MOUNT WILSON SOLAR OBSERVATORY.* 



George E. Hale, Director. 



The persistence of the period of minimum solar activity, marked 

 by the almost complete absence of sun-spots and other evidences 

 of disturbance, has been an important factor in the work of the 

 year. While it has prevented a continuance of our observations of 

 sun-spot phenomena, compensation has been found in the study 

 of the sun's general magnetism, where the minute manifestations of 

 the Zeeman effect might be wholly masked by the prevalence of the 

 hundredfold greater displacements caused by local magnetic fields. 

 For this investigation the completion of the 150-foot tower telescope 

 was most opportune. In exploring the magnetic phenomena of the 

 sun's polar regions the large solar image given by the new telescope 

 is indispensable, while the great dispersion of the 75-foot spectro- 

 graph is no less essential for the detection of the barely measurable 

 displacements of the solar lines on which the investigation is based. 

 The direct observational evidence of the sun's magnetism now 

 appears to be beyond question, leaving us free to advance from the 

 period of proof into that of definitive research on the nature of this 

 important phenomenon. 



In certain other fields of solar research, as Mr. St. John's admirable 

 results attest, there has also been no interruption of progress. Great 

 activity has also marked the prosecution of the stellar and laboratory 

 work, especially in Mr. Adams's department, where the measurement 

 of stellar velocities has continued at an unprecedented rate. In the 

 selection of objects for study, and in the discussion of the data 

 obtained. Professor Kapteyn has exercised his usual sound discrimi- 

 nation and breadth of view. The evidence he has amassed in sup- 

 port of the view that light is absorbed in space is so impressive that 

 we intend to devote much attention to this subject in the future. 

 It not only offers an expljination of otherwise obscure phenomena, 

 but promises to give what appears to be the only possible method 

 of measuring the most profound depths of the universe. The impor- 

 tant results obtained by Professor Stormer, of Christiania, in his 

 theoretical investigations of solar vortices; by Professor Hertzsprung, 

 of Potsdam, in his Mount Wilson observations bearing on the absorp- 

 tion of Hght in space; and by Professor Koch, of Munich, in applying 

 his registering micro-photometer to the study of our solar, stellar, 

 and laboratory spectra, are interesting features of the present report. 



*Situated on Mount Wilson, California. Address Pasadena, California. Grant No. 

 866, $165,631 for construction, investigations, and maintenance during 1913. (For pre- 

 vious reports see Year Books Nos. 3-il.) 



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