vapors at different levels, and the proper-motions, temperature, and pressure 

 of the two spots. 



Professor Stormer's Investigations. 



Prof, Carl Stormer, of the University of Christiania, Research Associate 

 of the Carnegie Institution of Washington, has been engaged for some years 

 in a study of the aurora, on the theory that it is caused by ions entering our 

 atmosphere from the sun under the influence of the earth's magnetic field. 

 As it seemed possible that the application of similar methods to an investi- 

 gation of the hydrogen (Ha) flocculi would lead to important results, Pro- 

 fessor Stormer was invited to spend several weeks at the Observatory in 

 June and July. 



A preliminary study of the spectroheliograph plates led him to the conclu- 

 sion that, in the case of single spots, the simplest elementary curves resem- 

 bling the hydrogen flocculi in form are logarithmic spirals. An additional 

 reason for adopting these curves as a first approximation was the fact that the 

 current lines in terrestrial cyclones are also approximately logarithmic spirals. 



It then became necessary to solve the following mathematical problems 

 for application to sun-spots : 



(i) Find the magnetic field in space due to a plane current sheet, in 

 which the current lines are all concentric logarithmic spirals of the same 

 form. 



(2) Find the field of two such current sheets, situated in parallel planes 

 with common axis and' connected by a short central helix (model of a 

 cyclonic vortex). 



All the necessary mathematical formulae were derived and brought into a 

 form suitable for convenient numerical computation. 



The next step, the calculation of the magnetic field of two opposite whirls, 

 corresponding to the bipolar type of sun-spots, follows at once from the ap- 

 plication of the formula, and the computation of the numerical data in each 

 case then becomes only a question of time. The case of a number of vor- 

 tices of different signs can be treated in the same manner. The application 

 of these results to bipolar and multipolar configurations of hydrogen flocculi 

 will be made later. 



The theory of the sun's general magnetic field, on the hypothesis that it is 

 due to the rotation of an electrically charged sphere, was also investigated. 

 The results will be compared with Professor Stormer's researches on the 

 form of the coronal streamers, based on the hypothesis developed in the 

 Comptes Rendus of February 20 and March 6, 1911. 



