210 a\llNEGIE INSTITUTION OF WASHINGTON. 



X5506 is common to the 1912 and 1913 investigations, but an entirely 

 new series of plates was made for the common region. The Pasa- 

 dena plates were taken by Mr. St. John and Mr. Babcock with the 

 30-foot plane spectrograph, using a remarkably fine grating by 

 Anderson, which gives diffraction patterns of the most perfect sym- 

 metry in the case of sharp lines. The Mount Wilson plates made by 

 JNIr, St. John with the 75-foot spectrograph in conjunction with the 

 150-foot tower telescope, using a large Michelson grating, give excel- 

 lent definition for both bright and dark lines. In both series the Pfund 

 arc was used upon a 110-volt direct-current circuit. By employing 

 a series of overlapping plates, the standards have been combined in 

 various ways and are interlocked throughout the region investigated, 

 thus yielding a very high degree of precision. 



The pessimistic views of various observers as to the possibility of 

 determining the position of standard lines to the third decimal place 

 have led to a careful investigation of the structure of lines in various 

 parts of the arc by Mr. St. John and Mr. Babcock. The preliminary 

 results indicate that the main cause of the large discrepancies between 

 the results of different observers is to be found in the unsymmetrical 

 widening of the lines as the negative pole is approached. If com- 

 parison be made between these sensitive lines, when of equal breadth 

 at the center of the arc and at the negative pole, the differences in 

 wave-length are very slight, but these differences apparently increase 

 enormously when the widened lines near the poles are measured. 

 They have therefore discarded the use of a slit parallel to the axis of 

 the are, as used by other observers, substituting a slit placed at right 

 angles to the axis of the arc at the middle point of an enlarged image. 

 Under these circumstances the lines with a short slit have good edges 

 and uniform width throughout their length, and quite consistent 

 results can be obtained, even in the case of lines which have hitherto 

 given the largest discrepancies. 



The chief conclusions of the investigation are summarized at the 

 beginning of this report. 



PUOFESSOR StoRMEH's INVESTIGATIONS ON SoLAU VoRTICES. 



As stated in the last annual report, Professor Carl Stormer, of the 

 University of Christiania, came to Pasadena during the summer of 

 1912 as a Research Associate of the Carnegie Institution of Wash- 

 ington. Since his return to Christiania he has continued his theo- 

 retical investigations begun here, and has obtained very important 

 results on the nature of the vortices in sun-spots. 



The preliminary mathematical study of the subject led to the 

 view that the hydrogen whirls of the flocculi are not real current 

 lines, but lines of magnetic force due to a whirl at a lower level, 

 hidden behind the upper layers of the sun's atmosphere. The cur- 



